Autoimmune aspects of type 2 diabetes mellitus - a mini-review

Abstract

Autoimmunity is a well-known pathogenic component in type 1 diabetes (T1DM). The assumption that the pathogenesis of type 2 diabetes (T2DM) also encompasses autoimmune aspects is recognized increasingly, based on the presence of circulating autoantibodies against β cells, self-reactive T cells, but also on the glucose-lowering efficacy of some immunomodulatory therapies in T2DM. The identification of these autoantibodies in elderly patients with slowly progressive manifestation of diabetes led to the introduction of a distinct clinical entity termed latent autoimmune diabetes of the adult (LADA), which combines features of both T1DM and T2DM. The autoantibody cluster differs in patients with LADA from patients with T1DM, but their presence indicates steady progression towards β-cell death and subsequent need for initiation of insulin treatment in a shorter period of time compared to autoantibody-negative T2DM patients. Autoimmune aspects in T2DM are not solely restricted to autoantibodies and thus LADA. They include the self-reactive T cells or defects in regulatory T cells (Tregs), which have been detected in autoantibody-negative T2DM patients as well. One contributor to the autoimmune activation in T2DM seems to be the chronic inflammatory state, characteristic of this disease. Upon inflammation-induced tissue destruction, cryptic 'self' antigens can trigger an autoimmune response, which in turn accelerates β-cell death. Both innate and adaptive immune system components, specifically macrophages and self-reactive T cells, contribute to an increased secretion of inflammatory cytokines involved in inflammatory and autoimmune processes. However, the extent to which inflammation overlaps with autoimmunity is not known. Our review focuses on autoimmune involvement in T2DM, with an emphasis on LADA and the humoral immune response, on the involvement of chronic inflammation in autoimmunity, and specifically the role of B and T cells as links between inflammatory and autoimmune reactions. We will further stress the consequences of autoimmune activation for T2DM patients and present novel therapeutic approaches for T2DM management that rely on immune modulation.