Immune responses are essential for pathogen elimination but also cause tissue damage, leading to disease or death. However, it is unclear how the host immune system balances control of infection and protection from the collateral tissue damage. Here, we show that PD-1-mediated restriction of immune responses is essential for durable control of chronic LCMV infection in mice. In contrast to responses in the chronic phase, PD-1 blockade in the subacute phase of infection paradoxically results in viral persistence. This effect is associated with damage to lymphoid architecture and subsequently decreases adaptive immune responses. Moreover, this tissue damage is type I interferon dependent, as sequential blockade of the interferon receptor and PD-1 pathways prevents immunopathology and enhances control of infection. We conclude that PD-1-mediated suppression is required as an immunoregulatory mechanism for sustained responses to chronic viral infection by antagonizing type-I interferon-dependent immunopathology
