Type 2 immunity is a cornerstone of effective responses against parasites. However, a dysregulated type 2 immune response causes allergy and asthma. Although T helper 2 cells are the key to type 2 immunity, my PhD thesis has expanded this dogma that group innate lymphoid cell 2 (ILC2) and T follicular helper cell (Tfh) are two important players in the regulation of type 2 immune responses. Particularly, a protein c-Rel regulates ILC2-dependent allergic responses, while Tfh cell responses that are highly heterogenous mediate effective responses against parasitic worms, paving the way for new therapeutic strategies for allergy and worm infections.