A MONOCLONAL-ANTIBODY TO THE GP120-CD4 COMPLEX HAS DIFFERENTIAL-EFFECTS ON HIV-INDUCED SYNCYTIUM FORMATION AND VIRAL INFECTIVITY

A murine monoclonal antibody (MAb F-91-55) raised against the complex of soluble CD4 and human immunodeficiency virus type 1 (HIV-1) gp120 h ad previously been found to inhibit syncytium formation without inhibi ting the interaction of CD4 with gp120, and its binding site was local ized within the first two domains (D1/D2) of CD4. We investigated whet her this antibody inhibited the infectivity of HIV-1 in the CD4(+) T c ell lines A3.01, Sup-T1 and H9. We also examined the effect of the ant ibody on syncytium formation between these cells and chronically infec ted H9 cells. Syncytium formation was found to depend critically on th e incubation medium used. The effect of the MAb on HIV-1 infectivity w as very limited with A3.01 and Sup-T1 cells, although it inhibited syn cytium formation between A3.01 or Sup-T1 and chronically infected H9 c ells. In contrast, the MAb inhibited significantly the infectivity of HIV-1 in H9 cells, but it also inhibited syncytium formation between H 9 and chronically infected H9 cells to a greater extent than in the ca se of the other cell lines. Our results indicate that cellular systems used for syncytium assays differ in their susceptibility to inhibitor y antibodies. In the A3.01 and Sup-T1 cell systems, the differences in the ability of the MAb to block viral entry or syncytium formation ra ise the possibility that the mechanisms of interaction of gp 120/gp41 with cell membrane CD4 may be different in cell-cell and virus-cell me mbrane fusion.