In vitro interactions between murine macrophages and Eimeria falciformis sporozoites

A short-term (2 h) assay was used to investigate the in vitro fate of Eimeria falciformis sporozoites in murine peritoneal macrophages. In minimal medium, uptake of sporozoites was low by both normal (naive) and immune macrophages. However, when heat-inactivated serum from immune mice was added to the incubation medium, sporozoite uptake was much more efficient. Sporozoite lysis was observed only in immune macrophages and required both antibodies and complement. Pretreatment of immune macrophages with chloroquine inhibited sporozoite lysis and resulted in an accumulation of sporozoites within the cells. Immunoabsorption assays revealed that IgG2a was the major isotype mediating entry of sporozoites into macrophages, both in early (6 days post-primary) and late (second) infections.