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The global trend toward intensive livestock production has led to significant public health risks and industry-associated losses due to an increased incidence of disease and contamination of livestock-derived food products. A potential factor contributing to these health concerns is the prospect that selective pressure within a particular host may give rise to bacterial strain variants that exhibit enhanced fitness in the present host relative to that in the parental host from which the strain was derived. Here, we assessed 184 Salmonella enterica human and animal clinical isolates for their virulence capacities in mice and for the presence of the Salmonella virulence plasmid encoding the SpvB actin cytotoxin required for systemic survival and Pef fimbriae, implicated in adherence to the murine intestinal epithelium. All (21 of 21) serovar Typhimurium clinical isolates derived from animals were virulent in mice, whereas many (16 of 41) serovar Typhimurium isolates derived from human salmonellosis patients lacked this capacity. Additionally, many (10 of 29) serovar Typhimurium isolates derived from gastroenteritis patients did not possess the Salmonella virulence plasmid, in contrast to all animal and human bacteremia isolates tested. Lastly, among serovar Typhimurium isolates that harbored the Salmonella virulence plasmid, 6 of 31 derived from human salmonellosis patients were avirulent in mice, which is in contrast to the virulent phenotype exhibited by all the animal isolates examined. These studies suggest that Salmonella isolates derived from human salmonellosis patients are distinct from those of animal origin. The characterization of these bacterial strain variants may provide insight into their relative pathogenicities as well as into the development of treatment and prophylactic strategies for salmonellosis.

11beta-Hydroxysteroid dehydrogenase type 1 (11betaHSD1) performs end-organ metabolism of glucocorticoids (GCs) by catalyzing the conversion of C(11)-keto-GCs to C(11)-hydroxy-GCs, thereby generating activating ligands for the GC receptor. In this study, we report that 11betaHSD1(-/-) mice are more susceptible to endotoxemia, evidenced by increased weight loss and serum TNF-alpha, IL-6, and IL-12p40 levels following LPS challenge in vivo. Peritoneal and splenic macrophage (splnMphi) from these genetically altered mice overproduce inflammatory cytokines following LPS stimulation in vitro. Inflammatory cytokine overexpression by 11betaHSD1(-/-) splnMphi results from an increased activation of NF-kappaB- and MAPK-signaling cascades and an attenuated PI3K-dependent Akt activation. The expression of SHIP1 is augmented in 11betaHSD1(-/-) Mphi and contributes to inflammatory cytokine production because overexpression of SHIP1 in primary bone marrow Mphi (BMMphi) leads to a similar type of hyperresponsiveness to subsequent LPS stimulation. 11betaHSD1(+/+) and 11betaHSD1(-/-) BMMphi responded to LPS similarly. However, 11betaHSD1(-/-) BMMphi derived in the presence of elevated GC levels up-regulated SHIP1 expression and increased their capacity to produce inflammatory cytokines following their activation with LPS. These observations suggest the hyperresponsiveness of 11betaHSD1(-/-) splnMphi results from myeloid cell differentiation in the presence of moderately elevated GC levels found within 11betaHSD1(-/-) mice. GC-conditioning of BMMphi enhanced SHIP1 expression via up-regulation of bioactive TGF-beta. Consistently, TGF-beta protein expression was increased in unstimulated CD11b(-) cells residing in the BM and spleen of 11betaHSD1(-/-) mice. Our results suggest that modest elevations in plasma GC levels can modify the LPS responsiveness of Mphi by augmenting SHIP1 expression through a TGF-beta-dependent mechanism.

Salmonella enterica serovar Typhimurium that lacks the DNA adenine methylase (Dam) ectopically expresses multiple genes that are preferentially expressed during infection, is attenuated for virulence, and confers heightened immunity in vaccinated hosts. The safety of dam mutant Salmonella vaccines was evaluated by screening within infected mice for isolates that have an increased capacity to cause disease relative to the attenuated parental strain. Since dam mutant strains are sensitive to the DNA base analog 2-aminopurine (2-AP), we screened for 2-AP-resistant (2-AP r ) isolates in systemic tissues of mice infected with dam mutant Salmonella . Such 2-AP r derivatives were isolated following intraperitoneal but not oral administration and were shown to be competent for infectivity via intraperitoneal but not oral infection of naïve mice. These 2-AP r derivatives were deficient in methyl-directed mismatch repair and were resistant to nitric oxide, yet they retained the bile-sensitive phenotype of the parental dam mutant strain. Additionally, introduction of a mutH null mutation into dam mutant cells suppressed the inherent defects in intraperitoneal infectivity and nitric oxide resistance, as well as overexpression of SpvB, an actin cytotoxin required for Salmonella systemic survival. These data suggest that restoration of intraperitoneal virulence of dam mutant strains is associated with deficiencies in methyl-directed mismatch repair that correlate with the production of systemically related virulence functions.

The mucosal immune system provides the host with a first line of adaptive immune defense against invasion by many species of pathogenic microorganisms and their secreted products. Calcitriol, the active form of Vitamin D3 (VD3), promotes the induction of mucosal immunity in mice when added to subcutaneously administered vaccine formulations. Dendritic cells (DCs) activated at vaccination sites where VD3 is present gain the capacity to bypass sequestration in the draining lymph node and traffic to the Peyer's Patches (PP) of immunized animals. By employing protocols that allow the effective tracking of endogenous or adoptively transferred myeloid DCs in vivo, we found that VD3 influences on the trafficking of fully differentiated immature DCs were temporary, and occur without negative effects to antigen processing or peptide presentation to CD4+ T cells. In contrast, DCs differentiated from hematopoietic precursors in the presence of VD3 (conditioned DCs), were markedly compromised in their antigen presenting properties, while manifesting clear alterations to their trafficking properties in vivo. Similar to the recent finding of VD3-mediated enhancement of innate immune protection, our findings suggest that VD3 could also play an important role in controlling the types of immune effector responses elicited subsequent to either infection or vaccination.

We have demonstrated that in aged mice, the titer of serum antibody induced against tetanus toxoid correlates with resistance to local paralysis caused by injection of tetanus toxin. Only mice immunized shortly after oral dosing with DHEAS demonstrated high serum antibody titers and complete protection from paralysis. These results became the basis for initiating proof-of-principle studies in human volunteers above age 65 using a licensed influenza vaccine and tetanus toxoid in two independent studies. The use of an oral delivery form of DHEAS before influenza vaccination was associated with a demonstrable increase in the number of individuals with a fourfold increase in HAI titers following vaccination. The overall mean increase in HAI titers was highest in the DHEAS-treated group. The use of DHEAS in the immunization of elderly subjects against tetanus toxoid, while unable to enhance the responses, was not a detriment to antibody response. We conclude that further studies will justify the use of DHEAS as an adjuvant for antigens that represent primary responses in the elderly.

Expression of the nuclear hormone receptor peroxisome proliferator-activated receptor α (PPARα) in resting lymphocytes was recently established, although the physiologic role(s) played by this nuclear hormone receptor in these cell types remains unresolved. In this study, we used CD4+ T cells isolated from PPARα−/− and wild-type mice, as well as cell lines that constitutively express PPARα, in experiments designed to evaluate the role of this hormone receptor in the regulation of T cell function. We report that activated CD4+ T cells lacking PPARα produce increased levels of IFN-γ, but significantly lower levels of IL-2 when compared with activated wild-type CD4+ T cells. Furthermore, we demonstrate that PPARα regulates the expression of these cytokines by CD4+ T cells in part, through its ability to negatively regulate the transcription of T-bet. The induction of T-bet expression in CD4+ T cells was determined to be positively influenced by p38 mitogen-activated protein (MAP) kinase activation, and the presence of unliganded PPARα effectively suppressed the phosphorylation of p38 MAP kinase. The activation of PPARα with highly specific ligands relaxed its capacity to suppress p38 MAP kinase phosphorylation and promoted T-bet expression. These results demonstrate a novel DNA-binding independent and agonist-controlled regulatory influence by the nuclear hormone receptor PPARα.

Peroxisome proliferator-activated receptors (PPARs) are transcription factors that belong to the nuclear hormone receptor superfamily. PPARα and PPARγ ligands have been demonstrated to exert anti-inflammatory activities in macrophages by repressing the activities of several transcription factors. PPARγ is expressed in T lymphocytes and may play a role in cytokine production, cellular proliferation, and susceptibility to apoptosis. Herein, we demonstrate that T and B lymphocytes constitutively express PPARα. PPARα represents the predominant isoform expressed in lymphocytes, whereas PPARγ dominates in all cell types of the myeloid lineage. PPARα expression was down-regulated following T-cell activation while PPARγ expression increased under the same activating conditions. PPARα expression in T cells may be regulated by microenvironmental factors, because Peyer's patch T cells expressed far greater levels of PPARα than T cells isolated from peripheral lymphoid organs. Exposure to specific ligand determined that PPARα in lymphocytes can effectively transactivate a peroxisome proliferator response element reporter construct. PPARα's ability to regulate endogenous genes, however, required treatment with histone deacetylase inhibitors. Finally, ligand activation of lymphocyte PPARα antagonized NF-κB. Our observation that a functional PPARα exists within T cells and B lymphocytes suggests an expanding role for this nuclear receptor in cells of the immune system.

The present studies demonstrate that the immunization of aged mice with Diphtheria toxoid in formulations containing unmethylated immunostimulatory CpG motifs, promotes the successful development of immune responses that are qualitatively and quantitatively comparable to those induced in young animals vaccinated in a similar manner. Aged mice given vaccines containing CpG oligodeoxynucleotides (ODNs) expressed primary and secondary systemic humoral immune responses having isotype profiles consistent with an enhancement in Th-1 type immunity. The ability to generate common mucosal immunity was also restored in aged animals given CpG ODN-containing vaccines. Dendritic cells (DCs) were determined to represent one of the cellular targets of CpG ODN activities in aged mice since restoration of immune function was observed when DCs from aged donors were pulsed with antigen and CpG ODNs, prior to injection into syngeneic young adult or aged recipients. Interestingly, antigen-pulsed DCs from young donors were fully capable of stimulating immune responses following their injection into syngeneic young adult or aged hosts, without a need for exposure to CpG ODNs. Although the mechanism(s) by which CpG DNA exerts its beneficial adjuvant effects on the aged immune system remains unclear, our findings suggest that the incorporation of CpG ODNs into vaccine formulations provided to the aged could prove useful in the development of more effective vaccines for the elderly.

Salmonella isolates that lack or overproduce DNA adenine methylase (Dam) elicited a cross-protective immune response to different Salmonella serovars. The protection afforded by the Salmonella enterica serovar Typhimurium Dam vaccine was greater than that elicited in mice that survived a virulent infection. S. enterica serovar Typhimurium Dam mutant strains exhibited enhanced sensitivity to mediators of innate immunity such as antimicrobial peptides, bile salts, and hydrogen peroxide. Also, S. enterica serovar Typhimurium Dam − vaccines were not immunosuppressive; unlike wild-type vaccines, they failed to induce increased nitric oxide levels and permitted a subsequent robust humoral response to diptheria toxoid antigen in infected mice. Dam mutant strains exhibited a low-grade persistence which, coupled with the nonimmunosuppression and the ectopic protein expression caused by altered levels of Dam, may provide an expanded source of potential antigens in vaccinated hosts.

Our previous studies have shown that the enzymatic activities of Neu-1, an endogenous sialidase encoded in the murine MHC, are involved in promoting IL-4 synthesis by naive CD4 + T cells. Our present studies have characterized responsible sialoconjugate targets of Neu-1 and questioned possible biochemical mechanisms responsible for their regulatory influences on IL-4 gene expression. These studies determined that treatment of T cells with the naturally occurring ganglioside GM3 inhibited the production of IL-4 without affecting the production of IL-2. An analysis of IL-4-primed CD4 + T cells further demonstrated that GM3 treatment specifically inhibited the restimulated production of IL-4, IL-5 and IL-13, without inhibiting the production of IL-2 and IFN-γ. The inhibitory effects of GM3 could be overcome by treatment with thapsigargin or ionomycin, suggesting ganglioside regulation occurs upstream of activation-induced calcium mobilization. GM3 treatment attenuated the level of calcium influx following CD3ϵ crosslinking, and CD4 + T cells from Neu-1-deficient B10.SM strain mice ( neu-1 a and IL-4-deficient) expressed reduced levels of intracellular calcium following activation. Our results indicate that activities by membrane gangliosides can influence the cytokine programs in CD4 + T cells, possibly through the modulation of calcium responses induced by T cell activation.

The properties of various vaccine-adjuvant formulations that are capable of inducing both systemic and common mucosal immunity subsequent to their intradermal administration are described. Effective mucosal adjuvants, including bacterial toxins, chemical enhancers of cyclic AMP, and the active form of vitamin D3, all shared the ability to promote dendritic cell migration from the skin to Peyer's patches subsequent to antigen induced maturation. Our data suggests that skin dendritic cells may function as effective antigen presenting cells for the induction of mucosal immune responses, if microenvironmental conditions are appropriately manipulated subsequent to their stimulation by antigen.

Common mucosal immune responses were depressed in aged mice that were orally immunized with Haemophilus influenzae type b oligosaccharide conjugated to Diphtheria CRM197 protein (Hib-DT) vaccine using cholera toxin as the mucosal adjuvant. Both common mucosal and systemic humoral immune responses were also depressed in aged mice that were subcutaneously immunized with vaccine formulations containing Hib-DT plus 1 α ,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ). Dietary supplementation of aged mice with either the antioxidant vitamin E, or with known activators of the alpha isoform of the peroxisome proliferator activated receptor (PPAR- α ) was capable of restoring their mucosal and systemic humoral immune responses to mature adult levels, by both the oral and subcutaneous routes of immunization. These data support a hypothesis that some aspects of immunosenescence are due to dysregulations in cellular functions, and are not due to any irreversible defects in cellular components of the immune system.

Alterations in transcription factor activities in aged mice may lead to the production of many inflammatory molecules in the absence of exogenous stimulation. Splenocytes from 22-month-old female C57BL/6 mice are dysregulated in their capacity to control the inducible nitric oxide synthase gene as a result of elevations in the endogenous levels and activity of interferon (IFN)-gamma. Splenocytes from aged mice produced high levels of IFN-gamma in vitro and active STAT-1 was found in nuclear extracts from these splenocytes. Administration to aged mice of neutralizing antibodies against IFN-gamma imposed appropriate regulation over nitric oxide production by stimulated splenocytes. Reestablishment of normal redox balance following dietary supplementation of aged mice with activators of the peroxisome proliferator-activated receptor alpha or the antioxidant alpha-tocopherol (vitamin E) restored appropriate regulation over both the production of IFN-gamma and the secretion of nitric oxide.

Synthetic forms of glucocorticoids (GCs) with high potency are widely used to treat a number of dermatological conditions having an inflammatory or autoimmune etiology. While GCs are generally effective in their ability to suppress inflammatory processes, their chronic use can lead to detrimental systemic side effects. In this report, we describe a method by which the localized antiinflammatory potential of the natural GC cortisol can be significantly augmented without increasing the risk of negative systemic effects. 11Beta-hydroxysteroid dehydrogenase (11beta-HSD) is a naturally occurring enzyme in the skin. 11Beta-HSD functionally converts biologically active 11-hydroxy GCs to their biologically inactive 11-keto metabolites, thereby limiting the ability of GCs to mediate antiinflammatory activities. By topically applying specific inhibitors of 11beta-HSD in conjunction with low doses of GCs, the antiinflammatory properties of cortisol can be significantly potentiated. It was observed that the generation of the effector phase of contact hypersensitivity (CH) responses could be suppressed by this combined treatment under conditions where the 11beta-HSD inhibitor alone, or cortisol alone were only minimally effective. Only the combined treatment was effective at inhibiting the progression of an ongoing CH response.

The reduced efficiency of antibiotics, caused as a consequence of acquired drug resistance, necessitates the development of new approaches to deal effectively with infectious diseases. Intervention strategies which enhance innate defence mechanisms offer one such possibility. This report demonstrates that mice prophylactically treated with low doses of an extract derived from Solanum species containing both solanine and chaconine were rendered resistant to challenge with lethal doses of Salmonella typhimurium. Single or multiple treatment(s) with low doses of purified glycoalkaloids also provided mice with significant protection against infection. Treated animals were found to rapidly clear bacteria from various target organs. An enhancement of innate defences by glycoalkaloid administration offers an alternative to antigen-specific vaccines and prophylactic antibiotic treatment. © 1998 John Wiley & Sons, Ltd.

The pathophysiology of many disease states observed in aged individuals has been linked to the dysregulated production of several pleiotropic cytokines. We have demonstrated that NF-kappa B, a major transcriptional regulator of these aberrantly expressed cytokines, exists in a constitutively activated state in cells obtained from the major lymphoid organs of aged animals. Therapeutic treatment with dietary antioxidants or with agents capable of activating the peroxisome proliferator-activated receptor (PPAR)-alpha was able to correct the abnormal nuclear NF-kappa B activity, reduce lipid peroxide levels, and eliminate the dysregulated expression of cytokines and other genes under NF-kappa B control. These results suggest that abnormal activation of NF-kappa B in aging contributes to the dysregulated expression of certain pleiotropic cytokines. Effective therapeutic regimens for aging and other inflammatory disease states might benefit from the administration of antioxidants or other agents which specifically activate PPAR-alpha.

Interleukin (IL)-12 or IL-4 produced early in an immune response directs the differentiation of naive antigen-activated CD4 + T cells down a Th1 or Th2 pathway. The NK1.1 + subset of T cells promptly produces IL-4 following activation in vivo. We demonstrate here that NK1.1 + T cells can be directly induced to produce IL-4 in vitro when activated under serum-free culture conditions. Platelet-derived growth factor in cell culture medium was inhibitory to the production of IL-4 by NK1.1 + T cells in vitro. Lymphocytes obtained from secondary lymphoid organs of aged mice produced greater quantities of IL-4 following stimulation than lymphocytes from mature adult animals. Aged mice expressed elevated percentages of NK1.1 + T cells in their secondary lymphoid organs and peripheral blood. While this cell type was responsible for the total early IL-4 produced by lymphocytes from mature adult mice, both NK1.1 + and memory phenotype (CD44 high , CD45RB low , NK1.1 − ) T cells from aged donors produced IL-4 following polyclonal T cell activation.

Elderly individuals often exhibit a poorer immune response and shorter duration of immunity to vaccines than younger persons. Improvement in vaccine response has been demonstrated when administering the hormone dehydroepiandrosterone sulfate (DHEAS) as an adjuvant in animal trials. Two separate, randomized, double-blinded vaccine trials were therefore conducted using DHEAS as an oral adjuvant in individuals age 65 or older. Sixty-six individuals were randomized to DHEAS, 50 mg po bid for 4 days, or a placebo capsule. Tetanus vaccination was given immediately before the fifth dose. At entry the level of protective antibody was age-dependent ( P =0.009), and by 28 days post-vaccination most individuals had protective levels of antibody, with no difference noted between treatment groups. In the second study, 67 individuals received placebo capsules or DHEAS immediately before and 24 h after influenza vaccination. The number of individuals who developed protective titers (≥ 1:40) was not different in the two groups. The mean log increase in HAI response was greater in the DHEAS group to all three vaccine components, although this did not achieve significance, Minimal side-effects of DHEAS administration were noted. Given the trend toward improved response in the elderly to influenza, larger trials using DHEA as an adjuvant in vaccines that are neoantigens may be indicated.

The immunoregulatory effects of glucocorticoids (GCS) are linked to their capacity to alter the production of various species of cytokines associated with immune and inflammatory processes. The present study determined that the influences of GCS within particular lymphoid organs vary, depending on the specific activity of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) within the tissue. This enzyme converts active GCS to inactive metabolites and was found to display greater activity in peripheral than in mucosal lymphoid organs. A direct correlation was found between 11 beta-HSD activity and the preferential production of type 1 cytokines by T-cells residing within certain lymphoid organs. It was established that lymphoid organ 11 beta-HSD was localized in the immobile stromal cell components. Inhibition of 11 beta-HSD activity in vivo reduced type 1 and enhanced type 2 cytokine production by activated T-cells, and it also depressed the ability of animals to generate contact hypersensitivity responses. We conclude that GCS levels can be controlled within lymphoid organs through oxidative inactivation by 11 beta-HSD. GCS action is, therefore, dependent on tissue levels of 11 beta-HSD activity, the number of GCS receptors in a responsive cell, and the concentration of circulating GCS.

Peripheral lymphoid cells isolated from the spleens and peritoneal cavities of aged mice were found to constitutively secrete the multifunctional cytokine interleukin (IL)-10 when cultured in vitro. B-Lymphocytes were implicated as the cell type responsible. Abnormal expression of this cytokine was also detected in vivo because high levels of mRNA for IL-10 were present in splenocytes freshly isolated from aged animals. In addition to the spontaneous secretion of IL-10, lymphoid cells from aged donors were hyperresponsive to exogenous stimulation with endotoxin, producing exaggerated quantities of both IL-10 and IL-6 in culture. Treatment of aged animals with dehydroepiandrosterone sulfate (DHEAS), a natural steroid, reversed the age-associated alterations in cytokine production, rendering the treated mice quite similar to mature adult controls. DHEAS treatment of aged mice also resulted in a lowering in the number of B 1 cells present in the peritoneal cavity and also reduced the titers of circulating autoantibodies specific for phosphatidylcholine (PtC). Based on its wide range of biologic activities, a dysregulation in the mechanisms that control IL-10 production could be a major contributor to immunosenescence. The ability of DHEAS treatment to restore normal control over the expression of IL-10 may explain how this steroid enhances immunocompetence in aged animals.

To investigate potential immunologic mechanisms of resistance to recurrent herpes simplex labialis, we assayed serum antibody titers and cultured peripheral blood mononuclear cell (PBMC) cytokine production among patients with a history of frequent episodes (H+S+), herpes simplex virus (HSV)-seropositive individuals without a history of herpes labialis (H-S+) and HSV-seronegative persons (H-S-). In addition, H+S+ patients were exposed to experimental ultraviolet radiation (UVR) on the lips and the immunologic assay results compared among those who developed experimental lesions and those who did not. H+S+ patients were found to have higher median serum titers of HSV antibody and trends to lower levels of HSV-specific PBMC IFN-gamma and IL-2 than H-S+ control patients (123 vs 66, P = 0.04; 424 vs 548 pg/ml, P = 0.08; 14 vs 26 pg/ml, P = 0.14, respectively). Correlation of the results with the occurrence of experimental lesions showed the inverse: the subgroup of H+S+ patients with UVR-induced lesions had lower titers of antibody and trends to higher levels of IFN-gamma and IL-2 than H+S+ patients who could not be induced (93 vs 149, P = 0.02; 501 vs 347 pg/ml, P = NS; 26 vs 11 pg/ml, P = NS, respectively). The size and duration of UVR-induced lesions showed positive correlations with IFN-gamma and IL-2 levels (r = 0.60-0.67, P = 0.02-0.04). Although the small number of patients limited the power of this study, the overall pattern of the findings suggests that a Th1-like cytokine response (IFN-gamma and IL-2 production) may be associated with resistance to naturally occurring episodes of herpes labialis. The development and severity of experimental UVR-induced herpes labialis appears to be regulated differently and may involve an immunopathologic mechanism.

Lipopolysaccharide (LPS) administration has been known to cause murine fetal death for over 50 years, but the responsible mechanism(s) remains unclear. We used the LPS-hyporesponsive murine strain, C3H/HeJ, to 1) establish whether LPS-induced fetal death is due to a maternal or fetal response to LPS and 2) to investigate the involvement of tumor necrosis factor alpha (TNF alpha) in fetal death caused by LPS. C3H/HeJ (LPS-hyporesponsive) or C3H/HeN (LPS-responsive) females were mated with C57B1/6 or C3H/HeN males (both LPS-responsive). Administration of 10 micrograms LPS caused fetal death in C3H/HeN mothers. However, up to 1000 micrograms LPS did not result in the death of LPS-responsive fetuses when administered to C3H/HeJ mothers. Systemic administration of TNF alpha was able to cause fetal death in both C3H/HeN and C3H/HeJ strains of mice. Pretreatment of pregnant C3H/HeN mice with anti-TNF alpha antibodies significantly reduced fetal death caused by LPS administration. The administration of a sublethal dose of TNF alpha plus 10 micrograms LPS to pregnant C3H/HeJ mice restored abortifacient activity. These results indicate that LPS-induced fetal death is due to a maternal response as opposed to a direct fetal response to LPS and that TNF alpha appears to be an important mediator of fetal death caused by LPS.

The reduced efficiency of the mammalian immune system with aging increases host susceptibility to infectious and autoimmune diseases. However, the mechanisms responsible for these pathologic changes are not well understood. In this study, we demonstrate that the bone marrow, blood, and secondary lymphoid organs of healthy aged mice possess increased numbers of immature myeloid cells that are phenotypically similar to myeloid-derived suppressor cells found in lymphoid organs of mice with progressive tumors and other pathologic conditions associated with chronic inflammation. These cells are characterized by the presence of Gr1 and CD11b markers on their surfaces. Gr1+CD11b+ cells isolated from aged mice possess an ability to suppress T cell proliferation/activation and produce heightened levels of proinflammatory cytokines, both constitutively and upon activation, including IL-12, which promotes an excessive production of IFN-γ. IFN-γ priming is essential for excessive proinflammatory cytokine production and the suppressive activities by Gr1+CD11b+ cells from aged mice. These cells suppress T cell proliferation through an NO-dependent mechanism, as depletion of splenic Gr1+ cells reduces NO levels and restores T cell proliferation. Insights into mechanisms responsible for the proinflammatory and immune suppressive activities of Gr1+CD11b+ cells from aged mice have uncovered a defective PI3K–Akt signaling pathway, leading to a reduced Akt-dependent inactivation of GSK3β. Our data demonstrate that abnormal activities of the Gr1+CD11b+ myeloid cell population from aged mice could play a significant role in the mechanisms responsible for immune senescence.

The mammalian immune system possesses the intrinsic capacity to evoke a wide variety of functionally distinct effector mechanisms following stimulation by a particular antigenic substance. Such diversity in available responses is absolutely essential to the immunocompetent host, which must continually deal with a diverse set of potential pathogens within its ever-changing environment. The development of appropriate types of immune responses, therefore, represents a highly dynamic process that requires that an equivalent consideration be given to a large array of components, any one of which is capable of modulating the final outcome. While the nature and complexity of the antigen(s), plus the intracellular or extracellular mode of presentation, provide specificity and some selection to the developing process, the route of antigen entry, as well as the physiological status of the host at the time of antigen insult, also contribute significantly to the formation of any immune response. The overall objective of this article is to introduce the concept that platelet-derived growth factor (PDGF) (either preformed or synthesized in response to stimulation), plus a number of steroid hormones (some of which are end-organ metabolized at local tissue sites), can all play significant roles in the genesis of immunologic responses in vivo.

We have investigated the ability of dehydroepiandrosterone (DHEA) to alter the production of interleukin-2 (IL-2) and to bind to a specific binding complex in antiCD3 epsilon activated T cells. Binding activity correlated with the presence of a specific DHEA binding complex in the cytosol and nuclei of DHEA-responsive T-cell hybridomas, as well as in CD4+ and CD8+ cells isolated from peripheral lymph nodes of normal mice. Scatchard analysis determined that intact lymphocytes and cytosolic fractions contained high affinity binding for [3H]DHEA (approx. 2.6 nM) with 1000-7000 binding sites existing per cell. Five of the T-cell hybridomas tested both responded to DHEA treatment with increased production of IL-2 and also contained specific high affinity [3H]DHEA binding. Four additional T-cell hybridomas were found to contain no specific [3H]DHEA binding and were also unresponsive to DHEA influences on IL-2 production. Sucrose density gradients demonstrated a 3-4s [3H]DHEA binding complex in high salt and a 7-8s binding complex in low salt. Specific binding was inhibited by preincubation of the cytosol fractions with either trypsin or chymotrypsin, or by heating to 60 degrees C for 1 h (less than 15% of control). [3H]DHEA binding was unaffected by preincubation of the cytosol fractions with ribonuclease, deoxyribonuclease, or phospholipase A. The DHEA-protein complexes bound to DNA-cellulose with the amount of binding being slightly increased by preincubation at 25 degrees C as compared to 4 degrees C. As expected, [3H]DHEA binding was inhibited by the addition of unlabeled DHEA, but was also modestly inhibited by dihydrotestosterone and cortisol. Binding of DHEA was unaffected by progesterone, dexamethasone, estradiol, androsterone, DHEAS, and beta-etiocholanolone at all concentrations tested. DHEA was incapable of inhibiting the binding of [3H]DHT to the androgen receptor or [3H]dexamethasone to the glucocorticoid receptor. Collectively, these findings suggest that murine T cells contain a specific DHEA receptor. We believe that DHEA is a steroid hormone that is directly involved in the regulation of IL-2 production by both normal and some T-cell hybridomas.

The addition of monophosphoryl lipid A, a minimally toxic derivative of LPS, to nonmucosally administered vaccines induced both systemic and mucosal immune responses to coadministered Ags. This was dependent on an up-regulated expression of 1α-hydroxylase (CYP27B1, 1αOHase), the enzyme that converts 25-hydroxycholecalciferol, a circulating inactive metabolite of vitamin D3, into 1,25(OH)2D3 (calcitriol). In response to locally produced calcitriol, myeloid dendritic cells (DCs) migrated from cutaneous vaccination sites into multiple secondary lymphoid organs, including classical inductive sites of mucosal immunity, where they effectively stimulated B and T cell immune responses. The endogenous production of calcitriol by monophosphoryl lipid A-stimulated DCs appeared to be Toll-IL-1R domain-containing adapter-inducing IFN-β-dependent, mediated through a type 1 IFN-induced expression of 1αOHase. Responsiveness to calcitriol was essential to promote the trafficking of mobilized DCs to nondraining lymphoid organs. Collectively, these studies help to expand our understanding of the physiologically important roles played by locally metabolized vitamin D3 in the initiation and diversification of adaptive immune responses. The influences of locally produced calcitriol on the migration of activated DCs from sites of vaccination/infection into both draining and nondraining lymphoid organs create a condition whereby Ag-responsive B and T cells residing in multiple lymphoid organs are able to simultaneously engage in the induction of adaptive immune responses to peripherally administered Ags as if they were responding to an infection of peripheral or mucosal tissues they were designed to protect.

UV irradiation has been shown to activate the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) in cell culture; however, only limited studies have been described in vivo. UV light has been categorized as UV-A (400 to 315 nm), -B (315 to 280 nm), or -C (less than 280 nm); the longer wavelengths are less harmful but more penetrative. Highly penetrative UV-A radiation constitutes the vast majority of UV sunlight reaching the earth's surface but is normally harmless. UV-B irradiation is more harmful but less prevalent than UV-A. In this report, the HIV-1 LTR-luciferase gene in the skin of transgenic mice was markedly activated when exposed to UV-B irradiation. The LTR in the skin of transgenic mice pretreated topically with a photosensitizing agent (psoralen) was also activated to similar levels when exposed to UV-A light. A 2-h exposure to sunlight activated the LTR in skin treated with psoralen, whereas the LTR in skin not treated with psoralen was activated after 7 h of sunlight exposure. The HIV-1 LTR-beta-galactosidase reporter gene was preferentially activated by UV-B irradiation in a small population of epidermal cells. The transgenic mouse models carrying HIV-1 LTR-luciferase and LTR-beta-galactosidase reporter genes have been used to demonstrate the in vivo UV-induced activation of the LTR and might be used to evaluate other environmental factors or pharmacologic substances that might potentially activate the HIV-1 LTR in vivo.

The present study examined the effects of the androgen steroid, dihydrotestosterone (DHT), on murine T-cell production of a number of lymphokines. Direct exposure of murine T cells to DHT in vitro was found to reduce the amount of interleukin-4 (IL-4), IL-5, and gamma- interferon (gamma IFN) produced after activation with anti-CD3 without affecting the production of IL-2. Exposure of T cells to either androstenedione or testosterone (the metabolic precursors of DHT) affected no change in the biosynthesis of either of these lymphokines. We have determined that macrophages possess 5 alpha-reductase, and are thus competent to metabolize testosterone to DHT. This physicochemical information is complemented by a functional analysis of macrophage metabolism of testosterone. By incubating bone marrow macrophages with testosterone, before their use as accessory cells, the IL-4 and IL-5 producing potential of the activated T cells cocultured with them was depressed. That the observed effect was mediated by the conversion of testosterone to DHT was further corroborated by illustrating that the inhibition of IL-4 production was abrogated if 4MA, a specific 5 alpha- reductase inhibitor, was added to macrophage cultures containing testosterone. The biologic role of DHT in lymphokine and immune response regulation in vivo was addressed using several lines of investigation. First, transdermal delivery of DHT to groups of mice altered the capacity of T cells residing in the draining lymph nodes, only, to produce lymphokines. Second, treatment of either aged mice or the T cells isolated from them with a combination of dehydroepiandrosterone and DHT restored the capacity of their T cells to produce IL-2, IL-4, and gamma IFN to levels equivalent to that of younger mice. Finally, we observed a difference between males and females of a given age to produce IL-2, IL-4, and gamma IFN, with both IL-4 and gamma IFN production being elevated in females. Collectively, our findings indicate that DHT, similar to other steroid hormones, may play an important role in lymphokine regulation in vivo.

This article reviews the physiology of adrenal androgen secretion. The effects of glucocorticoid administration, age, stress, and other drugs on the secretion of adrenal androgens are discussed. The biologic effects of dehydroepiandrosterone on cytokine secretion by lymphocytes, reduction of neoplasia, obesity, and endothelial injury and stimulation of bone growth appear to be unexplained by metabolism of this adrenal androgen to other steroid hormone, suggesting that dehydroepiandrosterone is a steroid hormone.

in this manuscript we present data to support the existence of an mechanism wich involves both enhancer and repressor activities of steroid hormones on lymphokine synthesis

Freshly isolated lymph node (LN) cells cultured in serum-containing medium were restricted to produce primarily interleukin 2 (IL-2) subsequent to T cell activation. Only minimal amounts of IL-4, IL-5, or interferon gamma (IFN-gamma) were produced under these conditions. Similar populations of LN cells cultured in serum-free medium were able to produce a variety of lymphokines after T cell activation, with the relative quantities of each species being dependent upon the lymphoid organ source of the lymphocytes. A similar relationship in the patterns of lymphokines produced by activated T cell hybridomas maintained under serum-free conditions was also observed, whereas activation in serum-supplemented media resulted in a predominant restriction to the secretion of IL-2. Additional studies determined that the entity in serum responsible for restricting T cell function in vitro was platelet-derived growth factor (PDGF). The PDGF-BB isoform was established to be the most active in the regulation of T cell function, enhancing IL-2 while depressing the production of IL-4, IL-5, and IFN-gamma at concentrations below 1 ng/ml. PDGF-AB was also found to be quite active, however, this isoform of PDGF was incapable of influencing IFN-gamma production at the concentrations tested. PDGF-AA was very weakly active. It therefore appears that PDGF, acting primarily through a beta receptor subunit (either alpha/beta- or beta/beta-type receptors) is able to influence profoundly the behavior of T cells, with some of its modulatory effects exhibiting isoform specificity. This is reflected by an enhancement in the production of IL-2, while simultaneously depressing the secretion of IL-4, IL-5, and IFN-gamma (PDGF-BB only) after T cell activation. Kinetic studies, where cell supernatants were analyzed both 24 and 48 h after T cell activation, suggested that "desensitization" to PDGF influences can occur naturally in vitro. Those species of lymphokines that were inhibited by PDGF over the first 24 h after activation could be produced at normal levels over the subsequent 24-h period. Finally, lymphokines maintained in the presence of PDGF-BB for greater than 24 h before their activation lost sensitivity to this growth factor. These cells regained responsiveness to PDGF after an additional incubation period in PDGF-free medium. Collectively, our data imply that the pattern of T cell lymphokines produced, plus the kinetics of their production after activation, are being controlled by the potent serum growth factor PDGF.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunity conferred by conventional vaccines is restricted to a narrow range of closely related strains, highlighting the unmet medical need for the development of vaccines that elicit protection against multiple pathogenic serotypes. Here we show that aSalmonellabivalent vaccine comprised of strains that lack and overproduce DNA adenine methylase (Dam) conferred cross-protective immunity to salmonella clinical isolates of human and animal origin. Protective immunity directly correlated with increased levels of cross-reactive opsonizing antibodies and memory T cells and a diminished expansion of myeloid-derived suppressor cells (MDSCs) that are responsible for the immune suppression linked to several conditions of host stress, including chronic microbial infections, traumatic insults, and many forms of cancer. Further, aged mice contained increased numbers of MDSCs and were more susceptible toSalmonellainfection than young mice, suggesting a role for these cells in the immune declines associated with the natural aging process. These data suggest that interventions capable of reducing MDSC presence and activities may allow corresponding increases in B- and T-cell stimulation and benefit the ability of immunologically diverse populations to be effectively vaccinated as well as reducing the risk of susceptible individuals to infectious disease.

The molecular mechanisms by which pertussis toxin (PTX) inhibits lymphocyte homing to peripheral lymph nodes (PLN) remain poorly understood. PTX-treated lymphocytes express homing receptors, yet cannot extravasate into PLN in vivo. Methylation of PTX, a procedure known to inactivate the B-oligomer of the toxin, restored high endothelial venule (HEV) binding capacity. In vitro studies established that toxin exposure inhibited the accessory role of LFA-1 in HEV binding. In contrast, PTX-exposed lymphocytes exhibited normal MEL-14-mediated HEV binding. Analysis of membrane fluidity revealed a 20% decrease in fluorescence polarization in PTX-exposed lymphocytes. On the basis of the current experiments, we propose a "zipper" model of lymphocyte-HEV interaction, in which lateral mobility of adhesion receptors in the cell membrane toward a site of endothelial contact is necessary to maintain adhesion against the shear force due to blood flow. PTX inhibits these processes by decreasing membrane fluidity, and by altering accessory adhesion molecule function.

We determined whether purified immunoglobulin G from patients with antiphospholipid antibodies causes fetal loss in pregnant mice. Sera were obtained from nonpregnant parous women (group 1) and nonpregnant women with antiphospholipid antibodies and a history of fetal loss (group 2). Pregnant BALB/c mice were given an intraperitoneal injection of 15 mg of IgG on day 8 of pregnancy. Typically, mice treated with IgG from antiphospholipid antibodies aborted within 48 hours. When animals were sacrificed on days 9 to 15, the uterus of each animal was inspected for the presence of live, dead, or resorbing fetuses. In contrast to mice injected with control IgG or saline solution, each mouse injected with IgG from antiphospholipid antibodies aborted and no live fetuses were found (p less than 0.05). Histologic examination of the uteroplacental interface showed decidual necrosis in the mice treated with IgG containing antiphospholipid antibodies, and immunofluorescent studies also showed prominent intravascular decidual IgG and fibrin deposition. We conclude that IgG from antiphospholipid antibodies of women with fetal loss causes fetal loss in BALB/c mice. It appears that the fetal loss is mediated by IgG binding in the maternal decidual vasculature.

Dehydroepiandrosterone (DHEA) is an adrenal steroid hormone produced in abundance by humans and most other warm-blooded animals, is uniquely sulfated (DHEAS) prior to export into the plasma, and exhibits an age-related decline in production with progressive age. No major physiological functions have been ascribed to the activity of this steroid, although DHEA is known to serve as an intermediary in sex steroid synthesis. Studies on the effects of glucocorticoids (GCS) on the immune system led us to question whether DHEA had effects on the ability of activated lymphocytes to produce interleukin 2 (IL 2). We determined that (a) lymphocytes from DHEA- or DHEAS-treated mice consistently produced much greater levels of IL 2 than normals in response to stimulation, (b) direct lymphocyte exposure to DHEA at low doses (10(-10)-10(-7) M) caused an enhanced capacity to secrete IL 2 following activation, (c) IL 2 production by activated cloned T cell lines could be augmented by DHEA treatment, and (d) GCS-induced depressions in IL 2 synthesis by T cells or T cell clones could be overcome in vitro and in vivo by exposure to the effects of DHEA. These findings suggest that DHEA, presumably through receptor-mediated mechanisms similar to other types of steroid hormones, may represent a natural and important regulator of IL 2 production in both normal and pathologic conditions.

We investigated the capacity of murine T lymphocytes, isolated from various lymphoid organs of normal or antigen-primed donors, to produce IL-2 or IL-4 after activation with anti-CD3 or specific antigen. Our results established that T cells resident within lymphoid organs being drained by nonmucosal tissue sites (e.g., axillary, inguinal, brachial lymph nodes, or spleen) produced IL-2 as the predominant T cell growth factor (TCGF) after activation. Conversely, activated T cells from lymphoid organs being drained by mucosal tissues (Peyer's patches, and cervical, periaortic, and parathymic lymph nodes) produced IL-4 as the major species of TCGF. Analysis of the lymphoid tissues obtained from adoptive recipients of antigen-primed lymphocytes provided by syngeneic donors provided evidence that direct influences were being exerted on T cells during their residence within defined lymphoid compartments. These lymphoid tissue influences appeared to be responsible for altering the potential of resident T cells to produce distinct species of TCGF. Steroid hormones, known transcriptional enhancers and repressors of specific cellular genes, were implicated in the controlling mechanisms over TCGF production. Glucocorticoids (GCs) were found to exert a systemic effect on all recirculating T cells, evidenced by a marked dominance in IL-4 production by T cells obtained from all lymphoid organs of GC-treated mice, or after a direct exposure of normal lymphoid cells to GCs in vitro before cellular activation with T cell mitogens. Further, the androgen steroid DHEA appeared to be responsible for providing an epigenetic influence to T cells trafficking through peripheral lymphoid organs. This steroid influence resulted in an enhanced potential for IL-2 secretion after activation. Anatomic compartmentalization of the DHEA-facilitated influence appears to be mediated by differential levels of DHEA-sulfatase in lymphoid tissues. DHEA-sulfatase is an enzyme capable of converting DHEA-sulfate (inactive) to the active hormone DHEA. We find very high activities of this enzyme isolated in murine macrophages. The implications of our findings to immunobiology are very great, and indicate that T cells, while clonally restricted for antigen peptide recognition, also appear to exhibit an extreme flexibility with regards to the species of lymphokines they produce after activation. Regulation of this highly conservative mechanism appears to be partially, if not exclusively, controlled by cellular influences being exerted by distinct species of steroid hormones, supplied in an endocrine or a paracrine manner where they mediate either systemic or tissue-localized influences, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Summary Cathelicidin production by human myeloid cells stimulated through toll-like receptor (TLR) 2/1, the migration of human CD8 + T cells to inflamed skin sites, and the ability of murine dendritic cells (DCs) to migrate from skin sites of vaccination to mucosal lymphoid organs all occur via calcitriol-dependent mechanisms. Herein, we report that murine DCs exposed to TLR3/TLR4 ligands upregulate their expression of 1α-hydroxylase, the enzyme that converts circulating 25(OH)D 3 to calcitriol, the active form of vitamin D3. TLR3/TLR4 ligands injected subcutaneously affect DC migration in vivo , allowing their trafficking to both draining and non-draining systemic and mucosal lymphoid organs. Subcutaneously delivered vaccines containing TLR3/TLR4 ligands and antigen stimulate the induction of both systemic and mucosal immune responses. Vaccines containing TLR9 ligands fail to stimulate 1α-hydroxylase protein expression, are incapable of redirecting DC migration into Peyer's patches and do not induce mucosal immune responses. These findings support a hypothesis that active metabolites of vitamin D3 produced locally are able to affect various aspects of innate and acquired immune responses.

The immunomodulatory effects of glucocorticoids (GCs) have been described as bimodal, with high levels of GCs exerting immunosuppressive effects and low doses of GCs being immunopermissive. While the mechanisms used by GCs to achieve immunosuppression have been investigated intensely, the molecular mechanisms underlying the permissive effects of GCs remain uncharacterized. Herein, we demonstrate that GC conditioning during the differentiation of myeloid progenitors into macrophages (Mφs) results in their enhanced LPS responsiveness, demonstrated by an overexpression of the inflammatory cytokines TNF-α, IL-6, and IL-12. Inflammatory cytokine overexpression resulted from an increased activation of NF-κB and the MAPK signaling cascade and a reduced activation of the PI3K-Akt pathway following LPS stimulation. GC conditioning during Mφ differentiation induced an increase in the expression of SHIP1, a phosphatase that negatively regulates the PI3K signaling pathway. Small interfering RNA-mediated knockdown of SHIP1 expression increased PI3K-dependent Akt activation and subsequently decreased inflammatory cytokine expression, suggesting GC-mediated up-regulation of SHIP1 expression is responsible for the augmentation in inflammatory cytokine production following LPS stimulation. We also show that splenic Mφs purified from normal mice that were implanted with timed-release GC pellets exhibited an enhanced LPS responsiveness and increased SHIP1 expression, indicating that GCs can regulate SHIP1 expression in vivo. Our results suggest that minor fluctuations in physiological levels of endogenous GCs can program endotoxin-responsive hemopoietic cells during their differentiation by regulating their sensitivity to stimulation.

The elderly suffer impairments to their immune system, evidenced by higher susceptibility to infections, cancer, and many diseases believed to be autoimmune in nature. A dysregulated overexpression of many proinflammatory cytokines also occurs with aging, as does the synthesis of enzymes that control expression of inflammatory lipid mediators and reactive oxygen species. An inappropriate activation of redox-controlled transcription factors, like nuclear factor-kappaB, occurs in many tissues from aged donors, and has been linked to excesses in cellular oxidative stress. Recently, the peroxisome proliferator-activated receptor-alpha (PPARalpha) has been evaluated for its effects on inflammatory and adaptive immune processes. PPARalpha provides redox-balancing influences on various lymphoid cell types and their inducible responses. We recently discovered that PPARalpha transiently suppresses the transcription of gamma-interferon (IFNgamma) by inhibiting the induction of T-bet. We now report that PPARalpha expression in CD4+ T cells is affected by the aging process. Lower PPARalpha levels are present in aged CD4+ T cells, and appear responsible for the suppressed interleukin-2 and exaggerated IFNgamma responses by these cells. Restoration of PPARalpha, T-bet, interleukin-2, and IFNgamma responses was found in T cells from aged animals supplemented with vitamin E, suggesting that interventions that focus on restoring redox balance might benefit the ailing aged immune system.

The transcription factor nuclear factor kappaB (NFkappaB) is constitutively active in many types of cancercells and regulates the expression of several antiapoptotic genes. Previous studies demonstrated a role for the inhibition of NFkappaB in cancer therapyusing a transgenic approach in mice. We found that NFkappaB was transiently activated much greater than background constitutive levels during colon cancer cell readhesion, which rendered the readhering colon cancer cells exquisitely susceptible to apoptosis in the presence of soluble NFkappaB inhibitors. These compounds greatly reduced colon cancer cell implantation in an in vivo seeding model of metastasis. The ability of soluble NFkappaB inhibitors to significantly induce apoptosis of readherent colon cancer cells makes them prospective candidates for preventing colon cancer metastasis.

Lipids and lipid metabolism have well-documented regulatory effects on inflammatory processes. Recent work has highlighted the role of the peroxisome proliferator-activated receptors (PPARs)--a subset of the nuclear-hormone-receptor superfamily that are activated by various lipid species--in regulating inflammatory responses. Here, we describe how the PPARs, through their interactions with transcription factors and other cell-signalling systems, have important regulatory roles in innate and adaptive immunity.

Peroxisome proliferator-activated receptor (PPAR) α represents an important member of the nuclear hormone receptor superfamily that can be activated by a variety of natural fatty acids, some of their metabolites and by commonly-used anti-lipidaemic drugs. We recently demonstrated PPARα expression in T lymphocytes, where it controls the initiation of transcription of T-box expressed in T-cells (T-bet) independent of added agonist. T-bet is an activation-inducible transcription factor regulator of interleukin 2 (suppression) and interferon γ (stimulation) synthesis. A suppressed ability to produce interleukin 2 and an enhanced production of interferon γ occurs in activated T-cells from PPARα-/- mice, as well as in T-cells from wild-type aged animals whose lymphocytes express lowered basal levels of PPARα. The dysregulated expression and/or function of cytokines, glucocorticoids or leptin that occurs with advanced age could all be responsible for the reduced expression of PPARα. Dietary supplementation of aged mice with vitamin E, or supplementation with known agonists of PPARα, was associated with elevation of lymphocyte expression of this nuclear hormone receptor, restoration of control over T-bet expression and elimination of the dysregulated production of interleukin 2 and interferon γ following lymphocyte activation. Interleukin 2 and interferon γ play very important roles in the initiation and/or regulation of immune, inflammatory and autoimmune disease states. Thus, the mechanisms that control the timing, magnitude and duration of specific cytokine production by activated T lymphocytes need clarification before appropriate nutritional or therapeutic strategies can be devised to treat disease conditions where cytokine expression and/or activities are deemed to be dysregulated and responsible.

It has been reported that common mucosal immunity can be efficiently induced in mice following immunization through the skin with vaccine formulations containing either the active form of vitamin D, or chemical agents capable of locally enhancing cyclic adenosine monophosphate levels. Herein, we report that exposure of skin to ultraviolet radiation B (UVB) can be employed as a means to alter systemic humoral immune responses and to promote the induction of mucosal immunity to protein antigens delivered into UVB-exposed skin sites. Our data indicates that the skin, as a vaccination site, can be manipulated to allow efficient induction of common mucosal and systemic immune responses.

Peroxisome proliferator-activated receptors (PPARs) are transcription factors that belong to the nuclear hormone receptor superfamily. PPARalpha and PPARgamma ligands have been demonstrated to exert anti-inflammatory activities in macrophages by repressing the activities of several transcription factors. PPARgamma is expressed in T lymphocytes and may play a role in cytokine production, cellular proliferation, and susceptibility to apoptosis. Herein, we demonstrate that T and B lymphocytes constitutively express PPARalpha. PPARalpha represents the predominant isoform expressed in lymphocytes, whereas PPARgamma dominates in all cell types of the myeloid lineage. PPARalpha expression was down-regulated following T-cell activation while PPARgamma expression increased under the same activating conditions. PPARalpha expression in T cells may be regulated by microenvironmental factors, because Peyer's patch T cells expressed far greater levels of PPARalpha than T cells isolated from peripheral lymphoid organs. Exposure to specific ligand determined that PPARalpha in lymphocytes can effectively transactivate a peroxisome proliferator response element reporter construct. PPARalpha's ability to regulate endogenous genes, however, required treatment with histone deacetylase inhibitors. Finally, ligand activation of lymphocyte PPARalpha antagonized NF-kappaB. Our observation that a functional PPARalpha exists within T cells and B lymphocytes suggests an expanding role for this nuclear receptor in cells of the immune system.