NHA were treated with or without heroin (10−7 M, 24 hr), infected with HIV-1 and then cultured for 15 days. The culture supernatants were quantitated for p24 antigen (ng mL−1) using Retrotek, HIV-1 p24 ELISA from ZeptoMetrix (Cat # 0801111, Buffalo, NY) with a minimum detection range of 1 pg p24 antigen mL−1. Data are presented as the mean ± SD of 3 independent experiments. Statistical significance was calculated by Students’ ‘t’ – test