Nature of the effector cells responsible for antibody-dependent cell-mediated killing of Cryptococcus neoformans

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Abstract
Studies were performed to identify the types of human peripheral blood leukocytes capable of killing C. neoformans in the presence of anticryptococcal antibody in vitro. A total of 24.1 .+-. 2.7% (mean .+-. SE of the mean of 4 experiments) of the original cryptococcal inoculum survived in a mixed mononuclear cell preparation (.apprx. 30% monocytes) after 4 h incubation at 37.degree. C with rabbit anticryptococcal antibody. When phagocytic cells were removed, there was 36.4 .+-. 4.6% survival in 6 experiments, compared with 52.8% survival in the presence of purified granulocytes (mean of 2 experiments) and 96.9 .+-. 1% survival in the presence of purified T [thymus derived] cells. There was never any significant killing in control mixtures that contained leukocytes with normal rabbit serum nor in those that contained anticryptococcal antibody without effector leukocytes. Significant antibody-dependent fungicidal activity was seen with ratios of effector to target cells as low as 6.25:1. Multiple types of peripheral blood leukocytes, excluding T cells, are apparently capable of antibody-dependent fungicidal activity.