IL33 and pulmonary arterial hypertension: Furthermore, IL-33 is an alarmin released by barrier tissues in response to helminths to coordinate early type 2 immune defense and is integral to pulmonary tissue repair after viral challenge.38 While localized IL-33 suppression to limit EndMT in PAH is a promising strategy, it must be carefully balanced against the high risk of losing beneficial IL-33 effects in the heart and at barrier surfaces.