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T helper cell 22
T helper cell 22, also known as the Th22 cell, are a type of immune cell. Th22 are a derivative of naïve CD4+ T cells induced by the ligand activation of the transcription factor aryl hydrocarbon receptor (AhR),[1] which uses environmental, metabolic, microbial, and dietary cues to control complex transcriptional programmes.[2] Th22 cell’s function is mediated by its ligand specific cytokine interleukin-22 (IL-22).[3] Differentiation and cytokine expressionTh22 were distinguished as their own class of helper cells due to the stimulation and production of IL-22 independent of IFN- γ, IL-4, or IL-17 stimulation that are associated with Th1, Th2, and Th17 respectively.[1][4] Th22 cell differentiation is stimulated by IL-6 and TNF-α, but others have found Th22 can be stimulated using Langerhans cells and dermal DCs.[3] Th22 cells are known to secrete IL-22, IL-13, IL-26, TNF-α, and granzyme B.[5] In the immune responseTh22 cells express the chemokine receptors CCR4, CCR6, and CCR10 which direct the cells to barrier surfaces such as the skin and tissue.[3][5][6] Similarly, IL-22, the characteristic cytokine produced by Th22 cells has little effect on immune cells and instead acts on mucosal barriers.[5] Due to mucosal barrier interactions Th22 and subsequently IL-22 play a significant role in a variety of skin diseases, intestinal diseases, autoimmune diseases, and allergy conditions. Many of these diseases are characterized by increased circulation of Th22 cells and concomitant increased IL-22 expression.[3] In psoriasis, there is a positive feedback loop between Th22 and IL-22 expression.[3] Increased expression of IL-22 is observed during lesion formation that augments the expression of anti-microbials and induces chemokine ligand (CCL)-20 recruiting CCR6, which is expressed on Th22 cells increasing their concentration in the lesion.[3] Similarly, Th22 cells are found throughout the intestinal wall in irritable bowel diseases, facilitating IL-22 secretion and subsequent induction of tissue specific genes.[3][7] Interestingly, Th22 cells induced expression of IL-22 in allergic asthma has been seen to have a protective effect against lung hypertension and tissue damage in murine models.[3] References
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