CD169 macrophages regulate PD-L1 expression via type I interferon and thereby prevent severe immunopathology after LCMV infection.

Upon infection with persistence-prone virus, type I interferon (IFN-I) mediates antiviral activity and also upregulates the expression of programmed death ligand 1 (PD-L1), and this upregulation can lead to CD8 T-cell exhaustion. How these very diverse functions are regulated remains unknown. This study, using the lymphocytic choriomeningitis virus, showed that a subset of CD169 macrophages in murine spleen and lymph nodes produced high amounts of IFN-I upon infection. Absence of CD169 macrophages led to insufficient production of IFN-I, lower antiviral activity and persistence of virus. Lack of CD169 macrophages also limited the IFN-I-dependent expression of PD-L1. Enhanced viral replication in the absence of PD-L1 led to persistence of virus and prevented CD8 T-cell exhaustion. As a consequence, mice exhibited severe immunopathology and died quickly after infection. Therefore, CD169 macrophages are important contributors to the IFN-I response and thereby influence antiviral activity, CD8 T-cell exhaustion and immunopathology.