In immunocompetent mice, it was shown that while two consecutive airway exposures to A. fumigatus conidia stimulate neutrophil and macrophage recruitment to the lung and prime a Th1 response to the fungus, repeated exposures to A. fumigatus conidia does not result in invasive aspergillosis or fatal disease, but does result in the development of chronic pulmonary inflammation

[74] mediated by Th2 and Th17 responses. Therefore, it is likely that repeated pulmonary exposure to A. fumigatus conidia eventually leads to immune homeostasis and the induction of non-T-cell regulatory pathways that result in the least possible tissue damage while still controlling conidial germination [75, 76]. Candida albicans has been shown to have the capacity to “train” innate immunity toward other microorganisms,

selleck chemicals such as intestinal and skin bacteria [77-79]. Furthermore, Saccharomyces cerevisiae, this website previously considered a transient microorganism in the intestinal tract, has been increasingly reported to be present in the human skin as well [17, 80-82]. We recently observed that the presence of S. cerevisiae among the gut microbiota “educates” the host immune response by means of training the immune system to better cope with a secondary infection (Rizzetto et al., unpublished and De Filippo et al., unpublished). The immunomodulatory role of commensal organisms has been formalized by the “hygiene hypothesis,” which suggests that reduced early exposure to microorganisms is the main cause of the early onset of autoimmune or chronic inflammatory disorders in the industrialized world [83]. Several microorganisms, including

some Clostridium spp., have been shown to drive immunoregulation and to block or treat allergic and autoimmune disease and IBD [84-86]. The immunoregulatory mechanisms used by several bacteria, such as Bacteroides fragilis, Clostridium [84], or by helminths [85] are based on the specific induction of Treg cells in the colon or skin, or by the induction of regulatory DCs [87]. triclocarban We speculate that an overall reduction in early exposure of humans to beneficial microbiota is not simply causing a reduction in anti-inflammatory signals but is more importantly decreasing the “training” of our immune system to handle pathogenic microorganisms, possibly resulting in uncontrolled immune responses. Collectively, these findings show that eukaryotic and prokaryotic communities are kept in equilibrium by mutual interactions that include the production of immune modulating molecules, helping to accommodate fungi, either commensals or ubiquitous, within the immune homeostasis and its dysregulation. The skin represents the primary interface between the human host and the environment. Cutaneous inflammatory disorders such as psoriasis, atopic dermatitis (AD), and rosacea have been associated with dysbiosis in the cutaneous microbiota [88, 89].