Few studies have addressed the biological effects of VIP and PACAP during HIV-1 infection, which have mainly focused on the repercussion of VIP and PACAP receptor ligation on HIV-1 production, describing that VPAC1 facilitates productive HIV-1 infection in CD4+ T cell lines [27], and that VPAC2 stimulation diminishes HIV-1 production in peripheral blood mononuclear cells (PBMCs) and in CD4+ T cell lines [28]. Here, CD4 is linked to HIV-1 infection.