T-CELL RECOGNITION OF CARBOHYDRATES ON TYPE-II COLLAGEN

A critical event in an immune response is the T cell recognition of pe ptides bound to major histocompatibility complex (MHC) molecules on th e surface of an antigen presenting cell (APC). Although the majority o f eukaryotic proteins are glycosylated, it has not yet been shown that T cell recognition of such proteins involves recognition of the bound carbohydrates. Type II collagen (CII), the major protein constituent of joint cartilage, is posttranslationally modified by hydroxylation a nd glycosylation of lysines. In this report we show that posttranslati onal modifications of the immunodominant peptide CII(256-270) generate a structural determinant that is distinct from the determinant repres ented by the corresponding synthetic peptide. Elimination of carbohydr ates, present on CII, by two different biochemical methods revealed th at the carbohydrates, O-linked to the hydroxylysines within the CII(25 6-270) determinant, were crucial for the reactivity towards the posttr anslationally modified peptide. Furthermore, a T cell hybridoma specif ic for the glycosylated determinant was stimulated by tryptic CII-pept ides presented by fixed APCs, thus showing that the carbohydrates are involved in the trimolecular complex T cell receptor/peptide/MHC. Fina lly, the importance of the bound carbohydrates for the arthritogenicit y of CII was investigated by comparing the development of arthritis af ter immunization with carbohydrate-depleted and glycosylated CII, resp ectively. Incidence, time of onset, and severity of the disease were s ignificantly affected by the elimination of carbohydrates, whereas no significant difference in anti-CII antibody titers was seen.