The ST2 gene was originally identified as a gene induced by serum or oncogene expression in fibroblasts. The gene produces a shorter soluble secreted form (ST2) and a longer, transmembrane form (ST2L) by alternative splicing. Soluble ST2 has been shown to downregulate the expression of TLR1 and TLR4. ST2L negatively regulates TLR4 signaling and induces endotoxin tolerance, and enhances Th2 responses. IL-33 is the specific ligand for ST2L.