Chemotactic response of macrophages to Acanthamoeba castellanii antigen and antibody-dependent macrophage-mediated killing of the parasite

The chemotactic potential of antigens of Acanthamoeba castellanii for macrophages and the ability of naive and immune rat peritoneal macrophages to kill A. castellanii in vitro were assessed. The amoebolytic capacity of immune rat serum and complement was also examined. No parasite was killed in the presence of heat-inactivated naive rat serum. Low numbers of parasites were lysed in the presence of heat-inactivated immune rat serum, whereas significantly greater numbers of parasites were lysed in the presence of nonheat-inactivated naive and immune rat sernm. Macrophages from naive rats were capable of lysing some parasites. However, the amoebolytic capability of these cells was significantly increased in the presence of serum from immune rats. Regardless of the source of serum used, macrophages from immune rats demonstrated about twice the amoebolytic proficiency of cells from naive rats. Macrophages from naive rats showed their highest capacity for lysing amoebae when incubated in the presence of gamma interferon and immune rat serum. The greatest overall proficiency in lysing parasites was displayed by cells from immune rats incubated with A. castellanii in the presence of gamma interferon and nonheat-inactivated serum from immune rats. The results indicate that low numbers of parasites lyse in the presence of anti-A. castellanii antibody alone; that the parasite activates the alternate complement pathway, which results in complement-mediated lysis of significant numbers of A. castellanii; that a substantial component of the ability of both naive and immune macrophages to lyse the parasite is anti-A castellanii antibody dependent; and, that gamma interferon dramatically activates macrophages from both immune and naive rats in terms of their ability to lyse the parasite. The chemotactic response of macrophages from naive and immune rats to zymosan-activated rat serum (ZAS), medium alone, or A. castellanii antigen was examined. In terms of their response to ZAS, cells from immune rats showed a greater chemotactic response than did cells from naive rats. The chemotactic response of these 2 groups of cells was similar to medium alone and to parasite antigen. Parasite antigen did not alter the chemotactic response of naive rat cells to ZAS. These results suggest that macrophages from both naive and immune rats are attracted to the antigen of the parasite.