PDCD1 and rheumatoid arthritis: The increase in membrane-boundPD-1 may lead to a secondary increase in sPD-1 levels.It seems that similar to rheumatoid arthritis patients, PD-1 and PD-L1 overexpressed, and the sPD-1/sPD-L1concentrations also increased to prevent the regulatoryeffect of membrane-bound PD-1 and PDL1 (28).