Microneme antigens of Eimeria bovis recognized by two monoclonal antibodies

Abstract

Two IgG1 monoclonal antibodies (mAbs 8-23F9 and 9-21G9) were developed after immunization of mice with homogenates of Eimeria bovis first-generation merozoites. Both mAbs reacted with antigens in the apical two-thirds of the parasites and immune electron microscopy determined the micronemes as targets. When tested by immunoblotting, mAb 8-23F9 failed to react with antigens separated under reducing conditions; under nonreducing conditions it recognized two components of >200 kDa. mAb 9-21G9 bound to antigens of 135 and 180 kDa after electrophoresis under reducing conditions and to a series of components when separated without reduction. The epitope of mAb 8-23F9 was destroyed by treatment of the antigen with endoglycosidase H and removal of phosphocholine (PC) by phospholipase C. Since mAb 8-23F9 does not recognize cytidine-linked PC, the data suggest that PC in combination with N-linked sugars and/or N-glycans is part of its epitope. In the case of mAb 9-21G9, endoglycosidase H did not alter the epitope. When E. bovis merozoite antigen was treated with phospholipase C the number of mAb 9-21G9-reactive constituents increased, suggesting that PC may otherwise mask the epitope. mAb 8-23F9 also bound to the apical area and the surface of E. bovis sporozoites and recognized a >200-kDa sporozoite component. When sporozoites invaded Vero cells in vitro, epitope-bearing components were released onto the host cell surface and became part of the early parasitophorous vacuole wall. At day 5 the binding of the mAb was again confined to the intracellular parasite. mAb 9-21G9 did not react with sporozoites but recognized the apical area of intra-cellular trophozoites on day 5 after invasion of host cells in vitro. When testing was done against a variety of other Apicomplexa in various assays, the only cross-reaction observed occurred with mAb 8-23F9, which bound to a conformationally determined 180-kDa component of Toxoplasma gondii cystozoites.