Following 7 days of daily IMQ application, PD-1-cKO (PD-1fl/flCD8Cre) mice were found to have developed more severe IMQ-induced psoriasis-like dermatitis than littermate Ctrl (PD-1fl/+CD8Cre) mice (Fig. 4c), when evaluated clinically by the change in ear swelling from the baseline to day 7 (17 ± 1.4 μm vs. 6.8 ± 0.75 μm, P < 0.0001 by two-way ANOVA, Fig. 4d), PASI score at day 7 (6.3 ± 0.42 vs. 3.8 ± 0.25, P = 0.0001 by two-way ANOVA, Fig. 4e), and pathologically by epidermal thickness at day 7 (59.5 ± 2.6 μm vs. 37.4 ± 3.7 μm, P = 0.008 by Mann–Whitney U test, Fig. 4f, g). This evidence concerns the gene PDCD1 and psoriasis.