MMP9 and arthritic joint disease: Of these, MMP-9 (92–96 kD gelatinase B), whose substrates include type IV collagen in basement membrane [11], has been thought to be involved in the cellular invasion of the basement membrane by cells involved in arthritis and cancer (e.g. T cells, mononuclear phagocytes, synovial fibroblasts, and metastatic tumor cells) [12-15].