A chicken anti-conoid monoclonal antibody identifies a common epitope which is present on motile stages of Eimeria, Neospora, and Toxoplasma

The chicken monoclonal antibody (mAb) 6D12-G10, raised against Eimeria acervulina sporozoites, has previously been shown to recognize the conoid of E. acervulina sporozoites and inhibit sporozoite invasion of lymphocytes in vitro. In indirect immunofluorescent assay, the mAb 6D12-G10 also reacted with merozoites from E. acervulina and identified a 21-kDa merozoite protein on western blots. By confocal laser scanning microscopy, the conoid of sporozoites from 6 different avian Eimeria species (E. brunetti, E. maxima, E. mitis, E. necatrix, E. praecox, and E. tenella) were reactive with 6D12-G10 mAb. Furthermore, the 6D12-G10 mAb also showed cross-reactivity with motile stages of 2 closely related apicomplexans, Neospora, and Toxoplasma. These results indicate that the mAb 6D12-G10 identifies a conserved epitope on the conoid that is important in host cell invasion by the apicomplexan parasites.