Figure 1: The many roles of CD4 T cells in promoting antiviral immunity multiple direct and indirect cellular interactions with CD4 T cells promotes antiviral immunity. CD4 T cells can promote affinity maturation and antibody class switching by B cells, enhance antigen presentation and costimulation of dendritic cells (DC), induce the phagocytic activity of macrophages, and promote the development of CD8 T cells into cytotoxic T lymphocytes (CTLs) and functional memory cells. A lesser known role for CD4 T cells is the development of cytotoxic activity directed against infected target cells.