Host defense mechanisms against nematode parasites: destruction of newborn Trichinella spiralis larvae by human antibodies and granulocytes.

The capacity of human leukocytes from normal donors to kill the nematode Trichinella spiralis in vitro in the presence of serum from infected individuals and complement was studied. Eosinophils and neutrophils attached to the newborn larval stage of the parasite and exerted a cytotoxic effect manifested as complete morphologic destruction of the organism; monocytes also attached to newborn larvae but did not mediate parasite destruction. The cytotoxic effect of granulocytes was dependent on the presence of parasite stage-specific IgG antibodies that appeared within three weeks of infection; these antibodies were distinct from IgM antibodies that reacted with muscle-stage larvae. Complement did not enhance the cytotoxic effect of granulocytes. These results suggest that host defense against T. spiralis in humans is in part mediated by granulocytes and dependent on the presence of IgG antibodies that are directed against the migratory stage of the parasite.