DC-SIGN expression is induced by IL-4 and is not required for HIV-1 transmission by blood myeloid DCs. A, CD14+ cells and BDCA1+ cells were cultured for 48 h with IL-4 (10 ng/ml), GM-CSF (100 IU/ml), or IL-4 and GM-CSF. Cells were stained with anti-DC-SIGN and analyzed by FACS. B, Myeloid DCs were cultured for 48 h with or without IL-4 (10 ng/ml), the latter to induce DC-SIGN expression. Part of the cultures were incubated for 20 min with 20 μg/ml anti-DC-SIGN mAb and AZN-D1 and then infected with BaL for 2 h and washed. Infected DCs (5 × 104) were cultured with 105 T blasts. Supernatants were collected at different time points and analyzed for p24 secretion by ELISA. C, Raji transfectants were studied in parallel.