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The Docile strain of lymphocytic choriomeningitis virus (LCMV) induces anemia in a number of inbred strains of mice, including C3HeB/FeJ and CBA/Ht animals. A difference in the kinetics of anemia and in compensatory reticulocytosis suggested that impaired erythropoiesis was the major pathogenic mechanism involved in CBA/Ht mice, but not in C3HeB/FeJ mice. In both mouse strains an antierythrocyte autoantibody production that depended on the presence of functional CD4+ T lymphocytes was observed. Although depletion of T helper lymphocytes prevented anemia in C3HeB/FeJ mice, this treatment largely failed to inhibit the development of the disease in CBA/Ht animals. This observation indicated that the antierythrocyte autoimmune response induced by the infection was at least partly responsible for the anemia of C3HeB/FeJ mice, but not of CBA/Ht mice. Erythrophagocytosis was enhanced in both mouse strains after LCMV infection, but did not appear to be a major cause of anemia. These data clearly indicate that similar disease profiles induced by the same virus in two different host strains can be the result of distinctly different mechanisms.

The effect of LCMV on CD4+ T lymphocytes was analyzed in C3HeB/FeJ mice after infection with the Docile strain of this virus. Our results indicated that LCMV triggers: i) an inhibition of Th2 lymphocyte differentiation induced by concomitant immunization with a nonviral protein antigen; ii) a depression of T helper-dependent antibody responses elicited by such an immunization; and iii) a CD4+ cell-mediated proliferation of spleen cells leading to increased interleukin-4 and interferon-gamma message expression and IgG2a-restricted total immunoglobulin secretion. Taken together, these results indicate that LCMV profoundly affects CD4+ cell-mediated immune responses in infected animals. Such modulations of T-helper functions may explain the preponderance of IgG2a in the antierythrocyte autoimmune response induced by the virus in C3HeB/FeJ mice.

C3HeB/FeJ mice infected with the docile strain of lymphocytic choriomeningitis virus (LCMV-d) develop a persistent infection with a transient haemolytic anaemia. Immunoglobulin can be eluted from the red blood cells (RBC) of these mice but it cannot be detected on the RBC by a conventional antiglobulin test. The present study demonstrates that RBC from such mice bear erythrocyte autoantibodies which are predominantly of the IgG2a subclass, with lower levels of autoantibodies of the IgG1, IgG2b and IgG3 subclasses. To identify the target antigen the autoantibodies were eluted from the RBC of LCMV-infected mice. The eluted autoantibody bound to intact normal RBC and precipitated a 105000 MW component that corresponds to murine Band 3 protein. A monoclonal antibody derived from mice infected with LCMV-d also precipitated mouse Band 3, and reacted specifically by enzyme-linked immunosorbent assay against a purified preparation of Band 3. This study has shown that in C3H mice infected with LCMV-d which develop autoimmune haemolytic anaemia, the target autoantigen is erythrocyte membrane Band 3.

Development of pathology varies widely between different strains of mice after intracerebral inoculation with the so-called 'docile' isolate of Lymphocytic Choriomeningitis (LCM) virus. The C3HeB/FeJ and B10. Br/SgSnJ mouse strains have been of special interest because they display autoimmune haemolytic anaemia with varying degrees of apparent immunological involvement. In this report, we examined the role of CD4+ T helper cells in this autoimmune response by treating mice with the CD4-specific GK1.5 monoclonal antibody. We also determined if polyclonal activation of B lymphocytes, induced either by LCM virus or by lactate dehydrogenase-elevating virus, another well known B cell activator, correlated with the development of anaemia in these mice. Our results strengthened the central role of the immune system in the anaemia in C3H mice by showing that depletion of CD4+ cells largely, if not completely, abrogated this anti-erythrocyte autoimmune reaction. As reported by others, we found that the anaemia was more mild in B10.BR mice than in C3H mice. However, we could not confirm the difference in the degree of B lymphocyte polyclonal activation between these mice. Furthermore, lactate dehydrogenase-elevating virus had no apparent effect on erythrocytes, even though this virus also induced a sharp increase in plasma IgG levels.

Natural or deliberate activation of the immune system of pathogen-free mice markedly affected their response to an autoimmune-inducing stimulus. Specifically, mice immunized with rat red blood cells were found to make antibodies reactive with both rat and mouse erythrocytes. Animals housed for an extended period in a conventional environment developed an autoimmune response twice as fast as those kept in isolators. In an attempt to emulate this effect, mice kept in a sterile environment were infected with a potent polyclonal activator of B lymphocytes, lactate dehydrogenase-elevating virus, at the same time as they were inoculated with rat erythrocytes. Whereas uninfected animals developed a progressively increasing autoantibody titer, infected mice quickly attained high anti-erythrocyte autoantibody titers that remained rather constant. Contrary to circulating autoantibodies, bound anti-erythrocyte antibodies decreased with time. Virus infection enhanced all the IgG subclass responses, with the exception of IgG1, to both rat and mouse erythrocytes. None of the modifications of the autoimmune responses resulted in anemia.

Lymphocytic Choriomeningitis (LCM) virus, substrain Docile, causes a chronic infection in adult C3HeB/FeJ mice. The virus also induces a severe anemia which, unlike the viremia, eventually resolves. Initially, there is frank bone marrow deficit, but the anemia persists well beyond a strong erythroid compensatory response. An immune-mediated basis for the hemolytic anemia was suggested by its abrogation in cyclophosphamide-treated mice, as well as an abnormal number of spherocytes in the circulation. We now show by ELISA assay, using either anti-mouse Ig or RBC membrane ghosts as catching antigen, that unusually high quantities of antibodies can be eluted from the RBCs of virus-infected mice. Furthermore, the high transient antibody concentration correlates with the severity of the anemia. With no evidence for complement playing a role in the anemia, these data indicate that erythrophagocytosis (via macrophage FcRs) may be the mechanism for RBC elimination. The possibility of molecular mimicry (antibody cross-reactivity between LCM and RBC membrane epitopes) was considered but appeared unlikely since the RBC antibody eluates gave no signal in an LCM-specific ELISA (which showed an ever increasing serum titer of virus-specific antibody). Isotype determination of the RBC eluates revealed the following: IgG2a much greater than IgG1 greater than IgG2b greater than IgG3 greater than IgM. The precise role, if any, of LCM-virus induced polyclonal activation (most strikingly in the IgG2a subclass) has yet to be determined.

Lymphocytic choriomeningitis virus (LCM) and Pichinde virus grew readily and produced cytopathology in MDCK and PK-15 cells. It is known that in these cell lines, the synthesis or function of defective interfering (DI) virus particles is restricted. Survival curves of single MDCK cells infected with low multiplicities of LCM showed one-particle-to-kill kinetics. At high multiplicities of infection, there was a maximum degree of cell-killing, or even a reduction in the amount of cell-killing, depending on how much DI virus was present in a particular standard virus stock. DI LCM virus could completely prevent standard virus from producing c.p.e. in MDCK monolayers with one-particle-to-protect kinetics. It could still prevent killing of the cells when added within a short time after infection with standard virus, but was able to interfere with synthesis of standard virus when added even later, On passage of LCM or Pichinde virus without dilution in MDCK cells, there was no homologous auto-interference. Furthermore, there was only slight interference with the synthesis of standard virus when these cells were pre-treated with DI virus.

After intracerebral inoculation of adult C3H mice, the 'docile' strain of lymphocytic choriomeningitis (LCM) virus multiplied to high titre in several visceral organs. Although the virus content of lung, liver, spleen and brain was high, these mice did not die but became long-term carriers of the virus. Injection of mice with the same dose of the 'aggressive' strain of LCM virus resulted in much lower virus titres in these organs; nevertheless, 100% of the mice died within 7 to 9 days. The results presented here show that mice infected with the 'aggressive' virus do not die if treated with anti-interferon globulin. Under these conditions the titres of 'aggressive' virus were as high in the different organs as in mice injected with the 'docile' virus. These results are consistent with the hypothesis that inhibition of LCM virus multiplication in various organs by interferon results in a lethal disease. The possible mechanisms underlying this seemingly paradoxical phenomenon are discussed.

Lymphocytic choriomeningitis (LCM) viruses isolated from the blood of persistently infected mice, could be clearly divided into two categories by observing the disease patterns they produced after intracerebral (i.c.) injection in a number of adult inbred and outbred mice. One type (aggressive) caused the classic pattern of convulsive death in 100% of the mice 7 to 9 days after infection, while the other (docile) caused a protracted disease with deaths occurring, if at all, 2 to 4 weeks after infection. Interferon could be detected in the serum of adult mice on the 3rd and 4th day after infection with several independently cloned aggressive, but not docile, viruses. The inability of docile virus to induce interferon was not due to poor or delayed virus replication in the brain. The aggressive pattern of disease could be provoked easily in docile virus-infected mice with the interferon inducers poly(rI) . poly(rC), tilorone hydrochloride or Newcastle disease virus. The amount of interferon produced had little effect on the mean day of death. Mice that differed over 10-fold in their serum interferon levels after LCM infection, either by genetic predisposition or by stimulation with increasing amounts of poly(rI) . poly(rC), presented almost identical patterns of mortality.

A Pichinde persitently infected BHK21/13S culture was established in which defective interfering (DI) virus continued to be synthesized after cessation of plaque-forming virus replication. This DI virus, concentrated from NaCl-polyethylene glycol treated tissue culture fluids, was shown to band over a much broader range than standard virus, in either discontinuous or continuous sucrose gradients. The polyacrylamide gel profile of the RNAs extracted from standard virus contained six components with sedimentation coefficients corresponding to 31, 28, 22, 18, 15 and 4-6S. All RNAs extracted from DI virus preparations, however, did not contain the 22 and 15S species. Furthermore, a new 20S fraction was observed in DI virus taken from cultures which had been maintained for more than 175 generations after the initial infection, whereas it was absent in DI virus synthesized prior to that time.

A so-called 'docile' strain of Lymphocytic Choriomeningitis Virus (LCMV) lacks the ability to cause the fatal central nervous system syndrome, commonly associated with most other strains of this virus, in C3HeB/FeJ mice. Hematological evaluation during a 5 week period revealed that every mouse experienced a pancytopenia which was the most severe around three weeks post-infection. The abnormal red blood cell (RBC) morphology seen in the peripheral blood along with the increased reticulocyte count and marked erythroid hyperplasia in the bone marrow indicated peripheral destruction, rather than stem cell inhibition, as the mechanism causing the anemia. An increase in the 59Fe uptake into the blood confirmed the fact that there was no loss in the erythropoietic capabilities in these mice at this time. Although it was clear that the RBCs were being destroyed in the periphery, there was no evidence of a microangiopathic hemolytic anemia nor of a direct viral infection of these cells. Cyclophosphamide treatment, however, prevented the phenomenon. Thus, it seemed likely that the virus-induced hemolytic anemia in these mice was immune-mediated. The late, but not the early drop in the white blood cell counts and the thrombocytopenia, on the other hand, could be traced to granulocyte and megakaryocyte inhibition in the bone marrow.

The pathogenicity of lymphocytic choriomeningitis virus (LCMV) inoculated intracerebrally (i.c.) varies with virus strain and dose as well as with the mouse strain used as host. Recently, results have indicated that susceptibility to lethal disease correlates directly the ability of the host to produce early and high virus-specific Tc activity. However, in the present studies we demonstrate that even though this holds true in many mouse/virus combinations, it does not apply in others. Thus, in C3H mice infected with (moderately) high doses of Traub strain LCMV, early and high Tc activity was found despite a mortality rate of only 10-20%. Similarly, in C3H mice inoculated with the aggressive and docile substrains of UBC strain LCMV, which differ markedly in their pathogenicity for this mouse strain, similar kinetics of Tc induction were observed. Finally, in DBA/2 mice which do not die following infection with the otherwise lethal aggressive substrain, Tc induction could be found to be as efficient as in BALB/c mice, all of which die from acute LCM disease when infected with this virus isolate. The results indicate, therefore, that early and high Tc activity does not constitute a sufficient prerequisite for lethal disease, and that different Tc response profiles may be associated with low mortality following i.c. inoculation with LCMV.

Two types of lymphocytic choriomeningitis (LCM) viruses were studied which, upon intracerebral injection into adult C3H mice, provoked either (a) acute fatal central nervous system (CNS) disease or (b) life-long persistent infection. Both virus types, (a) aggressive and (b) docile, had been found to induce LCM-specific lymphocytes with comparable in vitro lytic activity (11). Because the requirement for T cells in the development of adult LCM disease has been extensively documented, we sought other reasons for the lack of acute disease in mice infected with docile virus. A striking correlation was found between the outcome of the infection and spread of virus to visceral organs. Adoptive transfer experiments showed that a 300-plaque forming unit inoculum of docile virus induced a population of T cells in donor mice fully capable of causing CNS disease in identically infected recipients. This disease causing ability was lost if the interaction was delayed beyond 3 d after infection of the recipients, but could be preserved by lowering the size of the viral inoculum in the recipients. Furthermore, without adoptive transfer, very low intracerebral doses of docile virus (which mimicked the normally slow spread of aggressive virus) were lethal. On the other hand, very high doses of aggressive virus, which mimicked the normally rapid spread of docile virus, did not induce fatal CNS disease. The results suggest that rapid dissemination of the LCM infection creates multiple target organs which divert the focused lethal T cell attack on the brain.

Adoptive transfer of lymph node and spleen cells from mice infected with LCM virus to similarly infected immunocompromised recipients has been the classic way to demonstrate the lethal role of T cells in the CNS disease caused by this virus. Isolation and adoptive transfer techniques are presented here which show that Thy-1+ cells isolated from the meningeal infiltrates (MI) of LCM virus-infected mice possess this property. We compared various T cell functions of MI cells taken from mice infected with two strains of LCM virus differing markedly in their pathogenicities. One of these strains, termed aggressive, caused a typical, invariably fatal, CNS disease within 7 to 10 days after infection. The other virus, termed docile, killed few mice after the standard intracerebral inoculation, and could persist in the mice for 6 mo or more. The yields of MI leukocytes from mice infected with docile virus varied from 50 to 100% of those found in mice infected with aggressive virus (3 X 10(6) cells/brain). On a cell-to-cell basis, the CTL activity in the MI of mice infected with docile virus ranged from 50 to 100% of that found in the MI of mice infected with aggressive virus. MI cells from mice infected with aggressive virus consistently caused lethal disease by adoptive transfer into immunocompromised (irradiated) recipients infected with either strain of virus. All attempts to induce lethal disease by adoptive transfer of MI cells (or splenocytes) from mice infected with docile virus into irradiated recipients failed. The latter experiments with the docile-MI cells were performed with six times the number of aggressive-MI cells needed to kill irradiated recipients by adoptive transfer. The possible reasons for this discordance between CTL and in vivo killer function are discussed.

The ability of two lymphocytic choriomeningitis virus substrains to induce cytotoxic T-lymphocyte (CTL) responses in intracerebrally infected mice was examined. One strain, designated A (aggressive), provoked a convulsive type of death in 100% of the mice within 8 to 9 days, whereas the other strain, designated D (docile), killed less than 10% of the mice during 28-day observation periods. CTL activity was assessed by the capacity of partially purified splenocytes to lyse 51Cr-labeled L-cell targets infected with either type of lymphocytic choriomeningitis substrain. The CTL population was identified by its sensitivity to anti-Thy-1 serum and its inability to lyse uninfected target cells or infected target cells with which it differed at the level of antigens controlled by the major histocompatibility gene complex. A strong CTL response developed in mice infected with either lymphocytic choriomeningitis substrain, although the activity provoked by substrain D was somewhat less than that seen after substrain A infection. Peak CTL activities induced by both strains occurred at about the same time. Even though docile virus replicated more extensively in the brain than did aggressive virus and fluorescent antibody staining revealed similar distributions of viral antigen, no inflammatory response was noted in the brains of mice infected with docile virus. These results are discussed with regard to the role of CTLs in mediating classic central nervous system pathology.

Intracerebral infection of adult immunocompetent mice with most strains of lymphocytic choriomeningitis virus (LCMV) caused a systemic infection and led to severe meningoencephalitis and death due to the induced T cell immune response. The susceptibility of congenic mice to the two plaque variants Docile and Aggressive of LCMV strain UBC was shown to be mouse strain-dependent. To investigate the possible correlation between acid-stable interferon (IFN) and natural killer (NK) cell responses and the susceptibility to the two UBC LCMV substrains, serum titres of acid-stable antiviral activity, presumably IFN-alpha, beta and NK cell activities were determined in various mouse strains at different times after intracerebral infection. The two viral isolates induced comparable IFN-alpha, beta serum titres and caused similar NK activities in the same mouse strain. Between different mouse strains, marked differences in the kinetics and amount of IFN production were observed, yet there was no correlation with the susceptibility to the two UBC LCMV substrains. Additionally, there was no correlation between the magnitude of the IFN-alpha, beta serum titres and the NK activities induced in the spleen by the viral inocula. Overall, the findings suggest that levels of circulating IFN-alpha, beta are only of minor importance for the development of LCM disease.

MDCK cells that normally would have been killed by standard lymphocytic choriomeningitis (LCM) virus were saved either by pre- or co-infection with defective interfering (DI) virus. The ability of these spared cells to produce virus-specific antigen (as well as infectious virus) and resist being killed by standard virus challenge was followed for at least 35 days. During this period both types of cultures displayed unique cycling patterns for the above characteristics. The most striking difference was the longevity of the infections. Cultures exposed to DI particles prior to standard virus became persistently infected, while co-infection with both virus types led to spontaneous curing with no trace of the previous infection. The basis for these dissimilar outcomes was traced to a hitherto undetected non-defective LCM virus (called SP) in the DI virus stocks used to preinfect MDCK cells. SP virus was not present in standard virus stocks but arose in long-term persistently infected L cells that had been initially infected with standard virus. Cloned SP virus shared species-specific antigens with standard virus, was resistant to inhibition by DI virus and was capable of turning self-curing cultures into cultures persistently synthesizing both DI and SP virus.

Two groups of compounds, identifiable by structural similarity, have been found to interfere with the in vitro replication of arenaviruses. All 4 members of the benzimidazole group contain dipolar fused benzene and 5-membered nitrogen-containing rings and share potential chelating ability through the different bidentate structures formed with their side-chains. The biological activity of one of these compounds, metisazone, has been shown to depend on the presence of divalent metals of the first transition series, Cu(++) being the most effective. Furthermore, whereas metisazone inactivates cell-free virus, two other members of the group, HBB and 1,2-bis(5-methoxy-1H-benzimidazol-2-yl)-1,2-ethanediol, act intracellularly. The site of action of the fourth member, SKF 30097, is not known. Using murine lymphocytic choriomeningitis infections as an in vivo model, the bisbenzimidazole derivative has been found to increase life-span without interfering with virus replication. Medication with SKF 30097 or metisazone and copper (2(+)) sulfate did not significantly or reproducibly change the expected day of death of the animals. The amantadine compounds of the second group have unusual symmetric structures with a 10-carbon cage. The parent compound acts intracellularly, while the site of action of an octachloro derivative is not known. Medication with the parent compound, but not the derivative, shortened the interval between LCM infection and death of the mouse. Tissue culture and animal screening of the many available derivatives in these two groups may uncover compounds more efficacious than those already examined.

N-methyl and N-ethyl isatin beta-thiosemicarbazones inactivate cell-free Parana and Pichinde viruses as well as three strains of lymphocytic choriomeningitis virus. This antiviral activity is abolished in the presence of the chelating agent EDTA. The rate of virus inactivation by N-methyl isatin beta-thiosemicarbazone is greatly enhanced and controlled by the addition of cupric sulphate. Divalent cations of other first transition series metals are less effective. A difference exists in the copper requirement for fast inactivation of the prototype arenavirus (lymphocytic choriomeningitis) and the Tacaribe Complex of viruses (Parana and Pichinde). In the presence of 20 muM-N-methyl isatin beta-thiosemicarbazone, LCM and Pichinde viruses can be inactivated at about the same rate if 20 muM-CuSO4 is added to the former and 160 muM-CuSO4 is added to the latter. Using 20 muM-N-methyl isatin beta-semicarbazone and CuSO4 the inactivation of LCM is reduced, but not eliminated, in the presence of an equal amount of infectious Pichinde virus. Crude and highly purified Pichinde virus are inactivated at the same rate when exposed to identical concentrations of N-methyl isatin beta-thiosemicarbazone and cupric sulphate. There is little detectable change in the inactivation rates when Pichinde or LCM viruses are grown in a variety of different cell lines.

The dihydrochloride salt of (S,S)-1,2-bis(5-methoxy-2-benzimidazolyl)-1,2-ethandiol (A37536) inhibits the synthesis of lymphocytic choriomeningitis (LCM), Parana, and Pichinde viruses in L-929 cells. The compound has no direct inactivating effect on LCM virus nor does it affect the adsorption of LCM virus to L cells. The drug-cell interaction is slow. Maximal activity is observed only by exposing cells to the drug at least 8 h prior to LCM virus infection, or by concomitant drug treatment and infection at a low multiplicity. Addition of serum-free media to L cells after LCM virus infection diminishes the activity of A37536. Whereas A37536 exhibits its antiviral activity at concentrations that have little or no effect on L cell division rate, a marked change can be noted in the cell's sensitivity to lysis by standard trypsin dispersal procedures. A37536 has no specific antiviral activity in LCM virus-infected BHK, HeLa, or Vero cells. All of the four tested derivatives of A37536 showed antiviral activity against LCM virus but only at concentrations that reduced the growth rate or were toxic to L cells.

Resistance to the acute lethal disease caused by the docile strain of lymphocytic choriomeningitis (LCM) virus varies widely between different mouse strains. In order to study the inheritance of host influence on susceptibility to this strain of LCM virus, we crossed the F1 to the parent with the recessive disease phenotype. In all cases, susceptibility was dominant. In backcross progeny obtained from matings of parental strains differing in both major histocompatibility complex (MHC) and non-MHC (SWR; C3H), 90% of the challenged mice died, indicating that at least three loci controlled susceptibility to the disease. When the parental strains carried similar MHC haplotypes but dissimilar background genes (B10.BR; CBA), 78% of the backcross mice succumbed, indicating that at least two non-MHC loci influenced disease susceptibility. It is unlikely, however, that the same two non-MHC loci are critical in all genetic combinations, since F1 produced from two H-2 identical, resistant strains (B10.BR; C3H) were found to be fully susceptible. When congenic mice, differing only in the D-end of the MHC region, were analysed, 50% of the backcross animals died, indicating that one gene in the MHC region was important; segregation analysis comparing MHC serotype and disease outcome indicated the H-2D locus itself as the determining factor.

Pichinde virus (PV), a member of the Arenaviridae family, protects mice from a lethal inoculation with the sarcoma 180 (S180) tumor cell line. Virus replication, which is required for protection, occurs primarily in the spleen and tumor. During the first 4 days, elevated natural killer (NK) cell activity parallels an increase in serum interferon in PV-infected mice. On day 7 after infection virus-specific cytotoxic T cells (CTLs) are found in the mouse. This strong response peaks on day 13 and gradually declines over the next 17 days. The tumor-specific CTL response appears more slowly and is less intense than the virus-specific response, especially in the uninfected mouse. However, CTLs from either type of mouse recognize PV-infected tissue culture S180 target cells better than uninfected ones. Even though the primary tumor-specific immune response appears weak, mice that have cleared both virus and tumor are refractory to a subsequent challenge with S180 cells and rapidly produce tumor-specific CTLs. Thus, our data indicate a number of ways in which virus infection could lead to immune elimination of tumors: (1) Virus-induced interferon stimulates NK-cell activity, which in turn could control tumor load until a specific response is mounted against the S180 cells; (2) early onset of the tumor-specific T-cell response could be brought about by viral-enhanced tumor antigen presentation to the immune system; and (3) the tumor-specific T-cell response could be augmented through a "bystander' phenomenon involving factors associated with T cells responding specifically and vigorously to the virus itself.

The long-term sequelae to infection of neonatal rats with lymphocytic choriomeningitis virus were studied by a variety of approaches, including indirect ophthalmoscopic, electroretinographic, and histopathologic methods. Data from these studies demonstrated that a progressive chronic retinitis develops after the acute, virus-specific, immune-mediated retinopathy. This chronic inflammation eventually leads to a total destruction of the retinal architecture. An autoimmune reaction against normally sequestered retinal antigens, released during the acute state of necrotizing retinitis, is probably the initiating mechanism of the chronic disease. This experimental disease, triggered by infection with a relatively harmless virus, constitutes a very convenient animal model of chronic retinitis.

Susceptibility to some human diseases is linked, albeit weakly, to major transplantation antigens (HLA) encoded by the major histocompatibility gene complex (MHC). Here we have studied MHC/disease association in inbred strains of mice after intracerebral (i.c.) injection of lymphocytic choriomeningitis virus (LCMV). This route of infection leads to a lymphocytic choriomeningitis (LCM) which is not the result of direct cytopathic effects of the virus but is caused by the induced T-cell immune response: immunocompetent mice die whereas T-cell-deficient mice survive. By using two plaque variants of LCMV strain UBC (refs 7,8), we found that susceptibility to LCM was dependent on the LCMV strain used ('aggressive' versus 'docile' UBC-LCMV) and on the various genes of the host mouse strains. In addition, susceptibility to LCM caused by docile UBC-LCMV was clearly linked to the murine major histocompatibility locus H-2D: in MHC-congeneic C57BL/10 mice, susceptibility correlated with early onset and high activity of measurable LCMV-specific cytotoxic T cells in meninges and spleens and could be mapped to H-2D. This model shows that a severe immunopathologically mediated clinical disease in mice can be regulated directly by MHC genes of class I type and supports the notion that many MHC/disease associations directly reflect MHC-restricted and MHC-regulated T-cell reactivity.

Intracerebral (i.c.) infection of adult mice with lymphocytic choriomeningitis (LCM) virus can result in acute lethal central nervous system (CNS) disease which is the result of the host's thymus-derived lymphocyte (T cell) response against the virus. Whether the specific effector function of the T cell is that of a cytotoxic cell (Tc) or a delayed-type hypersensitivity cell (Td) is still under debate. We assumed that if Td cells were important in pathogenesis then accessory cells in the brain (specifically, glass-adherent macrophages) might vary with the outcome of i.c. infection. We found that accumulation of macrophages in the brain (washed from meninges and skull cap) appeared to be independent of the severity of the infection (controlled by the mouse strain as well as the strain and dose of virus used). However, differentiation of macrophages was clearly linked to whether or not the infection caused rapid death. In mice that were destined to survive, macrophages became large, extensively vacuolated, and phagocytically active. In lethally-infected mice macrophages were small and had poor phagocytic abilities. At present this dichotomy could be viewed as either a cause or a consequence of disease outcome. However, the data are not inconsistent with the hypothesis that Td lymphocytes may be of primary importance in pathogenesis.

Seventy percent of the mice receiving (S,S)-1,2-bis(5-methoxy-2-benzimidazolyl)-1,2-ethandiol (A36683) in their drinking water lived at least four times longer than control mice when infected with 10 or 100 mean lethal doses of lymphocytic choriomeningitis virus strain UBC. In the next 4 months, most of the survivors died with lymphocytic choriomeningitis-like symptoms. Drug treatment during the first 7 days after infection was found to have no significant effect on virus titers in various organs. The sparing effect of the drug is discussed in terms of immunosuppression.

Amantadine hydrochloride inhibits the CA1371, UBC, and WE strains of LCM in both BHK21/13S and L-929 cells. The compound has no direct inactivating effect on virus infectivity nor does it affect the adsorption of virus to cells. By observing the susceptibility of cell-adsorbed virus to neutralizing antibody, amantadine was shown to delay virion penetration. Furthermore, addition of the drug at any time during ongoing viral replication, with all cells scoring as infective centers, inhibits virus synthesis and release.

Biological, biochemical, and biophysical properties of three lymphocytic choriomeningitis (LCM) virus strains were compared. The biological property examined was the concentration range of virus which would, when injected into neonates, cause a carrier state. The dosage range for the CA1371 and Traub strains was found to be as broad as the limits examined (5 to 100 ld(50) units/mouse). The WCP strain, however, would only produce carriers within a 3 to 5 ld(50) range. The biochemical properties examined were the growth rates in tissue culture and the effect of varying the input ratio of virus to cells. With identical input ratios, the Traub strain reached a peak titer 32 hr after infection. The CA1371 and WCP strain reached their peaks at the 40th hr. With a 10-fold decrease in the amount of CA1371 virus per cell, peak titer (as high as in the above experiments) was not obtained until 56 hr postinfection. The biophysical properties examined were stability in density gradients and inactivation rates at 4C. In potassium tartrate gradients, full recovery of the CA1371 and WCP strain could be achieved. However, inactivation kinetics showed that only the CA1371 strain was much more stable than the Traub-LCM. The realization that marked differences in LCM strains exist is discussed in relation to certain inconsistencies in the literature.

Persistent infections were established in suspension cultures of BHK21/13S cells with both Parana and lymphocytic choriomeningitis viruses. Four generations after infection with either virus, more than 90% of the cells scored as infective centers, with concomitant peaks in extracellular virus yields. In both cultures the synthesis of detectable plaque-forming units (PFU) ceased about the 50th generation postinfection, and this condition was maintained until the 350th cell generation when the cultures were discontinued. The generation time of each culture was identical to that of uninfected parent controls, and at no time were cytopathic effects evident. In spite of the absence of infectivity, over 90% of the cells sampled at various times contained viral antigen demonstrable by immunofluorescence. When either of these persistently infected cell lines was substituted for normal cells in the standard plaque assay, very low efficiencies of plating were observed for homotypic and heterotypic viruses. Plaque formation by several heterologous viruses was virtually unaffected. The mechanism of homotypic plaque exclusion in both cell lines was shown to occur beyond the virion adsorption stage. The original infecting virus genome persisted in both cell lines after standard virus was no longer detectable. This was shown with the lymphocytic choriomeningitis virus-infected cells after storage in liquid nitrogen. After thawing, such cells were found to synthesize standard virus for a brief period. Although the Parana virus-infected cells did not behave this way, the growth medium from these cells would initiate PFU synthesis in normal cells within 36 hr after infection.