Schistosoma mansoni: inhibition in vitro of granulocyte cytotoxicity against schistosomula by autologous mononuclear cells from patients.

Granulocytes and mononuclear cells from normal subjects are able to kill Schistosoma mansoni schistosomula in the presence of human complement in vitro. In contrast, mononuclear cells from chronic schistosomiasis patients failed to kill the parasites. The relative efficiencies expressed in terms of the mean percentage killing of schistosomula for 15 experiments were 50.5 +/- 3.2 and 49.7 +/- 3.5 for granulocytes from normal and infected patients, and 50.8 +/- 2.8 against 23.0 +/- 3.2 for mononuclear cells from normal and infected patients, respectively. The killing effect of granulocytes dropped from 48.7 +/- 2.8 to 22.1 +/- 2.2 when autologous mononuclear cells from chronically infected patients were added to the system. Similar inhibitory effect of granulocyte function was obtained when these cells were incubated with normal mononuclear cells precultured with concanavalin A. Extracts prepared from mononuclear cells obtained from infected patients had the same inhibitory effect of intact cells on the complement-dependent granulocyte cytotoxicity.