Serum levels of soluble programmed death-1 and programmed death ligand-1 in systemic sclerosis: Association with extent of skin sclerosis.

The interaction of programmed death-1 (PD-1) with its ligand, programmed death ligand-1 (PD-L1), has been considered to play a key role in the negative regulation of immune responses. Patients with diffuse cutaneous systemic sclerosis (SSc) had higher levels of soluble PD-1 (sPD-1) than those with limited cutaneous SSc and healthy individuals. Serum sPD-1 levels positively correlated with the severity of skin sclerosis. In contrast, serum sPD-L1 levels were significantly increased in patients with SSc compared with healthy individuals. Moreover, serum sPD-L1 levels were not associated with the extent of skin sclerosis and were elevated not only in patients with diffuse cutaneous SSc, but also in those with limited cutaneous SSc. These results suggested that serum sPD-1 levels may increase in patients with SSc and correlate with the severity of skin sclerosis. PD-1/PD-L1 interaction may contribute to the development of skin sclerosis in SSc.