The rate of PD‐1+ cells among the extracted cells increased visibly on the 5th day (p < 0.001) and 7th day (p < 0.0001) after infection; the quantity of PD‐1+ cells increased on the 5th day (p = 0.0001) and 7th day (p = 0.0002) after infection, comparing with the normal mice (Figure 1C). Here, PDCD1 is linked to infection.