IL-13 blocks HIV-1 replication in alveolar macrophages coinfected with HCMV. Alveolar macrophages were cultured at a density of 1 × 10⁶ cells per well for 7 days before exposure to HCMV and/or HIV-1. Half the cultures also received 50 ng/mL IL-13 for 2 days before virus challenge. Different cultures were then incubated with HIV-1_BAL (5 × 10⁵ cpm RT activity) with or without HCMV Davis (MOI of 1) as indicated. After 4 hours, the viruses were removed and the cultures were washed three times with 1 mL HBSS, then refed either with macrophage growth medium alone or supplemented with the same concentration of IL-13. Mock exposed alveolar macrophages received growth medium alone. Culture supernatants were removed and replaced with fresh growth medium at 5, 8, 13, 17, 20, 22, 26, and 30-days postinfection and stored at −20°C until assayed for HIV-1 p24 antigen production by ELISA (DuPont).