Allergic arthritis induced by cationic proteins: role of molecular weight.

Previous studies have shown that chronic murine allergic arthritis can only be induced with cationized BSA, related to excellent retention of the cationic antigen in the joint. We now investigate the impact of size of cationic proteins on their potential to induce this form of arthritis. After intra-articular injection, antigen retention is much enhanced with high molecular weight cationized proteins, like albumin or immunoglobulin, compared to small-sized proteins like myoglobulin and lysozyme. Consequently, severe chronic arthritis was only found with the former ones. The role of size is further substantiated with poly-L-lysine-coupled lysozyme. This derivative shows excellent retention in vivo and causes a chronic destructive arthritis in preimmunized mice, in contrast to the poor arthritis seen with native cationic lysozyme. Control experiments made it clear that antigen retention is the most important denominator and that differences in chronicity are not related to gross variations in T-cell reactivity. Retention studies in vitro revealed that the potential to bind to joint structures is similar for the various proteins, suggesting that in vivo conditions determine size-related differences in antigen clearance. Our data indicate that cationicity per se does not make a protein a proper arthritogen.