Immunohistochemical demonstration of calcium-dependent cysteine proteinase (calpain) in collagen-induced arthritis in mice.

The mechanisms whereby destructive changes in joints develop in rheumatoid arthritis (RA) are not fully understood, but cartilage degradation is considered one of the most important factors. Calpain, a calcium-dependent cysteine proteinase that degrades a variety of substrate proteins in various tissues, may be among the proteolytic enzymes that mediate cartilage degradation associated with RA and other inflammatory arthritides. The object of this study is to ascertain immunohistochemically whether calpain is present in the inflamed joints of mice with collagen-induced arthritis (CIA), as an experimental animal model of inflammatory arthritis such as RA. Murine hindpaws with CIA were decalcified, frozen-sectioned, and stained by immunoperoxidase method (PAP) using a polyclonal antibody against calpain II. Calpain was present in the articular tissues affected by CIA: positive staining was observed in 1) proliferating synovia, and 2) surface, matrix, and chondrocyte lacunae of articular cartilage. It was postulated that calpain functions as one of the enzymes responsible for the cartilage degradation associated with CIA.