Interleukin-33 (IL-33) is a dual-function molecule that regulates gene expression in nuclei and, as a cytokine, conveys proinflammatory signals from outside of cells via its specific receptor ST2L. There are still a lot of questions about localization and processing of IL-33 gene products. In the course of re-evaluating human IL-33 gene, we found distinct promoter usage depending on the cell type, similar to the case in the ST2 gene. Furthermore, we found a novel exon 2E in the conventional intron 2 whose open reading frame corresponded to a transmembrane protein of 131 amino acids. Dependence of exon 2E expression on differentiation of HUVEC cells is of great interest in relation to human IL-33 function. (C) 2012 Elsevier Inc. All rights reserved.