From obesity through immunity to type 2 diabetes mellitus

Abstract

Diabetes mellitus is a metabolic disorder that leads to the development of a number of complications. The etiology of each metabolic complication is undoubtedly multifactorial. Patients with diabetes have increased susceptibility to and severity of infections. The course of infections is also more complicated in the patient group. One of the possible causes of this increased prevalence of infections is defect in immunity. Different disturbances in humoral innate immunity have been described in patients with diabetes. Concerning cellular innate immunity, most studies show decreased functions of polymorphonuclear cells and monocyte/macrophages of these patients compared to cells of healthy subjects. Several studies have shown alterations in peripheral blood mononuclear cells from patients with type 2 diabetes, an effect that contributes to the high incidence of infections in these patients. The gut microbiota plays different roles such as the following: protects against pathogens, helps in the maturation of the immune system, regulates the intestinal hormone secretion, synthesizes vitamin K and several vitamins B, and produces short-chain fatty acids (SCFAs). It also plays a role in immunomodulation and might contribute to the alterations in glucose metabolism. In the present review, I focused on the role of obesity, the immune system, and the gut microbiota in the pathogenesis of type 2 diabetes mellitus, and as a second point, how type 2 diabetes impairs the immune system.