Intestinal Regulatory CD4+ T Cells

Abstract The immune system protects the host from invasion by microorganisms, such as bacteria, viruses, and fungi. Interestingly, certain microorganisms live intimately associated with our body, for example, in the lumen of the intestine (commensals), establishing a mutualistic relationship with the host. Usually the immune system does not respond to the commensal organisms and it is even educated by this unique combination of microorganisms. The intestine is indeed the place where regulatory T cells are abundant and where mainstream T cells can be programmed into regulatory T cells; thus, it is a site important for the maintenance of immune homeostasis. This chapter focuses on CD4 + regulatory T cells present in the intestine and how they work in concert to maintain the equilibrium of the immune response.