Chitinase-like proteins promote IL-17-mediated neutrophilia in a tradeoff between nematode killing and host damage.

Type 2 immune responses are often associated with the expression of chitinase-like Ym proteins, but their role is unclear. Allen and colleagues show that Ym1 and Ym2 act on γδ T cells to increase their expression of IL-17A and enhance the recruitment of neutrophils.