Binding of immunoglobulins and immune complexes to cartilage derived extracts

Cartilage extracts with affinity for heat aggregated immunoglobulins were prepared from human articular and bovine nasal cartilage. These extracts, containing predominantly collagen, also bound both to immune complexes (IC) prepared in vitro and to immunoglobulins from sera of many patients with rheumatoid arthritis (RA). Cryoprecipitation of rheumatoid sera removed material reacting with the extract and density gradient fractionation of a positive serum showed correlation between binding to the extract and to C1q. These results indicate that the binding materials in rheumatoid sera were likely to be IC. We suggest that some assays which apparently demonstrate anti-collagen autoantibodies in fact measure IC. These findings also have implications for models of the pathogenesis of RA.