CD4 and infection: Initial studies using in vitro cultured monocytes-derived dendritic cells (MDDCs) and cell lines expressing DC-SIGN demonstrated that DCs could sequester infectious HIV-1 for several days after uptake, leading to the hypothesis that DCs might initiate primary infections by carrying HIV-1 from mucosal sites of exposure to lymphoid tissues and transferring infection to CD4 T cells in the lymph node [29].