CD4 and asthma: Recent studies have indicated that YPFS affects expression of T cell receptor (TCR) and major histocompatibility complex (MHC) class II expression on CD4+ T cells in a mouse model of asthma, regulates the balance of T helper(Th)1/Th2 cells in murine allergic airway disease [6], and decreases interleukin(IL)-17 level [7].