B1 cells contribution to susceptibility in experimental paracoccidioidomycosis: immunoglobulin isotypes and repertoire determination.

Paracoccidioidomycosis (PCM) is the most prevalent systemic mycosis in Latin America. The experimental murine model has been used to approach the disease, with susceptible and resistant mice strains that reproduce most of the main human immunological features. Since the hypergammaglobulinemia observed in susceptible mice and humans might have an influence on B1 cells, we investigated its role during the experimental infection with Paracoccidiodes brasiliensis. CBA/Nxid mice, deficient in B1 cells, and CBA/Nxid reconstituted with B1 cells isolated from the non-mutant CBA/J strain were infected with 106 yeast forms of P. brasiliensis. At the 8th and 22nd week post infection the DTH response of CBA/Nxid mice was significantly higher after 24 h of P. brasiliensis antigens inoculation and the specific humoral response was reduced, in comparison to CBA/J or recCBA/Nxid. Production of NAbs is a hallmark of the B1 subset. Higher Ig productions to auto antigens such as DNA, MBP and RBC were observed in CBA/J infected mice or recCBA/Nxid. Anti P. brasiliensis IgG2a was produced by CBA/Nxid mice early in infection, while CBA/J or recCBA/Nxid presented increased levels of this isotype only after the 8th week of infection. Furthermore, western blotting analysis showed that CBA/Nxid mice expanded less clones against P. brasiliensis antigens, with weakly detectable anti-gp43 antibodies while CBA/J mice produce IgM anti-gp43 at the 2nd week of infection and IgG anti-gp43 at the 2nd and 8th week. On the other hand, recognition of gp70, a fungal antigen that, as gp43, inhibits macrophage activation was not compromised in B1 deficient mice. These results suggest that B1 cells might have influence in the kinetic of production of protective isotypes of immunoglobulins and their repertoire that could contribute to an early drive towards a Th2 response, affecting the cellular response in susceptible mice during experimental paracoccidiodomycosis.