IF staining of brain tissue sections confirmed that PD‐L1 was expressed in CX3CR1‐GFP+ cells on the 7th day after infection (Figure 2H), and the CX3CR1‐GFP+ cells were close to PD‐1+ cells (Figure 2I), while few PD‐1+ or PD‐L1+ cells were found in the normal brain (data not shown). Here, PDCD1 is linked to infection.