Mast cells are recognised as important effectors in allergic disease. However, it is increasingly clear that mast cells may fulfil more diverse roles within the immune system and may be pathogenic in a number of diseases not typically associated with T-helper type 2 immune responses.1 Indeed, studies have described the presence of degranulated mast cells within inflamed rheumatoid arthritis (RA) synovium and as such implicate mast cells as potential mediators in the pathogenesis of RA.2 Consistent with these observations, the severity of arthritis, induced by antibody transfer, is reduced in mast cell-deficient strains of mice, W/W^v and Sl/Sl^d, and can be restored by adoptive transfer of mast cells.3 4

Murine collagen-induced arthritis is a well-characterised model of RA that combines adaptive and innate immune effector components. When complete Freund's adjuvant/collagen …