IL-33 has been identified as alarmin with a dual function; an IL-1 family cytokine acting extracellularly and intracellularly as nuclear factor regulating gene expression. IL-33 is released to alert the immune system as a first line of defense. It is expressed and released after cell injury to initiate an immune response and to start repair processes by epithelial cells after damage as a result of an inflammatory process. IL-33 activates many immune cells including ILC2, mast cells, eosinophils, basophils, DCs and Th2 cells. This explains the direct relation to allergic inflammation. Besides, IL-33 is implicated infectious diseases like pathogenic infection, cardiovascular disease, IBD and diabetes. IL-33 signals via ST2 (suppression of tumorigenesis 2), a member of the Toll-like/IL1 receptor (TIR domain containing) superfamily. There are 2 forms of ST2 receptor, membrane bound and a soluble form that acts as a decoy receptor. Via IL33/ST2 activation ILC2 cells produce Th2 cytokines such as IL-5&-13. Intracellularly, IL-33 functions as transcriptional repressor of NF-κB mediated gene expression. This makes it an inhibitor of pro-inflammatory signaling.