Adjuvant arthritis: immunopathological and hyperalgesic features

Adjuvant arthritis is an experimental immunopathy that is thought to share many features of human rheumatoid arthritis and, as such, is one of the most widely used models for studying the anti-inflammatory properties of compounds. Adjuvant arthritis can be induced in the rat by the injection of various bacterial cell walls or their components; however, the exact immunogen remains unknown. Recently, an autoantibody response to type II collagen was described not only in the collagen-induced arthritic model but in the adjuvant-induced disease as well. This response thus suggests that shared antigenic determinants exist between type II collagen and the responsible immunogen in the bacterial cell wall components. The contribution of the T lymphocyte to the pathogenesis of adjuvant arthritis is well known. It has now been shown that under specific conditions, adjuvant arthritis can be either enhanced or suppressed with pharmacologic or surgical manipulation, thus suggesting the heterogenicity of T lymphocytes capable of influencing the course of the disease. Levamisole was shown to reverse the augmentation of adjuvant disease seen after adult thymectomy, which suggests that levamisole can restore an aberrant immune response. Monoclonal antibodies are now being developed to evaluate T cell subsets in the rat. The use of these antibodies to study or selectively deplete lymphocyte subpopulations in this disease model promises to reveal immunologic characteristics that may lead to the development of new classes of immunoregulant drugs. Finally, the adjuvant rat has been found useful as a pain model capable of detecting the analgesic properties of both central and the newer peripheral analgesics. The above studies further corroborate the similarities between the immunopathological and hyperalgesic features of human rheumatoid arthritis and adjuvant disease. Recently developed immunologic technology may allow a new look at an old model and may result in the ability to evaluate new classes of immunoregulating agents.