NM (4 mg/ml) and 12 nM (0.6 mg/ml), respectively (Figure 1A). In CD42CCR5+ cells, sCD4 activated infection of HIV-1(AD8) much more efficiently than that of HIV-1(YU2). A similar pattern of HIV-1 activation and inactivation was observed for the NBD-556 analogue, JRC-II-191, herein referred to as 191. The affinity of 191 for the HIV-1YU2 gp120 envelope glycoprotein (Kd = 760 nM) is significantly low