CONICET | Buscador de Institutos y Recursos Humanos

The intestine is a complex environment where it coexists a dynamic community of microorganisms called microbiota. The microorganisms reside in the intestine in harmony with the host cells (1) and the establishments of these microorganisms are essential for the development of the immune system. The local effects of the microbiota on gut homeostasis (2) and gut immune development have been delineated (3, 4); however, studies have addressed the systemic effect of the microbiota (5) as a result of the translocation of it from the gut lumen into the circulation, but the mechanisms involved are still poorly understood (6). Studies performed in the laboratory using conventional BALB/C mice showed that the administration of the probiotic bacterium: Lactobacillus casei (L. casei) CRL431 not only exerted activation of the innate immunity in the gut but also had effect in the systemic immunity response with enhanced of the phagocytic activity of peritoneal macrophages. Previous studies demonstrated that the TLR, principally the TLR2, are involved in the intestinal signals initiated when probiotic bacteria were administrated to conventional mice in the drinking water (7). In the present work we investigated the capacity of a probiotic bacterium to modulate the macrophage activation using TLR2-, TLR4- or the MyD88- deficient mice involved in the innate immunity. We also evaluated the systemic immune response by measured the IgG anti-Ovalbumin. Mice were given with the probiotic bacterium L. casei CRL 431 in the drinking water during 7 consecutive days or with a commercial probiotic fermented milk (5 days). After that, by ex vivo assays we evaluated the phagocytic activity of peritoneal macrophages. Other groups of animal previously administered with the probiotic bacterium or with the PFM were sensitized with three subcutaneously injections of 1% ovalbumin, the blood samples were obtained 10 days after the last injection. Ex vivo results showed that TLR2, TLR4 and the adaptor molecules MYD88 were involved in the phagocytic process of probiotics and the phagocytosis and the probiotic administration could not improve the macrophages phagocytic activity. In vitro results obtained from IL-10 production by macrophages following probiotics treatment since only MyD88 is required in the production of this cytokine. The results showed that the levels of anti-Ovalbumin IgG were dependent of the TLR2 or TLR4 or MyD88 expression being dispensable for this activation. Taken together, our results which show a critical role of the TLR/MyD88 signaling pathway in both the some innate immune responses and in the IL-10 response induced by L. casei, also suggest that TLR/MyD88-independent mechanisms participate to the immunomodulation induced by probiotics. Reference 1- Hooper LV, Gordon JI. (2001). Commensal host-bacterial relationships in the gut. Science. 292(5519), 1115-8. 2- Rakoff-Nahoum, S., Paglino, J., Eslami-Varzaneh, F., Edberg, S. & Medzhitov, R. (2004) Recognition of commensal microflora by Toll-like receptors is required for intestinal homeostasis. Cell 118, 229241. 3- Hall, J.A. et al. (2008). Commensal DNA limits regulatory T cell conversion and is a natural adjuvant of intestinal immune responses. Immunity 29, 637-649 4- Uematsu, S. et al. (2008). Regulation of humoral and cellular gut immunity by lamina propria dendritic cells expressing Toll-like receptor 5. Nat. Immunol. 9, 769-776 5- Mazmanian, S.K., Liu, C.H., Tzianabos, A.O. & Kasper, D.L. (2005).An immunomodulatory molecule of symbiotic bacteria directs maturation of the host immune system. Cell 122, 107-118 6- Macpherson AJ, Harris NL. (2004). Interactions between commensal intestinal bacteria and the immune system. Nat Rev Immunol. 4(6), 478-85. 7- Maldonado Galdeano, C. & Perdigón, G. (2006).The probiotic bacterium Lactobacillus casei induces activation of the gut mucosal immune system through the innate immunity. Clinical and Vaccine Immunol. 13 (2), 219-226.