T helper type 22 (Th22) cells are a subset of CD4+ effector T cells that has been suggested to be recruited to the skin, where it defends against microbial pathogens and may be involved in tissue repair and remodeling. Th22 cells develop from naïve CD4+ T cells in the presence of IL-6 and TNF-alpha. They produce high levels of IL-22, but not IL-17, IFN-gamma, or IL-4. In addition to IL-22, these cells express CCR4, CCR6, CCR10, several fibroblast growth factors (FGFs), IL-13, TNF-alpha, and the aryl hydrocarbon receptor (AHR) transcription factor. Although Th22 cells share many similarities with Th17 cells including expression of CCR4, CCR6, and IL-22, Th22 cells are distinguished from Th17 cells in that they express CCR10 and lack expression of both CD161 and IL-17. Since hematopoietic cells lack a functional IL-22 receptor, Th22 cells are thought to act primarily on epithelial and stromal cells. An increase in the frequency of Th22 cells and IL-22 has been found in a variety of inflammatory skin and autoimmune diseases including psoriasis, atopic dermatitis, rheumatoid arthritis, and multiple sclerosis.