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The probiotic effects ascribed to lactic acid bacteria (LAB) and their fermented dairy products arise not only from whole microor- 14 ganisms and cell wall components but also from peptides and extracellular polysaccharides (exopolysaccharides) produced during theganisms and cell wall components but also from peptides and extracellular polysaccharides (exopolysaccharides) produced during the 15 fermentation of milk. There is a lack of knowledge concerning the immune mechanisms induced by exopolysaccharides produced by lac-fermentation of milk. There is a lack of knowledge concerning the immune mechanisms induced by exopolysaccharides produced by lac- 16 tic acid bacteria, which would allow a better understanding of the functional effects described to them. The aim of this study was totic acid bacteria, which would allow a better understanding of the functional effects described to them. The aim of this study was to 17 investigate the in vivo immunomodulating capacity of the exopolysaccharide produced by Lactobacillus kefiranofaciens by analyzinginvestigate the in vivo immunomodulating capacity of the exopolysaccharide produced by Lactobacillus kefiranofaciens by analyzing 18 the profile of cytokines and immunoglobulins induced at the intestinal mucosa level, in the intestinal fluid and blood serum. BALB/cthe profile of cytokines and immunoglobulins induced at the intestinal mucosa level, in the intestinal fluid and blood serum. BALB/c 19 mice received the exopolysaccharide produced by L. kefiranofaciens for 2, 5 or 7 consecutive days. At the end of each period of admin-mice received the exopolysaccharide produced by L. kefiranofaciens for 2, 5 or 7 consecutive days. At the end of each period of admin- 20 istration, control and treated mice were sacrificed and the numbers of IgA+ and IgG+ cells were determined on histological slices of theistration, control and treated mice were sacrificed and the numbers of IgA+ and IgG+ cells were determined on histological slices of the 21 small and large intestine by immunofluorescence. Cytokines (IL-4, IL-6, IL-10, IL-12, IFNc and TNFa) were also determined in the gutsmall and large intestine by immunofluorescence. Cytokines (IL-4, IL-6, IL-10, IL-12, IFNc and TNFa) were also determined in the gut 22 lamina propria as well as in the intestinal fluid and blood serum. There was an increase of IgA+ cells in the small and large intestinelamina propria as well as in the intestinal fluid and blood serum. There was an increase of IgA+ cells in the small and large intestine 23 lamina propria, without change in the number of IgG+ cells in the small intestine. This study reports the effects of the oral administrationlamina propria, without change in the number of IgG+ cells in the small intestine. This study reports the effects of the oral administration 24 of the exopolysaccharide produced by L. kefiranofaciens in the number of IgA+ cells in the small and large intestine, comparing simul-of the exopolysaccharide produced by L. kefiranofaciens in the number of IgA+ cells in the small and large intestine, comparing simul- 25 taneously the production of cytokines by cells of the lamina propria and in the intestinal fluid and blood serum. The increase in the num-taneously the production of cytokines by cells of the lamina propria and in the intestinal fluid and blood serum. The increase in the num- 26 ber of IgA+ cells was not simultaneously accompanied by an enhance of the number of IL-4+ cells in the small intestine. This findingber of IgA+ cells was not simultaneously accompanied by an enhance of the number of IL-4+ cells in the small intestine. This finding 27 would be in accordance with the fact that, in general, polysaccharide antigens elicit a T-independent immune response. For IL-10+,would be in accordance with the fact that, in general, polysaccharide antigens elicit a T-independent immune response. For IL-10+, 28 IL-6+ and IL-12+ cells, the values found were slightly increased compared to control values, while IFNc+ and TNFa+ cells did notIL-6+ and IL-12+ cells, the values found were slightly increased compared to control values, while IFNc+ and TNFa+ cells did not 29 change compared to control values. The effects observed on immunoglobulins and in all the cytokines assayed in the large intestine afterchange compared to control values. The effects observed on immunoglobulins and in all the cytokines assayed in the large intestine after 30 kefiran administration were of greater magnitude than the ones observed in the small intestine lamina propria, which may be due to thekefiran administration were of greater magnitude than the ones observed in the small intestine lamina propria, which may be due to the 31 saccharolytic action of the colonic microflora. In the intestinal fluid, only IL-4 and IL-12 increased compared to control values. In bloodsaccharolytic action of the colonic microflora. In the intestinal fluid, only IL-4 and IL-12 increased compared to control values. In blood 32 serum, all the cytokines assayed followed a pattern of production quite similar to the one found for them in the small intestine laminaserum, all the cytokines assayed followed a pattern of production quite similar to the one found for them in the small intestine lamina 33 propria. We observed that the exopolysaccharide induced a gut mucosal response and it was able to up and down regulate it for pro-propria. We observed that the exopolysaccharide induced a gut mucosal response and it was able to up and down regulate it for pro- 34 tective immunity, maintaining intestinal homeostasis, enhancing the IgA production at both the small and large intestine level and influ-tective immunity, maintaining intestinal homeostasis, enhancing the IgA production at both the small and large intestine level and influ- 35 encing the systemic immunity through the cytokines released to the circulating blood.encing the systemic immunity through the cytokines released to the circulating blood.