Antigen-presenting cells containing bacterial peptidoglycan in synovial tissues of rheumatoid arthritis patients coexpress costimulatory molecules and cytokines

Objective. Rheumatoid arthritis (RA) is a chronic inflammatory disease char acterized by intimal lining hyperplasia and massive infiltration of the syn ovial sublining by antigen-presenting cells (APCs), lymphocytes, and plasma cells. Peptidoglycan (PG), a major cell wall component of gram-positive ba cteria, which is abundantly expressed in all mucosa, is believed to be invo lved in the pathogenesis of RA because of its ability to induce the product ion of proinflammatory cytokines as well as to induce arthritis in rodents. While PG has been detected in APCs in RA joints, little is known about the role of these cells in RA, In this study, the presence and immune competen ce of PG-containing cells in synovial tissues from 14 RA and 14 osteoarthri tis (OA) patients were analyzed in situ, Methods. Using immunohistochemistry, we examined the coexpression of phenot ypic markers, costimulatory molecules, and cytokines by PG-containing cells . Results. PG was present in higher numbers in RA than in OA synovial tissues , although the difference was not significant, PG-containing cells were mai nly macrophages, but some mature dendritic cells also contained PG, A high percentage of PG-containing cells in both RA and OA synovial tissues coexpr essed HLA-DR. CD40, CD80, and CD86 expression by PG-containing cells was hi gher in RA than in OA tissues. Furthermore, PG-containing cells coexpressed cytokines, which modulate inflammatory reactions, in particular, tumor nec rosis factor alpha and interleukins 6 and 10. Conclusion. The results suggest that PG-containing cells may contribute to inflammation within the microenvironment of the joint in RA patients.