PRODUCTION OF SOLUBLE HLA-CLASS-I MOLECULES BY IFN-GAMMA-INDUCED COLON-ADENOCARCINOMA CELLS

High levels of soluble HLA-class-1 molecules (sHLA) were found to be p roduced in a time- and dose-dependent manner by colon-adenocarcinoma C olo205 cells in response to IFN-gamma stimulation. Among other cytokin es tested, only IL-6, TNF, IFN-alpha and IFN-beta showed weak inducibi lity. IFN-gamma-induced production of sHLA was synergistically enhance d by IL-1 alpha, IL-6 or TNF, and combined treatment with TNF and IL-6 exhibited an additive to synergistic induction. Expression of sHLA is unlikely to result from IFN-gamma-induced enhancement of overall HLA- class-1 expression, as at low concentrations IFN-alpha, IFN-beta and I FN gamma stimulated increased expression of cell membrane HLA-class-1 molecules in Colo205 cells with almost equal efficiency, whereas only IFN-gamma induced high level production of sHLA. Immunoblotting with a monoclonal antibody recognizing beta(2)-microglobulin-free HLA-class- 1 heavy chain revealed 3 major forms of sHLA heavy chain, i.e., 45/43- , 37- and 33-kDa molecules, in the culture supernatants of IFN-gamma-i nduced Colo205 cells. The 45/43-kDa proteins can be partitioned into T riton X-114, representing intact HLA-class-1 heavy chains shed from th e cell membrane. The hydrophilic 37- and 33-kDa heavy chain, which rem ained almost exclusively in the aqueous phase after extraction with Tr iton X-114, could well be due to alternative RNA splicing, with deleti on of exon 5 encoding the hydrophobic transmembrane region of membrane -anchored HLA-class-1 heavy chain. (C) 1995 Wiley-Liss, Inc.