Interestingly, Boasso et al. demonstrated that IFN-α-induced indoleamine 2,3-dioxygenase (IDO) from pDC inhibited CD4+ T-cell proliferation during HIV infection (37), and blockade of gp120/CD4 interactions was found to inhibit HIV-mediated induction of IDO and IFN-α (38, 39). Here, CD4 is linked to HIV infectious disease.