Effects of Intestinal Contents from Normal and Immunized Mice on Sporozoites of Eimeria falciformis1

The interaction of Eimeria falciformis sporozoites with the intestinal epithelium and with the intestinal contents from the cecum and colon of normal and specifically immunized mice was studied by light (LM) and scanning electron (SEM) microscopy. Fecal (FM) and enterocyte-associated (EAM) mucus were removed from the cecum and colon of normal mice and mice that had been immunized 1, 6, 12, or 20 days earlier with a series of oral inoculations of E. falciformis oocysts. Sporozoite-specific IgA, but neither IgM nor IgG, was detected by the immunofluorescent antibody test in FM and EAM from immunized mice. No sporozoite-specific immunoglobulin was detected in normal mice. When examined by LM, sporozoites exposed to all FM and EAM preparations exhibited greater motility and excystation from sporocysts. At 4 h after incubation in FM or EAM from normal or immune mice, about 10% of the sporozoites appeared damaged, being non-motile and non-refractile. Immune FM and EAM caused agglutination of sporozoites and sporocysts and oocyst walls of E. falciformis. but did not agglutinate those of E. ferrisi. Scanning electron microscopy of in vitro interactions between E. falciformis sporozoites and intestinal contents revealed that sporozoites exposed to immune EAM were coated with particulate material whereas those exposed to normal EAM were relatively clean. Sporozoites exposed to immune FM were usually embedded within the mucus whereas those exposed to normal FM were situated on top of the mucus. No significant differences occurred between the length/width (L/W) ratios of sporozoites incubated in normal FM and EAM or in PBS. Sporozoites exposed to immune FM had significantly greater L/W ratios than those exposed to normal FM whereas those exposed to immune EAM had significantly shorter L/W ratios than ones exposed to normal EAM. Few of the sporozoites observed on the luminal surface of the colon and cecum of normal mice were covered by mucus and none was altered in shape or showed pellicular damage. Only a few sporozoites were observed on the luminal surface of the colon and cecum of immunized mice. Most of these were covered by mucus and some exhibited pellicular alterations.