A monoclonal antibody reacts species-specifically with amylopectin granules of Eimeria bovis merozoites

Abstract

An IgG1 monoclonal antibody (mAb 35B9) developed against first-generation merozoites of Eimeria bovis was shown by immunoelectron microscopy to react selectively with antigens localized in amylopectin granules. Amylopectin does not contribute to the epitope, as enzymatic degradation of carbohydrates in the parasite did not alter the binding pattern of mAb 35B9. When tested by immunoblotting, despite its organelle specificity the mAb recognized a variety of E. bovis merozoite I components with predominant molecules of 135 and 200 kDa. The epitope was not affected by treatment with endoglycosidase H; thus, N-linked sugar residues should not be involved in it. Alkaline cleavage (beta-elimination), however, destroyed the epitope; thus, the involvement of O-linked carbohydrates cannot be excluded. Treatment of E. bovis merozoite extract with phospholipase C changed the binding pattern of mAb 35B9 in a way that suggests the presence of phosphorylcholine molecules on several antigens recognized by the mAb, albeit not belonging to the epitope but rather masking it. The epitope was not found in free sporozoites of E. bovis or young intracellular parasites up to day 4 after invasion of cells in vitro, whereas 5-day-old trophozoites were found to contain it. It seems to be species-specific, as it could not be shown in sporozoites or merozoites of E. tenella or in stages of several other Coccidia.