Immunological basis for susceptibility and resistance to pulmonary blastomycosis in mouse strains

The immunological basis for a >10-fold resistance of outbred CD-1 mice compared to inbred BALB/c mice to pulmonary blastomycosis was investigated. Bronchoalveolar macrophages (BAM) from CD-1 mice killed yeast cells of Blastomyces dermatitidis (Bd) by 25% and this increased to 59% when activated by IFN-γ. In contrast, BAM from BALB/c mice lacked significant killing (5%) of Bd but could be activated by IFN-γ for enhanced killing (19%). Peritoneal macrophages (PM) from CD-1 mice had significant fungicidal activity for Bd (43%) and this increased to 63% with IFN-γ treatment. By contrast, PM from BALB/c mice did not significantly kill Bd (14%) but were activated by IFN-γ for significant killing (24%). Fungicidal activity of peripheral blood polymorphonuclear neutrophils (PMN) from CD-1 (87%) was greater than that of BALB/c (75%) (P < 0.05). Macrophage inflammatory protein-1α (MIP-1α) production by BAM from BALB/c was significantly less than that from CD-1 in response to co-culture with Bd. IFN-γ production by CD-1 spleen cells in response to concanavalin A (Con A, 1 μg/ml) was 8-fold greater than that by BALB/c spleen cells. In contrast, BAM and PM from BALB/c mice in co-culture with Bd secreted several-fold more TNFα than BAM or PM from CD-1 mice. IL-2 production by BALB/c spleen cells in response to Con A was 3- to 4-fold greater than that by CD-1 spleen cells. Depressed IL-2 production by Con A stimulated CD-1 spleen cells correlated with depressed proliferative responses. Resistance of CD-1 mice to pulmonary blastomycosis correlates with enhanced fungicidal activity of BAM, PM, PMN, and IFN-γ production by Con A stimulated spleen cells, compared to BALB/c mice. Consistent with the in vitro enhancement of effector cell function by IFN-γ, in vivo therapy with IFN-γ significantly (P < 0.0001) improved survival of BALB/c mice with pulmonary blastomycosis.