Toxicity to Candida albicans mediated by human serum and peripheral blood mononuclear cells

This study evaluates the conditions in which peripheral blood mononuclear cells mediate toxicity to Candida albicans opsonized with heat-inactivated human serum. Serum concentrations as low as 1% resulted in 50% inhibition of C. albicans metabolic activity after incubation with peripheral blood mononuclear cells at an effector to target ratio of 8. Measurable inhibition was also achieved at lower effector to target ratios and lower serum concentrations, and at least a portion of the metabolic inhibition reflected fungal cell death. Depletion of C. albicans-specific antibody decreased the toxic effect while opsonization with purified human IgG restored toxicity, and cell-cell contact between peripheral blood mononuclear cells and fungus was required. Depletion of or enrichment for monocytes from the peripheral blood mononuclear cells preparation diminished the toxic effect and the monocytic cell line, THP-1, was likewise incapable of toxicity. These studies provide evidence that antibody augments antifungal host defense and underscore the complex interrelationship between humoral and cellular immunity in these infections.