Control of lymphocyte homeostasis and effector function by the aryl hydrocarbon receptor

• AhR is widely expressed in adaptive and innate lymphocytes.
• AhR controls the homeostasis and effector function of adaptive lymphocytes such as Th17, Th22, Treg and plasma cells.
• AhR controls the homeostasis and effector function of innate-like or innate lymphocytes such as γδ T cells and ILC3s.
• AhR enables both adaptive and innate lymphocytes to sense environmental cues through AhR ligands.

The adaptive immune system, composed of lymphocytes, recognizes diversified antigens and generates immunological memory. According to the canonical model, it is the innate immune system that captures pathogens and senses environment to activate adaptive lymphocytes through antigen presentation, costimulatory signals and cytokine milieu. Emerging evidence indicates that environmental cues can be directly conveyed to lymphocytes by the aryl hydrocarbon receptor (AhR). AhR is a ligand-activated transcription factor that widely expresses in many immune cell lineages and recognizes a broad range of ligands including endogenous and dietary metabolites, microbial derivatives and xenobiotics. This review will focus on the regulatory role of AhR in not only adaptive but also innate lymphocytes including recently discovered innate lymphoid cells.