Abstract
The immunological basis for differences in resistance to pulmonary blastomycosis between young (3 to 4-week-old) and adult (7 to 8-week-old) CD-1 mice is unknown. We assessed whether there were differences in fungicidal activity of phagocytes and Th-1 lymphocyte cytokine production. The fungicidal activity of young bronchoalveolar macrophages (BAM) (20%) against Blastomyces dermatitidis (Bd) was comparable to killing by adult BAM (25%). However, IFN-γ enhanced the killing by adult BAM (from 30 to 69%) to a greater extent than BAM from young animals (from 20 to 30%). Killing of Bd by young peritoneal macrophages (PM) (46%) and adult PM (42%) was similar, and the enhancement of cells of both by IFN-γ was similar. TNFα production by young macrophages (BAM or PM), when cocultured with Bd for 18 h, was half of TNFα secreted by adult macrophages. We found that polymorphonuclear neutrophils (PMN) from young mice had deficient fungicidal activity against Bd (37%) compared with adult PMN (80%). Interferon-γ (IFN-γ) treatment increased PMN killing of Bd by PMN of young animals from 37 to 80%. In an assessment of innate responses, we found spleen cells from young mice produced three-fold less IFN-γ and three-fold less IL-2 than adult spleen cells in response to 1 µg/ml concanavalin A (Con A). The young spleen cells also produced more NO, which we demonstrated reduced Con A-induced proliferation. These in vitro results demonstrate several immunological deficiencies in cells from young mice and these deficiencies correlate with susceptibility. In a pilot reconstitution experiment in pulmonary blastomycosis, treatment of infected young mice with IFN-γ (18.5×103 U, s.c.) on days 0, 1, and 2 significantly increased survival.