Dietary plasma proteins, the intestinal immune system, and the barrier functions of the intestinal mucosa

The intestinal mucosa contributes to homeostasis by preventing the entrance of biological and chemical agents across the epithelium that could alter the stability of the system. This protective function is especially important at the time of weaning, when animals are exposed to infectious agents and to numerous stresses such as the change of environment and diet. Diets supplemented with spray-dried plasma or plasma protein fractions have been shown to improve growth performance of farm animals and have been proposed as an alternative to antibiotics. In this review, we summarize our findings on the mechanism of action of dietary plasma proteins using a rat model of intestinal inflammation, based on the administration of Staphylococcus aureus enterotoxin B (SEB). Staphylococcal enterotoxin B activates the gut-associated lymphoid tissue (GALT), increasing T-lymphocytes in Peyer's patches and the number of activated T lymphocytes in mesenteric lymph nodes (organized GALT). In the lamina propria SEB increased cytotoxic T gammadelta and natural killer cell populations of the diffuse GALT. Staphyloccocal enterotoxin B significantly increased proinflammatory cytokines in Peyer's patches and mucosa. Plasma protein supplements modulated the mucosal immune response in organized and diffuse GALT, protecting GALT from possible excessive activation by the SEB challenge. These effects are accompanied by a reduction of proinflammatory cytokine production, supporting the view that changes in cytokine production mediate the effects of dietary plasma proteins during intestinal inflammation. The increase in mucosal permeability and intestinal secretion induced by SEB was associated with decreased expression of mucosal tight-junction and adherent-junction proteins. Both plasma and plasma protein fractions prevented the effects of SEB on intestinal permeability, thus reducing the exposure of the host to microbial and food antigens across the interstitial space. These findings indicate that dietary plasma proteins modulate functional and structural properties of the intestinal mucosa.