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

Abstract

Studies were performed to identify the types of human peripheral blood leukocytes capable of killing Cryptococcus neoformans in the presence of anticryptococcal antibody in vitro. A total of 24.1 ± 2.7% (mean ± standard error of the mean of 4 experiments) of the original cryptococcal inoculum survived in a mixed mononuclear cell preparation (approximately 30% monocytes) after 4 hr of incubation at 37°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 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. These observations indicate that multiple types of peripheral blood leukocytes, excluding T cells, are capable of antibody dependent fungicidal activity.