HLA Transgenic Mice as a Model to Uncover Biomarkers and Therapeutic Strategies for Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic disease involving inflammation of the joints. While the etiology of RA remains unknown, evidence exists for a significant contribution of the major histocompatibility complex (MHC). Environmental factors are also indicated as playing an etiological role. Since it is impossible to define the mechanisms contributing to disease onset and progression in humans, mouse models have been used widely. While many animal models have been generated by immunization with self‐proteins to induce arthritis, type II collagen (CII)‐induced arthritis is one of the most commonly used models utilized to understand the immunopathology of RA. CII constitutes 80% to 90% of total collagen content of hyaline cartilage found in joints and is a genetically conserved sequestered protein. Immunization with heterologous CII with an adjuvant in mice leads to cellular and humoral responses to heterologous and autoreactive CII‐specific responses and collagen‐induced arthritis (CIA). Mice immunized with CII develop inflammatory arthritis that shares many similarities in clinical, serological, and radiological features with RA in humans. However, selecting an antigen for inducing arthritis and the mouse strain are important, as not all strains are susceptible to CIA. A critical difference between RA and CIA is that in mice that lack the expression of human MHC II, the development of CIA is linked to the H2A locus, which is the homologue of HLA‐DQ, while most human studies have linked RA susceptibility with HLA‐DR alleles. Mice expressing HLA‐DQ and HLA‐DR molecules have been used to understand the role of MHC genes in susceptibility to RA. The protocols for inducing CIA in the HLA expressing transgenic mice described in this article can be used to understand how the different HLA molecules confer susceptibility to RA.