CD4 and infection: In this respect, the role of NS5 proteins belonging to different flaviviruses, including DENV NS5, was proposed to inhibit HIV-1 replication when co-expressed in HIV-1-infected cells through CD4 receptor downmodulation [136,137], while yellow fever virus (YFV) infection of macrophages was shown to inhibit HIV-1 replication in infected cells, also correlating with CD4 downmodulation [137].