SCD5 and HIV-1 infection: We then tested the effect of sCD4 doses on HIV-1 infection (Bru-3, Bru-Yu2 and Mj4) and found that at 1 μg/ml or higher a concentration-dependent inhibition of HIV-1 infection by sCD4 was observed; while below 1 μg/ml no significant inhibition by sCD4 was observed (Zhou et al. data not shown).