Submitted to: Experimental Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 9, 1994
Publication Date: N/A
Interpretive Summary: Coccidiosis is a parasitic disease of many avian species that causes an estimated $350 million annual loss to U.S. poultry producers. Although the disease is being controlled by anti-coccidial drugs, many drug-resistant strains of the parasite emerge making this type of treatment ineffective. For this reason and the exorbitant cost of producing new anti-coccidials (>$20 million per drug) thre is great interest in developing alternative methods of controlling the disease. The present study shows that coccidian parasites that are exposed to high dose of gamma irradiation are rendered incapable of eliciting protective immunity against challenge infection. Parasites that have either not been exposed or have been exposed to low levels of gamma irradiation are capable of inducing a protective immune response. It appears also that "protective" forms of the parasite are metabolically active within avian cells and produce metabolites that are not produced by "non-protective" forms of the parasite. These studies indicate which developmental stage of the parasite is important in the protective immune response and at least one antigen that is produced during infection of avian cells. Attempts to produce vaccines by genetic engineering techniques can now concentrate on obtaining genes and proteins from these particular developmental stages of the parasite.
Eimeria tenella sporozoites were exposed in the oocyst form to either an optimum (15 kRad) or a high (25 kRad) dose of gamma irradiation and used to infect cultured chicken embryo fibroblasts (CEF). The sporozoite-infected monolayer was pulsed at time of infection or 24 h post-infection with 3H-uracil and harvested 24 h later to measure sporozoite metabolic activity ySporozoites exposed to either 0 or 15 kRad gamma irradiation incorporated similar (P > .05) amounts of 3H-uracil during the first and second 24 hr period after infection. However, there was a significant decrease (P< .05) in 3H-uracil uptake by 25 kRad exposed-sporozoites compared to non- irradiated and 15 kRad-irradiated sporozoites. Indirect immunofluorescence (IFA) staining of E. tenella sporozoite-infected CEFs using monoglonal antibodies (MAb) specific for somatic or "metabolic" antigens showed that gamma irradiation also affected the release of intracellular metabolites. Regardless of irradiation dose, extracellular sporozoites exhibited simlar antigen- or metabolic antigen-reactive MAb. Also, somatic antigen expression was similar for intracellular parasites irrespective of radiation dose. However, metabolic 7-10 kDa antigen expression by 25 kRad- irradiated sporozoites was markedly reduced compared to non-irradiated or 15 kRad-irradiated intracellular sporozoites. These results were corroborated by immunostaining sporozoite/CEF protein-impregnated Immobilon membrane with somatic or metabolic 7-10 kDa antigen-reactive MAb. These findings may indicate that the metabolic 7-10 kDa antigen is involved in protective immunity elicited by non-irradiated and/or 15 kRad-irradiated E. tenella sporozoites.