Freshly isolated and cultured human monocytes obtained by plasmapheresis kill schistosomula of Schistosoma mansoni

Abstract

The efficacy of human peripheral blood monocytes (PBM) in killing of schistosomula is controversial. The purpose of this study was to determine the schistosomulacidal activity of human monocytes isolated by two different techniques. Peripheral blood monocytes were obtained either by venipuncture (PBMv) or plasmapheresis (PBMp), purified on Ficoll-Paque, and cultured briefly. The cells then were incubated with schistosomula (cell parasite ratio of 10(4):1) for 16 to 18 hours with or without interferon-gamma IFN-gamma (600 U/ml) or sera from patients with schistosomiasis as a source of antischistosomal antibodies (HASA). Freshly isolated PBMv treated with IFN-gamma or HASA did not kill schistosomula. Freshly isolated PBMp alone killed 22 +/- 13% (mean +/- standard deviation [SD]; n = 9) of worms over background and after incubation with IFN-gamma and HASA, 30 +/- 17%. PBMp cultured in vitro for 7 days killed 50 +/- 15% (mean +/- SD; n = 12) of the schistosomula. Pretreatment of the cells with IFN-gamma and incubation with HASA did not significantly enhance the parasite killing beyond this level. Electron microscopy showed that freshly isolated PBMp attached to the worms and fused occasionally with the outer tegumental membrane. Granules constituted 1.4% of the cytoplasmic volume. Degranulation onto the parasite surface was not observed. Peripheral blood monocytes obtained by plasmapheresis accumulated glycogen during in vitro culture with the parasite and released threefold more H2O2 than PBMv after exposure to phorbol myristate acetate. Thus plasmapheresis increases the schistosomulacidal activity of PBM, enhances the generation of H2O2 and promotes the accumulation of glycogen.