NINJ1 is a restriction factor for HSV-1 in mouse macrophages

Restriction factors block multiple stages of viral infection. Here we describe how NINJ1 controls HSV-1 infection of mouse macrophages, a key cell type during systemic and local acute infection. We observed that Ninj1 ^−/– macrophages are more susceptible to infection than WT cells. Ninj1 ^−/– macrophages exhibited earlier and stronger expression of all kinetic classes of viral proteins, resulting in higher production of infectious viral particles, with initial differences seen in the first few hours post infection. Given the important role of NINJ1 during cell death, we next investigated if NINJ1 restricts HSV-1 in a manner related to its role in cell death. However, infected Ninj1 -deficient cells did not exhibit differences in cell death compared to WT controls at early time points in infection where we observe a difference in infection rates. Instead, the higher infection rate in Ninj1 ^−/– macrophages correlated to enhancement in the average numbers of viral particles entering each cell. Finally, we determined the consequences of the altered entry and found higher ISG RNA expression in infected Ninj1 ^−/– cells, which we ascribe to both TLR signaling and STING-mediated recognition. Together, this indicates that the NINJ1 present on WT macrophages reduces HSV-1 entry, which has consequences for the inflammatory phenotype associated with HSV-1 infection.