TLR2, but not TLR4, is required for effective host defence against Chlamydia respiratory tract infection in early life

Chlamydia pneumoniae commonly causes respiratory tract infections in children, and epidemiological investigations strongly link infection to the pathogenesis of asthma. The immune system in early life is immature and may not respond appropriately to pathogens. Toll-like receptor (TLR)2 and 4 are regarded as the primary pattern recognition receptors that sense bacteria, however their contribution to innate and adaptive immunity in early life remains poorly defined. We investigated the role of TLR2 and 4 in the induction of immune responses to Chlamydia muridarum respiratory infection, in neonatal wild-type (Wt) or TLR2-deficient ((-/-)), 4(-/-) or 2/4(-/-) BALB/c mice. Wt mice had moderate disease and infection. TLR2(-/-) mice had more severe disease and more intense and prolonged infection compared to other groups. TLR4(-/-) mice were asymptomatic. TLR2/4(-/-) mice had severe early disease and persistent infection, which resolved thereafter consistent with the absence of symptoms in TLR4(-/-) mice. Wt mice mounted robust innate and adaptive responses with an influx of natural killer (NK) cells, neutrophils, myeloid (mDCs) and plasmacytoid (pDCs) dendritic cells, and activated CD4(+) and CD8(+) T-cells into the lungs. Wt mice also had effective production of interferon (IFN)γ in the lymph nodes and lung, and proliferation of lymph node T-cells. TLR2(-/-) mice had more intense and persistent innate (particularly neutrophil) and adaptive cell responses and IL-17 expression in the lung, however IFNγ responses and T-cell proliferation were reduced. TLR2/4(-/-) mice had reduced innate and adaptive responses. Most importantly, neutrophil phagocytosis was impaired in the absence of TLR2. Thus, TLR2 expression, particularly on neutrophils, is required for effective control of Chlamydia respiratory infection in early life. Loss of control of infection leads to enhanced but ineffective TLR4-mediated inflammatory responses that prolong disease symptoms. This indicates that TLR2 agonists may be beneficial in the treatment of early life Chlamydia infections and associated diseases.     

Toll-like receptors 2 and 4 regulate the frequency of IFNγ-producing CD4+ T-cells during pulmonary infection with Chlamydia pneumoniae

TLR2 and TLR4 are crucial for recognition of Chlamydia pneumoniae in vivo, since infected TLR2/4 double-deficient mice are unable to control the infection as evidenced by severe loss of body weight and progressive lethal pneumonia. Unexpectedly, these mice display higher pulmonary levels of the protective cytokine IFNγ than wild type mice. We show here, that antigen-specific CD4(+) T-cells are responsible for the observed IFNγ-secretion in vivo and their frequency is higher in TLR2/4 double-deficient than in wild type mice. The capacity of TLR2/4 double-deficient dendritic cells to re-stimulate CD4(+) T-cells did not differ from wild type dendritic cells. However, the frequency of CD4(+)CD25(+)Foxp3(+) T-cells was considerably higher in wild type compared to TLR2/4 double-deficient mice and was inversely related to the number of IFNγ-secreting CD4(+) effector T-cells. Despite increased IFNγ-levels, at least one IFNγ-mediated response, protective NO-secretion, could not be induced in the absence of TLR2 and 4. In summary, CD4(+)CD25(+)Foxp3(+) regulatory T-cells fail to expand in the absence of TLR2 and TLR4 during pulmonary infection with C. pneumoniae, which in turn enhances the frequency of CD4(+)IFNγ(+) effector T-cells. Failure of IFNγ to induce NO in TLR2/4 double-deficient cells represents one possible mechanism why TLR2/4 double-deficient mice are unable to control pneumonia caused by C. pneumoniae and succumb to the infection.     

CD4+ T Cells Are Necessary and Sufficient To Confer Protection against Chlamydia trachomatis Infection in the Murine Upper Genital Tract

Chlamydia trachomatis infection is the most common bacterial sexually transmitted disease in the United States. Chlamydia infections that ascend to the upper genital tract can persist, trigger inflammation, and result in serious sequelae such as infertility. However, mouse models in which the vaginal vault is inoculated with C. trachomatis do not recapitulate the course of human disease. These intravaginal infections of the mouse do not ascend efficiently to the upper genital tract, do not cause persistent infection, do not induce significant inflammation, and do not induce significant CD4(+) T cell infiltration. In this article, we describe a noninvasive transcervical infection model in which we bypass the cervix and directly inoculate C. trachomatis into the uterus. We show that direct C. trachomatis infection of the murine upper genital tract stimulates a robust Chlamydia-specific CD4(+) T cell response that is both necessary and sufficient to clear infection and provide protection against reinfection.     

Host genetic background affects regulatory T-cell activity that influences the magnitude of cellular immune response against Mycobacterium tuberculosis

Using two mouse strains with different abilities to generate interferon (IFN)-γ production after Mycobacterium tuberculosis infection, we tested the hypothesis that the frequency and activity of regulatory T (Treg) cells are influenced by genetic background. Our results demonstrated that the suppressive activity of spleen Treg cells from infected or uninfected BALB/c mice was enhanced, inhibiting IFN-γ and interleukin (IL)-2 production. Infected C57BL/6 mice exhibited a decrease in the frequency of lung Treg cells and an increased ratio CD4(+):CD4(+)Foxp3(+) cells compared with infected BALB/c mice and uninfected C57BL/6 mice. Moreover, infected C57BL/6 mice also had a decrease in the immunosuppressive capacity of spleen Treg cells, higher lung IFN-γ and IL-17 production, and restricted the infection better than BALB/c mice. Adoptive transfer of BALB/c Treg cells into BALB/c mice induced an increase in bacterial colony-forming unit (CFU) counts. Furthermore, BALB/c mice treated with anti-CD25 antibody exhibited lung CFU counts significantly lower than mice treated with irrelevant antibody. Our results show that in BALB/c mice, the Treg cells have a stronger influence than that in C57BL/6 mice. These data suggest that BALB/c and C57BL/6 mice may use some different mechanisms to control M. tuberculosis infection. Therefore, the role of Treg cells should be explored during the development of immune modulators, both from the perspective of the pathogen and the host.     

Type I IFN negatively regulates CD8+ T cell responses through IL-10-producing CD4+ T regulatory 1 cells

Pleiotropic, immunomodulatory effects of type I IFN on T cell responses are emerging. We used vaccine-induced, antiviral CD8(+) T cell responses in IFN-beta (IFN-beta(-/-))- or type I IFN receptor (IFNAR(-/-))-deficient mice to study immunomodulating effects of type I IFN that are not complicated by the interference of a concomitant virus infection. Compared with normal B6 mice, IFNAR(-/-) or IFN-beta(-/-) mice have normal numbers of CD4(+) and CD8(+) T cells, and CD25(+)FoxP3(+) T regulatory (T(R)) cells in liver and spleen. Twice as many CD8(+) T cells specific for different class I-restricted epitopes develop in IFNAR(-/-) or IFN-beta(-/-) mice than in normal animals after peptide- or DNA-based vaccination. IFN-gamma and TNF-alpha production and clonal expansion of specific CD8(+) T cells from normal and knockout mice are similar. CD25(+)FoxP3(+) T(R) cells down-modulate vaccine-primed CD8(+) T cell responses in normal, IFNAR(-/-), or IFN-beta(-/-) mice to a comparable extent. Low IFN-alpha or IFN-beta doses (500-10(3) U/mouse) down-modulate CD8(+) T cells priming in vivo. IFNAR- and IFN-beta-deficient mice generate 2- to 3-fold lower numbers of IL-10-producing CD4(+) T cells after polyclonal or specific stimulation in vitro or in vivo. CD8(+) T cell responses are thus subjected to negative control by both CD25(+)FoxP3(+) T(R) cells and CD4(+)IL-10(+) T(R1) cells, but only development of the latter T(R) cells depends on type I IFN.     

Resistance to malarial infection is achieved by the cooperation of NK1.1(+) and NK1.1(-) subsets of intermediate TCR cells which are constituents of innate immunity

We previously reported that the major expanding lymphocytes were intermediate TCR (TCR(int)) cells (mainly NK1.1(-)) during malarial infection in mice. Cell transfer experiments of TCR(int) cells indicated that these T cells mediated resistance to malaria. However, TCR(int) cells always contain NK1.1(+)TCR(int) cells (i.e., NKT cells) and controversial results (NKT cells were effective or not for resistance to malaria) have been reported by different investigators. In this study, we used CD1d((-/-)) mice, which almost completely lack NKT cells in the liver and other immune organs. Parasitemia was prolonged in the blood of CD1d((-/-)) mice and the expansion of lymphocytes in the liver of these mice was more prominent after an injection of Plasmodium yoelii-infected erythrocytes. However, these mice finally recovered from malaria. In contrast to B6 mice, CD4(-)8(-) NKT cells as well as NK1.1(-)CD3(int) cells expanded in CD1d((-/-)) mice after malarial infection, instead of CD4(+) (and CD8(+)) NKT cells. These newly generated CD4(-)8(-)NKT cells in CD1d((-/-)) mice did not use an invariant chain of Valpha14Jalpha281 for TCRalpha. Other evidence was that severe thymic atrophy and autoantibody production were accompanied by malarial infection, irrespective of the mice used. These results suggest that both NK1.1(-) and NK1.1(+) subsets of TCR(int) cells (i.e., constituents of innate immunity) are associated with resistance to malaria and that an autoimmune-like state is induced during malarial infection.     

An MHC class Ib-restricted CD8+ T cell response to lymphocytic choriomeningitis virus

Conventional MHC class Ia-restricted CD8(+) T cells play a dominant role in the host response to virus infections, but recent studies indicate that T cells with specificity for nonclassical MHC class Ib molecules may also participate in host defense. To investigate the potential role of class Ib molecules in anti-viral immune responses, K(b-/-)D(b-/-)CIITA(-/-) mice lacking expression of MHC class Ia and class II molecules were infected with lymphocytic choriomeningitis virus (LCMV). These animals have a large class Ib-selected CD8(+) T cell population and they were observed to mediate partial (but incomplete) virus clearance during acute LCMV infection as compared with K(b-/-)D(b-/-)β(2)-microglobulin(-/-) mice that lack expression of both MHC class Ia and class Ib molecules. Infection was associated with expansion of splenic CD8(+) T cells and induction of granzyme B and IFN-γ effector molecules in CD8(+) T cells. Partial virus clearance was dependent on CD8(+) cells. In vitro T cell restimulation assays demonstrated induction of a population of β(2)-microglobulin-dependent, MHC class Ib-restricted CD8(+) T cells with specificity for viral Ags and yet to be defined nonclassical MHC molecules. MHC class Ib-restricted CD8(+) T cell responses were also observed after infection of K(b-/-)D(b-/-)mice despite the low number of CD8(+) T cells in these animals. Long-term infection studies demonstrated chronic infection and gradual depletion of CD8(+) T cells in K(b-/-)D(b-/-)CIITA(-/-) mice, demonstrating that class Ia molecules are required for viral clearance. These findings demonstrate that class Ib-restricted CD8(+) T cells have the potential to participate in the host immune response to LCMV.     

Seasonal FluMist vaccination induces cross-reactive T cell immunity against H1N1 (2009) influenza and secondary bacterial infections

T cell epitopes have been found to be shared by circulating, seasonal influenza virus strains and the novel pandemic H1N1 influenza infection, but the ability of these common epitopes to provide cross-protection is unknown. We have now directly tested this by examining the ability of live seasonal influenza vaccine (FluMist) to mediate protection against swine-origin H1N1 influenza virus infection. Naive mice demonstrated considerable susceptibility to H1N1 Cal/04/09 infection, whereas FluMist-vaccinated mice had markedly decreased morbidity and mortality. In vivo depletion of CD4(+) or CD8(+) immune cells after vaccination indicated that protective immunity was primarily dependent upon FluMist-induced CD4(+) cells but not CD8(+) T cells. Passive protection studies revealed little role for serum or mucosal Abs in cross-protection. Although H1N1 influenza infection of naive mice induced intensive phagocyte recruitment, pulmonary innate defense against secondary pneumococcal infection was severely suppressed. This increased susceptibility to bacterial infection was correlated with augmented IFN-γ production produced during the recovery stage of H1N1 influenza infection, which was completely suppressed in mice previously immunized with FluMist. Furthermore, susceptibility to secondary bacterial infection was decreased in the absence of type II, but not type I, IFN signaling. Thus, seasonal FluMist treatment not only promoted resistance to pandemic H1N1 influenza infection but also restored innate immunity against complicating secondary bacterial infections.     

Increased protection from vaccinia virus infection in mice genetically prone to lymphoproliferative disorders

Mutations in the genes that encode Fas or Fas ligand (FasL) can result in poor restraints on lymphocyte activation and in increased susceptibility to autoimmune disorders. Because these mutations portend a continuously activated immune state, we hypothesized that they might in some cases confer resistance to infection. To examine this possibility, the immune response to, morbidity caused by, and clearance of vaccinia virus (VACV) Western Reserve was examined in 5- to 7-week-old Fas mutant (lpr) mice, before an overt lymphoproliferative disorder was observable. On day 6 after VACV infection, C57BL/6-lpr (B6-lpr) mice had decreased morbidity, decreased viral titers, and an increased percentage and number of CD4(+) and CD8(+) T cells. As early as day 2 after infection, B6-lpr mice had decreased liver and spleen viral titers and increased numbers of and increased gamma interferon (IFN-γ) production by several different effector cell populations. Depletion of individual effector cell subsets did not inhibit the resistance of B6-lpr mice. Uninfected B6-lpr mice also had increased numbers of NK cells, γδ(+) T cells, and CD44(+) CD4(+) and CD44(+) CD8(+) T cells compared to uninfected B6 mice. Antibody to IFN-γ resulted in increased virus load in both B6 and B6-lpr mice and eliminated the differences in viral titers between them. These results suggest that IFN-γ produced by multiple activated leukocyte populations in Fas-deficient hosts enhances resistance to some viral infections.     

Chronic lymphocytic choriomeningitis virus infection actively down-regulates CD4+ T cell responses directed against a broad range of epitopes

Activation of CD4(+) T cells helps establish and sustain CD8(+) T cell responses and is required for the effective clearance of acute infection. CD4-deficient mice are unable to control persistent infection and CD4(+) T cells are usually defective in chronic and persistent infections. We investigated the question of how persistent infection impacted pre-existing lymphocytic choriomeningitis virus (LCMV)-specific CD4(+) T cell responses. We identified class II-restricted epitopes from the entire set of open reading frames from LCMV Armstrong in BALB/c mice (H-2(d)) acutely infected with LCMV Armstrong. Of nine epitopes identified, six were restricted by I-A(d), one by I-E(d) and two were dually restricted by both I-A(d) and I-E(d) molecules. Additional experiments revealed that CD4(+) T cell responses specific for these epitopes were not generated following infection with the immunosuppressive clone 13 strain of LCMV. Most importantly, in peptide-immunized mice, established CD4(+) T cell responses to these LCMV CD4 epitopes as well as nonviral, OVA-specific responses were actively suppressed following infection with LCMV clone 13 and were undetectable within 12 days after infection, suggesting an active inhibition of established helper responses. To address this dysfunction, we performed transfer experiments using both the Smarta and OT-II systems. OT-II cells were not detected after clone 13 infection, indicating physical deletion, while Smarta cells proliferated but were unable to produce IFN-gamma, suggesting impairment of the production of this cytokine. Thus, multiple mechanisms may be involved in the impairment of helper responses in the setting of early persistent infection.     

Reactive oxygen species produced by the NADPH oxidase 2 complex in monocytes protect mice from bacterial infections

Chronic granulomatous disease (CGD) is an inherited disorder characterized by recurrent life-threatening bacterial and fungal infections. CGD results from defective production of reactive oxygen species by phagocytes caused by mutations in genes encoding the NADPH oxidase 2 (NOX2) complex subunits. Mice with a spontaneous mutation in Ncf1, which encodes the NCF1 (p47(phox)) subunit of NOX2, have defective phagocyte NOX2 activity. These mice occasionally develop local spontaneous infections by Staphylococcus xylosus or by the common CGD pathogen Staphylococcus aureus. Ncf1 mutant mice were more susceptible to systemic challenge with these bacteria than were wild-type mice. Transgenic Ncf1 mutant mice harboring the wild-type Ncf1 gene under the human CD68 promoter (MN(+) mice) gained the expression of NCF1 and functional NOX2 activity specifically in monocytes/macrophages, although minimal NOX2 activity was also detected in some CD11b(+)Ly6G(+) cells defined as neutrophils. MN(+) mice did not develop spontaneous infection and were more resistant to administered staphylococcal infections compared with MN(-) mice. Most strikingly, MN(+) mice survived after being administered Burkholderia cepacia, an opportunistic pathogen in CGD patients, whereas MN(-) mice died. Thus, monocyte/macrophage expression of functional NCF1 protected against spontaneous and administered bacterial infections.     

Cutting edge: in the absence of TGF-β signaling in T cells, fewer CD103+ regulatory T cells develop, but exuberant IFN-γ production renders mice more susceptible to helminth infection

Multiple factors control susceptibility of C57BL/6 mice to infection with the helminth Heligmosomoides polygyrus, including TGF-β signaling, which inhibits immunity in vivo. However, mice expressing a T cell-specific dominant-negative TGF-β receptor II (TGF-βRII DN) show dampened Th2 immunity and diminished resistance to infection. Interestingly, H. polygyrus-infected TGF-βRII DN mice show greater frequencies of CD4(+)Foxp3(+)Helios(+) Tregs than infected wild-type mice, but levels of CD103 are greatly reduced on both these cells and on the CD4(+)Foxp3(+)Helios(-) population. Although Th9 and Th17 levels are comparable between infected TGF-βRII DN and wild-type mice, the former develop exaggerated CD4(+) and CD8(+) T cell IFN-γ responses. Increased susceptibility conferred by TGF-βRII DN expression was lost in IFN-γ-deficient mice, although they remained unable to completely clear infection. Hence, overexpression of IFN-γ negatively modulates immunity, and the presence of Helios(+) Tregs may maintain susceptibility on the C57BL/6 background.     

The interaction between IL-18 and IL-18 receptor limits the magnitude of protective immunity and enhances pathogenic responses following infection with intracellular bacteria

The binding of IL-18 to IL-18Rα induces both proinflammatory and protective functions during infection, depending on the context in which it occurs. IL-18 is highly expressed in the liver of wild-type (WT) C57BL/6 mice following lethal infection with highly virulent Ixodes ovatus ehrlichia (IOE), an obligate intracellular bacterium that causes acute fatal toxic shock-like syndrome. In this study, we found that IOE infection of IL-18Rα(-/-) mice resulted in significantly less host cell apoptosis, decreased hepatic leukocyte recruitment, enhanced bacterial clearance, and prolonged survival compared with infected WT mice, suggesting a pathogenic role for IL-18/IL-18Rα in Ehrlichia-induced toxic shock. Although lack of IL-18R decreased the magnitude of IFN-γ producing type-1 immune response, enhanced resistance of IL-18Rα(-/-) mice against Ehrlichia correlated with increased proinflammatory cytokines at sites of infection, decreased systemic IL-10 production, increased frequency of protective NKT cells producing TNF-α and IFN-γ, and decreased frequency of pathogenic TNF-α-producing CD8(+) T cells. Adoptive transfer of immune WT CD8(+) T cells increased bacterial burden in IL-18Rα(-/-) mice following IOE infection. Furthermore, rIL-18 treatment of WT mice infected with mildly virulent Ehrlichia muris impaired bacterial clearance and enhanced liver injury. Finally, lack of IL-18R signal reduced dendritic cell maturation and their TNF-α production, suggesting that IL-18 might promote the adaptive pathogenic immune responses against Ehrlichia by influencing T cell priming functions of dendritic cells. Together, these results suggested that the presence or absence of IL-18R signals governs the pathogenic versus protective immunity in a model of Ehrlichia-induced immunopathology.     

Unified immune modulation by 4-1BB triggering leads to diverse effects on disease progression in vivo

4-1BB (CD137) is a powerful T-cell costimulatory molecule in the treatment of virus infections and tumors, but recent studies have also uncovered regulatory functions of 4-1BB signaling. Since 4-1BB triggering suppresses autoimmunity by accumulating indoleamine 2,3-dioxygenase (IDO) in dendritic cells (DCs) in an interferon (IFN)-γ-dependent manner, we asked whether similar molecular and cellular changes were induced by 4-1BB triggering in virus-infected mice. 4-1BB triggering increased IFN-γ and IDO, and suppressed CD4(+) T cells, in C57BL/6 mice infected with the type 1 KOS strain of Herpes simplex virus (HSV-1), as it does in an autoimmune disease model. Detailed analysis of the CD4(+) T suppression showed that freshly activated CD62L(high) T cells underwent apoptosis in the early phase of suppression, and CD62L(low) effector/memory T cells in the later phase. Although 4-1BB triggering resulted in similar cellular changes - increased CD8(+) T and decreased CD4(+) T cells, it had different effects on mortality in mice infected with HSV-1 RE, influenza, and Japanese encephalitis virus (JEV); it increased mortality in influenza-infected mice but decreased it in JEV-infected mice. Since the dominant type of immune cell generated to protect the host was different for each virus - CD4(+) T cells and neutrophils in HSV-1 RE infection, both CD4(+) T and CD8(+) T cells in influenza infection, and a crucial role for B cells in JEV infection, 4-1BB triggering resulted in different therapeutic outcomes. We conclude that the therapeutic outcome of 4-1BB triggering is determined by whether the protective immunity generated against the virus was beneficially altered by the 4-1BB triggering.     

IFN-γ-producing CD4+ T cells promote experimental cerebral malaria by modulating CD8+ T cell accumulation within the brain

It is well established that IFN-γ is required for the development of experimental cerebral malaria (ECM) during Plasmodium berghei ANKA infection of C57BL/6 mice. However, the temporal and tissue-specific cellular sources of IFN-γ during P. berghei ANKA infection have not been investigated, and it is not known whether IFN-γ production by a single cell type in isolation can induce cerebral pathology. In this study, using IFN-γ reporter mice, we show that NK cells dominate the IFN-γ response during the early stages of infection in the brain, but not in the spleen, before being replaced by CD4(+) and CD8(+) T cells. Importantly, we demonstrate that IFN-γ-producing CD4(+) T cells, but not innate or CD8(+) T cells, can promote the development of ECM in normally resistant IFN-γ(-/-) mice infected with P. berghei ANKA. Adoptively transferred wild-type CD4(+) T cells accumulate within the spleen, lung, and brain of IFN-γ(-/-) mice and induce ECM through active IFN-γ secretion, which increases the accumulation of endogenous IFN-γ(-/-) CD8(+) T cells within the brain. Depletion of endogenous IFN-γ(-/-) CD8(+) T cells abrogates the ability of wild-type CD4(+) T cells to promote ECM. Finally, we show that IFN-γ production, specifically by CD4(+) T cells, is sufficient to induce expression of CXCL9 and CXCL10 within the brain, providing a mechanistic basis for the enhanced CD8(+) T cell accumulation. To our knowledge, these observations demonstrate, for the first time, the importance of and pathways by which IFN-γ-producing CD4(+) T cells promote the development of ECM during P. berghei ANKA infection.     

An inclusion membrane protein from Chlamydia trachomatis enters the MHC class I pathway and stimulates a CD8+ T cell response

During its developmental cycle, the intracellular bacterial pathogen Chlamydia trachomatis remains confined within a protective vacuole known as an inclusion. Nevertheless, CD8(+) T cells that recognize Chlamydia Ags in the context of MHC class I molecules are primed during infection. MHC class I-restricted presentation of these Ags suggests that these proteins or domains from them have access to the host cell cytoplasm. Chlamydia products with access to the host cell cytoplasm define a subset of molecules uniquely positioned to interface with the intracellular environment during the pathogen's developmental cycle. In addition to their use as candidate Ags for stimulating CD8(+) T cells, these proteins represent novel candidates for therapeutic intervention of infection. In this study, we use C. trachomatis-specific murine T cells and an expression-cloning strategy to show that CT442 from Chlamydia is targeted by CD8(+) T cells. CT442, also known as CrpA, is a 15-kDa protein of undefined function that has previously been shown to be associated with the Chlamydia inclusion membrane. We show that: 1) CD8(+) T cells specific for an H-2D(b)-restricted epitope from CrpA are elicited at a significant level (approximately 4% of splenic CD8(+) T cells) in mice in response to infection; 2) the response to this epitope correlates with clearance of the organism from infected mice; and 3) immunization with recombinant vaccinia virus expressing CrpA elicits partial protective immunity to subsequent i.v. challenge with C. trachomatis.     

Gamma interferon controls mouse polyomavirus infection in vivo

Human polyomaviruses are associated with substantial morbidity in immunocompromised patients, including those with HIV/AIDS, recipients of bone marrow and kidney transplants, and individuals receiving immunomodulatory agents for autoimmune and inflammatory diseases. No effective antipolyomavirus agents are currently available, and no host determinants have been identified to predict susceptibility to polyomavirus-associated diseases. Using the mouse polyomavirus (MPyV) infection model, we recently demonstrated that perforin-granzyme exocytosis, tumor necrosis factor alpha (TNF-α), and Fas did not contribute to control of infection or virus-induced tumors. Gamma interferon (IFN-γ) was recently shown to inhibit replication by human BK polyomavirus in primary cultures of renal tubular epithelial cells. In this study, we provide evidence that IFN-γ is an important component of the host defense against MPyV infection and tumorigenesis. In immortalized and primary cells, IFN-γ reduces expression of MPyV proteins and impairs viral replication. Mice deficient for the IFN-γ receptor (IFN-γR(-/-)) maintain higher viral loads during MPyV infection and are susceptible to MPyV-induced tumors; this increased viral load is not associated with a defective MPyV-specific CD8(+) T cell response. Using an acute MPyV infection kidney transplant model, we further show that IFN-γR(-/-) donor kidneys harbor higher MPyV levels than donor kidneys from wild-type mice. Finally, administration of IFN-γ to persistently infected mice significantly reduces MPyV levels in multiple organs, including the kidney, a major reservoir for persistent mouse and human polyomavirus infections. These findings demonstrate that IFN-γ is an antiviral effector molecule for MPyV infection.     

Early induction of CCL7 downstream of TLR9 signaling promotes the development of robust immunity to cryptococcal infection

We investigated mechanisms by which TLR9 signaling promoted the development of the protective response to Cryptococcus neoformans in mice with cryptococcal pneumonia. The afferent (week 1) and efferent (week 3) phase immune parameters were analyzed in the infected wild-type (TLR9(+/+)) and TLR-deficient (TLR9(-/-)) mice. TLR9 deletion diminished 1) accumulation and activation of CD11b(+) dendritic cells (DCs), 2) the induction of IFN-γ and CCR2 chemokines CCL7, CCL12, but not CCL2, at week 1, and 3) pulmonary accumulation and activation of the major effector cells CD4(+) and CD8(+) T cells, CD11b(+) lung DCs, and exudate macrophages at week 3. The significance of CCL7 induction downstream of TLR9 signaling was investigated by determining whether CCL7 reconstitution would improve immunological parameters in C. neoformans-infected TLR9(-/-) mice. Early reconstitution with CCL7 1) improved accumulation and activation of CD11b(+) DCs at week 1, 2) restored early IFN-γ production in the lungs, and 3) restored the accumulation of major effector cell subsets. CCL7 administration abolished the difference in lung fungal burdens between TLR9(+/+) and TLR9(-/-) mice at week 3; however, significant reduction of fungal burdens between PBS- and CCL7-treated mice has not been observed, suggesting that additional mechanism(s) apart from early CCL7 induction contribute to optimal fungal clearance in TLR9(+/+) mice. Collectively, we show that TLR9 signaling during the afferent phase contributes to the development of protective immunity by promoting the early induction of CCL7 and IFN-γ and the subsequent early recruitment and activation of DCs and additional effector cells in mice with cryptococcal pneumonia.