Inhibition of the in vitro development of Eimeria tenella in chick kidney cells by immune chicken splenocytes.

An in vitro microbicidal assay was used to study the immune response of chickens to Eimeria tenella by measuring the effect of splenocytes from immunized chickens on intracellular development of E. tenella. Splenocytes were prepared from specific-pathogen-free chickens [strain P2a(B19B19) or N2a(B21B21)], immunized one, two, or three times with non-lethal doses of E. tenella. Twelve hours following infection of chick kidney cells (CKCs) with E. tenella sporozoites, splenocytes were added to infected CKCs for 4, 8, or 36 hours. Intracellular E. tenella development was allowed to continue until 72 hours after sporozoite infection, when intracellular development was quantitated by counting merzoites. Immune splenocytes significantly inhibited E. tenella intracellular development after one, two, or three immunizations. Significant inhibition occurred with 4, 8, or 36 hours of coculture and was no greater with longer co-culture times. Immune P2a splenocytes significantly reduced merozoite development in both syngeneic P2a and allogeneic N2a infected CKCs, whereas immune N2a splenocytes had little effect on E. tenella development in either N2a or P2a infected CKCs. These results suggest that immune splenocytes are induced and act relatively rapidly and are not apparently restricted by the major histocompatibility complex, consistent with natural killer cell activity.