Intestinal Microbiota as Modulators of the Immune System

The gastrointestinal immune system is exposed to a large amount of different products mainly innocuous (derived from “friendly” bacteria and/or food antigens) but sometimes also dangerous and infectious (as invading bacteria or viruses). Despite that, it is effective in discriminating between them and hence maintaining immune tolerance against the natural inhabitants of our gut, but initiating immune responses against the harmful invading microorganisms [1, 2]. In the last decades, the western lifestyle has seen an increase in the prevalence of immunoregulatory disorders which has been linked to changes in the microbiota composition due to the increased use of antibiotics and the absence of intestinal parasites as proposed in the “hygiene hypothesis.” Indeed, the immune system has become more dependent upon the microbiota and the natural environment [3]. However, recent data indicate that helminth-induced immunomodulation occurs independently of changes in the microbiota [4].