Ileal and jejunal Peyer's patches play distinct roles in mucosal immunity of sheep.

The majority of pathogens enter the body through mucosal surfaces and it is now evident that mucosal immunity can provide effective disease protection. However, the induction of mucosal immunity will require efficient targeting of mucosal vaccines to appropriate mucosa-associated lymphoid tissue. An animal model, based upon the surgical preparation of sterile intestinal 'loops' (blind-ended segments of intestine), was developed to evaluate mucosal and systemic immune responses to enteric vaccines in ruminants. The effectiveness of end-to-end intestinal anastomoses was evaluated and fetal surgery did not disrupt normal intestinal function in lambs up to 6-7 months after birth. The immunological competence of Peyer's patches (PP) within the intestinal 'loops' was evaluated with a human adenovirus 5 vector expressing the gD gene of bovine herpesvirus-1. This vaccine vector induced both mucosal and systemic immune responses when injected into intestinal 'loops' of 5-6-week-old lambs. Antibodies to the gD protein were detected in the lumen of intestinal 'loops' and serum and PP lymphocytes proliferated in response to gD protein. The immune competence of ileal and jejunal PP was compared and these analyses confirmed that jejunal PP are an efficient site for the induction of mucosal immune responses. This was confirmed by the presence of gD-specific antibody-secreting cells in jejunal but not ileal PP. Systemic but not mucosal immune responses were detected when the vaccine vector was delivered to the ileal PP. In conclusion, this model provided an effective means to evaluate the immunogenicity of potential oral vaccines and to assess the immunological competence of ileal and jejunal Peyer's patches.