Inflammation occurs in adipose tissue in obesity. We have examined whether IL-33, a recently identified IL-1 gene family member, and its associated receptors are expressed In human adipocytes. IL-33, IL-1RL1 and IL-1RAP gene expression was observed in human visceral white far, in preadipocytes and in adipocytes (SGBS cells). Treatment with TNF alpha for 24 h induced a 6-fold increase in IL-33 mRNA level in preadipocytes and adipocytes. Time-course studies with adipocytes showed that the increase in IL-33 mRNA with TNF alpha was maximal (>55-fold) at 12 h. This response was markedly different to IL-1 beta (peak mRNA increase at 2 h; 5.4-fold) and IL-18 (peak mRNA increase at 6 h: >1500-fold). Exposure of adipocytes to hypoxia (1% O-2, 24 h) did not alter IL-33 mRNA level: in preadipocytes, however, there was a 3-fold increase. Human adipocytes and preadipocytes express IL-33, but the various IL-1 family members exhibit major differences in responsiveness to TNF alpha. (c) 2009 Elsevier Inc. All rights reserved.