TPH2 and allergic asthma: Most interestingly, CXCR5− Tph, CXCR5−ICOS+PD-1+ Tph and Tph2 subtypes were weakly positively correlated with serum total IgE level, suggesting that CXCR5− Tph, CXCR5−ICOS+PD-1+ Tph and Tph2 subtypes may play an important role in the excessive accumulation of serum total IgE in allergic asthma.