In Situ IgM Production and Clonal Expansion of B-1 Cells in Peritoneal Cavity Promote Elimination of C. albicans Infection in IgH Transgenic Mice with V(H) Derived from a Natural Antibody

B-1 cells are innate-like cells that play important roles in host defense against infection. However, the function of B-1 cells in fungi infection remains unclear. Previously we produced IgH transgenic mice TgV(H)3B4 with V(H) derived from a natural antibody 3B4 that can identify C. albicans, and found that TgV(H)3B4 mice were resistant to intraperitoneal (i. p.) and intravenous C. albicans infection. Most of the peritoneal cavity (PEC) B-1 cells in TgV(H)3B4 mice express transgenic BCR that binds C. albicans. In the present study, we explored the response of B-1 cells to C. albicans infection by applying i. p. inoculation of fungi in TgV(H)3B4 mice. We found that C. albicans was cleared more efficiently in TgV(H)3B4 mice after i. p. inoculation than that of littermate control. The level of C. albicans-reactive IgM in PEC of TgV(H)3B4 mice was much higher than that of control, and the number of B-1a B cells was also elevated in TgV(H)3B4 mice, which was mainly due to enhanced proliferation of B-1 cells. Additionally, numbers of C. albicans-specific B cells increased greatly in TgV(H)3B4 mice after C. albicans inoculation. Our data suggested that in situ IgM production and clonal expansion of B-1 cells in PEC participate in host defense against C. albicans infection.