CD274 and infection: PD-L1 was also found to be up-regulated on myeloid DCs and monocytes in HIV-infected subjects with progressive infection, but expressed at lower levels in ART treated subjects and controllers and long-term non-progressors, HIV-encoded TLR ligands up-regulated PD-L1 on DC and monocytes [82,87] and exposure of monocytes to HIV in vitro resulted in PD-L1 up-regulation by an IFN-dependent mechanism [86].