Activation of latent collagenase by serum proteinases that interact with immobilized immunoglobulin G

It has been previously observed that collagen destruction occurs in the vicinity of immune complexes present in articular cartilages of patients with rheumatoid arthritis. When IgG is covalently linked to Sepharose it behaves as if it has reacted with an antigen to form an immune complex, in that it binds the complement component C1 from human serum. Other serum components also interact with this matrix, though their interaction may not be specific for IgG. Two of these components were shown to possess proteolytic activity, one being kallikrein and the other having the properties of plasmin. Both of the activities could activate latent human collagenase. Whilst the binding of the plasmin activity is probably nonspecific, the binding of the kallikrein activity may be selective for IgG (although it is not certain whether this binding is direct or indirect via another molecule). These results therefore suggest that active proteinases such as plasma kallikrein may be selectively concentrated on immune complexes in vivo, where they may locally activate latent proteinases such as collagenase thereby initiating tissue destruction.