Protective immunity to Candida albicans and Aspergillus fumigatus is mediated by antigen-specific Th1 cells. To define the role of B cells and antibodies in the generation of antifungal immune resistance, B cell-deficient (mu MT) mice were assessed for immune resistance to primary and secondary infections with both fungi. The results showed that, although passive administration of antibodies increased the fungal clearance, the innate and Th1-mediated resistance to the primary and secondary infections were both heightened in mu MT mice with candidiasis and aspergillosis. However, although capable of efficiently restricting the fungal growth, mu MT mice did not survive the re-infection with C. albicans, and this was concurrent with the failure to generate IL-10-producing dendritic cells and regulatory CD4(+)CD25(+) T cells. Antifungal opsonizing antibodies restored IL-10 production by dendritic cells from mu MT mice, a finding suggesting that the availability of opsonizing antibodies may condition the nature of the dendritic cell interaction with fungi, possibly impacting on the development of long-lasting antifungal immunity.