T follicular helper and T H 2 cells in allergic responses

IL-4 is a cytokine commonly secreted by TH2 and follicular helper T (TFH) cells after antigenic sensitization. TH2 cells have been thought to be the major contributor of B cell help as a source of IL-4 responsible for class switch recombination to Immunoglobulin G1 (IgG1) and Immunoglobulin E (IgE). Importantly, there are some differences in transcriptional regulation between these two T cell subsets. The IL-4 production by TH2 and TFH cells is distinctively regulated by two pathways, GATA-3-mediated Il4-HS2 enhancer and Notch mediated Il4-CNS-2 enhancer. IgE and IgG1 antibody responses are mainly controlled by IL-4-secreting TFH cells, but not by TH2 cells. In this review, we discuss the role of TH2 and TFH cells in IgE production and allergic responses.