Electrical charge of a protein determines penetration and localization in hyaline articular cartilage. Quantitative and autoradiographic studies on cartilage of different species, including man.

Sufficient antigen retention in joint structures is a prerequisite for sustained antigen-induced arthritis. In this in vitro study we investigated the retention of native and charge-modified bovine serum albumin (BSA) with patellar cartilage of different species (mouse, rat, rabbit, and man). Association of BSA with cartilage due to charge of the protein with that due to immune complex formation was compared. Using radiolabeled proteins we showed quantitatively that the retention of highly positively charged BSA is considerably higher (200-500 times) than retention of the anionic BSA in all cartilage species examined. Mouse, rat, and human cartilage bind more protein per mg dry weight, compared to rabbit cartilage. No clear-cut relation was found with the glycosaminoglycans (GAG) contents. Retention of native BSA by anti-BSA antibodies was low in the dense hyaline patellar cartilage in all species. Enhanced immune-complex formation was found in marginal regions of rabbit patellar cartilage, consisting of fibrous-like cartilage. Localization studies by autoradiography showed that cationic BSA penetrates deeply into the cartilage matrix. Even in a thick cartilage specimen, such as rabbit cartilage, very deep penetration into the calcified zone was demonstrated. This study indicates that binding and deep penetration of cationized protein in cartilage is not restricted to mouse specimen, as had been found previously, but is a general phenomenon.