A soluble form of CD83 is released from activated dendritic cells and B lymphocytes, and is detectable in normal human sera

CD83 is an inducible glycoprotein expressed predominantly by dendritic cell s (DC) and B lymphocytes. Expression of membrane CD83 (mCD83) is widely use d as a marker of differentiated/ activated DC but its function and ligand(s ) are presently unknown. We report the existence of a soluble form of CD83 (sCD83). Using both a sCD83-specific ELISA and Western blotting, we could d emonstrate the release of sCD83 by mCD83(+) B cell and Hodgkin's disease-de rived cell lines, but not mCD83(-) cells. Inhibition of de novo protein syn thesis did not affect the release of sCD83 during short-term (2 h) culture of cell lines although mCD83 expression was significantly reduced, suggesti ng sCD83 is generated by the release of mCD83. Isolated tonsillar B lymphoc ytes and monocyte-derived DC, which are mCD83(low), released only low level s of sCD83 during culture. However, the differentiation/activation of these populations both up-regulated mCD83 and increased sCD83 release significan tly. Analysis of sera from normal donors demonstrated the presence of low l evels (121 +/- 3.6 pg/ml) of circulating sCD83. Further studies utilizing p urified sCD83 and the analysis of sCD83 levels in disease may provide clues to the function and ligand(s) of CD83.