Further, compared to IgG Ctrl-treated PD-1−/− mice, MR16-1-treated PD-1−/− mice presented significantly suppressed levels of psoriasis-related cytokine mRNAs IL-6, IL-17a, and IL-23a in the ear skin at day 7 (P = 0.003, P = 0.03 and P = 0.02, respectively, by Mann–Whitney U test, Fig. 5g), and significantly decreased serum levels of IL-17A and IL-23A (P = 0.03 by Mann–Whitney U test) to the baseline level at day 7 (Fig. 5h). Here, PDCD1 is linked to psoriasis.