Relationship of Il-5 with Th1 and Th2 Cytokines in Individuals with or without Type-2 Diabetes

Obesity is linked to metabolic syndrome including insulin resistance, type-2 diabetes (T2D), and cardiovascular disease. Persistent low-grade inflammation is associated with metabolic disorders. Changes in plasma cytokines have been reported in obesity and T2D. Functionally polarized CD4+ T cells are classified as Th1, Th2, Th17, and Treg subsets depending on the pattern of their cytokine production. Th1 cytokines, such as interleukin (IL)-2 and interferon (IFN)-γ activate macrophages and are involved in inflammatory immune responses whereas Th2 cytokines, such as IL-4, IL-5, IL-10, and IL-13 have antiinflammatory properties and are involved in antibody production, eosinophil activation, and suppression of macrophage functions. Th1/Th2 cytokine imbalance has been reported in chronic disease progression and in metabolic syndrome. IL-2 is a proinflammatory cytokine that promotes synthesis of tumor necrosis factor (TNF)-α and IFN-γ from natural killer cells (NK) cells and is associated with atherogenesis and T2D. IFN-γ is related with the production of macrophage mediators, chemokines, induction of leukocyte adhesion molecules and class II major histocompatibility antigens, and potentiates the antigen presenting cell functioning. IL-4 which is secreted by activated Th2 cells, basophils, and mast cells has pleiotropic functions including Th2 differentiation, B-cell proliferation and immunoglobulin class switching. IL-10 is an antiinflammatory cytokine which attenuates inflammation induced by IL-1, IL-6, and TNF-α while it also promotes the release of anti-inflammatory IL-1RA.

IL-5 is an important T cell-derived cytokine that regulates the expression of diverse genes involved in proliferation, cell survival, as well as maturation and effector functioning of B cells and eosinophils. IL-5 plays a pivotal role in both the innate and adaptive immune responses and the biologic effects of IL-5 are best characterized for eosinophils in humans. It is not clear whether plasma IL-5 levels are modulated and also relate with the Th1/Th2 cytokine profile in metabolic disorders such as obesity and T2D. The aim of the study was, therefore, to determine the circulatory IL-5 levels in diabetic and nondiabetic individuals and evaluate the relationship of IL-5 levels with Th1/Th2 cytokine profile in these two populations. Here, we show that plasma IL-5 levels were significantly lower in diabetic individuals and these changes correlated with Th1/Th2 cytokines and clinical metabolic markers differentially between diabetics and non-diabetics.