B-1 cells facilitate Paracoccidioides brasiliensis infection in mice via IL-10 secretion.

Protective immunity in paracoccidioidomycosis is mainly mediated by cellular immunity. The role of B cells in this disease, in particular B-1 cells, is poorly understood. The aim of this study was to characterize the participation of B-1 cells in resistance or susceptibility of BALB/c and BALB/Xid mice to P. brasiliensis (Pb) pulmonary infection. BALB/Xid, which lacks B-1 cells, exhibited higher resistance to infection when compared with BALB/c mice. However, adoptive transfer of B-1 cells to BALB/Xid mice drastically increased the susceptibility of these animals to Pb infection. The fungal burden in BALB/c and B-1-reconstituted BALB/Xid was significantly higher as compared to BALB/Xid strain. Compact, well-organized granulomas were observed in the lungs of BALB/Xid mice, whereas large lesions with necrotic center with a plethora of fungi developed in BALB/c mice. It was also shown that B-1 cells impair phagocytosis of Pb by macrophages in vitro via secretion of IL-10, which was increased upon stimulation with a purified Pb antigen, gp43. Finally, in vivo blockade of IL-10 led to a better control of infection by the highly susceptible B10.A mouse. These findings suggest that B-1 cells play a major role in resistance/susceptibility to Pb infection in murine models, most likely via production of IL-10.

Tolerogenic property of B-1b cells in a model of allergic reaction.

Since B-1 cells were first described, their origin and function remain controversial. Given the ability to produce natural antibodies and large amounts of IL-10, there is a consensus about their role in innate immunity. More recently, however, B-1 cells have been associated to adaptive immunity as well, due to the demonstration of immunological memory and antigen presentation capability. Here we demonstrate that adoptive transfer of pre-sensitized B-1b cells (obtained from OVA-sensitized mice) to naïve B-1 deficient animals, drastically affects the ability of transplanted animals to mount an adaptive response upon immunization with OVA. In contrast to naïve B-1 populated mice, mice transplanted with sensitized B-1 exhibit lower anti-OVA antibody levels, milder footpad swelling in response to OVA subcutaneous injection and reduced granulomatous reaction to OVA-coated beads. Moreover, we show that these pre-sensitized B-1 cells, when acting as APCs, induce poor T cell proliferation in vitro when compared with macrophages or B-1 cells obtained from naïve mice. This property may be due in part to insufficient expression of the co-stimulatory molecule CD86, necessary for optimal antigen presentation. In conclusion, our data suggest a novel role for B-1 cells as part of suppressor mechanisms in the immune system.

Characterization of B-1b cells as antigen presenting cells in the immune response to gp43 from Paracoccidioides brasiliensis in vitro.

Antigen presentation is an essential stage in the development of immune response to a specific antigen. This response can lead to the production of antibodies and/or effector T lymphocyte activation. Macrophages, dendritic cells and B-lymphocytes, among others, act as antigen presenting cells. B-lymphocytes capture antigenic particles through a surface receptor of IgM nature. The interaction IgM-antigen leads to endocytosis of the complex and antigen processing which culminates in presentation of the antigen on the cell surface associated with a class II MHC molecule. At least three B cell subsets, B-1a (Ly-1B), B-1b and B-2, are present in the mouse periphery. B-1a and B1-b cells represent a small population in the adult spleen and are abundant in the peritonial and pleural cavities. It has been demonstrated in our laboratory that B-1b cells spontaneously proliferated in stationary cultures of adherent peritonial cells. Further, that these cells migrate to a non-specific inflammatory focus. Based on these findings, we investigated whether these cells are antigen presenting cells in vitro using as antigenic stimulus gp43 from Paracoccidioides brasiliensis. Results showed that B1-b cells express constitutively high levels of class II MHC and costimulatory molecules inducing an efficient proliferation of gp43 sensitized T lymphocytes.

Immunity and hypersensitivity to gp43 antigen in susceptible and resistant mice infected with Paracoccidioides brasiliensis.

Pathogenic mechanisms underlying paracoccidioidomycosis are still poorly understood. A well-established murine model of resistance (mouse lineage A/Sn) and susceptibility (lineage B10.A) to P. brasiliensis pulmonary infection was here employed to compare immune response to gp43, the major antigenic component of the fungus. Mice were infected and their cellular and humoral immunity to gp43 were investigated for up to 16 weeks. In both mouse strains, challenge with gp43 indistinguishably evoked a typical immediate-hypersensitivity response, followed by a 24-h late-phase reaction consistent with the same type of immunological activation. IL-4 was detected in cultures of gp43-stimulated lymph node cells only in susceptible animals 2 weeks post-infection, while IL-5 was found throughout the study in both mouse strains. IL-10 appeared in the supernatants of stimulated cells from resistant and susceptible animals in increasing amounts as infection advanced. Conversely, interferon (IFN)-gamma was produced under gp43 stimulation only by cells from A/Sn animals. The humoral response was characterized by low levels of anti-gp43. Titration of IgG isotypes, however, revealed a predominance of IgG1. IgG2a levels were highest in resistant animals, whereas IgG2b levels were highest in susceptible mice. In conclusion, immunity induced by gp43 exhibits common features in A/Sn and B10.A phenotypes, such as immediate hypersensitivity, late phase reaction and high levels of IL-10, but some differences between the strains are also seen.