Thus, to further dissect the phenotype of circulating CD8 T cells in psoriasis patients with mild-to-moderate disease severity, we examined the expression of co-signalling molecules (co-stimulatory: CD28, CD134 (OX40L), LIGHT; co-inhibitory: TIGIT, programmed cell death protein 1 (PD-1), BTLA) on circulating CD8 T cells. The gene discussed is PDCD1; the disease is psoriasis.