Intraperitoneal immunization promotes local intestinal immunity in chickens

The limited success in stimulating protective immunity in the intestine by traditional vaccination approaches has led to the search for novel strategies to improve intestinal immunity. In mammalian species we have demonstrated that whereas oral immunization produces poor intestinal responses, immunization by the intraperitoneal route using appropriate formulations is an effective means of priming the intestinal lymphoid tissue for an enhanced mucosal response to orally administered antigen. In the experiments reported here we extend these findings to chickens and compare the intestinal IgA response to a non-replicating antigen administered by the oral route alone or in oil emulsion formulations administered subcutaneously or intraperitoneally with or without oral boosting. Despite repeated daily dosing, oral immunization of unprimed animals produced only a small intestinal response. However, priming by the intraperitoneal route with antigen in either Freund's adjuvant or a biodegradable oil-in-water emulsion (Auspharm adjuvant) resulted in a markedly improved response, especially when additional oral boosting was given. The data also demonstrate that Quil A, a saponin derivative, further boosts the response when co-administered with the oil emulsion intraperitoneally. This study illustrates the efficacy of systemic immunization by the intraperitoneal route in priming for an intestinal IgA response in chickens.