IL4 and asthma: In addition to classical Th2 cytokines such as IL-4, IL-5, and IL-13, the epithelial-derived alarmin thymic stromal lymphopoietin (TSLP) has emerged as a critical upstream mediator of airway inflammation in asthma, and is now recognized as a major therapeutic target, most notably for the monoclonal antibody tezepelumab.