CD4 and Pleural effusion: Ye and Ribera E et al. demonstrated that the percentages of CD4+ T cells, such as Th1, Th9, Th17, Th22 and Treg cells, in the pleural effusion were higher than those in the peripheral blood in patients with TPE, and some pleural cytokines including IL-1β, IL-4, IL-6, TNF-α, and TGF-β exhibited significantly elevated levels in TPE, which could drive the differentiation of naive CD4+ T cells into different Th cell lineages[17–19].