Functional status of immune cells in patients with long-lasting type 2 diabetes mellitus

Although patients with diabetes contract infectious diseases at higher frequencies, and in more severe forms, compared to non-diabetics, the underlying defects of the immune function have not been defined clearly. To address this, we designed an immune monitoring protocol and analysed the functional status of various immune cells. Peripheral blood mononuclear cells (PBMCs) were stimulated with the proper ligands and the functional reactivity of each lineage of cells was subsequently measured. Patients with type 2 diabetes mellitus (T2DM) had PBMC composition ratios comparable to healthy controls, except for a higher frequency of B cell and effector T cell fractions. The capacity of myeloid cells to secrete proinflammatory cytokines was not diminished in terms of the sensitivity and magnitude of the response. Furthermore, cytolytic activity and interferon (IFN)-γ production of natural killer (NK) cells and CD8⁺ T cells were not decreased in T2DM patients. Phenotypical maturation of dendritic cells, indicated by the up-regulation of major histocompatibility complex (MHC) proteins and co-stimulatory molecules in response to lipopolysaccharide (LPS), was slightly enhanced in T2DM patients. Finally, the functional differentiation profiles of CD4⁺ T cells did not differ between T2DM patients and the control group. These data indicate that patients with long-lasting T2DM do not have any gross functional defects in immune cells, at least in circulating monocytes, dendritic cells, NK cells and T lymphocytes.