Involvement of C5a in biological activity of mast cell

Sonosuke Yukawa, Norifumi Sawamukai, Kunihiro Yamaoka, Kazuyoshi Saito, Yoshiya Tanaka
The First Department of Internal Medicine, University of Occupational and Environmental Health, Japan

C5a is a complement which is activated by immune complexes and its production level is known to reflect the disease activity of rheumatoid arthritis (RA). Additionally, mast cells (MCs) in the RA synovium are known to express C5a receptor (C5aR) and degranulation is induced by C5a. However, the mechanism that induces C5aR expression and the role of C5a in migration remains unclear. The aim of this study was to elucidate the involvement of C5a in MC migration and degranulation in connection with RA pathology.
CD34+ stem cells were purified from human umbilical cord blood and cultured with stem cell factor and IL-6 for 6 weeks to obtain cord blood-derived MCs (CBMCs). CBMCs did not express C5aR, however its expression was strongly induced by co-culture with RA-SF which exceeded CBMCs stimulated with IL-4, IL-1β or TNF-α. Migration of CBMCs was detectable from 0.01 nM of C5a whereas degranulation of was observed from 10 nM which both increased in a dose-dependent manner, but was not observed by C5 or C3. W-54011, a C5aR-specific antagonist, inhibited migration with a low dose of W-54011 (0.01nM) whereas degranulation of CBMCs was inhibited only with high dose (10 nM). To confirm the involvement of MCs in pathology of RA, synovium from RA and osteoarthritis patient was obtained and number of MCs in synovial tissue were detected by toluidine blue staining or c-kit immunostaining. NanoZoomer Digital Pathology was utilized to obtain MC density. The mean density of MCs in synovial tissue was significantly increased in RA compared with OA.
Our results imply that C5a plays an important role in migration and degranulation of MCs in RA synovium suggesting its involvement in pathology. In addition, only a small amount of C5a is necessary for migration whereas high amount of C5a is necessary for degranulation indicating the involvement of C5a on MCs in chronic inflammation.