Severe Paracoccidioidomycosis in a 14-Year-Old Boy.

Paracoccidioidomycosis (PCM) is the most important systemic mycoses in Latin America. We describe a severe case of paracoccidioidomycosis in a 14-year-old boy, with a rapid disease progression. The fungal strain was isolated and inoculated into a T and/or B cell immunocompromised mice, which revealed a highly virulent strain. The case report presented herein emphasizes the importance of considering PCM in the differential diagnosis of patients with other infectious diseases in endemic areas and highlights a novel isolate.

Resistance to Paracoccidioides brasiliensis infection is linked to a preferential Th1 immune response, whereas susceptibility is associated with absence of IFN-gamma production.

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.

Pathogenesis II: fungal responses to host responses: interaction of host cells with fungi.

Most of our knowledge concerning the virulence determinants of pathogenic fungi comes from the infected host, mainly from animal models and more recently from in vitro studies with cell cultures. The fungi usually present intra- and/or extracellular host-parasite interfaces, with the parasitism phenomenon dependent on complementary surface molecules. Among living organisms, this has been characterized as a cohabitation event, where the fungus is able to recognize specific host tissues acting as an attractant, creating stable conditions for its survival. Several fungi pathogenic for humans and animals have evolved special strategies to deliver elements to their cellular targets that may be relevant to their pathogenicity. Most of these pathogens express surface factors that mediate binding to host cells either directly or indirectly, in the latter case binding to host adhesion components such as extracellular matrix (ECM) proteins, which act as 'interlinking' molecules. The entry of the pathogen into the host cell is initiated by fungal adherence to the cell surface, which generates an uptake signal that may induce its cytoplasmic internalization. Once this is accomplished, some fungi are able to alter the host cytoskeletal architecture, as manifested by a rearrangement of microtubule and microfilament proteins, and this can also induce epithelial host cells to become apoptotic. It is possible that fungal pathogens induce modulation of different host cell pathways in order to evade host defences and to foster their own proliferation. For a number of pathogens, the ability to bind ECM glycoproteins, the capability of internalization and the induction of apoptosis are considered important factors in virulence. Furthermore, specific recognition between fungal parasites and their host cell targets may be mediated by the interaction of carbohydrate-binding proteins, e.g., lectins on the surface of one type of cell, probably a parasite, that combine with complementary sugars on the surface of host-cell. These interactions supply precise models to study putative adhesins and receptor-containing molecules in the context of the fungus-host interface. The recognition of the host molecules by fungi such as Aspergillus fumigatus, Paracoccidioides brasiliensis and Histoplasma capsulatum, and their molecular mechanisms of adhesion and invasion, are reviewed in this paper.

Knockout mice as experimental models of virulence.

Infection models with animals whose immune systems have been selectively altered by neutralization of endogenous cytokines or by deletion of a gene have provided a valuable means to study the function of cells or cytokines in the context of complex multidimensional interactions. In particular, knockout mice have allowed a deeper insight into the in vivo performance of antifungal innate and acquired immunity, whose interplay is considered fundamental in the general defense against infections. It is conceivable that such an integrated view of effector and regulatory immune mechanisms operating in opportunistic fungal infections would facilitate the search for cells, cytokines and molecular pathways that are essential to control fungal infectivity or oppose fungus-associated immunopathology.

Pathogenesis I: interactions of host cells and fungi.

The interactions of host cells and fungi during infection represent a complex interplay. Although T helper 1 (Th1)-mediated immunity is primarily responsible for acquired resistance to Paracoccidioides brasiliensis, studies have demonstrated that polymorphonuclear neutrophils play a critical role in providing an early resistance to this organism. One study has shown that the invasiveness of Candida albicans requires adherence, particularly to endothelial cells, which in turn are stimulated to express various cell-markers and pro-inflammatory cytokines as part of a proactive resistance to invasion. Somewhat in contrast to infection with C. albicans, it has been shown that the capsular glucuronoxylomannan of Cryptococcus neoformans causes the shedding of host-cell adherence molecules (L-selectins) needed for the migration of host-inflammatory cells to sites of infection and likely explains, in part, the reduced host inflammatory response to this organism. Resistance to aspergillosis is often associated with the immune status of the host. In one set of studies, it has been demonstrated that lymphocytes have little direct effect on the organism, but that antigen-presenting dendritic cells stimulate the production of Th1 cytokines, suggesting a positive role for the dendritic cell in host-response. Similarly, another study has shown that among the regulatory cytokine networks that Th2-associated cytokines (e.g., interleukin-10) likely play a detrimental role in the resistance of the host to Aspergillus fumigatus.

Depletion of CD8(+) T cells in vivo impairs host defense of mice resistant and susceptible to pulmonary paracoccidioidomycosis.

Using a pulmonary model of infection, we demonstrated previously that A/Sn and B10.A mice are, respectively, resistant and susceptible to Paracoccidioides brasiliensis infection. Employing the same experimental model, we examined herein the role of CD8(+) T cells in the course of paracoccidioidomycosis. Treatment with anti-CD8 monoclonal antibodies caused a selective depletion of pulmonary and splenic CD8(+) T cells in both mouse strains. The number of pulmonary CD4(+) T cells and immunoglobulin-positive cells was independent of the number of CD8(+) T cells. In susceptible mice, the loss of CD8(+) T cells by in vivo treatment with anti-CD8 monoclonal antibodies impaired the clearance of yeasts from the lungs and increased the fungal dissemination to the liver and spleen. The same treatment in resistant mice increased fungal dissemination to extrapulmonary tissues but did not alter the pulmonary fungal load. Furthermore, CD8(+) T-cell depletion did not modify delayed-type hypersensitivity reactions of A/Sn mice but increased these reactions in B10.A mice. The production of P. brasiliensis-specific antibodies by resistant and susceptible mice depleted of CD8(+) T cells was similar to that of mice given control antibody. Histopathologically, depletion of CD8(+) T cells did not disorganize the focal granulomatous lesions developed by both mouse strains. These results indicate that CD8(+) T cells are necessary for optimal clearance of the fungus from tissues of mice infected with P. brasiliensis and demonstrate more prominent protective activity by those cells in the immune responses mounted by susceptible animals.

Influence of the genetic background on the pattern of lesions developed by resistant and susceptible mice infected with Paracoccidioides brasiliensis.

To compare the sequential evolution of lesions developed by resistant (A/Sn) and susceptible (B10.A) mice to Paracoccidioides brasiliensis infection we inoculated a virulent isolate of the fungus and collected the pancreas/peripancreatic omentum monthly (from 1 to 6 months) post infection. After fixation, tissue sections were stained by conventional methods for light microscopy to investigate the cellular composition, the extracellular matrix (ECM) patterns and the morphology of the yeasts in the lesions. In both strains, the fungal lesions were localized mostly in the omentum; a few lesions in the pancreatic parenchyma were observed, mostly in B10.A mice. In both strains, macrophages and plasmocytes were the predominant cells in all lesions, followed by neutrophils (PMN) and macrophages transformed into giant and epithelioid cells. Remarkable differences were observed between resistant and susceptible mice, specially related to the ECM structure of the granulomatous lesions. In A/Sn mice, from the 1st month on, the coexistence of two types of lesions was observed: one type showed a well-defined encapsulated nodule, constituted mainly of type I collagen. Neutrophils were abundant in areas of massive fungal destruction and few viable yeasts were observed. The other type showed residual characteristics, with sparse collagen deposits and presence of xantomatous-like macrophages, containing degenerated fungi. Such residual lesions predominated after the 2nd month and were the only type observed from the 4th month on, indicating the control of the infection. In B10.A mice, on the contrary, only one type of lesion was observed, showing less tendency to encapsulation and the formation of multiple small granulomatous foci, individualized by reticular type III collagen fibers. There were many plasmocytes in the periphery and large numbers of budding yeasts, with no evidence of fungal destruction. In the course of the infection the lesions progressively increased in number and size. Altogether, the comparative histopathological analysis demonstrates the influence of the genetic pattern of the host on the lesions developed by resistant and susceptible mice to P. brasiliensis infection.

Cytokines produced by susceptible and resistant mice in the course of Paracoccidioides brasiliensis infection.

Paracoccidioidomycosis (PCM) is the most prevalent deep mycosis in Latin America and presents a wide spectrum of clinical manifestations. We established a genetically controlled murine model of PCM, where A/Sn mice develop an infection which mimics the benign disease (immune responses which favor cellular immunity) and B10.A animals present the progressive disseminated form of PCM (preferential activation of B cells and impairment of cellular immune responses). To understand the immunoregulatory phenomena associated with resistance and susceptibility in experimental PCM, A/Sn and B10.A mice were studied regarding antigen-elicited secretion of monokines (TNF-alpha and TGF-beta) and type-1 (IL-2 and IFN-gamma) and type-2 (IL-4,5,10) cytokines. Total lymph node cells from resistant mice infected i.p. with P. brasiliensis produced early and sustained levels of IFN-gamma and IL-2; type-2 cytokines (IL-4 and IL-5) started to appear 8 weeks after infection. In contrast, susceptible mice produced low levels of IFN-gamma concomitant with significant levels of IL-5 and IL-10 early in the infection. In the chronic phase of the disease, susceptible animals presented a transitory secretion of IL-2, and IL-4. In the pulmonary infection IL-4, IL-5 and IL-10 were preferentially detected in the lung cells washings of susceptible animals. After in vitro challenge with fungal antigens, normal peritoneal macrophages from B10.A mice secreted high levels of TGF-beta and low levels of TNF-alpha. In contrast, macrophages from A/Sn animals released high levels of TNF-alpha associated with a small production of TGF-beta. The in vivo depletion of IFN-gamma not only abrogated the resistance of A/Sn mice but also diminished the relative resistance of B10.A animals. The in vivo depletion of IL-4 did not alter the disease outcome, whereas administration of rIL-12 significantly enhanced resistance in susceptible animals. Taken together, these results suggest that an early secretion of high levels of TNF-alpha and IFN-gamma followed by a sustained secretion of IL-2 and IFN-gamma plays a dominant role in the resistance mechanisms to P. brasiliensis infection. In contrast, an early and ephemeral secretion of low levels of TNF-alpha and IFN-gamma associated with production of IL-5, IL-10 and TGF-beta characterizes the progressive disease of susceptible animals.

Cytokines produced by suscesptible and resistant mice in the course of Paracoccidioides brasiliensis infection

Paracoccidioidomycosis (PCM) is the most prevalent deep mycosis in Latin America and presents a wide spectrum of clinical manifestations. We established a genetically controlled murine model of PCM, where A/Sn mice develop an infection which mimics the benign disease (immune responses which favor cellular immunity) and B10.A animals present the progressive disseminated form of PCM (preferential activation of B cells and impairment of cellular immune responses). To understand the immunoregulatory phenomena associated with resistance and susceptibility in experimental PCM, A/Sn and B10.A mice were studied regarding antigen-elicited secretion of monokines (TNF-alpha and TGF-beta) and type-1 (IL-2 and IFN-gamma) and type-2 (IL-4,5,10) cytokines. Total lymph node cells from resistant mice infected ip with P. brasiliensis produced early and sustained levels of IFN-gamma and IL-2; type-2 cytokines (IL-4 and IL-05) started to appear 8 weeks after infection. In contrast, susceptible mice produced low levels of IFN-gamma concomitant with significant levels of IL-5 and IL-10 early in the infection. In the chronic phase of the disease, susceptible animals presented a transitory secretion of IL-2, and IL-4. In the pulmonary infection IL-4, IL-5 and IL-10 were preferentially detected in the lung cells washings of susceptible animals. After in vitro challenge with fungal antigens, normal peritoneal macrophages from B10.A mice secreted high levels of TGF-beta and low levels of TNF-alpha. In contrast, macrophages from A/Sn animals released high levels of TNF-alpha associated with a small production of TGF-beta. The in vivo depletion of IFN-gamma not only abrogated the resistance of A/Sn mice but also diminished the relative resistance of B10.B animals. The in vivo depletion of IL-4 did not alter the disease outcome, whereas administration of rIL-12 significantly enhanced resistance in susceptible animals. Taken together, these results suggest that an early secretion of high levels of TNF-alpha and IFN-gamma followed by a sustained secretion of IL-2 and IFN-gamma plays a dominant role in the resistance mechanisms to P. brasiliensis infection. In contrast, an early and ephemeral secretion of low levels of TNF-alpha and IFN-gamma associated with production of IL-5 IL-10 and TGF-beta characterizes the progressive disease of susceptible animals.

Protective role of gamma interferon in experimental pulmonary paracoccidioidomycosis.

We have developed a murine model of pulmonary infection by Paracoccidioides brasiliensis in which resistance was associated with immunological activities governed by gamma interferon (IFN-gamma). To better characterize this model, we measured type 1 and type 2 cytokines in the lungs and investigated the effect of endogenous IFN-gamma 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-gamma, interleukin-4 (IL-4), IL-5, and IL-10 higher than those in resistant mice. In both mouse strains, neutralization of endogenous IFN-gamma 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-gamma 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-gamma plays a protective role and that this cytokine is one major mediator of resistance against P. brasiliensis infection in mice.

Type 1 and type 2 cytokines: from basic science to fungal infections.

At the present time, it is clear that Th1 responses afford protection against the fungi; however, the development, maintenance and function of the protective immune responses are complex mechanisms and are influenced by multiple factors. The route of infection has been shown to affect initial cytokine production and, consequently, the induction of protective Th1 responses. The ability of different isolates of the same fungal agent to induce and sustain a protective response has also been emphasized. Protective immune responses have been shown to vary in genetically different mouse strains after infection. In addition, these protective responses, such as cellular influx and cytokine production, also vary within the same animal depending on the tissue infected. The functional dominance of certain cytokines over others in influencing development and maintenance of protective responses has been discussed. Certain cytokines may act differently in hosts lacking important components of their innate or immune repertoire. It is evident from these presentations that a more comprehensive understanding of the protective mechanisms against different fungal agents is emerging. However, there is still much to learn before cytokine modulatory therapy can be used effectively without risk in the human host.

Comparative studies on the antibody repertoire produced by susceptible and resistant mice to virulent and nonvirulent Paracoccidioides brasiliensis isolates.

The specific recognition pattern of antibodies produced by susceptible and resistant mice infected with the low virulence Paracoccidioides brasiliensis isolate (Pb265) was examined by an immunoblotting procedure and compared with that of antibodies produced by highly virulent isolate (Pb18) in infected mice. Both mouse strains produced IgG antibodies to 13 of the 16 major antigen bands, and showed a recognition pattern similar to sera from mice infected with the virulent isolate. Nevertheless, the reaction to components interposed among major bands (intermediate antigen bands of 75, 73, 68, 64, 33, 23, 22, and 12.5 kD) were detected exclusively with antibodies raised in response to the virulent P. brasiliensis isolate independent of the resistance pattern of the host. It was also demonstrated here that the most diversified repertoire of specific IgA was produced when the susceptible host and virulent fungus were associated.

Paracoccidioides brasiliensis infection in nude mice: studies with isolates differing in virulence and definition of their T cell-dependent and T cell-independent components.

Athymic and euthymic BALB/c mice infected with highly (Pb18) or slightly (Pb265) virulent Paracoccidioides brasiliensis isolates were compared regarding mortality, presence of viable yeasts, specific immunoglobulin M (IgM) and IgG titers, and the antigen recognition patterns of these antibodies. Isolate Pb18 caused a more severe disease in athymic mice, as supported by higher number of infected organs and shorter survival times. These animals, however, were resistant to Pb265 infection. High titers of antibodies were found only in euthymic mice, seven weeks after Pb18 infection. At this time, euthymic animals presented IgG antibodies to numerous protein bands that were not detected at four weeks postinfection or after Pb265 inoculation. In contrast, antibodies from athymic mice always reacted with few antigen bands. Although the majority of P. brasiliensis antigens are T cell-dependent, the immunodominant gp43 and also the 41.5- and 27.5-kD antigens are here, for the first time, characterized as T cell-independent antigens of P. brasiliensis.

Histopathology of paracoccidioidomycotic infection in athymic and euthymic mice: a sequential study.

We report the comparative and sequential histologic analysis of lesions developed by Paracoccidioides brasiliensis-infected athymic and euthymic BALB/c mice, using conventional and specific stain to characterize the morphology of fungi and inflammatory cells as well as the extracellular matrix patterns. In both groups, neutrophils and macrophages were the predominant cells; macrophage transition to giant and epithelioid cells was observed. Degenerated fungi and fungal dust were associated with local neutropil infiltration and the presence of pseudoxantomatous macrophages. Paracoccidioides brasiliensis are always found within an extracellular matrix microenvironment. The main differences between lesions developed by nu/+ and nude (nu/nu) mice resided in the more pronounced encapsulating tendency in the former ones. In both groups of animals, lesions in several organs were associated with extensive hemopoiesis. At the first week of infection, there was evidence of fungal destruction and control of its proliferation in both mouse groups. At the fourth and seventh weeks, nu/+ mice maintained the control of the infection, as shown by the scarce numbers of budding yeast cells, while experimental nu/nu mice showed a tumor-like progression of the disease with a striking increase in fungal load in many organs (e.g., omental and mesenteric milky spots, lymph nodes, spleen), some of which present their structure replaced by granulomatous lesions.

Neutrophil oxidative metabolism and killing of P. brasiliensis after air pouch infection of susceptible and resistant mice.

The oxidative burst of polymorphonuclear neutrophils (PMN) and their ability to inhibit Paracoccidioides brasiliensis growth was studied in susceptible (B10.A) and resistant (A/J) mice. The cells were obtained after subcutaneous inoculation in air pouches, yielding highly pure PMN preparations; the number of cells was similar for both strains at 24 h and five times higher in the resistant strain at 15 days. The oxidative metabolism of these PMN was evaluated by the luminol and lucigen-enhanced chemiluminescence upon stimulation with PMA or killed P. brasiliensis (Pb). At 24 h of infection PMN from both strains showed similar responses. However, at 15 days a great enhancement of the Pb-stimulated luminol-enhanced chemiluminescence was observed only in PMN from resistant mice. Such increase was markedly inhibited by the addition of catalase. Independent of the mouse strain or time of infection of lucigen-enhanced chemiluminescence showed the same intensity. The lucigen-enhanced chemiluminescence of PMN without stimuli from resistant mice did not change with the time of infection, however, after 15 days of infection a significantly lower chemiluminescence was detected with PMN from susceptible mice. At 15 days of infection the PMN from B10.A were unable to kill P. brasiliensis yeast cells in vitro. Because the lucigenin- and luminol-enhanced chemiluminescence detects, respectively, the O2- production and the myeloperoxidase/hydrogen peroxide halide system, the present data show parallels between deficiency in the production of oxygen-reactive species by PMN and lower fungicidal activity.

Influence of the genetic pattern and sex of mice in experimental paracoccidioidomycosis.

Eight genetically different strains of mice were compared regarding the dissemination of Paracoccidioides brasiliensis to the lungs, liver and omentum/pancreas, DTH responses and specific antibody production at 16 weeks after intraperitoneal infection with Pb18, a virulent P. brasiliensis isolate. The degree of dissemination of the infection varied: B10.A and C57B1/6, the most susceptible mouse strains, had positive cultures and high colony-forming unit (CFU) counts in all analysed organs. DBA/2 and A/Sn mice had negative cultures, being thus classified as the most resistant strains. CBA/J, C3H/HeJ, F1(A/SnxB10.A) and BALB/c mice were regarded as relatively resistant, since discrete fungal growth was observed only in one or two of the studied organs. All mouse strains, except B10.A mice, produced specific DTH responses which did not seem to be associated with the severity of disease. Production of high levels of specific antibodies was found in all strains except in the DBA/2 and C57B1/6 mice. The influence of the host sex on the outcome of paracoccidioidomycosis was evident only in susceptible animals: female B10.A mice displayed lower CFU counts in the three examined organs, whereas no differences were found between male and female A/Sn animals. The higher resistance of female B10.A mice was not accompanied by differences in their capacity to maintain a DTH reaction, nor in their production of antibody. This fact argues against the widely believed association of susceptibility to P. brasiliensis infection with both impaired DTH reactivity and increased humoral response.

Effect of macrophage blockade on the resistance of inbred mice to Paracoccidioides brasiliensis infection.

The effect of macrophage blockade on the natural resistance and on the adaptative immune response of susceptible (B10.D2/oSn) and resistant (A/Sn) mice to Paracoccidioides brasiliensis infection was investigated. B10.D2/oSn and A/Sn mice previously injected with colloidal carbon were infected ip with yeast cells to determine the 50% lethal dose, and to evaluate the anatomy and histopathology, macrophage activation, antibody production and DTH reactions. Macrophage blockade rendered both resistant and susceptible mice considerably more susceptible to infection, as evidenced by increased mortality and many disseminated lesions. P. brasiliensis infection and/or carbon treatment increased the ability of macrophages from resistant mice to spread up to 25 days after treatment. In susceptible mice the enhanced spreading capacity induced by carbon treatment was impaired at all assayed periods except at 1 week after infection. Macrophage blockade enhanced DTH reactions in resistant mice, but did not alter these reactions in susceptible mice, which remained anergic. To the contrary, macrophage blockade enhanced specific antibody production by susceptible mice, but did not affect the low levels produced by resistant mice. The effect of macrophage blockade confirms the natural tendency of resistant animals to mount DTH reactions in the course of the disease and the preferential antibody response developed by susceptible mice after P. brasiliensis infection. On the whole, macrophage functions appear to play a fundamental role in the natural and acquired resistance mechanisms to P. brasiliensis infection.

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.

Paracoccidioides brasiliensis-stimulated human gamma/delta T cells support antibody production by B cells.

Paracoccidioidomycosis patients show hyperactive humoral immune responses. Consequently, we investigated whether cytokines in supernatants from Paracoccidioides brasiliensis-stimulated gamma/delta T cells support B-cell activation. We detected proliferation of B cells and increased immunoglobulin M (IgM) and IgG production. Thus, gamma/delta T cells may participate in polyclonal B-cell activation during paracoccidioidomycosis.