Protective and memory immunity to Histoplasma capsulatum in the absence of IL-10

We determined whether the absence of IL-10 in mice influenced protective and memory immunity to Histoplasma capsulatum. IL-10(-/-) mice cleared primary and secondary infection more rapidly than wild-type controls. Administration of mAb to TNF-alpha or IFN-gamma, but not GM-CSF, abrogated protection in naive IL-10(-/-) mice; mAb to TNF-alpha, but not IFN-gamma or GM-CSF, subverted protective immunity in secondary histoplasmosis. The inflammatory cell composition in IL-10(-/-) mice was altered in those given mAb to IFN-gamma or TNF-alpha. More Gr-1(+) and Mac-3(+) cells were present in lungs of IL-10(-/-) mice given mAb to IFN-gamma, and treatment with mAb to TNF-alpha sharply reduced the number of CD8(+) cells in lungs of IL-10(-/-) mice. We ascertained whether the lack of IL-10 modulated memory T cell generation or the protective function of cells. The percentage of CD3(+), CD44(high), CD62(low), and IFN-gamma(+) cells in IL-10(-/-) mice was higher than that of wild-type at day 7 but not day 21 or 49 after immunization. Fewer splenocytes from immunized IL-10(-/-) mice were required to mediate protection upon adoptive transfer into infected TCR alphabeta(-/-) mice. Hence, deficiency of IL-10 confers a salutary effect on the course of histoplasmosis, and the beneficial effects of IL-10 deficiency require endogenous TNF-alpha and/or IFN-gamma. Memory cell generation was transiently increased in IL-10(-/-) mice, but the protective function conferred by cells from these mice following immunization is strikingly more vigorous than that of wild-type.     

Hepatitis C virus-specific Th17 cells are suppressed by virus-induced TGF-beta

IL-17-secreting T (Th17) cells play a protective role in certain bacterial infections, but they are major mediators of inflammation and are pathogenic in organ-specific autoimmune diseases. However, human Th17 cells appear to be resistant to suppression by CD4(+)CD25(+)FoxP3(+) regulatory T cells, suggesting that they may be regulated by alternative mechanisms. Herein we show that IL-10 and TGF-beta suppressed IL-17 production by anti-CD3-stimulated PBMC from normal individuals. TGF-beta also suppressed IL-17 production by purified CD4(+) T cells, whereas the inhibitory effect of IL-10 on IL-17 production appears to be mediated predominantly by its effect on APC. An examination of patients infected with hepatitis C virus (HCV) demonstrated that Ag-specific Th17 cells are induced during infection and that these cells are regulated by IL-10 and TGF-beta. PBMC from HCV Ab-positive donors secreted IL-17, IFN-gamma, IL-10, and TGF-beta in response to stimulation with the HCV nonstructural protein 4 (NS4). Furthermore, NS4 induced innate TGF-beta and IL-10 expression by monocytes from normal donors and at higher levels from HCV-infected patients. Neutralization of TGF-beta, and to a lesser extent IL-10, significantly enhanced NS4-specific IL-17 and IFN-gamma production by T cells from HCV-infected donors. Our findings suggest that both HCV-specific Th1 and Th17 cells are suppressed by NS4-induced production of the innate anti-inflammatory cytokines IL-10 and TGF-beta. This may represent a novel immune subversion mechanism by the virus to evade host-protective immune responses. Our findings also suggest that TGF-beta and IL-10 play important roles in constraining the function of Th17 cells in general.     

Attenuation of Th1 response in decoy receptor 3 transgenic mice

The soluble decoy receptor 3 (DcR3) is a member of the TNFR superfamily. Because DcR3 is up-regulated in tumor tissues and is detectable in the sera of cancer patients, it is regarded as an immunosuppressor to down-regulate immune responses. To understand the function of DcR3 in vivo, we generated transgenic mice overexpressing DcR3 systemically. In comparison with HNT-TCR (HNT) transgenic mice, up-regulation of IL-4 and IL-10 and down-regulation of IFN-gamma, IL-12, and TNF-alpha were observed in the influenza hemagglutinin(126-138) peptide-stimulated splenocytes of HNT-DcR3 double-transgenic mice. When infected with Listeria monocytogenes, DcR3 transgenic mice show attenuated expression of IFN-gamma as well as increased susceptibility to infection. The Th2 cell-biased phenotype in DcR3 transgenic mice is attributed to decreased IL-2 secretion by T cells, resulting in the suppression of IL-2 dependent CD4(+) T cell proliferation. This suggests that DcR3 might help tumor growth by attenuating the Th1 response and suppressing cell-mediated immunity.     

A role for CD44 in the production of IFN-gamma and immunopathology during infection with Toxoplasma gondii

The interaction of activated CD44 with its ligand, low m.w. hyaluronan, is involved in inflammation, but no role has been identified for this interaction in the regulation of an immune response to infection. In these studies, infection of C57BL/6 mice with Toxoplasma gondii resulted in increased expression of CD44 on T cells, B cells, NK cells, and macrophages, and a small percentage of CD4(+) T cells express an activated form of CD44. Administration of anti-CD44 to infected mice prevented the development of a CD4(+) T cell-dependent, infection-induced inflammatory response in the small intestine characterized by the overproduction of IFN-gamma. The protective effect of anti-CD44 treatment was associated with reduced production of IFN-gamma, but not IL-12, in vivo and in vitro. Furthermore, the addition of low m.w. hyaluronan to cultures of splenocytes or purified CD4(+) T cells from infected mice resulted in the production of high levels of IFN-gamma, which was dependent on IL-12 and TCR stimulation. Together, these results identify a novel role for CD44 in the regulation of IFN-gamma production by CD4(+) T cells during infection and demonstrate a role for CD44 in the regulation of infection-induced immune pathology.     

IL-17A produced by gammadelta T cells plays a critical role in innate immunity against listeria monocytogenes infection in the liver

IL-17A is originally identified as a proinflammatory cytokine that induces neutrophils. Although IL-17A production by CD4(+) Th17 T cells is well documented, it is not clear whether IL-17A is produced and participates in the innate immune response against infections. In the present report, we demonstrate that IL-17A is expressed in the liver of mice infected with Listeria monocytogenes from an early stage of infection. IL-17A is important in protective immunity at an early stage of listerial infection in the liver because IL-17A-deficient mice showed aggravation of the protective response. The major IL-17A-producing cells at the early stage were TCR gammadelta T cells expressing TCR Vgamma4 or Vgamma6. Interestingly, TCR gammadelta T cells expressing both IFN-gamma and IL-17A were hardly detected, indicating that the IL-17A-producing TCR gammadelta T cells are distinct from IFN-gamma-producing gammadelta T cells, similar to the distinction between Th17 and Th1 in CD4(+) T cells. All the results suggest that IL-17A is a newly discovered effector molecule produced by TCR gammadelta T cells, which is important in innate immunity in the liver.     

Differential regulation of IFN-gamma, TNF-alpha, and IL-10 production by CD4(+) alphabetaTCR+ T cells and vdelta2(+) gammadelta T cells in response to monocytes infected with Mycobacterium tuberculosis-H37Ra.

Mycobacterium tuberculosis bacilli readily activate CD4(+) and gammadelta T cells. CD4(+) and gammadelta T cells were compared for their ability to regulate IFN-gamma, TNF-alpha, and IL-10 production, cytokines with significant roles in the immune response to M. tuberculosis. PBMC from healthy tuberculin positive donors were stimulated with live M. tuberculosis-H37Ra. CD4(+) and gammadelta T cells were purified by negative selection and tested in response to autologous monocytes infected with M. tuberculosis. Both subsets produced equal amounts of secreted IFN-gamma. However, the precursor frequency of IFN-gamma secreting gammadelta T cells was half that of CD4(+) T cells, indicating that gammadelta T cells were more efficient producers of IFN-gamma than CD4(+) T cells. TNF-alpha production was markedly enhanced by addition of CD4(+) and gammadelta T cells to M. tuberculosis infected monocytes, and TNF-alpha was produced by both T cells and monocytes. No differences in TNF-alpha enhancement were noted between CD4(+) and gammadelta T cells. IL-10 production by M. tuberculosis infected monocytes was not modulated by CD4(+) or gammadelta T cells. Thus CD4(+) and gammadelta T cells had similar roles in differential regulation of IFN-gamma, TNF-alpha, and IL-10 secretion in response to M. tuberculosis infected monocytes. However, the interaction between T cells and infected monocytes differed for each cytokine. IFN-gamma production was dependent on antigen presentation and costimulators provided by monocytes. TNF-alpha levels were increased by addition of TNF-alpha produced by T cells and IL-10 production by monocytes was not modulated by CD4(+) or gammadelta T cells.     

IL-10 and TGF-beta redundantly protect against severe liver injury and mortality during acute schistosomiasis

The cytokines IL-10 and TGF-beta regulate immunity and inflammation. IL-10 is known to suppress the extent of hepatic damage caused by parasite ova during natural infection with Schistosoma mansoni, but the role of TGF-beta is less clear. Cytokine blockade studies in mice revealed that anti-IL-10R mAb treatment during acute infection modestly increased cytokine production and liver damage, whereas selective anti-TGF-beta mAb treatment had marginal effects. In contrast, mice administered both mAbs developed severe hepatic inflammation, with enlarged, necrotic liver granulomas, cachexia, and >80% mortality by 8 wk postinfection, despite increased numbers of CD4(+)CD25(+)Foxp3(+) T regulatory cells. Blocking both IL-10 and TGF-beta at the onset of egg production also significantly increased IL-4, IL-6, TNF, IFN-gamma, and IL-17 production and markedly increased hepatic, peritoneal, and splenic neutrophilia. In contrast, coadministration of anti-IL-10R and TGF-beta mAbs had little effect upon parasite ova-induced intestinal pathology or development of alternatively activated macrophages, which are required to suppress intestinal pathology. This suggests that inflammation is controlled during acute S. mansoni infection by two distinct, organ-specific mechanisms: TGF-beta and IL-10 redundantly suppress hepatic inflammation while intestinal inflammation is regulated by alternatively activated macrophages.     

Involvement of prostaglandins in the immunosuppression occurring during experimental infection by Paracoccidioides brasiliensis

We investigated whether PGE2 mediates the immunosuppression observed during Paracoccidioides brasilensis infection. Con-A-stimulated splenocytes, isolated from mice on days 15 and 60 of infection, release high amounts of PGE2, this release was inhibited by the treatment of animals with indomethacin, sodium salicylate or meloxicam. The treatment of the animals with salicylate or meloxicam, but not indomethacin, enhanced the release of IL-2 by splenocytes from animals on day 15, but not on day 60 of infection. Furthermore, we demonstrated that the productions of TNF-alpha, IFN-gamma, IL-4, and IL-10 by Con-A-stimulated splenocytes from mice at 15 days of infection were inhibited by treatment with salicylate or meloxicam. Indomethacin inhibited only TNF-alpha and IFN-gamma production. The three treatments caused reduction of granuloma areas in the liver and lungs of infected mice. In conclusion, results suggest that the PGE2 released by COX-2 mediates the immunosuppression early on (day 15), but not during the later phase (60 days) of P. brasiliensis infection by a mechanism dependent upon IL-4 and IL-10.     

IL-12-independent IFN-gamma production by T cells in experimental Chagas' disease is mediated by IL-18.

IL-12p35-deficient (IL-12p35(-/-)) mice were highly susceptible to Trypanosoma cruzi infection and succumbed during acute infection, demonstrating the crucial importance of endogenous IL-12 in resistance to experimental Chagas' disease. Delayed immune responses were observed in mutant mice, although comparable IFN-gamma and TNF-alpha blood levels as in wild-type mice were detected 2 wk postinfection. In vivo and in vitro analysis demonstrated that T cells, but not NK cells, were recruited to infected organs. Analysis of mice double deficient in the recombinase-activating gene 2 (RAG2) and IL-12p35, as well as studies involving T cell depletion, identified CD4(+) T cells as the cellular source for IL-12-independent IFN-gamma production. IL-18 was induced in IL-12p35(-/-) mice and was responsible for IFN-gamma production, as demonstrated by in vivo IL-18 neutralization studies. In conclusion, evidence is presented for an IL-12-independent IFN-gamma production in experimental Chagas' disease that is T cell and IL-18 dependent.     

IL-13 induces disease-promoting type 2 cytokines, alternatively activated macrophages and allergic inflammation during pulmonary infection of mice with Cryptococcus neoformans

In the murine model of Cryptococcus neoformans infection Th1 (IL-12/IFN-gamma) and Th17 (IL-23/IL-17) responses are associated with protection, whereas an IL-4-dependent Th2 response exacerbates disease. To investigate the role of the Th2 cytokine IL-13 during pulmonary infection with C. neoformans, IL-13-overexpressing transgenic (IL-13Tg(+)), IL-13-deficient (IL-13(-/-)), and wild-type (WT) mice were infected intranasally. Susceptibility to C. neoformans infection was found when IL-13 was induced in WT mice or overproduced in IL-13Tg(+) mice. Infected IL-13Tg(+) mice had a reduced survival time and higher pulmonary fungal load as compared with WT mice. In contrast, infected IL-13(-/-) mice were resistant and 89% of these mice survived the entire period of the experiment. Ag-specific production of IL-13 by susceptible WT and IL-13Tg(+) mice was associated with a significant type 2 cytokine shift but only minor changes in IFN-gamma production. Consistent with enhanced type 2 cytokine production, high levels of serum IgE and low ratios of serum IgG2a/IgG1 were detected in susceptible WT and IL-13Tg(+) mice. Interestingly, expression of IL-13 by susceptible WT and IL-13Tg(+) mice was associated with reduced IL-17 production. IL-13 was found to induce formation of alternatively activated macrophages expressing arginase-1, macrophage mannose receptor (CD206), and YM1. In addition, IL-13 production led to lung eosinophilia, goblet cell metaplasia and elevated mucus production, and enhanced airway hyperreactivity. This indicates that IL-13 contributes to fatal allergic inflammation during C. neoformans infection.     

Coordinated control of immunity to muscle stage Trichinella spiralis by IL-10, regulatory T cells, and TGF-beta

We previously demonstrated that IL-10 is critical in the control of acute inflammation during development of Trichinella spiralis in the muscle. In this study, we use gene-targeted knockout mice, adoptive transfer of specific T cell populations, and in vivo Ab treatments to determine the mechanisms by which inflammation is controlled and effector T cell responses are moderated during muscle infection. We report that CD4(+)CD25(-) effector T cells, rather than CD4(+)CD25(+) regulatory T cells, suppress inflammation by an IL-10-dependent mechanism that limits IFN-gamma production and local inducible NO synthase induction. Conversely, we show that depletion of regulatory T cells during infection results in exaggerated Th2 responses. Finally, we provide evidence that, in the absence of IL-10, TGF-beta participates in control of local inflammation in infected muscle and promotes parasite survival.     

Functional heterogeneity of cytokines and cytolytic effector molecules in human CD8+ T lymphocytes.

CD8(+) T cells use a number of effector mechanisms to protect the host against infection. We have studied human CD8(+) T cells specific for CMV pp65(495-503) epitope, or for staphylococcal enterotoxin B, for the expression patterns of five cytokines and cytolytic effector molecules before and after antigenic stimulation. Ex vivo, the cytolytic molecule granzyme B was detected in a majority of circulating CMV-specific CD8(+) T cells, whereas perforin was rarely expressed. Both were highly expressed after Ag-specific activation accompanied by CD45RO up-regulation. TNF-alpha, IFN gamma, and IL-2 were sequentially acquired on recognition of Ag, but surprisingly, only around half of the CMV-specific CD8(+) T cells responded to antigenic stimuli with production of any cytokine measured. A dominant population coexpressed TNF-alpha and IFN-gamma, and cells expressing TNF-alpha only, IFN-gamma only, or all three cytokines together also occurred at lower but clearly detectable frequencies. Interestingly, perforin expression and production of IFN-gamma and TNF-alpha in CD8(+) T cells responding to staphylococcal enterotoxin B appeared to be largely segregated, and no IL-2 was detected in perforin-positive cells. Together, these data indicate that human CD8(+) T cells can be functionally segregated in vivo and have implications for the understanding of human CD8(+) T cell differentiation and specialization and regulation of effector mechanisms.     

Protection from direct cerebral cryptococcus infection by interferon-gamma-dependent activation of microglial cells

The brain represents a significant barrier for protective immune responses in both infectious disease and cancer. We have recently demonstrated that immunotherapy with anti-CD40 and IL-2 can protect mice against disseminated Cryptococcus infection. We now applied this immunotherapy using a direct cerebral cryptococcosis model to study direct effects in the brain. Administration of anti-CD40 and IL-2 significantly prolonged the survival time of mice infected intracerebrally with Cryptococcus neoformans. The protection was correlated with activation of microglial cells indicated by the up-regulation of MHC II expression on brain CD45(low)CD11b(+) cells. CD4(+) T cells were not required for either the microglial cell activation or anticryptococcal efficacy induced by this immunotherapy. Experiments with IFN-gamma knockout mice and IFN-gammaR knockout mice demonstrated that IFN-gamma was critical for both microglial cell activation and the anticryptococcal efficacy induced by anti-CD40/IL-2. Interestingly, while peripheral IFN-gamma production and microglial cell activation were observed early after treatment, negligible IFN-gamma was detected locally in the brain. These studies indicate that immunotherapy using anti-CD40 and IL-2 can augment host immunity directly in the brain against C. neoformans infection and that IFN-gamma is essential for this effect.     

Mechanisms of spontaneous resolution versus fibrosis in granulomatous experimental autoimmune thyroiditis

When granulomatous experimental autoimmune thyroiditis (G-EAT) was induced in CBA/J or DBA/1 mice, thyroid lesions resolved in less severe (3+) G-EAT in wild-type mice or severe (5+) G-EAT in IFN-gamma(-/-) mice, but progressed to fibrosis in 5+ G-EAT in wild-type mice. To define the mechanisms leading to these distinct outcomes, the expression of inflammatory and apoptotic molecules and infiltrating cells was evaluated using immunohistochemistry, RT-PCR, and confocal microscopy. The ratio of CD4(+)/CD8(+) T cells in thyroid infiltrates was one factor that predicted G-EAT outcome. CD4(+) T cells outnumbered CD8(+) T cells when lesions progressed to fibrosis, while CD8(+) T cells outnumbered CD4(+) T cells in thyroids that resolved. Fas, Fas ligand, FLIP, TNF-alpha, inducible NO synthase, TGF-beta, and IFN-gamma were highly expressed by infiltrating cells when G-EAT progressed to fibrosis. The expression of active caspase-3 was low, possibly contributing to the persistence of CD4(+) T cells in fibrosis. In contrast, FLIP was mainly expressed by thyrocytes in resolving G-EAT, the expression of active caspase-3 was high, and resolution correlated with apoptosis of infiltrating cells. There was also relatively less expression of TGF-beta, IFN-gamma, TNF-alpha, and inducible NO synthase and higher expression of IL-10 in resolving G-EAT than in G-EAT that progressed to fibrosis. These differences were particularly striking when comparing IFN-gamma(-/-) vs wild-type mice. These results suggest that several opposing biological mechanisms contribute to the outcome of an ongoing autoimmune response. These include differential expression of pro- and antiapoptotic molecules, cytokines, and the ratio of CD4(+) vs CD8(+) T cells.     

IL-15 and the initiation of cell contact-dependent synovial fibroblast-T lymphocyte cross-talk in rheumatoid arthritis: effect of methotrexate

To characterize the molecules responsible for synovial fibroblast-T lymphocyte (TL) cross-talk in rheumatoid arthritis (RA), synovial fibroblasts from patients with established RA (RASFibs) were cocultured with TLs from peripheral blood of early RA patients (RAPBTL). TLs from peripheral blood of healthy controls and from synovial fluid of RA served as controls. Adhesion molecules and cytokines were determined by flow cytometry, ELISA, and real-time PCR. RAPBTL (n = 20) induced an up-regulation of ICAM-1, intracellular IL-8, IL-6, IL-15, and surface IL-15 in cocultured RASFibs. In turn, RAPBTL showed an up-regulation of TNF-alpha, IFN-gamma, IL-17, CD25, and CD69 expression. Responses seen with TLs from peripheral blood of healthy controls (n = 20) were significantly lower, whereas responses with TLs from synovial fluid of RA (n = 20) were maximal. Blocking Abs to IL-15 and CD54, but not an isotype-control Ab, down-regulated the increased TL cytokine and activation marker expression. Abs to CD69, CD11a, IL-17, TNF-alpha, and IFN-gamma significantly decreased the up-regulation of RASFib cytokine and CD54 expression. Cocultures using 0.4- micro m inserts did not result in up-regulation of surface molecules or cytokines. Methotrexate significantly inhibited RASFib/TL cross-talk signals and decreased adhesion of TL to RASFibs. In summary, RASFib production of IL-15 induces the proinflammatory cytokines TNF-alpha, IFN-gamma, and IL-17 in cocultured TLs through a cell contact-dependent mechanism. In turn, these cytokines stimulate the expression of IL-15, IL-8, and IL-6 in RASFibs, thereby creating a feedback loop that favors persistent synovial inflammation. Methotrexate seems to disrupt this loop by decreasing cell adhesion.     

Goblet cell-derived resistin-like molecule beta augments CD4+ T cell production of IFN-gamma and infection-induced intestinal inflammation

The secreted goblet cell-derived protein resistin-like molecule beta (RELMbeta) has been implicated in divergent functions, including a direct effector function against parasitic helminths and a pathogenic function in promoting inflammation in models of colitis and ileitis. However, whether RELMbeta influences CD4(+) T cell responses in the intestine is unknown. Using a natural model of intestinal inflammation induced by chronic infection with gastrointestinal helminth Trichuris muris, we identify dual functions for RELMbeta in augmenting CD4(+) Th1 cell responses and promoting infection-induced intestinal inflammation. Following exposure to low-dose Trichuris, wild-type C57BL/6 mice exhibit persistent infection associated with robust IFN-gamma production and intestinal inflammation. In contrast, infected RELMbeta(-/-) mice exhibited a significantly reduced expression of parasite-specific CD4(+) T cell-derived IFN-gamma and TNF-alpha and failed to develop Trichuris-induced intestinal inflammation. In in vitro T cell differentiation assays, recombinant RELMbeta activated macrophages to express MHC class II and secrete IL-12/23p40 and enhanced their ability to mediate Ag-specific IFN-gamma expression in CD4(+) T cells. Taken together, these data suggest that goblet cell-macrophage cross-talk, mediated in part by RELMbeta, can promote adaptive CD4(+) T cell responses and chronic inflammation following intestinal helminth infection.     

Neonatal T cells in an adult lung environment are competent to resolve Pneumocystis carinii pneumonia

Initiation of the pulmonary inflammatory response to Pneumocystis carinii is delayed by 3 wk in mice infected as neonates compared with adults. There was no difference in the proliferative response of draining lymph node T cells from mice infected as neonates compared with adults when stimulated in vitro with either Con A or anti-CD3 mAB: However, TNF-alpha and IFN-gamma mRNA expression in the lungs of P. carinii-infected neonates was significantly lower than in adults indicating a lack of appropriate activation signaling in the local environment. This may have been due to active suppression because TGF-beta mRNA expression was significantly elevated in neonatal lungs compared with adults. To determine whether T cells from 10-day-old mice would effect resolution of P. carinii if harbored in an adult lung environment, cells were adoptively transferred to SCID mice with established P. carinii infections. There was no difference in the kinetics of T cell migration into the lungs or of clearance of P. carinii organisms when SCID mice were reconstituted with splenocytes from young mice as compared with adult mice. Furthermore, splenocytes from young mice stimulated both TNF-alpha and IFN-gamma mRNA expression to levels that were similar to that in the lungs of SCID mice reconstituted with adult cells. These data indicate that neonatal lymphocytes are competent to resolve P. carinii infection when harbored in an adult lung environment, suggesting that the neonatal lung environment, and not the T cells, is ineffective at responding to P. carinii infection.     

IL-12p40-dependent agonistic effects on the development of protective innate and adaptive immunity against Salmonella enteritidis.

To study a potential IL-12p40-dependent but IL-12p75-independent agonistic activity regulating the immune response against Salmonella Enteritidis, the course of infection in IL-12p35-deficient mice (IL-12p35(-/-), capable of producing IL-12p40) was compared with that of IL-12p40(-/-) mice. Mice lacking IL-12p40 revealed a higher mortality rate and higher bacterial organ burden than mice capable of producing IL-12p40. This phenotype was found in both genetically susceptible (BALB/c, Ity(s)) and resistant mice (129Sv/Ev, Ity(r)) indicating Ity-independent mechanisms. The more effective control of bacteria in the IL-12p35(-/-) mice was associated with elevated serum IFN-gamma and TNF-alpha levels. In contrast, IL-12p40(-/-) mice showed reduced IFN-gamma production, which was associated with significantly elevated serum IgE levels. Early during infection (days 3 and 4 postinfection), as well as late (day 20 postinfection), the number of infected phagocytes was strongly increased in the absence of IL-12p40 indicating impaired bactericidal activity when IL-12p40 was missing. Liver histopathology revealed a decreased number of mononuclear granulomas in IL-12p40(-/-) mice. Depletion of CD4(+) or CD8(+) T lymphocytes in vivo suggested that both T cell subpopulations contribute to the IL-12p40-dependent protective functions. Analysis of IL-12p40 vs IL-23p19 mRNA expression revealed an up-regulation of only IL-12p40 mRNA during Salmonella infection. Together these data indicate that IL-12p40 can induce protective mechanisms during both the innate and the adaptive type 1 immune response in Salmonella infection. This novel activity of IL-12p40 complements the well described dominant and essential role of IL-12p75 in protective immunity to Salmonella infection.     

Multiple Chlamydia pneumoniae antigens prime CD8+ Tc1 responses that inhibit intracellular growth of this vacuolar pathogen

CD8(+) T cells play an essential role in immunity to Chlamydia pneumoniae (Cpn). However, the target Ags recognized by Cpn-specific CD8(+) T cells have not been identified, and the mechanisms by which this T cell subset contributes to protection remain unknown. In this work we demonstrate that Cpn infection primes a pathogen-specific CD8(+) T cell response in mice. Eighteen H-2(b) binding peptides representing sequences from 12 Cpn Ags sensitized target cells for MHC class I-restricted lysis by CD8(+) CTL generated from the spleens and lungs of infected mice. Peptide-specific IFN-gamma-secreting CD8(+) T cells were present in local and systemic compartments after primary infection, and these cells expanded after pathogen re-exposure. CD8(+) T cell lines to the 18 Cpn epitope-bearing peptides were cytotoxic, displayed a memory phenotype, and secreted IFN-gamma and TNF-alpha, but not IL-4. These CTL lines lysed Cpn-infected macrophages, and the lytic activity was inhibited by brefeldin A, indicating endogenous processing of CTL Ags. Finally, Cpn peptide-specific CD8(+) CTL suppressed chlamydial growth in vitro by direct lysis of infected cells and by secretion of IFN-gamma and other soluble factors. These studies provide information on the mechanisms by which CD8(+) CTL protect against Cpn, furnish the tools to investigate their possible role in immunopathology, and lay the foundation for future work to develop vaccines against acute and chronic Cpn infections.