Excystation of Eimeria tenella Sporozoites Impaired by Antibody Recognizing Gametocyte/Oocyst Antigens GAM22 and GAM56

Division of Molecular Parasitology and Biological and Medical Research Centre, Heinrich-Heine-University, Düsseldorf, Institute of Zoology, TU-Dresden, Dresden, Animal Health Business Group, Research & Development, Bayer AG Monheim, Germany

^* To whom correspondence should be addressed. Email: kruecken{at}uni-duesseldorf.de.

	Abstract

Eimeria tenella is the causative agent of coccidiosis in poultry. Infection of chicken intestine begins with ingestion of sporulated oocysts releasing sporocysts which in turn release invasive sporozoites. The monoclonal antibody E2E5 recognizes wall-forming bodies type II (WFBII) in gametocytes and the WFBII-derived inner wall of oocysts. Here, we describe that this antibody also binds to the stieda body of sporocysts and significantly impairs in vitro excystation of sporozoites. Using affinity chromatography and protein sequence analysis, E2E5 is shown to recognize EtGAM56, the E. tenella ortholog of the Eimeria maxima gametocyte-specific GAM56 protein. In addition, this antibody was used to screen a genomic phage display library presenting E. tenella antigens as fusion proteins with gene VIII product on the surface of phagemid particles and identified the novel 22 kDa histidine- and proline-rich protein EtGAM22. The Etgam22 mRNA is predominantly expressed at the gametocyte stage as detected by Northern blotting. Southern blot analysis in combination with data from the E. tenella genome project revealed that Etgam22 is an intronless multi-copy gene with approximately 12-22 copies in head to tail arrangement. Conspicuously, Etgam56 is also intronless and is localized adjacent to another gam56-like gene, Etgam59. Our data suggest that amplification is common for genes encoding oocyst wall proteins.