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The core polyprotein of feline immunodeficiency virus (FIV) was expressed in primary feline T-lymphocytes using a retroviral vector. These cells were used as antigen-presenting stimulator cells (APSC) for the in vitro induction of cytotoxic T-lymphocytes (CTL) from feline peripheral blood mononuclear cells (PBMC). CTL from 4 cats chronically infected with the Petaluma strain of FIV specifically lysed autologous FIV-infected targets in an MHC-restricted manner. The CD8 phenotype of more than 70% of the induced effector cells (97% for cells from one cat) was consistent with MHC class I-restricted cytotoxicity. In addition, it was possible to detect low levels of core polyprotein-specific lysis from effector cells of two of the FIV-infected cats. When observed, the level of lysis, measured as a percentage of specific 111In release, was lower for the transgenic gag-expressing targets than for FIV-infected targets. The difference in killing may reflect the low level of core CTL were not detected in either PBMC stimulated with cells transduced by a retroviral vector without the FIV gag sequence or PBMC from an uninfected cat stimulated with autologous transgenic APSC. The detection of FIV-specific CTL from infected cats following stimulation with transgenic APSC suggests a role for retroviral vectors in determining CTL specific for individual lentiviral proteins in protective immunity.

Feline immunodeficiency virus (FIV) antigen was detected by immunochemistry in salivary glands of cats experimentally inoculated with West Australian isolate T91. Six cats were inoculated subcutaneously with 1.0 ml of tissue culture supernatant fluid from a feline T-lymphoblastoid cell line (MYA-1) infected with T91. FIV antigens were detected in the interlobular ducts of the salivary gland of cats infected with FIV 2, 4 and 6 weeks previously. FIV antigen was not detected in the salivary glands of three FIV negative cats and one naturally infected cat. Further, FIV antigen was located only in interlobular duct epithelial cells. The distribution of FIV in the interlobular ducts confirms the important role of salivary glands as a major reservoir of FIV in the early phase of infection and strengthens suggestions that the salivary route is an important mode of transmission of FIV.

Definition of the immunological mechanisms involved in protective immunity against lentiviral infections is crucial to the development of an effective vaccine. The induction of gag- and env-specific cell-mediated immune responses was studied in cats following vaccination with whole inactivated feline immunodeficiency virus (FIV). Cats were immunized by inoculation with three doses of paraformaldehyde-inactivated FIV, derived from the feline lymphoid cell line, FL-4, which is persistently infected with the Petaluma isolate of FIV. Autologous or allogeneic skin fibroblasts either infected with recombinant FIV gag- or env-vaccinia virus or pulsed with FIV env peptides were used as targets in chromium-51 release assays. Effector cells were fresh peripheral blood mononuclear cells. Following the third immunization, all vaccinated cats, but none of the control cats immunized with adjuvant alone, had detectable FIV env-specific lymphocytotoxicity in their peripheral blood. Two cats also exhibited gag-specific activity. There was no recognition of either allogeneic skin fibroblasts infected with recombinant vaccinia virus or autologous target cells infected with wild-type vaccinia virus, indicating the specificity and MHC-restricted nature of the response. Vaccinated cats, but not control cats, were protected from challenge with the homologous Petaluma isolate of FIV. Partial epitope mapping of the env-specific cytotoxic response was performed using overlapping 10-amino acid peptides from the env V3 domain of FIV. This response appeared to be directed at env peptide 1 (RAISSWKQRN) and env peptide 3 (QRNRWEWRPD), which lie adjacent to a beta-turn within the V3 domain.(ABSTRACT TRUNCATED AT 250 WORDS)

Total immunoglobulin content and concentration of immune complexes (IC) were determined in the sera of 51 cats infected with feline immunodeficiency virus (FIV) and of 40 controls. IgG and IgM were quantified by radial immunodiffusion and circulating IC (CIC) by the CIC-conglutinin assay. IgG fractions were obtained by acid elution from kidney tissues of 15 FIV-infected and five negative control cats to investigate the possible role of IC in the genesis of renal damage observed in infected animals. Mean concentrations of IgG and circulating IC were higher in FIV-infected cats than in controls (29.6 +/- 6.7 versus 23.0 +/- 1.9 mg/dl (mean +/- s.d.) P < 0.001; and 66.5 +/- 17.0 versus 27.4 +/- 19.9% I, P < 0.001, respectively), while IgM levels were only slightly increased (0.9 +/- 0.05 versus 0.87 +/- 0.04 mg/dl, P < 0.02). Immunoglobulin fractions were eluted from 10 of the 15 renal tissue samples from FIV-infected cats and were found to be polyclonal and at least partly specific for FIV antigens. These findings confirm the presence of a B cell activation in FIV-infected cats and demonstrate the presence of high levels of CIC in their sera. The presence of immune deposits in renal tissues suggests that IC might play a role in the pathogenesis of the renal damage observed in FIV-infected cats.

Our aim was to develop a recombinant replication-defective adenovirus suitable for the vaccination of cats against feline immunodeficiency virus. We first demonstrated that this vector was able to transfer a marker gene (E. coli beta-galactosidase) in feline cells in vitro. We then constructed an adenovirus type 5 expressing the Feline Immunodeficiency Virus (FIV) envelope (ENV) gene of the Wo isolate in the absence of the rev gene (Ad-ENV-Wo). Ad-ENV-Wo was then tested in four cats in a 3 injections scheme (at day 0, day 30 and day 210). Four other control cats received Ad-gp50, a similar recombinant adenovirus expressing gp50 (Ad-gp50) of pseudorabies virus (PRV). Viruses were formulated in two different kind of oil adjuvants (water/oil and water/oil/water), a protocol previously shown to enhance the immune response against the virus-induced protein. The control cats developed neutralizing antibodies against PRV, demonstrating the potency of recombinant human adenovirus 5 (Ad5) as a vector in cats. Antibody responses appeared after the first injection and were higher with the water/oil/water formulation than with the water/oil controls. However, none of the four cats vaccinated with Ad-ENV-Wo developed antibodies against two peptides of the envelope protein. Animals were challenged with 20 infectious doses 50% of the strain Wo. All of them developed antibodies against FIV within 4 to 5 weeks, and FIV virus could be isolated from all.

The immune responsiveness of cats naturally or experimentally infected with feline immunodeficiency virus (FIV) was studied. Peripheral blood mononuclear cells (PBMC) from naturally infected, symptomatic animals displayed depressed proliferation and interleukin-2 (IL-2) production in response to mitogens, which was accompanied by a significant increase in IL-1, IL-6 and tumour necrosis factor (TNF) production. Longitudinal studies were performed over a period of 4 years in experimentally infected animals. The responses of cells from these cats to concanavalin A (Con A) were consistently less than those from uninfected cats throughout the period but, owing to variation between cats, were significantly lower on only a few occasions. By contrast, the responses of cells to pokeweed mitogen (PWM) were severely affected and declined progressively throughout the 4-year period. In general, responses to Con A but not PWM could be restored by the addition of exogenous IL-2. The decline in immune responsiveness was concurrent with a decline in feline (f)CD4+ cells and an inversion in the CD4:CD8 ratio. Peak production of IL-1, IL-6 and TNF coincided with periods of depressed immune responses. Additionally, immunodeficient responses and elevated levels of proinflammatory cytokines were concurrent with the presence of clinical signs. We conclude that, like human immunodeficiency virus (HIV), FIV infection results in significant perturbation of the immune response. Responses to PWM appear to correlate with disease progression which suggests that the CD3 pathway is affected in the earlier stages of the disease and that additional activation pathways such as CD2 may not be affected until the animal enters the acquired immune deficient syndrome (AIDS) stage of the disease.

A new enzyme-linked-immunosorbent assay (ELISA) for the detection of antibodies to feline immunodeficiency virus was compared with previously described ELISAs. Serum samples from 184 infected or uninfected cats were tested using a whole virus lysate kit and ELISAs based on recognition of one of two synthetic peptides (P237 and P253) localized in the transmembrane domain of the viral envelope. The whole virus lysate commercial kit led to the detection of 6% false positive and 4.3% false negative sera. The ELISA based on peptide P253 gave no false positive result and failed to detect only one serum that was subsequently shown to be positive by radio-immunoprecipitation assay. A sandwich-ELISA test using Galanthus nivalis agglutinin, a lectin that specifically binds terminal mannose groups of the envelope proteins was used as a confirmatory test for equivocal results with peptide ELISA and gave similar results. This study indicates that recognition of P253 could serve as a sensitive and specific test for the diagnosis of seropositivity to feline immunodeficiency virus, and moreover that the Galanthus nivalis ELISA could be useful in equivocal cases as a confirmatory test.

Cats were immunized three times with different recombinant feline immunodeficiency virus (FIV) candidate vaccines. Recombinant vaccinia virus (rVV)-expressed envelope glycoprotein with (vGR657) or without (vGR657 x 15) the cleavage site and an FIV envelope bacterial fusion protein (beta-Galactosidase-Env) were incorporated into immune-stimulating complexes or adjuvanted with Quil A. Although all immunized cats developed antibodies against the envelope protein, only the cats vaccinated with the rVV-expressed envelope glycoproteins developed antibodies which neutralized FIV infection of Crandell feline kidney cells. These antibodies failed to neutralize infection of thymocytes with a molecularly cloned homologous FIV. After the third immunization the cats were challenged with homologous FIV. Two weeks after challenge the cell-associated viral load proved to be significantly higher in the cats immunized with vGR657 and vGR657 x 15 than in the other cats. The cats immunized with vGR657 and vGR657 x 15 also developed antibodies against the Gag proteins more rapidly than the cats immunized with beta-Galactosidase-Env or the control cats. This suggested that immunization with rVV-expressed glycoprotein of FIV results in enhanced infectivity of FIV. It was shown that the observed enhancement could be transferred to naive cats with plasma collected at the day of challenge.

We have previously reported the presence of feline immunodeficiency virus (FIV)-specific, major histocompatibility complex (MHC)-restricted cytolytic T lymphocytes (CTL) in experimentally FIV-infected cats. However, the fine specificity of the CTL and the role of individual FIV proteins in inducing FIV-specific CTL responses remain unknown. In this study, we examined the in vitro induction and activity of FIV p24 capsid-specific CTL obtained from cats that had been experimentally infected with FIV Petaluma for 30 to 56 months. An amphotropic murine retroviral vector was used to generate transgenic primary feline T lymphoblasts that expressed the FIV capsid protein. When the autologous capsid-transduced T cells were used in vitro to stimulate CTL responses from peripheral blood mononuclear cells of chronically infected cats, MHC-restricted lysis of virus-infected target cells was observed. The majority of the CTL expressed CD8, and depletion of this population, but not CD4+ cells, effectively diminished the CTL activity. When the autologous capsid-transduced T cells were used as target cells, lysis by capsid-induced effectors was not observed. Analysis of capsid-transduced T cell clones revealed a variable and low level of capsid expression among the clones. This study demonstrates the potential for using retroviral vectors as a means of inducing CTL effector cells that will specifically kill lentivirus-infected cells during lentiviral infection.

The polymerase chain reaction (PCR) method was applied for measurement of the proviral DNA copy number of feline immunodeficiency virus (FIV) in peripheral blood mononuclear cells (PBMC) of cats experimentally and naturally infected with FIV. In experimentally infected cats except one cat infected with the Petaluma strain, FIV-specific DNAs were efficiently amplified with the PCR method under the conditions used in this study. In the naturally FIV-infected cats, the specific DNAs were also amplified. We established a quantitative method for measurement of proviral DNA copy number in PBMC from cats infected with TM2-type of FIV strains, and found that the number was variable among the six cats examined, ranging from 10(4.0) to 10(5.7) copies per 10(5) PBMCs. This method can be applicable to cats naturally infected with FIV of TM2-type. Proviral DNA quantitation developed here could be useful as an additional parameter to evaluate the relationships among the proviral load, immune response and development of the clinical symptoms, and to monitor efficacy of antiviral therapy in vivo.

Cytotoxic T-cell determinants should be an important component of a vaccine against feline immunodeficiency virus (FIV). Epitope mapping studies have revealed an immunodominant neutralization epitope within the third variable (V3) domain of the viral envelope glycoprotein comprizing 17 amino acids (residues 390-406: RAISSWKQRNRWEWRPD). We have investigated the induction of FIV-specific cytotoxicity and anti-peptide antibody in cats immunized with a multiple antigenic peptide (MAP) containing this epitope. Virus-specific lymphocytotoxicity was determined using autologous or allogeneic skin fibroblasts as target cells labelled with chromium-51 and pulsed with overlapping 10 amino acid peptides. Cytotoxic effector cells derived from fresh peripheral blood were detected in five out of 10 immunized cats. The cell-mediated immune response appeared to be directed to envelope peptide 1 (RAISSWKQRN) and peptide 2 (SWKQRNRWEW), with recognition of peptide 3 (QRNRWEWRPD) in only one cat. An antibody response to the 17 amino acid peptide immunogen was detected in seven immunized cats, which was directed to envelope peptides 2 and 3. These results suggest that different epitopes may be recognized by the cell-mediated and humoral immune responses. None of the cats was protected from challenge with the Glasgow8 isolate of FIV (FIV/GL-8). This study has implications for vaccine strategies using synthetic peptides to induce virus-specific cell-mediated immune responses.

To study the effect of interferon on feline leukemia virus (FeLV) infection, 30 specific pathogen free (SPF) cats were infected with the apathogenic FeLV A Glasgow. Unexpectedly, between 5 and 8 weeks after FeLV infection, all 19 cats with persistent FeLV infection but not the FeLV-negative cats died from a panleukopenia-like syndrome. No feline panleukopenia virus (FPLV) antigen was found in feces by latex agglutination, enzyme-linked immunosorbent assay (ELISA) or immunoelectron microscopy. No enteropathogenic bacteria were found. Histopathology revealed changes resembling those of FPLV infection such as destruction of crypts and pancytopenia of bone marrow. Neither clinical signs nor seroconversion to FPLV could be induced by transmitting intestinal extracts to two SPF cats. However, FPLV antigen was demonstrated by immunofluorescence assay in intestinal cryostat sections of diseased animals. FPLV could also be demonstrated in intestinal extracts by immunoelectron microscopy, by latex agglutination and ELISA after anti-FPLV antibodies were removed from immune-complexed FPLV by ultracentrifugation over a CsCl gradient at pH 2.0. From these experiments it was concluded that the panleukopenia-like syndrome of FeLV may not be caused by FeLV alone but at least in some cases by co-infection with FeLV and FPLV. In addition, some form of 'cooperation' between FeLV and FPLV must be postulated because neither virus alone induced symptoms.

We have vaccinated five groups of cats (n = 25) four times with five preparations of recombinant feline immunodeficiency virus (FIV) env gene products; one group (n = 7) served as control. The vaccine formulations were as follows: (1) envelope glycoprotein of FIV Zurich 2 (FIV Z2) expressed in a Baculovirus system and isolated by gel electroelution (denatured form); (2) insect cells expressing FIV Z2 glycoprotein; (3) envelope glycoprotein of a Boston strain (FIV Bangston) expressed in insect cells and isolated by gel electroelution (denatured form); (4) glycosylated Bangston envelope protein made in insect cells and isolated in a native form; (5) non-glycosylated Bangston envelope protein made in Escherichia coli. All cats were challenged with 20 50% cat infective doses (CID50) of FIV Z2 previously titrated in cats. All vaccinated cats developed high enzyme-linked immunosorbent assay (ELISA) antibodies to the homologous antigen; crossreactivity to heterologous antigens was seen at a lower level. Virus neutralizing antibodies (tested with Petaluma virus) reached titers up to 32. After challenge, all cats seroconverted (as judged by anti gag antibodies in Western blot) and became infected (as judged by virus isolation and/or polymerase chain reaction) between 4 and 11 weeks with the exception of one cat. It is concluded that it is relatively easy to induce high ELISA antibody titers using recombinant env gene products, ELISA antibody titers do not correlate with virus neutralization or with protection.

The lack of a safe, economical murine lentivirus model for human immunodeficiency virus type 1 (HIV-1) infection of humans has hampered the preclinical evaluation of potential antiviral compounds, vaccines, and biological response modifiers. A small animal model that does not employ HIV-1 is needed to minimize risk of accidental human exposure, enhance efficient use of scarce experimental compounds, and reduce laboratory space necessary to conduct statistically significant in vivo trials. Feline immunodeficiency virus (FIV), an immunosuppressive lentivirus of domestic cats, has been used extensively as an animal model for the pathogenesis and therapy of human HIV-1 infection. Cats, however, are not amenable to large-scale efficacy trials because of their relatively large size, high cost, and limited degree of physiologic characterization, particularly with regard to drug metabolism. To adapt the feline immune system to a small laboratory animal host, severe combined immunodeficient mice (SCID mice) were engrafted with feline lymphoid tissues (forming the SCID-fe mouse) and inoculated with FIV. Two quantitative parameters, the incidence of provirus detection in feline tissue grafts and the level of feline IgG in plasma, were used to demonstrate the antiviral efficacy of 3'-azido-3'-deoxythymidine (AZT, azidothymidine, Retrovir, zidovudine) in the SCID-fe system. Of 17 SCID-fe mice inoculated with 7 x 10(6) peripheral blood mononuclear cells (PBMC) from an FIV-infected cat, eight had detectable FIV provirus in both the feline thymus and feline lymph node implants, as measured by polymerase chain reaction (PCR)/Southern blot analysis. Treatment of these mice with AZT at a dose of 125 mg kg-1 day-1 in drinking water beginning 1 day prior to FIV inoculation and continuing throughout the study interval prevented the dual detection of provirus in feline lymph node and thymus grafts of all mice tested. In a separate experiment, the level of spontaneous feline IgG production was quantified by ELISA 2 weeks after FIV inoculation with and without AZT treatment. Mean plasma feline IgG level of five SCID-fe mice inoculated with 10(3) TCID50 cell-free FIV was 2.23 mg ml-1. Mean feline IgG level of five mice inoculated with the same quantity of FIV and treated with AZT beginning 1 day prior to virus inoculation and continuing for 2 weeks thereafter was 14.98 mg ml-1. AZT significantly (P < 0.05) enhanced feline humoral immune function at a virus inoculum titer of 10(3) TCID50.(ABSTRACT TRUNCATED AT 400 WORDS)

We developed an antibody detection enzyme-linked immunosorbent assay (ELISA) using recombinant surface (SU), transmembrane (TM) and capsid (CA) antigens of feline immunodeficiency virus (FIV) expressed in Escherichia coli. The three antigens were tested with sera collected from experimentally infected cats in order to follow the course of seroconversion and of the antibody levels throughout the infection. An early and marked increase of TM antibodies was observed. Antibodies to TM were demonstrated at high levels throughout the observation period. The immune response to SU and to CA was less pronounced and in some cats the level of antibodies to SU and CA tended to decline 6 months after infection. In addition, 413 FIV negative and positive cat sera were tested in order to define for each antigen the diagnostic sensitivity, specificity and efficiency. TM showed the highest diagnostic sensitivity (98%) while its specificity was 97%. Its diagnostic efficiency of 97% was better than that of SU and CA and exceeded that of tests utilizing conventionally grown and gradient purified FIV. Therefore, recombinant TM can be considered a very important antigen for FIV ELISA testing. An interesting perspective is offered in the combination of TM with other recombinant antigens in a dot assay form.

Crandell feline kidney cells and feline thymocytes, either feline immunodeficiency virus (FIV) infected or uninfected, were fixed with paraformaldehyde and used to vaccinate cats. The cells were mixed with a 30:70 water/mineral oil emulsion containing 250 micrograms ml-1 N-acetyl-D-glucosaminyl-beta-(1-4)-N-acetyl-muramyl-L-alanyl-D-isoglutam ine. Eighteen specific pathogen-free cats were vaccinated three times with 3-week intervals and challenged 21 days after the final boost with a low dose of the homologous FIV-UT113 strain. Eight out of ten cats that had received FIV-infected cell vaccines developed significant anti-FIV antibody titres to the envelope and core antigens. Neutralizing antibodies were detectable at the moment of challenge in the sera of these animals. Within 5 weeks after challenge 15 out of 18 cats became viraemic. Three animals, two that had been vaccinated with FIV-infected thymocytes and did not develop antibody, and one that had received an uninfected thymocyte preparation, remained uninfected for 6 months. Upon rechallenge of the three animals, two again resisted infection; these cats had been immunized with the infected and the uninfected thymocyte preparations, respectively.

Five groups of cats were vaccinated with different recombinant feline immunodeficiency virus (FIV) SU vaccines expressed either in Escherichia coli or in the Baculovirus system. In Part I of this series, we described the humoral immune response and outcome of intraperitoneal FIV challenge exposure. Additionally, all cats were monitored for clinical and hematological changes and the course of blood lymphocyte subsets. These results are described in this present paper. A great increase of antibodies was found after vaccination with different recombinant FIV antigens, which did not protect the cats from intraperitoneal FIV challenge infection. This observation was paralleled by an increase of eosinophils during vaccination which was even more pronounced after challenge infection. After FIV challenge, infection lymphadenopathy, gingivitis, pharyngitis, changes in total leukocytes and neutrophils and a decrease in the CD4+:CD8+ ratio were found in cats of all groups and were considered as a sign of the FIV infection taking place, independent of vaccination. The following observations suggest that in these cats a TH2-like immune response was elicited: the high counts of eosinophils, the nature of antigen and adjuvant (aluminium hydroxide) and the high amounts of antigens used for immunization. Clearly, this type of immune response did not protect the animals from intraperitoneal FIV challenge infection.

Viral progeny of two molecular clones of feline immunodeficiency virus (FIV), 19k1 and 19k32, were tested in a virus neutralization assay. In this assay the infection of thymocytes with FIV19k1 was neutralized by serum S1422, derived from an SPF cat 22 weeks after infection with FIV19k1. We previously reported that a point mutation at position 560 in hypervariable region-5 (HV-5) of 19k1 confers resistance to virus neutralization (Siebelink et al., 1993, J. Virol. 67:2202-2208). Viral progeny of the other molecular clone, FIV19k32, which differs in the envelope protein in only six amino acids from 19k1, was not neutralized. In order to map sites involved in virus neutralization we constructed chimeric clones by reciprocal exchange of 19k1 and 19k32 envelope gene fragments. Reciprocal exchange of a 1662 bp fragment, encoding almost the whole surface protein, which differs in five amino acids between these two clones, resulted in exchange of the phenotype. Amino acids of the envelope protein of 19k1 and 19k32, in which these clones differ, were substituted by point mutation. We demonstrated that one of these mutations, a substitution of leucine to serine at position 483 in HV-4, also conferred resistance of 19k1 to neutralization by serum S1422.

We have evaluated in vitro and in vivo whether it is possible to protect cat macrophages from feline immunodeficiency virus (FIV) infection by the administration of dideoxycytidine 5'-triphosphate (DDCTP). Since cell membranes are impermeable to phosphorylated drugs we have encapsulated DDCTP into autologous erythrocytes and modified erythrocyte membranes to target these drug-loaded cells to macrophages. DDCTP-loaded erythrocytes reduced FIV production by macrophages infected in vitro or obtained from naturally or experimentally infected cats. The same treatment protected the majority of peritoneal macrophages during a 7 month experimental FIV infection and reduced the percentage of circulating lymphocytes stained with an anti-p24 antibody. These results suggest that the administration of nucleoside analogues in phosphorylated form is feasible and their targeting to macrophages reduces FIV infection in vitro and in vivo.

The efficacy and the long-term protection of a recombinant feline leukemia virus (FeLV) vaccine were determined in 30 specified pathogen free cats for over 3 years. At the same time, in order to specify the effects of feline immunodeficiency virus (FIV) on the immune system, one half of the cats (n = 15) were previously infected with the Swiss isolate FIV Zurich 2. The second half of the animals (n = 15) served as non-infected controls. Eighteen (nine FIV-negative, nine FIV-positive) vaccinated and 12 (six FIV-negative, six FIV-positive) non-vaccinated cats were intraperitoneally challenged with FeLV A. Seventeen of 18 vaccinated cats were protected against persistent viremia, while ten of 12 non-vaccinated controls became infected. An increase of antibodies against FeLV SU was found in all protected cats after the challenge exposure. No difference in vaccine efficacy was found between FIV-negative and FIV-positive animals. The whole group of cats was observed for over 3 years. There were no further vaccinations during this period. CD4+ and CD8+ cell subsets, clinical outcome and time of survival of the cats were recorded. FIV-negative and FIV-positive animals were kept in two different rooms. However, FeLV-negative and FeLV viremic cats were housed together in both rooms in order to imitate a natural FeLV exposure situation. Anti-recombinant FeLV SU antibodies were measured by enzyme-linked immunosorbent assay. Although a continuous decline of antibodies was found in FeLV vaccinated cats, they remained protected against constant FeLV challenge for over 3 years. FIV infection had a stronger effect on the depression of the CD4+:CD8+ ratio than FeLV infection. Within the group of FIV-positive cats, the FeLV-vaccinated animals had significantly better survival rates as well as better clinical and laboratory parameters. FIV- and FeLV-coinfected cats showed the lowest CD4+:CD8+ ratio, mainly caused by decreased CD4+ lymphocyte counts. CD8+ lymphocytes with strong fluorescence (CD8(high)) disappeared and cells with weak fluorescence (CD8(low)) appeared instead. Prevention of coinfection by immunizing FIV-positive cats against FeLV infection improved the clinical outcome and prolonged the cat's life expectancy.

Although cryptococcosis is a well-characterised disease of cats, the factors predisposing individuals to infection are unknown. As an indication of the immune status of an individual, lymphocyte subsets can be analysed. Reference ranges for feline lymphocyte subsets (Pan T+, CD4+, CD8+ and B cells) were established using a rapid whole blood technique and flow cytometry. There were no effects of age or sex on lymphocyte subset values. The numbers of circulating leucocytes and lymphocyte subsets were determined in FIV-positive and FIV-negative cats with cryptococcosis and compared with a group of healthy control cats. There were only minor differences in the numbers of lymphocyte subsets among the subgroups of cats examined in the study and the predisposition to cryptococcosis in cats could not be explained by deficiencies in lymphocyte subsets. There was a tendency for FIV-negative cats with cryptococcosis to have reduced numbers of circulating CD4+ cells and lower CD4:CD8 ratios compared with normal cats, although the interpretation of this finding was complicated by the wide reference range for normal cats. The extent to which this is the cause of the fungal infection was not determined. The only difference in leucocyte or lymphocytes subset values between FIV-negative cats with cryptococcosis and FIV-positive cats with cryptococcosis was that the CD4+ percentage was lower in the FIV-positive cats. The absolute CD4+ count was similar however, in FIV-positive and FIV-negative cryptococcosis cases. On the basis of this and other available information, the categorisation of cryptococcosis as a disease defining the AIDS phase of FIV infection may be incorrect.

Feline oncornavirus and lentivirus infections have provided useful models to characterize the virus and host cell factors involved in a variety of marrow suppressive disorders and haematological malignancies. Exciting recent progress has been made in the characterization of the viral genotypic features involved in FeLV-associated diseases. Molecular studies have clearly defined the causal role of variant FeLV env gene determinants in two disorders: the T-lymphocyte cytopathicity and the clinical acute immunosuppression induced by the FeLV-FAIDS variant and the pure red cell aplasia induced by FeLV-C/Sarma. Variant or enFeLV env sequences also appear to play a role in FeLV-associated lymphomas. Additional studies are required to determine the host cell processes that are perturbed by these variant env gene products. In the case of the FeLV-FAIDS variant, the aberrant env gene products appear to impair superinfection interference, resulting in accumulation of unintegrated viral DNA and cell death. In other cases it is likely that the viral env proteins interact with host products that are important in cell viability and/or proliferation. Understanding of these mechanisms will therefore provide insights to factors involved in normal lymphohaematopoiesis. Similarly, studies of FeLV-induced haematological neoplasms should reveal recombination or rearrangement events involving as yet unidentified host gene sequences that encode products involved in normal cell growth regulation. These sequences may include novel protoncogenes or sequences homologous to genes implicated in human haematological malignancies. The haematological consequences of FIV are quite similar to those associated with HIV. As with HIV, FIV does not appear to directly infect myeloid or erythroid precursors, and the mechanisms of marrow suppression likely involve virus, viral antigen, and/or infected accessory cells in the marrow microenvironment. Studies using in vitro experimental models are required to define the effects of each of these microenvironmental elements on haematopoietic progenitors. As little is known about the molecular mechanisms of FIV pathogenesis, additional studies of disease-inducing FIV strains are needed to identify the genotypic features that correlate with virulent phenotypic features. Finally, experimental FIV infection in cats provides the opportunity to correlate in vivo virological and haematological changes with in vitro observations in a large animal model that closely mimics HIV infection in man.

The aberrant sleep documented in subjects with human immunodeficiency virus (HIV) infection is uniquely important because of the contribution this poor quality sleep makes to the fatigue, disability, and eventual unemployment that befalls these patients. Especially given this importance in clinical care, the research on the prominent sleep changes described in HIV infection remains modest in quantity. The chronic asymptomatic stage of HIV infection is associated with the most intriguing and singular sleep structure changes. Especially robust is the increase in slow wave sleep, particularly in latter portions of the sleep period. This finding is rare in other primary or secondary sleep disorders. The sleep structure alterations are among the most replicable of several pathophysiological sequelae in the brain associated with early HIV infection. It is unlikely that these sleep architecture changes are psychosocial in etiology, and they occur before medical pathology is evident. They are not associated with stress, anxiety, or depression. Evidence is accumulating to support a role for the somnogenic immune peptides tumor necrosis factor (TNF)alpha and interleukin (IL-1 beta) in the sleep changes and fatigue commonly seen in HIV infection. These peptides are elevated in the blood of HIV-infected individuals, and are somnogenic in clinical use and animal models. The peripheral production of these peptides may also have a role in the regulation of normal sleep physiology. The lentivirus family contains both HIV and the feline immunodeficiency virus (FIV). The use of the FIV model of HIV infection may provide a way to further investigate the mechanism of a neurotropic, neurotoxic virus initiating the immune acute phase response and affecting sleep. Neurotropic lentivirus infection is a microbiological probe facilitating neuroimmune investigation.

The lentivirus feline immunodeficiency virus (FIV) is a widespread pathogen of the domestic cat that is mainly transmitted through bites, although other means of transmission are also possible. Its prevalence ranges from 1 to 10% in different cat populations throughout the world, thus representing a large reservoir of naturally infected animals. FIV resembles the human immunodeficiency virus (HIV) in many respects. Similarities include the structural features of the virion, the general organization and great variability of the genome, the life cycle in the infected host, and most importantly, the pathogenic potential. Infection is associated with laboratory signs of immunosuppression as well as with a large variety of superinfections, tumors, and neurological manifestations. Our understanding of FIV is steadily improving and is providing important clues to the pathogenesis of immunodeficiency-inducing lentiviruses. The cellular receptor for FIV is different from the feline equivalent of the human CD4 molecule used by HIV; nevertheless, the major hallmark of infection is a progressive loss of CD4+ T lymphocytes as in HIV infection. The mechanisms by which FIV escapes the host's immune responses are being actively investigated. FIV causes lysis of infected T cells and also appears to predispose these cells to apoptosis. Infection of macrophages and other cell types has also been documented. For reasons yet to be understood, antibody-mediated neutralization of fresh FIV isolates is very inefficient both in vitro and in vivo. Vaccination studies have provided some encouraging results, but the difficulties encountered appear to match those met in HIV vaccine development. FIV susceptibility to antiviral agents is similar to that of HIV, thus providing a valuable system for in vivo preclinical evaluation of therapies. It is concluded that in many respects FIV is an ideal model for AIDS studies.

Specific-pathogen-free cats, immunized with a 22-amino-acid synthetic peptide designated V3.3 and derived from the third variable region of the envelope glycoprotein of the Petaluma isolate of feline immunodeficiency virus (FIV), developed high antibody titers to the V3.3 peptide and to purified virus, as assayed by enzyme-linked immunoassays, as well as neutralizing antibodies, as assayed by the inhibition of syncytium formation in Crandell feline kidney cells. V3.3-immunized animals and control cats were challenged with FIV and then monitored for 12 months; V3.3 immunization failed to prevent FIV infection, as shown by virus isolation, anti-whole virus and anti-p24 immunoglobulin G antibody responses, and positive PCRs for gag and env gene fragments. Sequence analysis of the V3 region showed no evidence for the emergence of escape mutants that might have contributed to the lack of protection. The sera of the V3.3-hyperimmunized cats and two anti-V3.3 monoclonal antibodies neutralized FIV infectivity for Crandell feline kidney cells at high antibody dilutions but paradoxically failed to completely neutralize FIV infectivity at low dilutions. Moreover, following FIV challenge, V3.3-immunized animals developed a faster and higher antiviral antibody response than control cats. This was probably due to enhanced virus replication, as also suggested by quantitative PCR data.

The ability of feline immunodeficiency virus (FIV) isolates from subtypes A and B to superinfect cats and cell cultures was tested. Three specific pathogen-free (SPF) cats were first inoculated with 10 ID50 of subtype B virus (FIVBang) and 30 weeks later inoculated with 100 ID50 of subtype A virus (FIVPet). On the basis of subtype-specific PCR analysis, both FIV subtypes were detected in the peripheral blood lymphocytes (PBLs) of two of three cats from 9 to 30 weeks following the second inoculation. Only the first virus was detected in the bone marrow (BM) cells of these two cats until 30 weeks following the second inoculation, at which time the second virus was finally detected in their BM cells. Both cats developed significant virus-neutralizing (VN) antibodies to the second virus by 15 weeks following the second inoculation; but only one cat had high VN titers to the first virus, which remained at the same level even after the second inoculation. The two control cats inoculated with only the second virus developed VN titers specifically to the second virus and were consistently PCR positive for the virus in PBLs and BM cells starting 9 weeks postinoculation. Thus a delay in BM infection with the second virus was observed in the two superinfected cats. In contrast, one of three cats had neither VN antibodies to the second virus nor PCR signal of the second virus in its PBLs, BM, and lymph node throughout the 30 weeks of study and it appeared to be resistant to superinfection.(ABSTRACT TRUNCATED AT 250 WORDS)

We report alterations in leucocytes numbers and lymphocyte subset percentages, determined by flow cytometry, for three observed and previously defined clinical stages (asymptomatic carrier (AC), AIDS-related complex (ARC) and AIDS) of naturally occurring FIV infection. Unstaged FIV-positive cats had significantly lower numbers of total leucocytes (WCC) and neutrophils, lower percentages of PanT+ and CD4+, lower CD4:CD8 ratio and a higher percentage of B cells compared with unstaged FIV-negative cats. When FIV-positive cats were separated into clinical stages and compared with matched FIV-negative cats, AC FIV-positive cats had a significantly lower WCC, lower absolute numbers of neutrophils and lymphocytes, lower percentages of CD4+ and CD8+ cells, lower CD4:CD8 ratios and a higher percentage of B cells than healthy FIV-negative cats. ARC FIV-positive cats had lower percentages of PanT+ and CD4+ cells, lower CD4:CD8 ratios and higher percentages of B cells than matched FIV-negative cats. FIV-positive cats with AIDS had significantly lower percentages of CD4+ cells than matched FIV-negative cats. Comparisons among the three observed clinical stages of FIV-positive cats showed that AC FIV-positive cats had significantly lower WCC, significantly lower absolute numbers of neutrophils and a significantly lower percentage of CD8+ cells than ARC FIV-positive cats. AIDS FIV-positive cats had a significantly lower percentage of B cells than AC or ARC FIV-positive cats. FIV-positive cats had a similar leucocyte response to illness as FIV-negative cats but had consistently lower percentages of CD4+ lymphocytes. Thus, in the staging of FIV, a rise in the percentage of CD8+ lymphocytes could be used to distinguish between AC and ARC and a fall in the percentage of B lymphocytes could distinguish AIDS from AC and ARC.

Molecularly cloned viruses are considered essential reagents for characterizing viral domains responsible for infectivity and disease pathogenesis in the host. The infectivity and hematological alterations associated with two molecularly cloned isolates of feline immunodeficiency virus (FIV-pPPR and FIV-pF34) and an uncloned isolate (FIV-PPR) were assessed by inoculation of cats. Inoculated cats were tested for viral antibody, viremia, and clinical pathological disease. Peripheral blood mononuclear cells isolated from inoculated cats were assayed for virus infection by virus isolation, amplification of proviral DNA (by polymerase chain reaction), and in situ hybridization for viral RNA. Over 50% of the cats inoculated with cloned virus FIV-pF34 failed to seroconvert even when coinfected with feline leukemia virus; these cats were consistently virus positive only by amplification of proviral DNA. All cats inoculated with cloned virus FIV-pPPR seroconverted and were found virus positive by at least two of three virus detection assays. Both cloned viruses were less capable of suppressing CD4:CD8 ratios when compared to the biological isolates from which they were cloned. Isolates which replicate efficiently in feline peripheral blood mononuclear cells (PBMC), i.e., FIV-pPPR or biological FIV-PPR, caused greater virus load and lower CD4:CD8 ratios when compared to cloned FIV-pF34, which replicates efficiently in feline adherent cell lines and macrophages but poorly in primary feline PBMC. Molecular clones FIV-pF34 and FIV-pPPR will be useful reagents for characterization of viral determinants of virus load and possibly, cell tropism in vivo.

Questionnaires were sent to veterinarians who had submitted a fibrosarcoma from a cat to the surgical pathology services of the veterinary schools of the University of Pennsylvania and Tufts University between Jan 1, 1991 and June 30, 1992. Questionnaire items included signalment, FeLV and feline immunodeficiency virus status, site of sarcoma, vaccination site, vaccines used, treatment, biologic behavior of the tumor, and final outcome. Data were analyzed, using Student's t-test for continuous data, chi 2 test for categoric data, and log-rank test for survival estimates. Comparing results for cats with vaccination-site (VS) tumors and nonvaccination-site (NVS) tumors, we determined that VS tumors developed in younger cats and were larger than NVS tumors. Although VS sarcomas were biologically aggressive and redeveloped more often than NVS sarcomas, metastasis was not detected, and cats with VS tumors survived longer than cats with NVS tumors. Vaccination-site sarcomas developed in cats after injection of many types of vaccines, administered singularly or in combination. Of the cats in the VS group administered a single vaccine, 37% were given rabies, 33% were given feline viral rhinotracheitis/calicivirus/panleukopenia virus, and 30% were given FeLV vaccines. Cats with VS tumors were more likely to have received FeLV vaccine and less likely to have received rabies vaccine than those with NVS tumors. Although vaccines produced by certain manufacturers were used most often in cats with VS and NVS sarcomas, it was believed that this probably represented marketing practices and brand popularity.(ABSTRACT TRUNCATED AT 250 WORDS)

Sixteen adolescent specific pathogen free cats were inoculated with the Petaluma strain of feline immunodeficiency virus (FIV) and two cats were then necropsied at each of 5, 10, 21, 28, 42, 56, 70, and 84 day time points following infection. Lymphadenopathy gradually increased starting at Day 10 and persisted for the duration. Gross clinical signs of fever, mild to severe malaise, anorexia, diarrhea, dehydration, and generalized soreness appeared around Day 42, peaked at Day 56, and disappeared by Days 70-84 post-infection. Leukopenia, associated initially with a mild lymphopenia and later by both a mild lymphopenia and a severe neutropenia, appeared 14-28 days following infection, troughed at Day 56, and persisted thereafter. The CD4+:CD8+ T cell ratio started to decrease around Day 28, reaching a nadir at Days 56-70. This decrease was due to a decline in the absolute numbers and percentage of CD4+ T cells and an increase in the percentage of CD8+ T cells. Significant histopathologic lesions included myeloid hyperplasia between Days 56-70 post-infection; thymitis with cortical involution and follicular hyperplasia starting at Day 42; lymphoid hyperplasia of peripheral and mesenteric nodes, spleen and tonsils beginning around Day 42; typhlitis most evident from Day 56 onward, and an interstitial nephritis and pneumonitis that was most intense after Day 42. Virus was isolated from peripheral blood mononuclear cells (PBMC) beginning 2 weeks post-infection, and plasma viremia appeared 1 week later. Plasma and PBMC-associated viremia peaked at 42-56 days following infection and decreased abruptly thereafter. Proviral DNA was detectable as early as 5 days after infection in blood leukocytes and after 10 days in other organs. The central nervous system, lungs, thymus, tonsils and mesenteric lymph nodes were the earliest sites of virus localization. Antibodies to the FIV capsid protein appeared 14 days following infection and reached peak levels by Days 42-56. Abnormalities occurring during the primary stage of FIV infection were consistent with those described for acute simian and human immunodeficiency virus-induced disease.

Specific pathogen-free cats were experimentally infected with feline immunodeficiency virus (FIV) and subsequently exposed to common infectious pathogens and immune stimuli over a 3-year period. Cats with preexisting FIV infection showed signs of disease after exposure to Haemobartonella felis, Toxoplasma gondii, feline herpesvirus-1, and feline calicivirus similar to signs in non-FIV-infected cats, although they were more severe. No adverse effects of immunization with inactivated rabies virus vaccine and a synthetic polyproline immunogen were observed in either FIV-infected or non-FIV-infected cats, whereas the application of a diphtheria-tetanus-pertussis vaccine caused transient fever and lymphadenopathy in both groups of animals. Primary immune responses to pathogens or immunogens were usually delayed or diminished in FIV-infected compared with non-FIV-infected cats. Repeated infections and immune activation had no significant effects on the levels of FIV-specific antibodies or on the proportion of peripheral blood mononuclear cells (PBMCs) containing FIV proviral DNA. However, FIV-infected cats that were not exposed to immune stimuli had lower CD4+ T-lymphocyte numbers and lower CD4+/CD8+ T lymphocyte ratios at the end of the 3-year study than FIV-infected cats exposed to cofactors. The latter also had normal levels of interleukin-3 receptor (IL-2R) and major histocompatibility class II (MHC-II) antigen expression on PBMCs, while FIV-infected cats not exposed to cofactors had up-regulated IL-2R and down-regulated MHC-II antigen expression. It was concluded that repeated immune stimulation did not have a deleterious effect on the course of FIV-induced immunodeficiency.

The compound 3'azido-2',3'-deoxythymidine (AZT) inhibits the replication of feline immunodeficiency virus (FIV) in cell culture, and treatment with the compound has been reported to induce some clinical improvement in some cases of feline FIV infection. In order to determine the effect of prophylactic treatment with AZT on experimental FIV infection, cats were treated with the compound at 0.2, 1.0, 5, 25 or 50 mg kg-1 day-1 for 29 days. One day after the treatment was started, they were inoculated with 150 cat infectious doses of FIV. All the cats became viraemic, seroconverted and developed lymphadenopathy, although the onset of each was delayed in the cats given higher doses of AZT. Anaemia developed in the cats given high doses of AZT. Virus re-isolated from the cats given 50 mg kg-1 day-1 was as susceptible to AZT in cell culture as the inoculated virus. Thus AZT is much less effective in cats than might have been expected from the results of in vitro studies.

Although HIV-1 and other mammalian lentiviruses infect macrophages, they are not cytopathic. Consequently, these infected long-lived cells serve as major virus reservoirs with a key role in the propagation of the virus throughout the body as well as in the pathogenesis of AIDS. Furthermore, well-differentiated macrophages possess low abilities to phosphorylate the most common reverse transcriptase inhibitors of the nucleoside analog family. In an attempt to overcome these problems we have evaluated in vitro and in vivo in a feline immunodeficiency animal model whether it is possible to protect macrophages from FIV infection by direct administration of dideoxycytidine-5'-triphosphate (ddCTP). Because the cell membranes are impermeable to phosphorylated drugs we have encapsulated ddCTP into autologous erythrocytes. The drug-loaded erythrocyte membranes were then modified to target these carrier cells to macrophages. ddCTP-loaded erythrocytes were able to reduce FIV production by macrophages infected in vitro or obtained from naturally or experimentally infected cats. Furthermore, the administration of ddCTP-loaded erythrocytes protected the majority of peritoneal macrophages during a 7-month experimental FIV infection and reduced the percentage of circulating lymphocytes stained by an anti-p24 antibody. These results suggest that the administration of nucleoside analogs in phosphorylate form is feasible and their targeting to macrophages reduces FIV infection both in vitro and in vivo.

The hemostatic function of 40 feline immunodeficiency virus (FIV) seropositive and 8 FIV and feline leukemia virus (FeLV) seropositive cats was evaluated and compared with reference values from 30 clinically healthy cats. The FIV-positive cats were divided into 3 groups: group I included asymptomatic carriers; group II comprised sick FIV-infected cats with illnesses not likely to influence the hemostatic system; and group III included FIV-positive cats with diseases potentially associated with coagulopathies. Platelet counts in FIV/FeLV-infected cats were significantly lower than in healthy cats (P < .003), whereas the differences in the 3 groups of FIV-positive cats were variable (group I, P = .009; II, P = .05; III, P = .09). Thrombocytopenia (< 145,000 platelets/microL) was present in 4 FIV-positive and 3 FIV/FeLV-positive cats. Platelet aggregation induced by collagen (0.5 and 0.25 micrograms/mL), adenosine diphosphate (ADP) (1 and 0.6 mumol/L), and thrombin (0.4 and 0.25 IU/mL) was not significantly different from that of healthy cats. The plasma coagulation system was evaluated by measuring one-stage prothrombin time (OSPT), activated partial thromboplastin time (APTT), thrombin time, fibrinogen concentration, coagulation factor assays, fibrinogen and fibrin degradation products (FDP), and plasma exchange test. The OSPT was similar in FIV-seropositive cats and in the healthy control group. Cats with FIV infection, however, had markedly shorter clotting times than healthy cats when using a modified test system (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Cats naturally infected with feline immunodeficiency virus (FIV) develop an AIDS-like syndrome whereas experimentally infected cats do not. To investigate the role of cofactors in the development of this disease in cats, 7 specific pathogen-free (SPF) and 12 random-source (RS) cats were infected with FIV. Over 4 years, infected cats developed similar phenotypic and functional immune abnormalities characterized by early and chronic inversion of CD4+:CD8+ cell ratios and significantly decreased mitogen responses compared with controls. Beginning 18-24 months after infection, 10 RS cats developed chronic clinical disease typical of feline AIDS, including stomatitis and recurrent upper respiratory disease; 4 SPF cats also developed chronic clinical disease, 2 with neurologic disease and 2 with B cell lymphomas. Thus, immunologic background is important in the type of disease that develops in cats infected with FIV, and FIV represents a promising animal model for studying the immunopathogenesis of AIDS in humans.

A malignant low-grade B-cell lymphoma, primarily in the kidney, is described in a specific-pathogen-free cat experimentally infected with feline immunodeficiency virus (FIV) and free of feline leukaemia virus. At the time of diagnosis the cat showed a marked reduction of circulating CD4+ T lymphocytes, was 2 years old, and had been infected for 18 months. FIV was isolated both from peripheral blood mononuclear cells and the neoplastic tissue. DNA of FIV gag gene was detected in several specimens, including the neoplastic tissue. Even if they do not demonstrate a direct role for virus promotion of lymphomas, these and previous observations indicate that B-cell malignant lymphoma might be associated with FIV infection as reported for human and simian immunodeficiency virus infections.

Young cats, when chronically infected with feline leukemia virus (FeLV), developed feline acquired immune deficiency syndrome (FAIDS). The syndrome was associated with a sequence of dysfunctions in the hypothalamic-pituitary-gonadal (HPG) and the immune system, manifested in the reduction of luteinizing hormone-releasing hormone (LHRH), follicle stimulating hormone (FSH), luteinizing hormone (LH), and testosterone in blood plasma. The average FSH and LH (in plasma or lymphocyte), testosterone, and LHRH concentrations in the 20 FeLV-infected cats were measured by radioimmunoassay. The results were compared with those of the 12 control cats that were not FeLV-infected. Four weeks after infection, the plasma LHRH concentration in the infected cats showed a 43% reduction. Five to six weeks after infection, the content of FSH and LH in lymphocyte was reduced by 50% and 28%, respectively, whereas, the plasma FSH and LH was reduced by 52% and 42%, respectively. A significant reduction in testosterone content was detected at Week 11 of infection. The onset of the immuno- and neuroendocrine dysfunctions in FAIDs cats followed this sequence: hypothalamus, lymphocyte, pituitary, adrenal gland, and gonads. Indirect immunofluorescence assay showed the presence of FeLV cytoplasmic antigens in the fibers of the hypothalamic preoptic region and the Leydig cells. The possible causal relationship between the dysfunction of the lymphocyte and HPG systems and the presence of FeLV was discussed.

Four hundred and thirty-nine feline serum samples from cats with different living conditions in the north of Italy were tested for antibodies to feline immunodeficiency virus (FIV) and for antigen of Feline Leukemia Virus by enzyme-linked immunosorbent assay. A Western blot technique was also used on the positive sera in order to confirm the presence of specific antibodies to FIV. The Western blot enabled the detection of a false positive serum. The prevalence of FIV infection in this population was 12.5% and among the seropositive cats a greater proportion was male (74.5%) than female (25.5%). A correlation between the clinical status and the evolution of the pathology is described together with a score based on the severity of the stomatitis in infected cats. The Western blot patterns of positive samples were then compared with the stage of the pathology. Statistical analysis on the distribution of FIV in stray cats, cats with garden and courtyard access and strictly house-confined cats showed a highly significant risk of the infection in the first group.

A panel of monoclonal antibodies (mAbs) detecting distinct B-cell epitopes on p24 core viral protein of feline immunodeficiency virus (FIV) were employed to develop immunoassays to measure p24 concentration in culture and serum samples, to localize p24 in FIV-infected cells and tissues, and to detect anti-p24 antibodies in cat sera. In its optimized configuration the p24 capture assay detected as little as 0.25 ng/ml of protein. The assay was found at least as sensitive as the reverse transcriptase activity assay in FIV-infected lymphocyte cultures and proved capable of detecting p24 antigen in acid pretreated sera from a high proportion of FIV-infected cats. The mAbs were also successfully used to detect the p24 antigen in permeated FIV-infected cells by flow cytometry and in tissue sections from FIV-infected cats by immunohistochemical staining. Anti-p24 antibodies in FIV-infected cat sera were assayed by a competitive capture ELISA which readily identified occasional false positive results provided by a standard ELISA using purified whole FIV-coated wells.

In order to monitor the antibody response to feline immunodeficiency virus (FIV) in cats, following experimental and natural infection, enzyme-linked immunosorbent assays (ELISAs) were developed using recombinant env and gag proteins and p24-specific monoclonal antibodies. It was shown that in experimentally infected cats an env protein-specific antibody response was directly followed by a gag protein-specific response. Furthermore, an ELISA for the detection of env protein-specific serum antibodies proved more sensitive in identifying experimentally and naturally infected cats than ELISAs demonstrating gag protein-specific antibodies. It was concluded that, like in HIV infection of humans, the detection of env protein-specific serum antibodies in addition to gag protein-specific antibodies is not only an important tool in the diagnosis of the infection but also in studies concerning the pathogenesis of the disease.

A new recombinant FeLV vaccine was evaluated in 30 specified pathogen-free cats 10 months of age cats. The vaccine consisted of the non-glycosylated FeLV envelope protein p45, aluminium hydroxide and a saponin adjuvant. The cats (n = 18) were vaccinated twice intramuscularly, 3 weeks apart. All animals were challenged intraperitoneally with FeLV subgroup A, 18 weeks later. While 94% of the vaccinated cats showed no viraemia or were only transiently viraemic, 80% of the non-vaccinated animals became persistently viraemic within 2 to 3 weeks. In our hands the preventable fraction of the vaccine was 93%. In order to determine the effect of a pre-existing infection with feline immunodeficiency virus on the efficacy of vaccination, 50% of the cats were previously infected with FIV. The infected cats were protected to the same degree as the non-infected animals. With prolonged duration of FIV infection the probability increases, that the immune system of the cat will fail and clinical signs will appear. In order to observe a state of possible immunodeficiency, an accurate clinical examination of every cat prior to vaccination seems of major importance.

This study was designed to examine the effects of a pre-existing, clinically asymptomatic feline immunodeficiency virus (FIV) infection on a primary challenge with Toxoplasma gondii. Parenteral challenge of FIV-infected cats with tachyzoites of the ME49 strain of T. gondii caused a precipitous drop in all lymphocytes (CD4+, CD8+, and B cells) and generalized severe toxoplasmosis. The predominant postmortem lesions included acute and often fatal interstitial pneumonia, dominated histologically by macrophages, and multifocal to coalescing hepatic necrosis. Immunohistochemistry revealed numerous T. gondii antigen and tachyzoites in macrophages and other cell types in the lung lesions. The proliferative response of peripheral blood mononuclear cells to specific (T. gondii antigen) and nonspecific (Concanavalin A) mitogens was defective in the dually infected cats, suggesting marked immunosuppression. In contrast to the dually infected cats, cats infected only with T. gondii developed a transient, mild clinical disease characterized by anorexia, lethargy, and multifocal chorioretinitis. Lymphocyte changes in T. gondii-infected cats included an early pan-lymphopenia followed by reestablishment of all lymphocyte subset profiles. These cats also showed a reduced proliferative response to Concanavalin A at 1 week after challenge, but a measurable in vivo response to T. gondii antigens, as evidenced by in vitro lymphocyte proliferation in the absence of a mitogenic stimulus. These results show that infection of cats with FIV-NCSU, markedly enhances their susceptibility to a primary T. gondii infection and provides a model to study the mechanisms of the underlying immunological defect(s) occurring early after HIV infection that may predispose individuals to development of acquired immunodeficiency syndrome and associated diseases.

The purposes of this study were to examine the cell-mediated immune response of the normal cat to the modified live feline viral rhinitis, calicivirus, and parvovirus (FVRCP) vaccine (Felocell CVR, Norden, Lincoln, NE), and to evaluate the intradermal skin test as a clinical measure of the immune response of cats. Vaccine and diluent were injected intradermally on the dorsal pinna of 34 normal adult cats. Skin thickness measurements, lymphocyte counts, and Concanavalin A mitogenesis indices were evaluated in 18 of these cats. Skin biopsies were obtained in 16 cats. In normal cats, the FVRCP vaccine induced a delayed hypersensitivity response characterized by a mononuclear infiltrate most pronounced at 72 h. Five cats with either feline leukemia (FeLV) or feline immunodeficiency virus (FIV) were tested and had a significantly reduced response to the skin test. The skin test provides a clinically useful method of evaluating immune function in cats and may be useful in development of a prognostic index.

Feline immunodeficiency virus (FIV) was first isolated in 1986 from a cat with an acquired immunodeficiency syndrome (AIDS)-like disease. This virus has many characteristics in common with human immunodeficiency virus which is an etiological agent of AIDS in human and is classified as a member of the lentivirus genus of the retrovirus family. Since the discovery of FIV, many researchers have studied the virus extensively from clinical, biological, and genetic aspects. In this review, the biological nature of FIV is summarized in four sections, i.e., morphological and biochemical properties of FIV biological properties of FIV, immunological aspects of FIV infection, and clinical aspects of FIV infection. This review includes some recent, unpublished data from our and other groups.

Previous experimental studies utilizing human recombinant interferon-alpha-2b (IFN alpha-2b) alone or with zidovudine (AZT) to treat established feline leukemia virus (FeLV) infection resulted in a significant reduction in circulating virus throughout a 49-day treatment period. However, the anti-FeLV effect of IFN alpha was limited by the production of IFN alpha-neutralizing antibodies detected 7 weeks after the start of treatment. AZT without IFN alpha had no effect on circulating virus load. To examine the hypothesis that combination chemoimmunotherapy might induce the clearance of FeLV infection, persistently infected cats were infused with activated lymphocytes, IFN alpha, and AZT 12 weeks after infection with FeLV. Recipient cats received weekly infusions of 1.46 x 10(8) lymphocytes activated in vitro with lectin/IL-2 comprised of 98% T cells and an even distribution of CD4+ and CD8+ lymphocytes. FeLV infection was cleared in 4 of 9 cats receiving combined therapy after four adoptive cell transfers. These cats remained negative for circulating virus during a 63-day treatment period (17 adoptive cell transfers) despite the production of anti-IFN alpha-neutralizing antibodies. Sequential development of virus-neutralizing and virus envelope antibody titers were detected in those cats which cleared retroviremia, an antiviral response that was absent in untreated control animals or nonresponders. Three of four responder cats remained negative for FeLV 95 days after treatment was discontinued. Treatment of cats with lymphocytes without chemotherapy failed to influence the course of FeLV infection. These results suggest that combined treatment using IFN alpha and adoptive lymphocyte transfer served to reconstitute antiviral humoral immunity, counteract immunosuppression, and induce the reversal of retroviremia.

Cats in the primary stage of Feline Immunodeficiency Virus (FIV) infection and FIV seronegative cats were vaccinated with a modified live Feline Panleukopenia virus vaccine (FPV-MLV). The FPV-MLV strain was not pathogenic for FIV seronegative cats, whereas in FIV infected cats it produced severe clinical signs, similar to those typically observed in cats naturally infected with field strains of FPV (fever, diarrhoea, leukopenia).

Sera from cats experimentally infected with five isolates of feline immunodeficiency virus (FIV) from various geographical regions and from FIV enzyme-linked immunosorbent assay-seropositive field cats from four European countries neutralized the Petaluma strain of FIV (FIV-P), originally isolated in California, at high titers. In addition, FIV-P and a European isolate proved equally susceptible to neutralization by all sera tested. Coupled with observations by Fevereiro et al. (M. Fevereiro, C. Roneker, A. Laufs, L. Tavares, and F. de Noronha, J. Gen. Virol. 72:617-622, 1991), these findings indicate that most if not all FIV strains circulating in Europe and the United States share important neutralization-inducing epitopes.

Experimental infection with the Mt. Airy isolate of feline immunodeficiency virus (FIVMA), a lentivirus isolated from a domestic cat exhibiting signs of an immunodeficiency-like syndrome, results in transient lymphadenopathy, fever, stomatitis, enteritis, neurologic abnormalities, and immunosuppression. The effects of FIVMA infection on neutrophil and natural killer cell (NK) function were examined in vitro. Suppression of neutrophil chemiluminescence (CL) responses, as well as reduction in NK-mediated cytotoxicity were demonstrated. Neutrophil CL was decreased by 50% in infected cats when compared to control values. This loss of CL was present through 6 months after infection. In addition, NK-mediated cytotoxicity was approximately 50% less in FIVMA infected cats than in controls. Loss of innate immunity was paralleled with inversion in feline CD4/CD8 lymphocyte ratios and decreases in lymphocyte mitogenesis seen as early as 5 weeks after infection. These results suggest that FIVMA infection induces an immunodeficiency disorder in infected cats similar to that seen in human immunodeficiency virus infections.