CD4 and allergic asthma: Previous study has shown that CXCR5+CD4+ follicular T helper cells (Tfh) and Foxp3+ follicular regulatory T cells (Tfr) for the regulation of B cell isotype switching and affinity maturation in germinal centers, can induce IgE production in allergic asthma, thereby playing crucial roles in the exacerbation of allergic asthma [45].