Pathophysiology

Patients with RP demonstrate both cell-mediated and humoral immunity against extracellular matrix components of cartilage, including type II, IX, and XI collagens, matrillin-1, cartilage oligomeric matrix protein, and proteoglycans. Evidence for cellmediated autoimmunity includes demonstration of T cells directed against type II collagen in patients with RP. Additionally, T cell clones have been isolated from an RP patient which were specific for an immunodominant epitope of type II collagen and were restricted to HLA-DRB1 * 0101/0401 alleles (9). T cell responses to type IX and XI collagens and matrillin-1 have also been reported in individual RP patients (10,11).

Humoral autoimmunity is demonstrated by the presence of immunoglobulin and complement deposits in affected tissues (12). Additionally, circulating autoantibodies against native and denatured type II, IX, and XI collagens, as well as matrillin-1, are found in some patients with RP (13,14). The exact role that these autoantibodies play in the pathogenesis of RP is yet to be determined.

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