Effect of redox status of peripheral blood on immune signature of circulating regulatory and cytotoxic T cells in streptozotocin induced rodent model of type I diabetes

Diabetes mellitus is an autoimmune chronic inflammatory disease manifested by hyperglycemia and associated with imbalance in redox status and inflammatory response. Oxidative stress has been reported to affect functions of T cell repertoire- regulatory T cells (Tregs) and cytotoxic lymphocytes (CTLs). Tregs are involved in prevention against autoreactive T cells and controlling inflammation while CTLs are major mediators of tissue injury. Hence the present study is novel as it contemplates to understand oxidative stress in diabetes vis-à-vis T cells. Comparative analysis was carried out between two groups, i.e., healthy Sprague Dawley (SD) and Streptozotocin (STZ) induced SD rat model of type1 diabetes (T1D). Various hematological, biochemical and oxidative stress parameters were assessed in plasma samples in the study. Peripheral blood mononuclear cells (PBMCs), Tregs and CTLs were evaluated for intracellular oxidative stress using 2′,7′-dichlorofluorescin diacetate (DCFDA), mitochondrial ROS using Mitosox-red, mitochondrial membrane potential using JC-1 in PBMCs. Treg populations expressing IL-4, IL-6 and IL-10 and CTLs expressing αβ-T cell receptor (αβ -TCR), interferon- γ (IFN-γ), perforin and granzyme were also considered. We found decreased activity of enzymes such as catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and reduced glutathione(GSH) and increased lipid peroxidation (LPO) in plasma indicated altered redox state in diabetic animals. Elevated intracellular reactive oxygen species (ROS) and mitochondrial superoxide was observed in T1D group confirming oxidative stress in cell specific manner. Cell population with hyperpolarized mitochondrial membrane potential was found to be elevated in T1D group. We found a decrease in Treg population in T1D group in comparison to healthy group. Treg population expressing IL-4, IL-6 were increased and those expressing IL-10 were found to be reduced in diabetic group. The CTL numbers were dropping whereas αβ-TCR, IFN-γ, perforin and granzyme expressing CTLs were on the rise in diabetic group. Our finding suggested an increased oxidative stress in Tregs and CTLs which might be responsible for progressive inflammatory environment built up due to persistent hyperglycemia. This was fortified by the statistical analyses where strong correlation between LPO and CTLs expressing TCR, IFN-γ, perforin and granzyme was noted. Lipid peroxidation was also found to be correlated to intracellular ROS in Tregs and CTLs along with other important revelations. The present study gives important insights into the significance of oxidative stress on immune system and its mediators in diabetes.