FIG. 4.

Influence of complement on the frequency of coiling phagocytosis of promastigotes from various Leishmania spp. Human peripheral blood monocytes (2 × 10⁶) were incubated with promastigotes from either L. major, L. donovani, or L. aethiopica (2 × 10⁷ each) for 30 min in the presence of 10% (vol/vol) hiFCS or fFCS, the latter with or without 1 mM SSH. Phagocytosis was evaluated in a blinded fashion by electron microscopy of randomly chosen ultrathin sections. The bars represent the relative frequencies of coiling phagocytosis, given as mean ± SEM of duplicate determinations in a typical experiment. Essentially the same results were observed in additional two experiments using phagocytes from different donors. Coiling and conventional phagocytosis of L. major and L. donovani, but not of L. aethiopica, was strongly reduced in presence of heat-inactivated or SSH-neutralized serum.