Effect of Gram positive and Gram negative indigenous and exogenous bacteria in the gut immunomodulation.

DOGI, C; PERDIGÓN, G

Boston, Massachusetts, USA

Congreso; 12th International Congress of Mucosal Immunology, Boston, Massachusetts, USA; 2005

Background: There is an intimate relationship between the normal gastrointestinal flora and the associated immune cells. This microflora is essential for the maturation of the immune system. Methods: We analyzed comparatively the effect on the gut immunomodulation between Gram + and Gram - indigenous and exogenous bacteria in BALB/c mice. Mice were fed during 2, 5 or 7 days with L. fermentum and L. acidophilus indigenous (104 CFU) and exogenous (108 CFU) and E. coli indigenous and exogenous (106 CFU/day/mouse). The daily dose was selected by determination of absence of the bacterial translocation to liver or spleen. The numbers of IgA, IL10, IL17 and MIP1a positive cells in the lamina propria of small intestine were determined by indirect immunofluorescence. These markers were selected considering that IgA is the main antibody at the mucosal surfaces, and due to the biological role of DC which in the lamina propria of the intestine are activated by luminal bacterial antigens. Some of these antigens induce to DC to produce IL23 which stimulates T cells to proliferate and produce inflammatory IL17, MIP1a, is a proinflammatory chemokine produced by DC and macrophages, and IL10 as regulatory cytokine. Result: We observed that Gram+ and Gram- indigenous and exogenous bacteria were able to increase the number of IgA+ cells compared with the unfed control. IL10 was increased by Gram+ bacteria and these bacteria did not increase the number of IL17 or MIP1a. In contrast exogenous E. coli, ƒnbut not indigenous, produced high levels of IL17 and MIP1a. This microorganism did not induce IL10. Conclusions: Exogenous and endogenous Gram+ bacteria as well as indigenous, E. coli would be more involved in the regulatory mechanisms, while exogenous E. coli would have a proinflammatory effect. In spite of these results, they are not excluding, and Gram+ bacteria would also be able to induce an inflammatory response as a way to initiate the innate immunity or bowel inflammatory diseases.