CD4 and allergic disease: Th17 cells are a new type of CD4+ T cells [28] and mainly exert inflammatory action by secreting orphan nuclear receptor yt (RORyt) and other effector cytokines such as IL-17A and IL-6, which can induce allergic asthma, systemic lupus erythematosus, rheumatoid arthritis, and other allergic diseases [29, 30].