T cell Recognition of Type II Collagen - A Cartilage Glycoprotein of Importance for Autoimmune Arthritis

Collagen-induced arthritis (CIA) is a T cell-dependent autoimmune disease that serves as an animal model for human rheumatoid arthritis. CIA can be induced in H-2q mice by a single immunization with the cartilage-specific protein type II collagen (CII). This study has focused on CII immunity and tolerance with respect to the interactions between antigen, antigen-presenting cells and T cells. CIA-resistant mice (H-2p) became susceptible by transgenic expression of the MHC class II Aqß-chain, despite that the Aqß-chain and Apß-chain differ only by 4 amino acids, thus demonstrating the impact of MHC class II polymorphism on development of autoimmune disease. Furthermore, the T cell response elicited after rat CII-immunization in H-2q mice was focused towards the 256-270 peptide of rat CII, and did not crossreact with the corresponding mouse peptide, despite only a single amino acid difference (Glu266 in rat CII, Asp266 in mouse CII). Moreover, the variable glycosylation of this determinant elicited a heterogenous T cell response in terms of T cell receptor structure, in which distinct T cells recognized different levels of glycosylation. Unlike conventional soluble antigens, CII was preferentially presented by macrophages and was not presented by dendritic cells. Furthermore, B cells from naive mice but not from CII-immunized mice presented CII, suggesting a tolerogenic role for CII-reactive B cells. Finally, when the CII 256-270 determinant was expressed in the systemically occurring type I collagen, neither a T cell response, B cell response, nor CIA development was observed, demonstrating that the restricted tissue-distribution of the auto-antigen is a critical factor influencing the development of autoimmune arthritis.