IL4 and Allergy: Interleukin 12 (IL-12) was found to be a common signal for the Th1 and Tfh responses, whereas interleukin 4 (IL-4) was found to direct the Th2 response against a helminth or contribute to an allergy, and interleukin 1 (IL-1) and interleukin 6 (IL-6) were found to promote the antibacterial response of the Th17 helper T cells.