IL33 and infection: Direct evidence for a role of IL-33 in enhancing Th2-mediated attack of migrating parasitic nematodes in the lung arises from two other studies: IL-33 release triggered by house dust mite allergen administration reduced numbers of Ascaris lumbricoides larvae in the lung during subsequent infection [40], while H. polygyrus infection-induced IL-33 reduced N. brasiliensis larvae counts in the lungs of C57BL/6 mice [41].