T cell subsets and their role in the pathogenesis of rheumatic disease

T lymphocytes are critical to the pathogenesis of systemic rheumatic diseases. Understanding of the roles of T cells in disease has been enriched by the description of highly distinct effector subsets of CD4 T lymphocytes. The purpose of this review is to describe selected advances in the biology of T lymphocytes that are pertinent to the pathogenesis or treatment of rheumatic diseases.Knowledge is expanding about not only pathogenic effector T cell subsets, such as the TH17 cells, but also of regulatory T cells (Treg), the functions of which are defective, but correctable, in several rheumatic diseases. Although the initial agent that demonstrated a role for T cells in rheumatoid arthritis was CTLA4-Ig (abatacept), use of this biologic is now expanding to other rheumatic diseases. Moreover, effects of other biologics are now understood to in part be mediated by effects on T cell subsets. Experimental model systems in rodents continue to be valuable testing grounds for future approaches to treatment of human disease. Meanwhile, the roles of effector T cell subsets are becoming clearer in conditions such as Sjogren's syndrome and scleroderma. Finally, rheumatic diseases, including rheumatoid arthritis and spondyloarthropathies, have been critical for identification of new innate-like T cell subsets.Imbalances in the numbers and functions of specific T cell subsets are key pathogenic derangements in systemic rheumatic diseases, and these insights are leading to changes in clinical practice.