Regulation of TH17 and regulatory T cells in patients with Behçet disease

Abstract

Behcet disease (BD) is a systemic inflammatory disorder with a diverse spectrum of clinical manifestations, including mucocutaneous, ocular, vascular, gastrointestinal, musculoskeletal, and central nervous system involvement. Although HLA-B51 is clearly defined as the major genetic risk factor, it can account for only a part of the genetic risk. BD is currently thought to be an autoimmune/autoinflammatory syndrome that is possibly induced by infections or other environmental factors. There are several hypotheses to explain the pathogenesis of BD. Recurrent orogenital ulcers,mucocutaneous acneiform-like lesions, and nondeforming arthritis typically present as episodes of unprovoked, recurrent inflammatory attackswith neutrophil-dominated infiltrates and resemble the recently named autoinflammatory disorders. Autoinflammatory disorders are disorders that typically respond to IL-1 antagonist therapies (which also seem towork in patients with BD). However, several studies also showed that polarization of CD4 T cells into TH1 cells and their cytokines, such as IFN-g and IL-12, play a central role in the pathogenesis of BD. Levels of IL-12, which drives the TH1 response in naive T cells, are increased in sera from patients with BD in correlation with the presence of TH1 lymphocytes. Tissue studies demonstrated TH1-type intestinal and cutaneous lesions, possibly drivenwith IL-12 and IL-23. A recent study also showed that natural killer type 2 cells, which produce IL-5 and IL-13, but not natural killer type 1 cells, which produce IFN-g and IL-10, were predominant in patients with BD in remission. However, as in the case of allergy and other autoimmune disorders, such as multiple sclerosis, only the TH1-TH2 paradigm cannot fully explain the full mechanism. The novel T-cell subsets TH9, TH17, TH22, and regulatory T (Treg) cells and their cytokines are intricately involved in inflammatory disorders.