CD4 and psoriasis: The key pathomechanism of psoriasis is that dendritic cells or macrophages can secrete IL-23 and then stimulate CD4+Th17 polarization, resulting in the secretion of cytokines, such as IL-17, IL22, TNF-α, etc. Moreover, IL-12 can activate the differentiation of CD4+Th1 cells, which induces INF-γ, IL-2, and TNF-α synthesis; CD8+ T cells are also known to be activated and can release pro-inflammatory cytokines, including TNF-α and INF-γ.