In IMIDs, an imbalance between cosignalling molecules, both costimulators (e.g., Cluster of differentiation 28 (CD28), CD40, Lymphocyte function-associated antigen 1 (LFA-1), LFA-3) and coinhibitors (CTLA-4 and programmed cell death 1 (PD-1)) has been postulated as a critical mechanism involved in psoriasis pathogenesis [28]. Here, PDCD1 is linked to psoriasis.