Exogenous Melatonin Up-Regulates Expression of CD62L by Lymphocytes in Aged Mice under Inflammatory and Non-Inflammatory Conditions

It is well documented that age-related impaired functioning of immunocompetent cells is associated with an increase in the rates of chronic inflammatory diseases. Recently, an ability of melatonin to modulate inflammatory processes by regulating leucocyte recruitment has been demonstrated. However, to date, no studies have attempted to determine the impact of melatonin on the expression of CD62L by lymphocytes. CD62L, also known as L-selectin, is required for the entry of lymphocytes into secondary lymphoid organs, sites of tumor growth and chronic inflammation through high endothelial venules. Here, we investigated the effect of melatonin at physiological concentrations on the expression of CD62L by T and NK cells in vivo and in vitro. We demonstrated that NK and CD3⁺ T cells obtained from the spleen of aged mice were characterized by decreased expression of CD62L compared to young mice. Melatonin administration up-regulated the levels of surface CD62L on NK and T cell populations in aged mice under non-inflammatory conditions and on CD8⁺ T cells in aged mice with chronic inflammation. Pre-incubation with melatonin prevented the reduction in CD62L expression by CD8⁺ T cells induced by the co-cultivation of peripheral blood mononuclear cells with human pancreatic adenocarcinoma cell line (MiaPaCa-2). The obtained results suggest that melatonin can modulate lymphocyte homing into lymph nodes and sites of chronic inflammation and, therefore, can stimulate immune responses in chronic inflammatory conditions associated with aging.