Chick intestinal immunity: a novel in vitro response of the pre-immune mucosal epithelium to Eimeria antigen exposure

Abstract

Selected physiologic changes of the chicken intestinal mucosa, in response to Eimeria infection, were investigated in the following studies. This manuscript describes local secondary immune response mechanisms associated with immunization or infection by Eimeria species. Specifically, in vitro secretory activity of the mucosal epithelium, as elicited by in vitro exposure of the intestinal mucosa to Eimeria protein antigens, with or without prior in vivo Eimeria immunization strategies in chickens was investigated. To measure in vitro correlates of intestinal immunity in chickens, Ussing-type clambers were used to measure ion secretion in the gut in response to mucosal exposure of the tissue with antigen. In the present investigation, measurements of ion secretion in chicken intestinal mucosal epithelium were compared to more traditional measures of coccidial immunity, gross lesion scores, as described by Johnson and Reid (1970), and body weight gain. Commercial broiler chicks were immunized with one of two commercially available coccidial vaccines. Results obtained from chickens in either of the two immunized groups, and a non-immunized control group, were compared to determine efficacy of immunization by evaluating lesion scores, body weight gains, and in vitro responsiveness of the mucosal epithelium to antigenic exposure. Following three successive immunizations of increasing immunogen, chicks designated for lesion scoring and body weight gain evaluation were challenged with 2.5 X 10⁴ locusts of one of two primary poultry isolates of Eimeria maxima. An additional subgroup from each immunized or non-immunized group was not challenged with field-strain Eimeria maxima and sections of small intestine from these chickens were subjected to antigen exposure in Ussing chambers for observation of in vitro correlates of intestinal immunity to coccidia. While not all results obtained in the present investigation tested to be statistically different, several interesting biological trends were observed. A high-degree of in vitro responsiveness of the chicken mucosal epithelium to coccidial antigenic challenge was associated with overall lower gross-lesion scores and increased body weight gains, when immunized groups of chickens were compared with non-immunized groups. These data suggest that measurable changes in the mucosal immune system, in response to coccidial antigen exposure are potentially associated with other, more traditional measures of coccidial immunity in chickens.