IHC analysis of murine ear skin samples revealed significantly increased numbers of CD8 T cells infiltrating into the epidermis of PD-1−/− mice and anti-PD-1 antibody-treated mice when compared to control mice (Fig. 3a and b, P = 0.008 by Mann–Whitney U test, and Supplemental Fig. 2F, P = 0.008 by Mann–Whitney U test), similar to what was seen in the patients with anti-PD-1 antibody-induced psoriasis-like dermatitis. Here, PDCD1 is linked to dermatitis.