Studies of the antibody-dependent killing of schistosomula of Schistosoma mansoni employing haptenic target antigens. II. In vitro killing of TNP-schistosomula by human eosinophils and neutrophils.

Purified human eosinophils and neutrophils were compared for their capacity to mediate anti-TNP antibody-dependent killing of schistosomula of Schistosoma mansoni surface labeled with TNBS. In contrast with findings from studies employing human anti-schistosome sera and unmodified larvae, neutrophils in addition to eosinophils were found to be potent killers of schistosomula. Indeed, neutrophils proved to be consistently more effective than eosinophils in killing haptenated larvae throughout the dose response of each of the components (i.e., the TNBS surface label, rabbit anti-TNP sera and cells) of the in vitro reaction. The capacity of neutrophils to kill haptenated parasites is not likely to be due to the use of rabbit antibodies in the assays, since these cells were ineffective in killing unlabeled schistosomula when either rabbit or human anti-schistosome sera were employed. Furthermore, the ability of neutrophils to destroy TNP-labeled schistosomula does not appear to result from sublethal damage induced by the labeling procedure, since haptenated parasites were found to be no more susceptible than unmodified worms to killing mediated by anti-schistosome sera plus eosinophils or complement and, like unlabeled parasites, could not be killed by anti-schistosome sera plus neutrophils. The lethal interaction of neutrophils and haptenated schistosomula was preceded by a rapid and marked adherence of the cells to the worms, an effect that was not observed in the nonlethal interaction of neutrophils with schistosomula induced by anti-schistosome sera. The results argue, therefore, that the capacity of different granulocyte populations to kill schistosomula may be determined by the kinetics and intensity with which the effector cells adhere to the parasites. The findings further suggest that a key factor influencing the differential adherence of the cells to the parasites and their subsequent death may be the nature of the specific antigen-antibody interaction occurring at the surface of the larvae.