Eimeria acervulina: cloning of a cDNA encoding an immunogenic region of several related merozoite surface and rhoptry proteins.

A cDNA encoding a recombinant Eimeria acervulina antigen, designated EAMZp30-47, that contains an epitope shared among several surface and rhoptry proteins of merozoites was characterized. The respective parasite proteins are between 30 and 47 kDa as revealed by immunostaining of nitrocellulose membrane containing extracts of 125I-labeled merozoites. As indicated by immunofluorescence and immunoelectron microscopic staining, the reactive epitope was localized to both the surface membrane and the internal rhoptries of this asexual stage of the parasite. The recombinant beta-galactosidase fusion protein EAMZp30-47 is 130 kDa, thus representing 15 kDa or 30-50% of the respective parasite protein. Purified EAMZp30-47 stimulates T cells from E. acervulina-immune inbred chickens, but is not recognized by immune chicken serum, suggesting that T cell and not B cell epitopes recognized by the host immune system during a natural infection are present on the recombinant protein. Northern and Southern blot hybridization experiments indicated that expression of EAMZp30-47 is restricted to the merozoite stage of the parasite and the gene occurs as a single copy sequence within the genome.