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

Abstract

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.

Figure 1

Comparison of PP tissue in ileal and jejunal ‘loops’ and the adjacent intestine of an 8-week-old lamb. HAd5-gD/E3 vector was injected into the intestinal ‘loops’ 3 weeks prior to tissue collection. Lymphoid follicles in normal ileal PP (a) were larger and more cellular than lymphoid follicles present in an immunized ileal ‘loop’ (b). Lymphoid follicles in normal jejunal PP (c) and the PP contained in a jejunal ‘loop’ (d) were similar in size and cellularity. However, there was a marked corona of cells in the dome region of follicles present in the immunized jejunal ‘loop’.

Figure 2

The gD-specific responses in ileal and jejunal PP following immunization with the HAd5-gD/E3 vector. The vector was injected either subcutaneously (s.c.) or directly into intestinal ‘loops’ that lacked a PP (non-PP) or contained either a jejunal (jej PP) or ileal (ileal PP) PP. (a) gD-specific proliferative responses were present only in jejunal PP isolated from intestinal ‘loops’ injected with the adenovirus vector. (b) The gD-specific antibody titre was measured by an ELISA that measured total antibody. Significantly higher antibody titres were detected in jejunal PP ‘loops’ injected with the adenovirus vector. (c) gD-specific ASC were measured by an ELISPOT. ASC were detected in jejunal but not ileal PP isolated from intestinal ‘loops’ injected with the adenovirus vector. Horizontal bars indicate mean value for each group and values for individual lambs are presented.

Figure 3

The gD-specific immune responses in 8–9-week-old lambs immunized by injecting HAd5-gD/E3 either subcutaneously (s.c.) or into intestinal ‘loops’ [non-Peyer’s patch ‘loop’ (non-PP), jejunal PP ‘loop’ (jej PP) and ileal PP ‘loop’ (ileal PP)]. Lambs were killed 3–4 weeks after immunization. (a) Antibody titre in serum were determined with an ELISA that detected total gD-specific antibody. (b) Stimulation index in splenocytes was determined by [³H]thymidine incorporation. Horizontal bars indicate mean value for each group and values for individual lambs are presented.