Role of IFN-gamma in regulating T2 immunity and the development of alternatively activated macrophages during allergic bronchopulmonary mycosis

Pulmonary Cryptococcus neoformans infection of C57BL/6 mice is an established model of a chronic pulmonary fungal infection accompanied by an "allergic" response (T2) to the infection, i.e., a model of an allergic bronchopulmonary mycosis. Our objective was to determine whether IFN-gamma plays a role in regulating the pulmonary T2 immune response in C. neoformans-infected C57BL/6 mice. Long-term pulmonary fungistasis was lost in IFN-gamma knockout (KO) mice, resulting in an increased pulmonary burden of fungi at wk 3. IFN-gamma was required for the early influx of leukocytes into the lungs but was not required later in the infection. By wk 3, eosinophil and macrophage numbers were elevated in the absence of IFN-gamma. The inducible NO synthase to arginase ratio was lower in the lungs of IFN-gamma KO mice and the macrophages had increased numbers of intracellular cryptococci and YM1 crystals, indicative of alternatively activated macrophages in these mice. There was evidence of pulmonary fibrosis in both wild-type and IFN-gamma KO mice by 5 wk postinfection. IFN-gamma production was not required for the development of T2 cytokine (IL-4, IL-5, IL-13) producing cells in the lungs and lung-associated lymph nodes or induction of an IgE response. At a number of time points, T2 cytokine production was enhanced in IFN-gamma KO mice. Thus, in the absence of IFN-gamma, C57BL/6 mice develop an augmented allergic response to C. neoformans, including enhanced generation of alternatively activated macrophages, which is accompanied by a switch from a chronic to a progressive pulmonary cryptococcal infection.     

IL-10 modulates host responses and lung damage induced by Pneumocystis carinii infection

Host responses to Pneumocystis carinii infection mediate impairment of pulmonary function and contribute to the pathogenesis of pneumonia. IL-10 is known to inhibit inflammation and reduce the severity of pathology caused by a number of infectious organisms. In the present studies, IL-10-deficient (IL-10 knockout (KO)) mice were infected with P. carinii to determine whether the severity of pathogenesis and the efficiency of clearance of the organisms could be altered in the absence of IL-10. The clearance kinetics of P. carinii from IL-10 KO mice was significantly enhanced compared with that of wild-type (WT) mice. This corresponded to a more intense CD4(+) and CD8(+) T cell response as well as an earlier neutrophil response in the lungs of IL-10 KO mice. Furthermore, IL-12, IL-18, and IFN-gamma were found in the bronchoalveolar lavage fluids at earlier time points in IL-10 KO mice suggesting that alveolar macrophages were activated earlier than in WT mice. However, when CD4(+) cells were depleted from P. carinii-infected IL-10 KO mice, the ability to enhance clearance was lost. Furthermore, CD4-depleted IL-10 KO mice had significantly more lung injury than CD4-depleted WT mice even though the intensity of the inflammatory responses was similar. This was characterized by increased vascular leakage, decreased oxygenation, and decreased arterial pH. These data indicate that IL-10 down-regulates the immune response to P. carinii in WT mice; however, in the absence of CD4(+) T cells, IL-10 plays a critical role in controlling lung damage independent of modulating the inflammatory response.     

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.     

CCR2 expression determines T1 versus T2 polarization during pulmonary Cryptococcus neoformans infection

Pulmonary clearance of the encapsulated yeast Cryptococcus neoformans requires the development of T1-type immunity. The objective of this study was to determine the role of CCR2 in leukocyte recruitment and development of T1-type cell-mediated immunity during pulmonary C. neoformans infection. Intratracheal inoculation of C. neoformans into CCR2 knockout (CCR2-/-) mice produced a prolonged pulmonary infection (5000-fold CFU at 6 wk compared with CCR2+/+ mice) and significant dissemination to the spleen and brain (160- and 800-fold greater). In addition, CCR2 deficiency resulted in significantly reduced recruitment of macrophages (weeks 1-3) and CD8+ T cells (weeks 1-2) into the lungs. The immune response in CCR2-/- mice was characterized by chronic pulmonary eosinophilia, crystal deposition in the lungs, pulmonary leukocyte production of IL-4 and IL-5 but not IFN-gamma, lack of anticryptococcal delayed-type hypersensitivity, and high levels of serum IgE. These results demonstrate that expression of CCR2 is required for the development of a T1-type response to C. neoformans infection and lack of CCR2 results in a switch to a T2-type response. Thus, CCR2 plays a critical role in promoting the development of T1- over T2-type immune responses in the lung following cryptococcus infection.     

Chlamydia trachomatis mouse pneumonitis lung infection in IL-18 and IL-12 knockout mice: IL-12 is dominant over IL-18 for protective immunity

BACKGROUND: Interferon (IFN)-gamma is a key to protective immunity against a variety of intracellular bacterial infections, including Chlamydia trachomatis. Interleukin (IL)-18, a recently identified Th1 cytokine, together with IL-12 is a strong stimulator for IFN-gamma production. We investigated the relative roles of IL-18 and IL- 12 in protective immunity to C. trachomatis mouse pneumonitis (MoPn) infection using gene knockout (KO) and wild-type (WT) mice. MATERIALS AND METHODS: Mice were intranasally infected with C. trachomatis MoPn and protective immunity was assessed among groups of mice by daily body weight changes, lung growth of MoPn, and histopathological appearances at day 10 postinfection. The corresponding immune responses for each group of mice at the same postinfection time point were evaluated by measuring antigen-specific antibody isotype responses and cytokine profiles. RESULTS: Our results showed that IL-18 deficiency had little or no influence on clearance of MoPn from the lung, although KO mice exhibited slightly more severe inflammatory reactions in lung tissues, as well as reduced systemic and local IFN-gamma production, compared with WT mice. Results with IL-18 KO mice were in sharp contrast to those observed with IL-12 KO mice that showed substantially reduced clearance of MoPn from the lungs, substantial reductions of antigen-specific systemic and lung IFN-gamma production, decreased ratio of MoPn-specific immunoglobulin G (IgG)2a/IgG1, and severe pathological changes in the lung with extensive polymorphonuclear, instead of mononuclear, cell infiltration. Exogenous IL-12 or IL-18 was able to increase IFN-gamma production in IL-18 KO mice; whereas, only exogenous IL-12, but not IL-18, enhanced IFN-gamma production in IL-12 KO mice. Caspase-1 is the key protease for activation of IL-18 precursor into the bioactive form, and caspase-1 KO mice also displayed similar bacterial clearance and body weight loss to that in WT mice at early stages of MoPn infection. This further confirmed that IL-18 was not essential for host defense against chlamydia infection. CONCLUSIONS: These results suggest that IL-12, rather than IL-18, plays the dominant role in the development of protective immunity against chlamydia lung infection, although both cytokines are involved in the in vivo regulation of IFN-gamma production.     

Matrix metalloproteinase-9 deficiency results in enhanced allergen-induced airway inflammation

Matrix metalloproteinases (MMPs) are a large family of endopeptidases that proteolytically degrade extracellular matrix. Many different cells produce MMP-9, and levels have been shown to be up-regulated in patients with allergic asthma. The aim of this study was to investigate the in vivo role of MMP-9 during allergen-induced airway inflammation. Acute allergic pulmonary eosinophilia was established in MMP-9 knockout (KO) and wild-type (WT) control mice by sensitization and challenge with OVA. Cell recruitment was significantly increased in both bronchoalveolar lavage (BAL) and lung tissue compartments in MMP-9 KO mice compared with WT mice. This heightened cell recruitment was primarily due to increased eosinophils and Th2 cells in the BAL and lung tissue of MMP-9 KO mice in comparison with WT controls. Moreover, levels of the Th2 cytokines, IL-4 and IL-13, and the chemokines eotaxin/CCL11 and macrophage-derived chemokine/CCL22 were substantially increased in MMP-9 KO mice compared with WT after OVA challenge. Resolution of eosinophilia was similar between MMP-9 KO and WT mice, but Th2 cells persisted in BAL and lungs of MMP-9 KO mice for longer than in WT mice. Our results indicate that MMP-9 is critically involved in the recruitment of eosinophils and Th2 cells to the lung following allergen challenge, and suggest that MMP-9 plays a role in the development of Th2 responses to allergen.     

Mycobacterial infection in TLR2 and TLR6 knockout mice

To investigate the role of TLR in the development of murine tuberculosis in vivo, TLR2 and TLR6 knockout (KO) mice were infected with Mycobacterium tuberculosis by placing them in the exposure chamber of an airborne infection apparatus. Both TLR2 and TLR6 KO mice survived until sacrifice at 12 weeks after infection. Infected TLR2 KO mice developed granulomatous pulmonary lesions with neutrophil infiltration, which were slightly larger in size than those in wild-type mice. Pulmonary levels of the mRNAs for inducible nitric oxide synthase (iNOS), TNF-alpha, TGF-beta, IL-1beta, and IL-2 were significantly lower, but levels of the mRNAs for IL-4 and IL-6 were higher, than in wild-type (WT) mice. No significant difference was recognized in cytokine mRNA expression between TLR2 KO and WT mice at 12 weeks after infection. DNA binding by NF-kappaB was low in TLR2 KO mice. On the other hand, TLR6 KO mice were not different from WT mice in terms of pulmonary histopathology, mRNA expression and CFU assay. Therefore, TLR2 does not play an essential role in the pathogenesis of murine tuberculosis, although it is important for defense against mycobacterial infection.     

Differential roles of CC chemokine ligand 2/monocyte chemotactic protein-1 and CCR2 in the development of T1 immunity

CCR2 and its major ligand, chemokine ligand 2 (CCL2)/monocyte chemotactic protein-1, have been found to influence T1/T2 immune response polarization. Our objective was to directly compare the roles of CCR2 and CCL2 in T1/T2 immune response polarization using a model of pulmonary Cryptococcus neoformans infection. Either deletion of CCR2 or treatment of wild-type mice with CCL2 neutralizing Ab produced significant and comparable reductions in macrophage and T cell recruitment into the lungs following infection. Both CCL2 neutralization and CCR2 deficiency resulted in significantly diminished IFN-gamma production, and increased IL-4 and IL-5 production by lung leukocytes (T1 to T2 switch), but only CCR2 deficiency promoted pulmonary eotaxin production and eosinophilia. In the lung-associated lymph nodes (LALN), CCL2-neutralized mice developed Ag-specific IFN-gamma-producing cells, while CCR2 knockout mice did not. LALN from CCR2 knockout mice also had fewer MHCII(+)CD11c(+) and MHCII(+)CD11b(+) cells, and produced significantly less IL-12p70 and TNF-alpha when stimulated with heat-killed yeast than LALN from wild-type or CCL2-neutralized mice, consistent with a defect in APC trafficking in CCR2 knockout mice. Neutralization of CCL2 in CCR2 knockout mice did not alter immune response development, demonstrating that the high levels of CCL2 in these mice did not play a role in T2 polarization. Therefore, CCR2 (but not CCL2) is required for afferent T1 development in the lymph nodes. In the absence of CCL2, T1 cells polarize in the LALN, but do not traffic from the lymph nodes to the lungs, resulting in a pulmonary T2 response.     

IL-17RA Signaling Reduces Inflammation and Mortality during Trypanosoma cruzi Infection by Recruiting Suppressive IL-10-Producing Neutrophils

Members of the IL-17 cytokine family play an important role in protection against pathogens through the induction of different effector mechanisms. We determined that IL-17A, IL-17E and IL-17F are produced during the acute phase of T. cruzi infection. Using IL-17RA knockout (KO) mice, we demonstrate that IL-17RA, the common receptor subunit for many IL-17 family members, is required for host resistance during T. cruzi infection. Furthermore, infected IL-17RA KO mice that lack of response to several IL-17 cytokines showed amplified inflammatory responses with exuberant IFN-γ and TNF production that promoted hepatic damage and mortality. Absence of IL-17RA during T. cruzi infection resulted in reduced CXCL1 and CXCL2 expression in spleen and liver and limited neutrophil recruitment. T. cruzi-stimulated neutrophils secreted IL-10 and showed an IL-10-dependent suppressive phenotype in vitro inhibiting T-cell proliferation and IFN-γ production. Specific depletion of Ly-6G+ neutrophils in vivo during T. cruzi infection raised parasitemia and serum IFN-γ concentration and resulted in increased liver pathology in WT mice and overwhelming wasting disease in IL-17RA KO mice. Adoptively transferred neutrophils were unable to migrate to tissues and to restore resistant phenotype in infected IL-17RA KO mice but migrated to spleen and liver of infected WT mice and downregulated IFN-γ production and increased survival in an IL-10 dependent manner. Our results underscore the role of IL-17RA in the modulation of IFN-γ-mediated inflammatory responses during infections and uncover a previously unrecognized regulatory mechanism that involves the IL-17RA-mediated recruitment of suppressive IL-10-producing neutrophils.     

Allergic Airway Disease in Mice Alters T and B Cell Responses during an Acute Respiratory Poxvirus Infection

Pulmonary viral infections can exacerbate or trigger the development of allergic airway diseases via multiple mechanisms depending upon the infectious agent. Respiratory vaccinia virus transmission is well established, yet the effects of allergic airway disease on the host response to intra-pulmonary vaccinia virus infection remain poorly defined. As shown here BALB/c mice with preexisting airway disease infected with vaccinia virus developed more severe pulmonary inflammation, higher lung virus titers and greater weight loss compared with mice inoculated with virus alone. This enhanced viremia was observed despite increased pulmonary recruitment of CD8⁺ T effectors, greater IFNγ production in the lung, and high serum levels of anti-viral antibodies. Notably, flow cytometric analyses of lung CD8⁺ T cells revealed a shift in the hierarchy of immunodominant viral epitopes in virus inoculated mice with allergic airway disease compared to mice treated with virus only. Pulmonary IL-10 production by T cells and antigen presenting cells was detected following virus inoculation of animals and increased dramatically in allergic mice exposed to virus. IL-10 modulation of host responses to this respiratory virus infection was greatly influenced by the localized pulmonary microenvironment. Thus, blocking IL-10 signaling in virus-infected mice with allergic airway disease enhanced pulmonary CD4⁺ T cell production of IFNγ and increased serum anti-viral IgG1 levels. In contrast, pulmonary IFNγ and virus-specific IgG1 levels were reduced in vaccinia virus-treated mice with IL-10 receptor blockade. These observations demonstrate that pre-existing allergic lung disease alters the quality and magnitude of immune responses to respiratory poxviruses through an IL-10-dependent mechanism.     

Role of IL-6 in the pleurisy and lung injury caused by carrageenan.

In the present study we used IL-6 knockout mice (IL-6KO) to evaluate the role of IL-6 in the inflammatory response caused by injection of carrageenan into the pleural space. Compared with carrageenan-treated IL-6 wild-type (IL-6WT) mice, carrageenan-treated IL-6KO mice exhibited a reduced degree of pleural exudation and polymorphonuclear cell migration. Lung myeloperoxidase activity and lipid peroxidation were significantly reduced in IL-6KO mice compared with those in IL-6WT mice treated with carrageenan. Immunohistochemical analysis for nitrotyrosine and poly(A)DP-ribose polymerase revealed a positive staining in lungs from carrageenan-treated IL-6WT mice. No positive staining for nitrotyrosine or PARS was found in the lungs of the carrageenan-treated IL-6KO mice. Staining of lung tissue sections obtained from carrageenan-treated IL-6WT mice with an anti-cyclo-oxygenase-2 Ab showed a diffuse staining of the inflamed tissue. Furthermore, expression of inducible nitric oxide synthase was found mainly in the macrophages of the inflamed lungs from carrageenan-treated IL-6WT mice. The intensity and degree of the staining for cyclo-oxygenase-2 and inducible nitric oxide synthase were markedly reduced in tissue sections obtained from carrageenan-treated IL-6KO mice. Most notably, the degree of lung injury caused by carrageenan was also reduced in IL-6KO mice. Treatment of IL-6WT mice with anti-IL-6 (5 microg/day/mouse at 24 and 1 h before carrageenan treatment) also significantly attenuated all the above indicators of lung inflammation. Taken together, our results clearly demonstrate that IL-6KO mice are more resistant to the acute inflammation of the lung caused by carrageenan injection into the pleural space than the corresponding WT mice.     

Essential role for the p40 subunit of interleukin-12 in neutrophil-mediated early host defense against pulmonary infection with Streptococcus pneumoniae: involvement of interferon-gamma

Interleukin (IL)-12 is a critical cytokine in the T helper (Th)1 response and host defense against intracellular microorganisms, while its role in host resistance to extracellular bacteria remains elusive. In the present study, we elucidated the role of IL-12 in the early-phase host defense against acute pulmonary infection with Streptococcus pneumoniae, a typical extracellular bacterium, using IL-12p40 gene-disrupted (IL-12p40KO) mice. IL-12p40KO mice were highly susceptible to S. pneumoniae infection, as indicated by the shortened survival time, which was completely restored by the replacement therapy with recombinant (r) IL-12, and increased bacterial counts in the lung. In these mice, recruitment of neutrophils in the lung was significantly attenuated when compared to that in wild-type (WT) mice, which correlated well with the reduced production of macrophage inflammatory protein (MIP-2) and tumor necrosis factor (TNF)-alpha in the infected tissues at the early phase of infection. In vitro synthesis of both cytokines by S. pneumoniae-stimulated lung leukocytes was significantly lower in IL-12p40KO mice than in WT mice, and addition of rIL-12 or interferon (IFN)-gamma restored the reduced production of MIP-2 and TNF-alpha in IL-12p40KO mice. Neutralizing anti-IFN-gamma monoclonal antibody (mAb) significantly decreased the effect of rIL-12. Anti-IFN-gamma mAb shortened the survival time of infected mice and reduced the recruitment of neutrophils and production of MIP-2 and TNF-alpha in the lungs. Our results indicated that IL-12p40 plays a critical role in the early-phase host defense against S. pneumoniae infection by promoting the recruitment of neutrophils to the infected tissues.     

IL-12 is required for antibody-mediated protective immunity against blood-stage Plasmodium chabaudi AS malaria infection in mice.

In this study, we investigated the role of endogenous IL-12 in protective immunity against blood-stage P. chabaudi AS malaria using IL-12 p40 gene knockout (KO) and wild-type (WT) C57BL/6 mice. Following infection, KO mice developed significantly higher levels of primary parasitemia than WT mice and were unable to rapidly resolve primary infection and control challenge infection. Infected KO mice had severely impaired IFN-gamma production in vivo and in vitro by NK cells and splenocytes compared with WT mice. Production of TNF-alpha and IL-4 was not compromised in infected KO mice. KO mice produced significantly lower levels of Th1-dependent IgG2a and IgG3 but a higher level of Th2-dependent IgG1 than WT mice during primary and challenge infections. Treatment of KO mice with murine rIL-12 during the early stage of primary infection corrected the altered IgG2a, IgG3, and IgG1 responses and restored the ability to rapidly resolve primary and control challenge infections. Transfer of immune serum from WT mice to P. chabaudi AS-infected susceptible A/J mice completely protected the recipients, whereas immune serum from KO mice did not, as evidenced by high levels of parasitemia and 100% mortality in recipient mice. Furthermore, depletion of IgG2a from WT immune serum significantly reduced the protective effect of the serum while IgG1 depletion had no significant effect. Taken together, these results demonstrate the protective role of a Th1-immune response during both acute and chronic phases of blood-stage malaria and extend the immunoregulatory role of IL-12 to Ab-mediated immunity against Plasmodium parasites.     

IL-23 is critical in the induction but not in the effector phase of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE), a T cell-mediated inflammatory disease of the CNS, is a rodent model of human multiple sclerosis. IL-23 is one of the critical cytokines in EAE development and is currently believed to be involved in the maintenance of encephalitogenic responses during the tissue damage effector phase of the disease. In this study, we show that encephalitogenic T cells from myelin oligodendrocyte glycopeptide (MOG)-immunized wild-type (WT) mice caused indistinguishable disease when adoptively transferred to WT or IL-23-deficient (p19 knockout (KO)) recipient mice, demonstrating that once encephalitogenic cells have been generated, EAE can develop in the complete absence of IL-23. Furthermore, IL-12/23 double-deficient (p35/p19 double KO) recipient mice developed EAE that was indistinguishable from WT recipients, indicating that IL-12 did not compensate for IL-23 deficiency during the effector phase of EAE. In contrast, MOG-specific T cells from p19KO mice induced EAE with delayed onset and much lower severity when transferred to WT recipient mice as compared with the EAE that was induced by cells from WT controls. MOG-specific T cells from p19KO mice were highly deficient in the production of IFN-gamma, IL-17A, and TNF, indicating that IL-23 plays a critical role in development of encephalitogenic T cells and facilitates the development of T cells toward both Th1 and Th17 pathways.     

Enhanced pulmonary histopathology induced by respiratory syncytial virus (RSV) challenge of formalin-inactivated RSV-immunized BALB/c mice is abrogated by depletion of interleukin-4 (IL-4) and IL-10.

In previous studies, children immunized with a formalin-inactivated respiratory syncytial virus vaccine (FI-RSV) developed severe pulmonary disease with greater frequency than did controls during subsequent natural RSV infection. In earlier efforts to develop an animal model for this phenomenon, extensive pulmonary histopathology developed in FI-RSV-immunized cotton rats and mice subsequently challenged with RSV. In mice, depletion of CD4+ T cells at the time of RSV challenge completely abrogated this histopathology. Furthermore, the predominant cytokine mRNA present in lungs of FI-RSV-immunized mice during subsequent infection with RSV was that characteristically secreted by Th2 T cells, namely interleukin-4 (IL-4). In the present studies, we sought to determine the relative contributions of gamma interferon (IFN-gamma), IL-2, IL-4, and IL-10 to the lymphocytic infiltration into the lungs observed following RSV challenge of mice previously immunized with FI-RSV. Mice previously immunized with FI-RSV or infected with RSV were depleted of IFN-gamma, IL-2, IL-4, or IL-10 immediately before RSV challenge, and the magnitude of inflammatory cell infiltration around bronchioles and pulmonary blood vessels was quantified. The phenomenon of pulmonary-histopathology potentiation by FI-RSV was reproduced in the present study, thereby allowing us to investigate the effect of cytokine depletion on the process. Simultaneous depletion of both IL-4 and IL-10 completely abrogated pulmonary histopathology in FI-RSV-immunized mice. Depletion of IL-4 alone significantly reduced bronchiolar, though not perivascular, histopathology. Depletion of IL-10 alone had no effect. Depletion of IFN-gamma, IL-2, or both together had no effect on the observed histopathology. These data indicate that FI-RSV immunization primes for a Th2-, IL-4-, and IL-10-dependent inflammatory response to subsequent RSV infection. It is possible that this process played a role in enhanced disease observed in infants and children immunized with FI-RSV.     

Invariant NKT cell defects in vitamin D receptor knockout mice prevents experimental lung inflammation

Vitamin D receptor (VDR) deficiency (knockout [KO]) results in a failure of mice to generate an airway hyperreactivity (AHR) response on both the BALB/c and C57BL/6 background. The cause of the failed AHR response is the defective population of invariant NKT (iNKT) cells in the VDR KO mice because wild-type (WT) iNKT cells rescued the AHR response. VDR KO mice had significantly fewer iNKT cells and normal numbers of T cells in the spleen compared with WT mice. In BALB/c VDR KO mice, the reduced frequencies of iNKT cells were not apparent in the liver or thymus. VDR KO and WT Th2 cells produced similar levels of IFN-γ and IL-5. On the BALB/c background, Th2 cells from VDR KO mice produced less IL-13, whereas on the C57BL/6 background, Th2 cells from VDR KO mice produced less IL-4. Conversely, VDR KO iNKT cells were defective for the production of multiple cytokines (BALB/c: IL-4, IL-5, and IL-13; C57BL/6: IL-4 and IL-17). Despite relatively normal Th2 responses, BALB/c and C57BL/6 VDR KO mice failed to develop AHR responses. The defect in iNKT cells as a result of the VDR KO was more important than the highly susceptible Th2 background of the BALB/c mice. Defective iNKT cell responses in the absence of the VDR result in the failure to generate AHR responses in the lung. The implication of these mechanistic findings for human asthma requires further investigation.     

Ig heavy chain complex-linked genes influence the immune response in a murine cryptococcal infection.

A murine pulmonary infection with Cryptococcus neoformans (Cne) has been used to determine mechanisms regulating effective T cell-mediated immunity in the lungs. In BALB/c and C.B-17 mice, following intratracheal deposition of Cne, the fungus initially grows rapidly and is then progressively cleared from the lungs. Cne clearance in C.B-17 mice requires CD4 and CD8 T cells, IFN-gamma, and NO. Clearance in congenic BALB/c mice proceeds more slowly than in C.B-17 mice, even though the only genetic difference between these strains is at the Ig H chain-containing region of chromosome 12. Examination of the pulmonary immune response in the two strains revealed that both cleared lung Cne by T cell-dependent mechanisms and generated equivalent levels of NO. Furthermore, both strains recruited equal numbers of macrophages, lymphocytes, and neutrophils to the lungs, although BALB/c mice recruited higher numbers of eosinophils. Notably, leukocytes isolated from BALB/c lungs during infection secreted lower levels of IFN-gamma and higher levels of the Th2 cytokines IL-4 and IL-5 as compared with lung leukocytes from C.B-17 mice. Furthermore, serum levels of IgM, IgG1, IgG2a, and IgG3 anti-Cne Abs generated during infection were significantly greater in BALB/c mice than C.B-17 mice. These data suggest that although both BALB/c and C.B-17 mice clear pulmonary cryptococcosis through T cell-mediated mechanisms, Ig H chain-linked genes in BALB/c mice are associated with a decreased effectiveness of the host response, which we suggest might influence the balance in Th1/Th2 T cell subset development or increase anti-Cne Abs, or both.     

Host Defense and Recruitment of Foxp3+ T Regulatory Cells to the Lungs in Chronic Mycobacterium tuberculosis Infection Requires Toll-like Receptor 2

Acute resistance to low dose M. tuberculosis (Mtb) infection is not dependent on Toll-like receptor (TLR) 2. However, whether TLR2 contributes to resistance in chronic Mtb infection has remained uncertain. Here we report that, following low dose aerosol infection with Mtb, mice lacking TLR2 (TLR2KO), in comparison with wild type (WT) mice, exhibit enhanced cellular infiltration and inflammation in the lungs, and fail to stably control bacterial burden during chronic infection. IFNγ and IL-17 was expressed at equivalent levels in the two groups; however, the characteristic accumulation of Foxp3⁺ T regulatory cells (Tregs) in pulmonary granulomas was significantly reduced in TLR2KO mice. Nonetheless, this reduction in Tregs was independent of whether Tregs expressed TLR2 or not. To directly link the reduced number of Tregs to the increased inflammation present in the TLR2KO mice, we used a macrophage adoptive transfer model. At seven weeks post-Mtb infection, TLR2KO mice, which were adoptively transferred with WT macrophages, displayed enhanced accumulation of Tregs in the lungs and a concomitant reduction in inflammation in contrast with control mice that received TLR2KO macrophages. However, the pulmonary bacterial burden between the two groups remained similar indicating that TLR2''s role in modulating immunopathology is functionally distinct from its role in restricting Mtb growth in chronic infection. Together, these findings unequivocally demonstrate that TLR2 contributes to host resistance against chronic Mtb infection and reveal a novel role for TLR2 in mediating the recruitment of Foxp3⁺ Tregs to the lungs to control inflammation.