Although different types of immune cells, such as CD4+, CD8+, γδT, NKT cells and innate lymphocyte cells 3 (ILC3) are known to produce IL-17A [32], there is evidences to support that an IL-17-producing subset of CD4+ T (Th17) cells or γδT (γδT17) cells is a major source of IL-17A and essential for the development of inflammatory diseases, including IMQ-induced psoriasis [23, 33, 34]. This evidence concerns the gene CD4 and psoriasis.