Arthritis Induced with Minor Cartilage Proteins

Type XI collagen (CXI) and cartilage oligomeric matrix protein (COMP) are minor components in cartilage, shown to be arthritogenic. CXI is a heterotrimeric triple helical fibrillar collagen and intermingled in the collagen fibers with type II (CII). COMP is the major noncollagenous protein of cartilage and is a homopentamer, interacting with the collagen fibers with each of its subunits. Similar to CII, homologous rat CXI also induces a chronic arthritis in rats but with a different major histocompatibility complex (MHC) genetic control and pathogenesis. CXI induced arthritis (C^XI IA) is characterized by a more pronounced chronic relapsing disease course. The MHC allele of importance is the RT1f haplotype and, surprisingly, some of the CII associated MHC alleles like RT1a are less permissive. Immunization with COMP induces a severe but self-limited arthritis in strains with a genetic background resistant to most other forms of arthritis or even autoimmune models, the E3 rat. The MHC association also differs between the different models (CIA, CXI, and COMPIA). An autoimmune response to COMP is triggered despite the circulation of COMP fragments in both physiologic and arthritic states. The induction of arthritis in rats with CXI or COMP provides an arthritis models with a distinct pathogenesis as compared with other induced arthritis models.