Vaccine-induced immunity against Helicobacter pylori infection is impaired in IL-18-deficient mice

Protective immunity against Helicobacter pylori infection in mice has been associated with a strong Th1 response, involving IL-12 as well as IFN-gamma, but recent studies have also demonstrated prominent eosinophilic infiltration, possibly linked to local Th2 activity in the gastric mucosa. In this study we investigated the role of IL-18, because this cytokine has been found to be a coregulator of Th1 development as well as involved in Th2-type responses with local eotaxin production that could influence gastric eosinophilia and resistance to infection. We found that IL-18(-/-) mice failed to develop protection after oral immunization with H. pylori lysate and cholera toxin adjuvant, indicating an important role of IL-18 in protection. Well-protected C57BL/6 wild-type (WT) mice demonstrated substantial influx of CD4(+) T cells and eosinophilic cells in the gastric mucosa, whereas IL-18(-/-) mice had less gastritis, few CD4(+) T cells, and significantly reduced numbers of eosinophilic cells. T cells in well-protected WT mice produced increased levels of IFN-gamma and IL-18 to recall Ag. By contrast, unprotected IL-18(-/-) mice exhibited significantly reduced gastric IFN-gamma and specific IgG2a Ab levels. Despite differences in gastric eosinophilic cell infiltration, protected WT and unprotected IL-18(-/-) mice had comparable levels of local eotaxin, suggesting that IL-18 influences protection via Th1 development and IFN-gamma production rather than through promoting local production of eotaxin and eosinophilic cell infiltration.     

Helicobacter pylori-induced mucosal inflammation is Th1 mediated and exacerbated in IL-4, but not IFN-gamma, gene-deficient mice

To elucidate the pathogenesis of Helicobacter pylori-associated gastritis, we studied immune responses of C57BL/6J wild-type (WT), SCID, and gene deficient (IFN-gamma-/- and IL-4-/-) mice following infection with a pathogenic isolate of H. pylori (SPM326). During early infection in WT mice, mononuclear and polymorphonuclear cells accumulated in the gastric lamina propria, and the numbers of cells in the inflamed mucosa expressing IFN-gamma, but not IL-4, mRNA rose significantly (p < 0.005), consistent with a local Th1 response. Splenic T cells from the same infected WT mice produced high levels of IFN-gamma, no detectable IL-4, and low amounts of IL-10 following in vitro H. pylori urease stimulation, reflecting a systemic Th1 response. Infected C57BL/6J SCID mice did not develop gastric inflammation despite colonization by many bacteria. Infected C57BL/10J and BALB/c mice also did not develop gastric inflammation and displayed a mixed Th1/Th2 splenic cytokine profile. These data imply a major role for the Th1 cytokine IFN-gamma in H. pylori-associated gastric inflammation in C57BL/6J mice. Compared with WT animals, infected IL-4-/- animals had more severe gastritis and higher levels of IFN-gamma production by urease-stimulated splenocytes (p < 0.01), whereas IFN-gamma-/- mice exhibited no gastric inflammation and higher levels of IL-4 production by stimulated splenocytes. These findings establish C57BL/6J mice as an important model for H. pylori infection and demonstrate that up-regulated production of IFN-gamma, in the absence of the opposing effects of IL-4 (and possibly IL-10), plays a pivotal role in promoting H. pylori-induced mucosal inflammation.     

Cutting edge: IL-18-transgenic mice: in vivo evidence of a broad role for IL-18 in modulating immune function

IL-18 has been shown to be a strong cofactor for Th1 T cell development. However, we previously demonstrated that when IL-18 was combined with IL-2, there was a synergistic induction of a Th2 cytokine, IL-13, in both T and NK cells. More recently, we and other groups have reported that IL-18 can potentially induce IgE, IgG1, and Th2 cytokine production in murine experimental models. Here, we report on the generation of IL-18-transgenic (Tg) mice in which mature mouse IL-18 cDNA was expressed. CD8+CD44high T cells and macrophages were increased, but B cells were decreased in these mice while serum IgE, IgG1, IL-4, and IFN-gamma levels were significantly increased. Splenic T cells in IL-18 Tg mice produced higher levels of IFN-gamma, IL-4, IL-5, and IL-13 than control wild-type mice. Thus, aberrant expression of IL-18 in vivo results in the increased production of both Th1 and Th2 cytokines.     

C57BL/6 mice genetically deficient in IL-12/IL-23 and IFN-gamma are susceptible to experimental autoimmune myasthenia gravis, suggesting a pathogenic role of non-Th1 cells

Immunization with Torpedo acetylcholine receptor (TAChR) induces experimental autoimmune myasthenia gravis (EAMG) in C57BL/6 (B6) mice. EAMG development needs IL-12, which drives differentiation of Th1 cells. The role of IFN-gamma, an important Th1 effector, is not clear and that of IL-17, a proinflammatory cytokine produced by Th17 cells, is unknown. In this study, we examined the effect of simultaneous absence of IL-12 and IFN-gamma on EAMG susceptibility, using null mutant B6 mice for the genes of both the IL-12/IL-23 p40 subunit and IFN-gamma (dKO mice). Wild-type (WT) B6 mice served as control for EAMG induction. All mice were immunized with TAChR in Freund's adjuvant. dKO mice developed weaker anti-TAChR CD4(+)T cells and Ab responses than WT mice. Yet, they developed EAMG symptoms, anti-mouse acetylcholine receptor (AChR) Ab, and CD4(+) T cell responses against mouse AChR sequences similar to those of WT mice. dKO and WT mice had similarly reduced AChR content in their muscles, and IgG and complement at the neuromuscular junction. Naive dKO mice had significantly fewer NK, NKT, and CD4(+)CD25(+)Foxp3(+) T regulatory (Treg) cells than naive WT mice. Treg cells from TAChR-immunized dKO mice had significantly less suppressive activity in vitro than Treg cells from TAChR-immunized WT mice. In contrast, TAChR-specific CD4(+) T cells from TAChR-immunized dKO and WT mice secreted comparable amounts of IL-17 after stimulation in vitro with TAChR. The susceptibility of dKO mice to EAMG may be due to reduced Treg function, in the presence of a normal function of pathogenic Th17 cells.     

Urokinase-type plasminogen activator is required for the generation of a type 1 immune response to pulmonary Cryptococcus neoformans infection.

Urokinase-type plasminogen activator (uPA)(-/-) mice cannot mount protective host defenses during infection with the opportunistic yeast Cryptococcus neoformans (52D). Because effective host defense against C. neoformans requires specific immune responses and the generation of type 1 (T1) cytokines, we determined how the absence of uPA impacts these processes. Wild-type (WT) and uPA(-/-) mice were inoculated with C. neoformans. Macrophage antifungal activity was assessed histologically, T lymphocyte responses in vivo and proliferation in vitro were quantified, and cytokine concentrations were determined by ELISA. uPA(-/-) macrophages have impaired antimicrobial activity. Regional lymph nodes of infected uPA(-/-) mice contained fewer cells than WT, suggesting impaired T cell proliferation in response to the pathogen in vivo. In vitro, uPA(-/-) T lymphocytes had impaired proliferative responses to C. neoformans rechallenge compared with WT. Infected WT mice generated T1 cytokines in the lung, characterized by high levels of IFN-gamma and IL-12. uPA(-/-) mice had decreased levels of IFN-gamma and IL-12, and increased IL-5, a type 2 cytokine. In the absence of uPA, the cytokine profile of regional lymph nodes shifted from a T1 pattern characterized by IFN-gamma and IL-2 to a weak, nonpolarized response. We conclude that in the absence of uPA, lymphocyte proliferative responses are diminished, and mice fail to generate protective T1 cytokines, resulting in impaired antimicrobial activity. This study provides novel evidence that uPA is a critical modulator of immune responses and of immune cell effector functions in vivo.     

Exacerbation of antigen-induced arthritis in IFN-gamma-deficient mice as a result of unrestricted IL-17 response

Proinflammatory Th1 responses are believed to be involved in the induction and perpetuation of rheumatoid arthritis. However, the role of IFN-gamma, the major cytokine produced by Th1 cells, is still incompletely defined. In the present study, we investigated the effects of IFN-gamma deficiency (IFN-gamma(-/-)) on the course of experimental murine Ag-induced arthritis (AIA). In the acute stage of disease, IFN-gamma(-/-) AIA mice showed significantly increased inflammatory responses compared with wild-type C57BL/6 AIA mice, i.e., exacerbated joint swelling, increased delayed-type hypersensitivity reaction, and increased histopathological scores of arthritis. Intraarticular administration of exogenous IFN-gamma at induction of AIA significantly suppressed these acute aggravation effects. Stimulated cells isolated from lymph nodes and spleen of IFN-gamma(-/-) AIA mice showed increased production of IL-2, IL-4, IL-5, IL-6, but most prominently of IL-17. These elevations were paralleled by decreased humoral immune responses, with low serum levels of total and Ag-specific IgG (IgG1, IgG2a(b), IgG2b, IgG3). At immunohistology, the knee joints of IFN-gamma(-/-) AIA mice showed massive neutrophil granulocyte infiltration. Treatment with mAbs neutralizing IL-17 diminished the acute inflammation. In vitro, Th cell expansion and production of IL-17 upon restimulation were effectively and dose dependently inhibited by IFN-gamma. These results clearly demonstrate that IFN-gamma has anti-inflammatory properties during the initial phase of AIA, and indicate that IFN-gamma deficiency exerts disease-promoting effects, preferentially via IL-17-modulated pathways.     

Reduced host resistance and Th1 response to Cryptococcus neoformans in interleukin-18 deficient mice

Using interleukin (IL)-18 deficient (IL-18(-/-)) mice, we examined the role of IL-18 in the host resistance and Th1 response against infection with Cryptococcus neoformans. Fungal clearance in the lung was reduced in IL-18(-/-) mice, although there was no significant change in the level of dissemination to the brain. The DTH response, as determined by footpad swelling, was also diminished in IL-18(-/-) mice compared to control wild-type (WT) mice. The levels of IL-12 and interferon (IFN)-gamma in the sera were significantly lower in IL-18(-/-) mice than in WT mice. Spleen cells from infected WT mice produced a high level of IFN-gamma upon stimulation with the microbe, while only a low level of IFN-gamma production was detected in spleen cells from infected IL-18(-/-) mice. Administration of IL-18 almost completely restored the reduced response in IL-18(-/-) mice, while IL-12 showed a marginal effect. These results demonstrated the important role of IL-18 in the resistance and Th1 response of mice to C. neoformans by potentiating the production of IFN-gamma.     

IFN-gamma-dependent nitric oxide production is not linked to resistance in experimental African trypanosomiasis

Resistance to African trypanosomes is dependent on B cell and Th1 cell responses to the variant surface glycoprotein (VSG). While B cell responses to VSG control levels of parasitemia, the cytokine responses of Th1 cells to VSG appear to be linked to the control of parasites in extravascular tissues. We have recently shown that IFN-gamma knockout (IFN-gamma KO) mice are highly susceptible to infection and have reduced levels of macrophage activation compared to the wild-type C57BL/6 (WT) parent strain, even though parasitemias were controlled by VSG-specific antibody responses in both strains. In the present work, we examine the role of IFN-gamma in the induction of nitric oxide (NO) production and host resistance and in the development of suppressor macrophage activity in mice infected with Trypanosoma brucei rhodesiense. In contrast to WT mice, susceptible IFN-gamma KO mice did not produce NO during infection and did not develop suppressor macrophage activity, suggesting that NO might be linked to resistance but that suppressor cell activity was not associated with resistance or susceptibility to trypanosome infection. To further examine the consequence of inducible NO production in infection, we monitored survival, parasitemia, and Th cell cytokine production in iNOS KO mice. While survival times and parasitemia of iNOS KO mice did not differ significantly from WT mice, VSG-specific Th1 cells from iNOS KO mice produced higher levels of IFN-gamma and IL-2 than cells from WT mice. Together, these results show for the first time that inducible NO production is not the central defect associated with susceptibility of IFN-gamma KO mice to African trypanosomes, that IFNgamma-induced factors other than iNOS may be important for resistance to the trypanosomes, and that suppressor macrophage activity is not linked to either the resistance or the susceptibility phenotypes.     

Development of proteoglycan-induced arthritis is independent of IL-17

IL-17 is the hallmark cytokine for the newly identified subset of Th cells, Th17. Th17 cells are important instigators of inflammation in several models of autoimmune disease; in particular, collagen induced arthritis (CIA) and experimental autoimmune encephalomyelitis (EAE), which were previously characterized as Th1-mediated diseases. Although high levels of IFN-gamma are secreted in CIA and EAE, disease is exacerbated in IFN-gamma- or IFN-gamma receptor-deficient mice due to the ability of IFN-gamma to suppress IL-17 secretion. However, in proteoglycan-induced arthritis (PGIA), severe arthritis is dependent on the production of IFN-gamma. We were therefore interested in determining the role of IL-17 in PGIA. We assessed the progression of arthritis in IL-17-deficient (IL-17-/-) mice and found the onset and severity of arthritis were equivalent in wild-type (WT) and IL-17-/- mice. Despite evidence that IL-17 is involved in neutrophil recruitment, synovial fluid from arthritic joints showed a comparable proportion of Gr1+ neutrophils in WT and IL-17-/- mice. IL-17 is also implicated in bone destruction in autoimmune arthritis, however, histological analysis of the arthritic joints from WT and IL-17-/- mice revealed a similar extent of joint cellularity, cartilage destruction, and bone erosion despite significantly reduced RANKL (receptor activator of NK-kappaB ligand) expression. There were only subtle differences between WT and IL-17-/- mice in proinflammatory cytokine expression, T cell proliferation, and autoantibody production. These data demonstrate that IL-17 is not absolutely required for autoimmune arthritis and that the production of other proinflammatory mediators is sufficient to compensate for the loss of IL-17 in PGIA.     

Transgenic expression of IL-10 in T cells facilitates development of experimental myasthenia gravis

Ab to the acetylcholine receptor (AChR) cause experimental myasthenia gravis (EMG). Th1 cytokines facilitate EMG, whereas Th2 cytokines might be protective. IL-10 inhibits Th1 responses but facilitates B cell proliferation and Ig production. We examined the role of IL-10 in EMG by using wild-type (WT) C57BL/6 mice and transgenic (TG) C57BL/6 mice that express IL-10 under control of the IL-2 promoter. We immunized the mice with doses of AChR that cause EMG in WT mice or with low doses ineffective at causing EMG in WT mice. After low-dose AChR immunization, WT mice did not develop EMG and had very little anti-AChR serum Ab, which were mainly IgG1, whereas TG mice developed EMG and had higher levels of anti-AChR serum Ab, which were mainly IgG2, in addition to IgG1. At the higher doses, TG mice developed EMG earlier and more frequently than WT mice and had more serum anti-AChR Ab. Both strains had similar relative serum concentrations of anti-AChR IgG subclasses and IgG and complement at the muscle synapses. CD8(+)-depleted splenocytes from all AChR-immunized mice proliferated in the presence of AChR and recognized a similar epitope repertoire. CD8(+)-depleted splenocytes from AChR-immunized TG mice stimulated in vitro with AChR secreted significantly more IL-10, but less of the prototypic Th1 cytokine IFN-gamma, than those from WT mice. They secreted comparable amounts of IL-4 and slightly but not significantly reduced amounts of IL-2. This suggests that TG mice had reduced activation of anti-Torpedo AChR Th1 cells, but increased anti-AChR Ab synthesis, that likely resulted from IL-10-mediated stimulation of anti-AChR B cells. Thus, EMG development is not strictly dependent on Th1 cell activity.     

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.     

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.     

Absence of IFN-gamma or IL-12 has different effects on experimental myasthenia gravis in C57BL/6 mice

Immunization with acetylcholine receptor (AChR) causes experimental myasthenia gravis (EMG). Th1 cells facilitate EMG development. IFN-gamma and IL-12 induce Th1 responses: we investigated whether these cytokines are necessary for EMG development. We immunized wild-type (WT) C57BL/6 mice and IFN-gamma and IL-12 knockout mutants (IFN-gamma-/-, IL-12-/-) with Torpedo AChR (TAChR). WT and IFN-gamma-/- mice developed EMG with similar frequency, IL-12-/-mice were resistant to EMG. All strains synthesized anti-AChR Ab that were not IgM or IgE. WT mice had anti-AChR IgG1, IgG2b, and IgG2c, IFN-gamma-/- mice had significantly less IgG2c, and IL-12-/- mice less IgG2b and IgG2c. All mice had IgG bound to muscle synapses, but only WT and IFN-gamma-/- mice had complement; WT mice had both IgG2b and IgG2c, IFN-gamma-/- only IgG2b, and IL-12-/- neither IgG2b nor IgG2c. CD4+ cells from all AChR-immunized mice proliferated in response to AChR and recognized similar epitopes. After stimulation with TAChR, CD4+ cells from IFN-gamma-/- mice secreted less IL-2 and similar amounts of IL-4 and IL-10 as WT mice. CD4+ cells from IL-12-/- mice secreted less IFN-gamma, but more IL-4 and IL-10 than WT mice, suggesting that they developed a stronger Th2 response to TAChR. The EMG resistance of IL-12-/- mice is likely due to both reduction of anti-TAChR Ab that bind complement and sensitization of modulatory Th2 cells. The reduced Th1 function of IFN-gamma-/- mice does not suffice to reduce all complement-fixing IgG subclasses, perhaps because as in WT mice a protective Th2 response is missing.     

Protection against Helicobacter pylori infection following immunization is IL-12-dependent and mediated by Th1 cells

The regulatory roles of Th1 and Th2 cells in immune protection against Helicobacter infection are not clearly understood. In this study, we report that a primary H. pylori infection can be established in the absence of IL-12 or IFN-gamma. However, IFN-gamma, but not IL-12, was involved in the development of gastritis because IFN-gamma(-/-) (GKO) mice exhibited significantly less inflammation as compared with IL-12(-/-) or wild-type (WT) mice. Both IL-12(-/-) and GKO mice failed to develop protection following oral immunization with H. pylori lysate and cholera toxin adjuvant. By contrast, Th2-deficient, IL-4(-/-), and WT mice were equally well protected. Mucosal immunization in the presence of coadministered rIL-12 in WT mice increased Ag-specific IFN-gamma-producing T cells by 5-fold and gave an additional 4-fold reduction in colonizing bacteria, confirming a key role of Th1 cells in protection. Importantly, only protected IL-4(-/-) and WT mice demonstrated substantial influx of CD4(+) T cells in the gastric mucosa. The extent of inflammation in challenged IL-12(-/-) and GKO mice was much reduced compared with that in WT mice, indicating that IFN-gamma/Th1 cells also play a major role in postimmunization gastritis. Of note, postimmunization gastritis in IL-4(-/-) mice was significantly milder than WT mice, despite a similar level of protection, indicating that immune protection is not directly linked to the degree of gastric inflammation. Only protected mice had T cells that produced high levels of IFN-gamma to recall Ag, whereas both protected and unprotected mice produced high levels of IL-13. We conclude that IL-12 and Th1 responses are crucial for H. pylori-specific protective immunity.     

Dendritic cell-intrinsic expression of NF-kappa B1 is required to promote optimal Th2 cell differentiation

A number of receptors and signaling pathways can influence the ability of dendritic cells (DC) to promote CD4(+) Th type 1 (Th1) responses. In contrast, the regulatory pathways and signaling events that govern the ability of DC to instruct Th2 cell differentiation remain poorly defined. In this report, we demonstrate that NF-kappaB1 expression within DC is required to promote optimal Th2 responses following exposure to Schistosoma mansoni eggs, a potent and natural Th2-inducing stimulus. Although injection of S. mansoni eggs induced production of IL-4, IL-5, and IL-13 in the draining lymph node of wild-type (WT) mice, NF-kappaB1(-/-) hosts failed to express Th2 cytokines and developed a polarized Ag-specific IFN-gamma response. In an in vivo adoptive transfer model in which NF-kappaB-sufficient OVA-specific DO11.10 TCR transgenic T cells were injected into OVA-immunized WT or NF-kappaB1(-/-) hosts, NF-kappaB1(-/-) APCs efficiently promoted CD4(+) T cell proliferation and IFN-gamma responses, but failed to promote Ag-specific IL-4 production. Further, bone marrow-derived DC from NF-kappaB1(-/-) mice failed to promote OVA-specific Th2 cell differentiation in in vitro coculture studies. Last, S. mansoni egg Ag-pulsed NF-kappaB1(-/-) DC failed to prime for Th2 cytokine responses following injection into syngeneic WT hosts. Impaired Th2 priming by NF-kappaB1(-/-) DC was accompanied by a reduction in MAPK phosphorylation in Ag-pulsed DC. Taken together, these studies identify a novel requirement for DC-intrinsic expression of NF-kappaB1 in regulating the MAPK pathway and governing the competence of DC to instruct Th2 cell differentiation.     

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.     

Dual roles for IFN-gamma,but not for IL-4, in spontaneous autoimmune thyroiditis in NOD.H-2h4 mice

Spontaneous autoimmune thyroiditis (SAT) is an organ-specific autoimmune disease characterized by chronic inflammation of the thyroid by T and B lymphocytes. To investigate the roles of Th1 and Th2 cytokines in the pathogenesis of SAT, IFN-gamma(-/-) and IL-4(-/-) NOD.H-2h4 mice were generated. IL-4(-/-) mice developed lymphocytic SAT (L-SAT) comparable to that of wild-type (WT) mice. They produced little anti-mouse thyroglobulin (MTg) IgG1, but had levels of anti-MTg IgG2b comparable to WT mice. Compared with WT mice, IFN-gamma(-/-) mice produced significantly less anti-MTg IgG1 and IgG2b. Absence of IFN-gamma resulted in abnormal proliferation of thyroid epithelial cells with minimal lymphocyte infiltration. Thyroids of IFN-gamma(-/-) mice had markedly reduced B lymphocyte chemoattractant expression, B cell and plasma cell infiltration, and decreased MHC class II expression on thyrocytes compared with WT mice. Adoptive transfer of WT splenocytes to IFN-gamma(-/-) mice restored the capacity to develop typical L-SAT, enhanced anti-MTg IgG1 and IgG2b production, up-regulated MHC class II expression on thyrocytes and decreased thyrocyte proliferation. These results suggest that IFN-gamma plays a dual role in the development of SAT. IFN-gamma is required for development of L-SAT, and it also functions to inhibit thyroid epithelial cell proliferation.