AN ANTI-FUSION REGULATORY PROTEIN-1 MONOCLONAL-ANTIBODY SUPPRESSES HUMAN PARAINFLUENZA VIRUS TYPE 2-INDUCED CELL-FUSION

Fusion regulatory protein-1 (FRP-1) regulates virus-mediated cell fusi on and induces polykaryocyte formation of monocytes without any fusoge n. We have recently reported that FRP-1 and the 4F2/CD98 heavy chain a re identical molecules. Cell fusion in Newcastle disease virus (NDV)-i nfected HeLa cells was enhanced when cells were incubated with anti-FR P-1 MAb. Anti-FRP-1 MAbs also induced human immunodeficiency virus gp1 60-mediated cell fusion. However, HBJ127, an anti-FRP-1/4F2/CD98 MAb t hat enhanced cell fusion in NDV-infected cells, delayed human parainfl uenza virus type 2 (HPIV-2)-induced cell fusion in HeLa cells, althoug h these viruses belong to the same genus Rubulavirus. No anti-FRP-1 MA bs enhanced cell fusion in HPIV-2-infected HeLa cells. Anti-FRP-1 MAbs including HBJ127 showed no effect on virus growth and expression leve ls of virus-specific polypeptides in HPIV-2-infected HeLa cells, indic ating that the delay in cell fusion by an anti-FRP-1 MAb is not due to suppression of virus replication. When HeLa cells were transfected wi th an expression vector harbouring HPIV-2 HN and F genes, cell fusion was also suppressed by HBJ127, but the effect was weak in comparison w ith virus-infected cells. These data indicate anti-FRP-1 antibodies no t only induce/enhance, but also inhibit/delay virus-induced cell fusio n and therefore FRP-1 molecules are multifunctional.