MMP1 and rheumatoid arthritis: Both MMP-1, capable of cleaving intact collagen [44], and MMP-3, responsible for the cleavage of other extracellular matrix components [45,46] and the subsequent increase of accessibility of collagen fibrils to other collagenases like MMP-1 [35,42,47], are presumed to be of major importance in the initial joint destruction in the pathogenesis of RA.