The loss of Th2 cell accumulation with Chit1 deficiency was responsible for attenuation of disease, because the use of IL-2 complexes to boost Th2 cell numbers (Fig. 6C) and associated cytokines (Fig. 6F) also hastened lethal disease in Chit1−/− mice compared with infection-matched, untreated Chit1−/− controls (Fig. 6D). Here, IL2 is linked to infection.