EXPRESSION OF FUSION REGULATORY PROTEINS (FRPS) ON HUMAN PERIPHERAL-BLOOD MONOCYTES - INDUCTION OF HOMOTYPIC CELL-AGGREGATION AND FORMATIONOF MULTINUCLEATED GIANT-CELLS BY ANTI-FRP-1 MONOCLONAL-ANTIBODIES

Fusion regulatory proteins (FRPs) are newly defined cell surface molec ules that enhance and/or induce virus-mediated cell fusion. Anti-FRP-1 Abs reacted with all of the established cells derived from humans and monkeys, whereas FRPs were found to be selectively expressed on a fra ction of monocytes in human PBMCs. Granulocytes expressed no FRP-1 mol ecules, but approximately 18% of granulocytes expressed FRP-2 molecule s. Alveolar macrophages also expressed FRP-1 molecules. FRP-1 expressi on was enhanced by culture of monocytes, but CD14 expression was not i nfluenced by cultivation. Anti-FRP-1 Abs induced homotypic cell aggreg ation and multinucleated giant cell formation of monocytes. Anti-beta 2 integrin Ab blocked anti-FRP-1 Ab-induced cell aggregation, and anti -beta 1 integrin Ab and fibronectin inhibited anti-FRP-1 Ab-induced po lykaryocyte formation. There was no competitive binding to monocytes b etween anti-FRP-1 Ab and anti-beta 1 or anti-beta 2 integrin Ab or fib ronectin. Furthermore, there was no enhancement of beta 1 and beta 2 i ntegrin expression by anti-FRP-1 Ab on monocytes. These findings sugge st that anti-FRP-1 Ab activated integrin systems, and that the functio ns of anti-FRP-1 Ab were demonstrated through the activated integrin s ystems. Furthermore, it is inferred that integrin systems are involved in polykaryocyte formation of monocytes.