IFNA1 and influenza: We then isolated pure populations of pDC by negative depletion of fresh PBMC from normal volunteers and co-cultured the pDC (purity 80–95%) with HIVBAL, HIVNL-43, or influenza [A/PR/8/34 (H1N1)] at an M.O.I. of 0.5 (for HIV, equivalent to 1.76 ng of p24 antigen) and measured IFN-α production in culture supernatant after 8 hours by ELISA.