CONICET | Buscador de Institutos y Recursos Humanos

Background: The gastrointestinal tract is one of the most microbiologically active ecosystems that play a crucial role in the working of the Mucosal Immune System (MIS). In this ecosystem, probiotic microorganisms that enter orally stimulate the Immune System and induce a network of signals mediated by the whole bacteria or their cell wall structure. The aim of this review is to describe the immunological mechanisms probiotics set in to display beneficial effects on the host.Summary: Once administered, oral probiotic bacteria interact with the intestinal epithelial cells (IECs) or immune cells associated to the lamina propria, through Toll like receptors (TLRs), and induce the production of different cytokines or chemokines. MCP1 (macrophage chemoattractant 1) produced by the IECs, sends signals to other immune cells leading to the activation of the MIS, characterized by an increase in IgA+ cells of the intestine, bronchus and mammary glands, and the activation of T cells Specifically, probiotics activate regulatory T cells that release IL-10. Interestingly, probiotics reinforce the intestinal barrier by an increase of the mucins, the tight junction proteins and the Goblet and Paneth cells. Accordingly, another proposed mechanism of probiotics is the modulating of intestinal microbiota by maintaining the balance and suppressing the growth of potential pathogenic bacteria in the gut. Furthermore, it has been demonstrated that long-term probiotics consumption does not affect the intestinal homeostasis.Probiotics viability is crucial in the interaction with the epithelial cells and macrophages favoring, mainly, the innate immune response. Macrophages and DCs play an important role in this immune response without inducing an inflammatory pattern, just a slight increase in the cellularity of the lamina propria. Besides, as part of the machinery that probiotics activate to protect against different pathogens, an increase in the microbicidal activity of peritoneal and spleen macrophages has been reported.In malnutrition models, Iike undernourishment and obesity, probiotic administration was able to increase the intestinal and systemic immune response of the mice. Besides, probiotics contribute to recover the histology of both the intestine and the thymus damaged in these disorders.Probiotic bacteria are emerging as a safe and natural strategy for allergy prevention and treatment. Different mechanisms such as the generation of cytokines from activated pro‐T‐helper type 1 which favour the production of IgG instead of IgE have been proposed.

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