PTPRC and rheumatoid arthritis: To investigate the effect of B cells on OBs in RA, we first examined the anatomic relationship between B cells (B220+) and OBs (osteocalcin [OCN]+) in 6-month-old TNF-Tg mice with severe arthritis and systemic bone loss, using double immunofluorescence (IF) staining on frozen sections of bone.