Identification of naturally secreted soluble form of TL1A, a TNF-like cytokine

TL1A, a TNF-like ligand, mediates signaling via its cognate receptor DR3, a death receptor whose activation was known to induce both death and survival factors. TL1A, like TNF, is also presumed to circulate as a homotrimeric soluble form. To identify soluble TL1A in the immune system, we have developed a quantitative ELISA by pairing a monoclonal antibody (MAb) with a biotinylated anti-TL1A polyclonal antibody (PAb) as capture and detection antibodies, respectively. The assay had a detection limit of 32 pg/ml. Overnight culture of human umbilical vein endothelial cells (HUVEC) expressed up to 160 pg/ml of TL1A, and that proinflammatory cytokines, IL-1 and TNF, significantly increased TL1A mRNA and soluble protein up to several folds in contrast to IL-6 and IL-11, which induced neither protein nor mRNA in the cells. IL-1 appeared to be a better stimulator of TL1A than TNF-alpha, and the induction of soluble TL1A in HUVEC in response to IL-1 was dose and time-dependent. We have also purified soluble TL1A from a large volume of IL-1 stimulated HUVEC conditioned medium using an anti-TL1A PAb-coupled affinity column. The protein eluted from the column was further reacted with anti-TL1A MAbs in Western blot: 30-kDa and 32-kDa under non-reducing and reducing conditions, respectively. Taken together, our results indicated that ELISA might be useful in studying soluble TL1A regulation in certain inflammatory conditions. (c) 2005 Elsevier B.V. All rights reserved.