The secretion of interferon-gamma (IFN-gamma), interleukin-2 (IL-2), IL-4, IL-5, and IL-10 by antigen-stimulated lymph node cells, eosinophil maturation, and the antibody isotypes produced were examined during intraperitoneal infection of susceptible (B10.A) and resistant (A/Sn) mice with Paracoccidioides brasiliensis. Lymph node cells from resistant mice produced early and sustained levels of IFN-gamma and IL-2, whereas susceptible animals secreted low to undetectable amounts of these type 1 cytokines. Both mouse strains presented late and transient production of IL-4, whereas IL-10 was produced constantly throughout the course of disease. Resistant animals produced increasing levels of IL-5 in the chronic phase of the infection (from the eighth week on), whereas susceptible mice showed two peaks of IL-5 production, at the first and twelfth weeks after infection. Only the susceptible strain presented medullary and splenic eosinophilia concomitant with the raised IL-5 production. In resistant mice, the levels of IgG2a antibodies were significantly higher than those observed in susceptible mice, which preferentially secreted IgG2b and IgA isotypes. Taken together, these results demonstrate that a sustained production of IFN-gamma and IL-2 and a predominant secretion of IgG2a antibodies are associated with resistance to P. brasiliensis. In contrast, the production of low levels of IFN-gamma, early secretion of high levels of IL-5 and IL-10, eosinophilia, and a preferential secretion of IgG2b and IgA isotypes characterize the progressive disease in susceptible animals.

We have developed a murine model of pulmonary infection byParacoccidioides brasiliensis in which resistance was associated with immunological activities governed by gamma interferon (IFN-γ). To better characterize this model, we measured type 1 and type 2 cytokines in the lungs and investigated the effect of endogenous IFN-γ depletion by monoclonal antibodies in the course of infection of susceptible (B10.A) and resistant (A/Sn) mice. At weeks 4 and 8 after infection, lungs from susceptible animals presented levels of IFN-γ, interleukin-4 (IL-4), IL-5, and IL-10 higher than those in resistant mice. In both mouse strains, neutralization of endogenous IFN-γ induced exacerbation of the pulmonary infection, earlier fungal dissemination to the liver and spleen, impairment of the specific cellular immune response resulting in significantly lower delayed-type hypersensitivity reactions, and increased levels of immunoglobulin G1 (IgG1)- and IgG2b-specific antibodies. Histopathological analysis demonstrated that depletion of IFN-γ changes the focal granulomatous lesions found in the lungs of B10.A and A/Sn mice into coalescent granulomata which destroy the pulmonary architecture. These results suggest that irrespective of the mouse strain, IFN-γ plays a protective role and that this cytokine is one major mediator of resistance against P. brasiliensis infection in mice.

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.

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Using a pulmonary model of infection, we demonstrated previously that