Absence of interleukin-4 determines less severe pulmonary paracoccidioidomycosis associated with impaired Th2 response

Host resistance to paracoccidiodomycosis, the main deep mycosis in Latin America, is mainly due to cellular immunity and gamma interferon (IFN-gamma) production. To assess the role of interleukin-4 (IL-4), a Th2-inducing cytokine, pulmonary paracoccidioidomycosis was studied in IL-4-deficient (IL-4(-/-)) and wild-type (WT) C57BL/6 mice at the innate and acquired phases of immune response. Forty-eight hours after infection, equivalent numbers of viable Paracoccidioides brasiliensis yeast cells were recovered from the lungs of IL-4(-/-) and WT mice intratracheally infected with one million fungal cells. Alveolar macrophages from infected IL-4(-/-) mice controlled in vitro fungal growth more efficiently than macrophages from WT mice and secreted higher levels of nitric oxide. Compared with WT mice, IL-4(-/-) animals presented increased levels of pulmonary IFN-gamma and augmented polymorphonuclear leukocyte influx to the lungs. Decreased pulmonary fungal loads were characterized in deficient mice at week 2 postinfection, concomitant with diminished presence of IL-10. At week 8, lower numbers of yeasts were recovered from lungs and liver of IL-4(-/-) mice associated with increased production of IFN-gamma but impaired synthesis of IL-5 and IL-10. However, a clear shift to a Th1 pattern was not characterized, since IL-4(-/-) mice did not alter delayed-type hypersensitivity anergy or IL-2 levels. In addition, IL-4 deficiency resulted in significantly reduced levels of pulmonary IL-12, granulocyte-macrophage colony-stimulating factor, IL-3, monocyte chemotactic protein 1, and specific antibody isotypes. In IL-4(-/-) mice, well-organized granulomas restraining fungal cells replaced the more extensive lesions containing high numbers of fungi and inflammatory leukocytes developed by IL-4-sufficient mice. These results clearly showed that genetically determined deficiency of IL-4 can exert a protective role in pulmonary paracoccidioidomycosis.     

Reciprocal immunomodulatory effects of gamma interferon and interleukin-4 on filaria-induced airway hyperresponsiveness

Tropical pulmonary eosinophilia (TPE) is a severe asthmatic syndrome of lymphatic filariasis, in which an allergic response is induced to microfilariae (Mf) in the lungs. Previously, in a murine model for TPE, we have demonstrated that recombinant interleukin-12 (IL-12) suppresses pulmonary eosinophilia and airway hyperresponsiveness (AHR) by modulating the T helper (Th) response in the lungs from Th2- to Th1-like, with elevated gamma-interferon (IFN-gamma) production and decreased IL-4 and IL-5 production. The present study examined the immunomodulatory roles of IL-4 and IFN-gamma in filaria-induced AHR and pulmonary inflammation using mice genetically deficient in these cytokines. C57BL/6, IL-4 gene knockout (IL-4(-/-)), and IFN-gamma(-/-) mice were first immunized with soluble Brugia malayi antigens and then inoculated intravenously with 200,000 live Mf. Compared with C57BL/6 mice, IL-4(-/-) mice exhibited significantly reduced AHR, whereas IFN-gamma(-/-) mice had increased AHR. Histopathologically, each mouse strain showed increased cellular infiltration into the lung parenchyma and bronchoalveolar space compared with na?ve animals. However, consistent with changes in AHR, IL-4(-/-) mice had less inflammation than C57BL/6 mice, whereas IFN-gamma(-/-) mice had exacerbated pulmonary inflammation with the loss of pulmonary architecture. Systemically, IL-4(-/-) mice produced significantly higher IFN-gamma levels compared with C57BL/6 mice, whereas IFN-gamma(-/-) mice produced significantly higher IL-4 levels. These data indicate that IL-4 is required for the induction of filaria-induced AHR, whereas IFN-gamma suppresses AHR.     

Cytokine regulation of murine leishmaniasis: interleukin 4 is not sufficient to mediate progressive disease in resistant C57BL/6 mice.

Neutralization of interleukin 4 (IL-4) at the time of infection with Leishmania major allowed susceptible BALB/c mice to heal. Recombinant IL-4, however, had little effect on the course of L. major infection in resistant C57BL/6 mice, nor did coinfection with Nippostrongylus brasiliensis, despite marked elevation of endogenous IL-4 levels.     

Infection with Toxoplasma gondii reduces established and developing Th2 responses induced by Nippostrongylus brasiliensis infection

Oral infection of C57BL/6 mice with 100 cysts of the protozoan parasite Toxoplasma gondii results in the development of small intestinal Th1-type immunopathology. In contrast, infection with intestinal helminths results in the development of protective Th2-type responses. We investigated whether infection with the helminth Nippostrongylus brasiliensis influences the development of T. gondii-induced Th1 responses and immunopathology in C57BL/6 mice infected with T. gondii. Prior as well as simultaneous infection of mice with N. brasiliensis did not alter the course of infection with 100 cysts of T. gondii. Coinfected mice produced high levels of interleukin-12 (IL-12) and gamma interferon (IFN-gamma), developed small intestinal immunopathology, and died at the same time as mice infected with T. gondii. Interestingly, local and systemic N. brasiliensis-induced Th2 responses, including IL-4 and IL-5 production by mesenteric lymph node and spleen cells and numbers of intestinal goblet cells and blood eosinophils, were markedly lower in coinfected than in N. brasiliensis-infected mice. Similar effects were seen when infection with 10 T. gondii cysts was administered following infection with N. brasiliensis. Infection of C57BL/6 mice with 10 T. gondii cysts prior to coinfection with N. brasiliensis inhibited the development of helminth-induced Th2 responses and was associated with higher and prolonged N. brasiliensis egg production. In contrast, oral administration of Toxoplasma lysate prior to N. brasiliensis infection had only a minor and short-lived effect on Th2 responses. Thus, N. brasiliensis-induced Th2 responses fail to alter T. gondii-induced Th1 responses and immunopathology, most likely because Th1 responses develop unchanged in C57BL/6 mice with a prior or simultaneous infection with N. brasiliensis. Our findings contribute to the understanding of immune regulation in coinfected animals and may assist in the design of immunotherapies for human Th1 and Th2 disorders.     

Antigen dose defines T helper 1 and T helper 2 responses in the lungs of C57BL/6 and BALB/c mice independently of splenic responses

To investigate the effect of antigen dose on immune response, C57BL/6 and BALB/c mice were sensitized with aluminum hydroxide gel (alum)-precipitated ovalbumin (OVA) then challenged with aerosolized OVA. Low-dose sensitization (less than 8 microg of OVA) elicited T helper 2 (Th2)-type immunoglobulins (Igs) secretion from C57BL/6 mice, including high levels of serum IgE, IgG1 and low levels of IgG2a, while BALB/c mice secreted T helper 1 (Th1)-type Igs, including low levels of IgE, IgG1 and high levels of IgG2a. In contrast, high-dose sensitization (more than 50 microgram) elicited Th1-type Igs secretion in C57BL/6mice, while BALB/c mice exhibited Th2-type Igs secretion. Furthermore, the number of eosinophils infiltrating into the lungs of low-dose OVA-sensitized C57BL/6 mice was significantly greater than in BALB/c mice sensitized with the same amount of OVA. Only a very high dose of OVA (1 mg) could induce greater eosinophil infiltration into the lungs of BALB/c mice compared with C57BL/6 mice. Additionally, low-dose sensitization generated Th2-type cytokines, including high levels of interleukin (IL) -4, IL-5 and a low level of interferon-gamma (IFN-gamma) in the lungs of C57BL/6 mice, while BALB/c mice generated Th1-type cytokines in their lungs, including low levels of IL-4, IL-5 and a high level of IFN-gamma. In contrast, high-dose sensitization elicited Th1-type cytokines production in the lungs of C57BL/6 mice, while BALB/c mice generated Th2-type cytokines in their lungs. Interestingly, splenocyte cultures from C57BL/6 mice produced Th1-type cytokines, while cultures from BALB/c mice produced Th2-type cytokines regardless of OVA sensitization dose (100 ng-1 mg). These results indicate that C57BL/6 and BALB/c mice have different susceptibilities to OVA-sensitization and OVA-induced pulmonary eosinophilia regulated by Th1- and Th2-type cytokines, independent of splenic Th1- and Th2-type cytokines production.     

C57BL/6 mice are more susceptible to antigen-induced pulmonary eosinophilia than BALB/c mice, irrespective of systemic T helper 1/T helper 2 responses

Inflammatory response differences between C57BL/6 and BALB/c mice following ovalbumin (OVA) sensitization and a single challenge were investigated. Serum immunoglobulin (Ig)E and IgG1 levels were higher in C57BL/6 mice than in BALB/c mice. In contrast, IgG2a levels in C57BL/6 mice were lower than in BALB/c mice. Furthermore, the number of eosinophils infiltrating into lungs in C57BL/6 mice was significantly higher than in BALB/c mice after OVA challenge. The levels of the T helper 2 (Th2)-type cytokines interleukin (IL)-4 and IL-5, generated in challenged C57BL/6 lung tissue, were also higher than in BALB/c lung tissue. The participation of IL-4 and IL-5 in the induction of eosinophil infiltration into the lungs was confirmed in both strains of mice by injection of anti-IL-4 and anti-IL-5 monoclonal antibodies (mAbs). However, following OVA stimulation, in vitro IL-4 and IL-5 production in splenocyte cultures from C57BL/6 mice was lower than in splenocyte cultures from BALB/c mice. These results indicate that C57BL/6 mice induce Th2-type responses in the lungs, while BALB/c mice induce T helper 1 (Th1)-type responses in the lungs, despite considerable production of IL-4 and IL-5 from splenocytes. Therefore, local immune responses are more important in the induction of allergic inflammation in the lungs and are different from systemic immune responses, which are thought to depend on genetic background.     

Gastrointestinal nematode expulsion in IL-4 knockout mice is IL-13 dependent

Female IL-4 knockout (KO) mice on a C57BL/6 background (F4KOC57) are susceptible to infection with the cecal-dwelling nematode Trichuris muris whereas wild-type C57BL/6 mice are resistant and expel the parasite. In this study we show that in sharp contrast, female IL-4 KO mice on a BALB/c background (F4KOB/c) are resistant to infection as are wild-type BALB/c mice. Although susceptible F4KOC57 make negligible levels of all type 2 cytokines, resistant F4KOB/c were capable of producing significant levels of antigen-specific IL-13 (a cytokine shown to be critical in resistance to T. muris). To examine if the IL-13 in F4KOB/c mice was of functional importance, it was neutralized in vivo using a fusion protein, A25 (sIL-13 R.Fc). The results presented here clearly demonstrate that neutralization of IL-13 in vivo did indeed prevent T. muris expulsion in normally resistant F4KOB/c mice. In addition, administration of recombinant mouse IL-13 to normally susceptible male IL-4KO BALB/c mice (M4KOB/c) caused an 87.85 % reduction in worm burden. Collectively, these data show that IL-13 is important in the poorly understood effector mechanisms resulting in the expulsion of T. muris from the gut. Moreover, the present data highlight the functional importance of gender and background strain in interpretation of studies using gene-targeted animals.     

In vivo regulation of nitric oxide production by tumor necrosis factor alpha and gamma interferon, but not by interleukin-4, during blood stage malaria in mice.

We investigated whether gamma interferon (IFN-gamma; a Th1 cytokine), tumor necrosis factor alpha (TNF-alpha), and interleukin-4 (IL-4; a Th2 cytokine) modulate nitric oxide (NO) production in vivo during blood stage infection with Plasmodium chabaudi AS. Treatment of resistant C57BL/6 mice, which resolve infection with P. chabaudi AS and produce increased levels of IFN-gamma, TNF-alpha, and NO early during infection, with anti-IFN- gamma plus anti-TNF-alpha monoclonal antibodies (MAbs) resulted in a reduction of both splenic inducible NO synthase mRNA and serum NO3- levels by 50 and 100%, respectively. Treatment with the anti-TNF-alpha MAb alone reduced only serum NO3- levels by 35%, and treatment with the anti-IFN-gamma MAb alone had no effect on NO production by these mice during infection. Susceptible A/J mice, which succumb to infection with P. chabaudi AS and produce increased levels of IL-4 but low levels of IFN-gamma, TNF-alpha, and NO early during infection, were treated with an anti-IL-4 MAb. The latter treatment had no effect on NO production by this mouse strain during infection. In addition, our results also demonstrate that treatment of resistant C57BL/6 mice with anti-IFN-gamma plus anti-TNF-alpha MAbs affects, in addition to NO production, other traits of resistance to P. chabaudi AS malaria such as the peak level of parasitemia and the development of splenomegaly. Furthermore, the change in spleen weight was shown to be an IFN-gamma-independent effect of TNF-alpha. Treatment of susceptible A/J mice during infection with an anti IL-4 MAb had no effect on these markers of resistance. Thus, these results demonstrate that TNF-alpha and IFN-gamma are critical in the regulation of NO production and other traits of resistance during P. chabaudi AS malaria in C57BL/6 mice. These data also indicate that treatment with an anti-IL-4 antibody alone is not able to induce NO production or confer resistance to A/J mice against P. chabaudi AS malaria.     

MyD88 signaling is required for efficient innate and adaptive immune responses to Paracoccidioides brasiliensis infection

The mechanisms that govern the initial interaction between Paracoccidioides brasiliensis, a primary dimorphic fungal pathogen, and cells of the innate immunity need to be clarified. Our previous studies showed that Toll-like receptor 2 (TLR2) and TLR4 regulate the initial interaction of fungal cells with macrophages and the pattern of adaptive immunity that further develops. The aim of the present investigation was to assess the role of MyD88, an adaptor molecule used by TLRs to activate genes of the inflammatory response in pulmonary paracoccidioidomycosis. Studies were performed with normal and MyD88(-/-) C57BL/6 mice intratracheally infected with P. brasiliensis yeast cells. MyD88(-/-) macrophages displayed impaired interaction with fungal yeast cells and produced low levels of IL-12, MCP-1, and nitric oxide, thus allowing increased fungal growth. Compared with wild-type (WT) mice, MyD88(-/-) mice developed a more severe infection of the lungs and had marked dissemination of fungal cells to the liver and spleen. MyD88(-/-) mice presented low levels of Th1, Th2, and Th17 cytokines, suppressed lymphoproliferation, and impaired influx of inflammatory cells to the lungs, and this group of cells comprised lower numbers of neutrophils, activated macrophages, and T cells. Nonorganized, coalescent granulomas, which contained high numbers of fungal cells, characterized the severe lesions of MyD88(-/-) mice; the lesions replaced extensive areas of several organs. Therefore, MyD88(-/-) mice were unable to control fungal growth and showed a significantly decreased survival time. In conclusion, our findings demonstrate that MyD88 signaling is important in the activation of fungicidal mechanisms and the induction of protective innate and adaptive immune responses against P. brasiliensis.     

Interleukin-4 (IL-4) and IL-13 signaling pathways do not regulate Borrelia burgdorferi-induced arthritis in mice: IgG1 is not required for host control of tissue spirochetes

Previous studies have suggested that interleukin-4 (IL-4) has a protective effect in host defense to Borrelia burgdorferi infection, both in limiting the severity of arthritis and in controlling spirochete numbers in tissues, and a mapping study revealed suggestive linkage to a cluster of genes on mouse chromosome 11, including the genes for IL-4 and IL-13. In contrast, other studies have questioned the importance of IL-4. In this study the involvement of IL-4 in murine Lyme disease was examined in C57BL/6J and BALB/cJ mice with targeted disruptions in the IL-4 gene, the IL-4Ralpha chain gene, or both. A spectrum of arthritis severity was seen in BALB/cJ mice, and ablation of IL-4, IL-4Ralpha, or both had no effect on the overall severity of arthritis as determined by joint swelling and histopathology. Wild-type C57BL/6J mice exhibited mild to moderate arthritis, and ablation of IL-4 again had no effect on arthritis severity. IL-4- and IL-4Ralpha-deficient mice produced extremely low levels of immunoglobulin G1 (IgG1) and showed increased production of IgG2b. This shift in immunoglobulin isotype had no effect on the host's ability to control spirochete growth in either strain of mouse, as determined by PCR detection of B. burgdorferi DNA from heart and ankle tissues. In summary, the IL-4-IL-4Ralpha pathway, including IL-13 signaling, neither limits arthritis severity nor is required for control of spirochete growth during B. burgdorferi infection of mice. Furthermore, the IgG1 isotype is not required to control B. burgdorferi cell numbers in tissues. These findings suggest the host defense against B. burgdorferi infection is not dependent on the Th1-Th2 paradigm of T-cell responses.     

Pulmonary paracoccidioidomycosis in resistant and susceptible mice: relationship among progression of infection, bronchoalveolar cell activation, cellular immune response, and specific isotype patterns.

Using the intraperitoneal route of infection, we demonstrated previously that A/Sn mice are resistant and B10.A mice are susceptible to Paracoccidioides brasiliensis infection. Since paracoccidioidomycosis is a deep systemic granulomatous disorder that involves primarily the lungs and then disseminates to other organs and systems, we herein investigated the course of the infection and the resulting immune responses developed by A/Sn and B10.A mice after intratracheal infection with P. brasiliensis yeast cells. It was observed that A/Sn mice develop a chronic benign pulmonary-restricted infection, whereas B10.A mice present a chronic progressive disseminated disease. A/Sn animals were able to restrict fungal infection to the lungs despite the increased fungal load at the beginning of the infection. This behavior was associated with low mortality rates, the presence of adequate and persistent delayed-type hypersensitivity reactions, oxidative burst by bronchoalveolar cells, and production of high levels of specific antibodies in which immunoglobulin G2a (IgG2a) and IgG3 isotype titers were significantly higher than those observed in the susceptible mice. In contrast, B10.A animals showed a constant pulmonary fungal load and dissemination to the liver and spleen. This infection pattern resulted in high mortality rates, discrete delayed-type hypersensitivity reactivity, poorly activated or nonactivated bronchoalveolar cells, and production of specific IgG2b isotype titers significantly higher than those observed in the resistant mice at week 4 of infection. Thus, A/Sn and B10.A mice maintain the same resistance patterns as those observed previously with the intraperitoneal route of infection. Furthermore, the obtained results suggest that resistance to paracoccidioidomycosis is associated with T-cell, macrophage, and B-cell activities that are known to be mediated by gamma interferon.     

Enhanced innate immune responsiveness to pulmonary Cryptococcus neoformans infection is associated with resistance to progressive infection

Genetically regulated mechanisms of host defense against Cryptococcus neoformans infection are not well understood. In this study, pulmonary infection with the moderately virulent C. neoformans strain 24067 was used to compare the host resistance phenotype of C57BL/6J with that of inbred mouse strain SJL/J. At 7 days or later after infection, C57BL/6J mice exhibited a significantly greater fungal burden in the lungs than SJL/J mice. Characterization of the pulmonary innate immune response at 3 h after cryptococcal infection revealed that resistant SJL/J mice exhibited significantly higher neutrophilia, with elevated levels of inflammatory cytokine tumor necrosis factor alpha (TNF-α) and keratinocyte-derived chemokine (KC)/CXCL1 in the airways, as well as increased whole-lung mRNA expression of chemokines KC/CXCL1, MIP-1α/CCL3, MIP-1β/CCL4, MIP-2/CXCL2, and MCP-1/CCL2 and cytokines interleukin 1β (IL-1β) and IL-1Ra. At 7 and 14 days after infection, SJL/J mice maintained significantly higher levels of TNF-α and KC/CXCL1 in the airways and exhibited a Th1 response characterized by elevated levels of lung gamma interferon (IFN-γ) and IL-12/IL-23p40, while C57BL/6J mice exhibited Th2 immunity as defined by eosinophilia and IL-4 production. Alveolar and resident peritoneal macrophages from SJL/J mice also secreted significantly greater amounts of TNF-α and KC/CXCL1 following in vitro stimulation with C. neoformans. Intracellular signaling analysis demonstrated that TNF-α and KC/CXCL1 production was regulated by NF-κB and phosphatidylinositol 3 kinase in both strains; however, SJL/J macrophages exhibited heightened and prolonged activation in response to C. neoformans infection compared to that of C57BL/6J. Taken together, these data demonstrate that an enhanced innate immune response against pulmonary C. neoformans infection in SJL/J mice is associated with natural resistance to progressive infection.     

Relationship of survival, organism containment, and granuloma formation in acute murine tuberculosis.

The relationship among organism growth, immunopathology, and survival was studied in C57BL/6 and A/J mice acutely infected with Mycobacterium tuberculosis (MTB) (Erdman). Although organisms grew at similar rates in the lungs of both mouse strains, A/J mice died prior to 14 days after infection, whereas C57BL/6 mice survived twice as long. The lungs of A/J mice exhibited necrotizing interstitial inflammation and widely distributed acid-fast bacilli without granuloma formation. In contrast, the lungs of C57BL/6 mice had relatively mild interstitial inflammation, which was replaced by focal granulomas, and acid-fast bacilli were primarily within granulomas. MTB induced similar granulomas for A/J and C57BL/6 mice in spleen and liver. In the lung, the A/J mice produced only transient messages for interferon-y (IFN-y), interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), IL-10, and inducible nitric oxide synthase (iNOS). The C57BL/6 mice, in contrast, produced a delayed but sustained response in the lung correlating with granuloma onset and characterized by high induction of IL-6, IFN-gamma, IL-1beta, IL-10, and TNF-alpha. Responses in the liver and spleen were also evaluated. These results demonstrate that histopathology and cytokine response to MTB infection varies among organs in mice. Increased survival during acute infection may, therefore, depend on the ability to contain organisms within granulomas in the lung.     

The Cnes2 Locus on Mouse Chromosome 17 Regulates Host Defense against Cryptococcal Infection through Pleiotropic Effects on Host Immunity

The genetic basis of natural susceptibility to progressive Cryptococcus neoformans infection is not well understood. Using C57BL/6 and CBA/J inbred mice, we previously identified three chromosomal regions associated with C. neoformans susceptibility (Cnes1, Cnes2, and Cnes3). To validate and characterize the role of Cnes2 during the host response, we constructed a congenic strain on the C57BL/6 background (B6.CBA-Cnes2). Phenotypic analysis of B6.CBA-Cnes2 mice 35 days after C. neoformans infection showed a significant reduction of fungal burden in the lungs and spleen with higher pulmonary expression of gamma interferon (IFN-γ) and interleukin-12 (IL-12), lower expression of IL-4, IL-5, and IL-13, and an absence of airway epithelial mucus production compared to that in C57BL/6 mice. Multiparameter flow cytometry of infected lungs also showed a significantly higher number of neutrophils, exudate macrophages, CD11b⁺ dendritic cells, and CD4⁺ cells in B6.CBA-Cnes2 than in C57BL/6 mice. The activation state of recruited macrophages and dendritic cells was also significantly increased in B6.CBA-Cnes2 mice. Taken together, these findings demonstrate that the Cnes2 interval is a potent regulator of host defense, immune responsiveness, and differential Th1/Th2 polarization following C. neoformans infection.     

Effects of interleukin-4 deprivation and treatment on resistance to Trypanosoma cruzi

Trypanosoma cruzi (Y strain)-infected interleukin-4(-/-) (IL-4(-/-)) mice of strains 129/J, BALB/c, and C57BL/6 showed no significant difference in parasitemia levels or end point mortality rates compared to wild-type (WT) mice. Higher production of gamma interferon (IFN-gamma) by parasite antigen (Ag)-stimulated splenocytes was observed only for C57BL/6 IL-4(-/-) mice. Treatment of 129/J WT mice with recombinant IL-4 (rIL-4), rIL-10, anti-IL-4, and/or anti-IL-10 monoclonal antibodies (MAbs) did not modify parasitism. However, WT mice treated with rIL-4 and rIL-10 had markedly increased parasitism and suppressed IFN-gamma synthesis by spleen cells stimulated with parasite Ag, concanavalin A, or anti-CD3. Addition of anti-IL-4 MAbs to splenocyte cultures from infected WT 129/J, BALB/c, or C57BL/6 mice failed to modify IFN-gamma synthesis levels; in contrast, IL-10 neutralization increased IFN-gamma production and addition of rIL-4 and/or rIL-10 diminished IFN-gamma synthesis. We conclude that endogenous IL-4 is not a major determinant of susceptibility to Y strain T. cruzi infection but that IL-4 can, in association with IL-10, modulate IFN-gamma production and resistance.     

Animal model of Mycobacterium abscessus lung infection

Chronic lung disease as a result of Mycobacterium abscessus is an emerging infection in the United States. We characterized the lung immune responses in mice and guinea pigs infected with M. abscessus. C57BL/6 and leptin-deficient ob/ob mice challenged with a low-dose aerosol (LDA) of M. abscessus did not develop an infection. However, when challenged with a high-dose aerosol (HDA), C57BL/6 and ob/ob mice developed an established infection and a pulmonary immune response consisting of an early influx of IFN-gamma+ CD4+ T cells; this immune response preceded the successful clearance of M. abscessus in both strains of mice, although mycobacterial elimination was delayed in the ob/ob mice. Infected guinea pigs showed an increased influx of lymphocytes into the lungs with bacterial clearance by Day 60. In contrast to the C57BL/6 and ob/ob mice and guinea pigs, IFN-gamma knockout (GKO) mice challenged with a LDA or HDA of M. abscessus showed a progressive lung infection despite a robust influx of T cells, macrophages, and dendritic cells, culminating in extensive lung consolidation. Furthermore, with HDA challenge of the GKO mice, emergence of IL-4- and IL-10-producing CD4+ and CD8+ T cells was seen in the lungs. In conclusion, IFN-gamma is critically important in the host defense against M. abscessus. As the number of effective drugs against M. abscessus is limited, the GKO mice provide a model for in vivo testing of novel drugs.     

IL-23 dampens the allergic response to Cryptococcus neoformans through IL-17-independent and -dependent mechanisms

The cytokines IL-23 and IL-17 have been implicated in resistance to cryptococcal disease, but it is not clear whether IL-23-mediated production of IL-17 promotes fungal containment following pulmonary challenge with Cryptococcus neoformans. We used mice lacking IL-23 (IL-23p19(-/-)) or IL-17RA (IL-17RA(-/-)), and wild type (WT) C57BL/6 mice to examine the IL-23/IL-17 axis after intranasal infection with the C. neoformans strain 52D. The absence of IL-23 or IL-17RA had no effect on pulmonary or brain fungal burden at 1 or 6 weeks after infection. However, survival of IL-23p19(-/-) mice was reduced compared to IL-17RA(-/-) mice. IL-I7 production by CD4 T cells and natural killer T (NKT) cells was impaired in IL-23p19(-/-) lungs, but was not completely abolished. Both IL-23p19(-/-) and IL-17RA(-/-) mice exhibited impaired neutrophil recruitment, increased serum levels of IgE and IgG2b, and increased deposition of YM1/YM2 crystals in the lung, but only IL-23p19(-/-) mice developed persistent lung eosinophilia. Although survival of IL-17RA(-/-) and WT mice was similar after 17 weeks of infection, only surviving IL-17RA(-/-) mice exhibited cryptococcal dissemination to the blood. These data demonstrate that IL-23 dampens the allergic response to cryptococcal infection through IL-17-independent suppression of eosinophil recruitment and IL-17-dependent regulation of antibody production and crystal deposition. Furthermore, IL-23, and to a lesser extent IL-17, contribute to disease resistance.     

Mycoplasma pneumoniae induces host-dependent pulmonary inflammation and airway obstruction in mice

Respiratory tract infections result in wheezing in a subset of patients. Mycoplasma pneumoniae is a common etiologic agent of acute respiratory infection in children and adults that has been associated with wheezing in 20-40% of individuals. The current study was undertaken to elucidate the host-dependent pulmonary and immunologic response to M. pneumoniae respiratory infection by studying mice with different immunogenetic backgrounds (BALB/c mice versus C57BL/6 mice). After M. pneumoniae infection, only BALB/c mice developed significant airway obstruction (AO) compared with controls. M. pneumoniae-infected BALB/c mice manifested significantly elevated airway hyperresponsiveness (AHR) compared with C57BL/6 mice 4 and 7 d after inoculation as well as BALB/c control mice. Compared with C57BL/6 mice, BALB/c mice developed worse pulmonary inflammation, including greater peribronchial infiltrates. Infected BALB/c mice had significantly higher concentrations of tumor necrosis factor-alpha, interferon-gamma, interleukin (IL)-1beta, IL-6, IL-12, KC (functional IL-8), and macrophage inflammatory protein 1alpha in the bronchoalveolar lavage fluid compared with infected C57BL/6 mice. No differences in IL-2, IL-4, IL-5, IL-10, and granulocyte/macrophage colony-stimulating factor concentrations were found. The mice in this study exhibited host-dependent infection-related AO and AHR associated with chemokine and T-helper type (Th)1 pulmonary host response and not Th2 response after M. pneumoniae infection.