H3C1 and rheumatoid arthritis: We next generated another Ig1&2-Fc-C226/229S protein containing a 3 aa (VRR) natural extension of the canonical isoform of PTPRS in replacement of the short linker (hVRR-A; Table 1) and found it was similarly effective at inhibiting RA FLS migration as h3-A (Figure 1G).