Multiple intestinal 'loops' provide an in vivo model to analyse multiple mucosal immune responses

Mucosal immunity plays an important role in preventing disease but the indu ction of protective mucosal immune responses remains a significant challeng e. We describe a novel in vivo model to analyze the induction of multiple m ucosal immune responses in the small intestine. A sterile segment of intest ine ('intestinal-segment'; 2-3 m long) was surgically prepared in the jejun um of 4-6-month-old lambs. This 'intestinal-segment' was then subdivided in to consecutive segments, designated as 'loops' (15-20 cm long), that includ ed a Peyer's patch (PP), or 'interspaces' (15-70 cm long), that lacked a vi sible PP. All 'loops' were sterile when collected 1-4 weeks post-surgery an d there was no macroscopic or histological evidence of altered lymph or blo od flow. Flow cytometric analysis of cells isolated from PP, mucosal epithe lium (IEL) and the lamina propria (LPL) revealed no significant alterations in the cell populations present in 'loop' tissues. The functional integrit y of M-cell antigen uptake in sterile intestinal 'loops' was evaluated by c omparing the immune response induced by varying doses of soluble versus par ticulate porcine serum albumin (PSA formulated in alginate microspheres). A dose-dependent, PSA-specific antibody-secreting cell response was restrict ed to PP present in 'loops' injected with particulate PSA. These observatio ns suggested that PP present in sterile 'loops', were functional and this c onclusion was confirmed by detecting cholera toxin-specific antibody-secret ing cells and secreted antibody in PP and intestinal contents, respectively , of immunized 'loops.' Thus, each 'loop' provided an independent site to a nalyze antigen-uptake and the induction of mucosal immune responses by a va riety of antigen or vaccine formulations. (C) 2001 Elsevier Science B.V. Al l rights reserved.