Microbiota, regulatory T cell subsets, and allergic disorders

Epidemiologic studies revealed a crucial role of the environment for the increased prevalence of allergic disorders. The microbiota as part of our immediate environment promotes immune diversity that facilitates a well-equilibrated balance between immunity and tolerance. Alterations of our symbiotic microbiota especially in early life is thought to play a fundamental role in defining susceptibility to the development of allergic diseases during adult life on the population level. Due to a high density of bacteria, viruses and fungi and a large contact surface area for host-microbiota interactions, the most relevant interaction between microbes and our immune system are thought to occur in the gut. The immune system co-evolved with the symbiotic microbiota and adopted a variety of mechanisms to allow a dynamic state of tolerance, including the induction of regulatory T cells (Tregs). Foxp3-expressing Tregs are well-described immune regulators in autoimmune and allergic disorders. However, recent years have shown that Tregs can come in different flavours with different regulatory potential and outcome for our immune system. This review summarizes novel findings from basic immunology research that may help to better understand the interaction between the microbiota, differentiation of Tregs and its consequences for the onset and regulation of allergic disorders.