We next determined the role of DC-SIGN on B cells in trans infection of T cells by treating IL-4– and CD40L-activated B cells with anti–DC-SIGN mAb or two nonspecific IgG as controls, one with the same isotype as the anti–DC-SIGN mAb (IgG2b) and the other of a different isotype (IgG1), prior to incubation with HIV-1 X4 or HIV-1 R5 and co-culture with T cells. This evidence concerns the gene CD40LG and infection.