Genetic analysis of collagen-induced arthritis in rats: a polygenic model for rheumatoid arthritis predicts a common framework of cross-species inflammatory/autoimmune disease loci

Collagen‐induced arthritis (CIA) is a useful model for dissecting the genetic patterns underlying susceptibility to rheumatoid arthritis (RA) and related chronic/inflammatory autoimmune diseases. CIA exhibits three phenotypes characteristic of autoimmune disease pathogenesis: abnormal levels of immune reactivity to self antigens; chronic inflammation of target organs expressing that specific autoantigen; activation and direct participation of invading mononuclear cells and resident tissue fibroblasts in organ damage. Over 25 different quantitative trait loci (QTL) regulating arthritis severity and autoantibody in rats with CIA are mapped. QTL‐congenic strains show that certain CIA–QTLs can modulate arthritis independently. These monogenic models are proving to be highly informative for fine mapping and function studies, revealing gender effects and evidence of gene clusters. Recent genome scans of RA populations identified RA‐susceptibility loci in chromosome regions homologous to rat chromosomal segments housing CIA–QTLs. Also, CIA–QTLs frequently co‐localize with susceptibility QTLs mapped in other rat arthritis models induced with non‐immunogenic adjuvant oils and/or in rat autoimmune models of multiple sclerosis and diabetes. Common autoimmunity genes and inflammation genes important to several human diseases are likely being detected in the various rat disease models. Continued dissection of the genetic underpinnings of rat arthritis models should provide candidate genes for investigation in human patients and lead to a clearer understanding of the complex genetics of RA.