CD4 and asthma: With the discovery of Th9 cells, a new subgroup of CD4+Th cells, more studies focused on the role of Th9 cells in the immunopathology of asthma showed that these cells can be differentiated from the Naïve CD4+T cells stimulated by IL-4 and TGF-β, producing a large amount of IL-9 [1], which is reported that Th9/IL-9 is pathogenic in asthma [2, 3].