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.

Increased serum concentrations of tumor necrosis factor α (TNFα) and transforming growth factor β‑1 (TGFβ‑1) in the blood of patients with pancreatic cancer (PC) have previously been demonstrated. In addition, exogenous exposure to these cytokines promotes various cancer cell invasive and cancer stem cell (CSC) phenotypes. However, their importance in pancreatic CSCs remains elusive. In the present study, the effects of TNFα and TGFβ‑1 on the human PC cell line MiaPaCa‑2 were examined. Using flow cytometry, it was revealed that TNFα and TGFβ‑1 synergistically increase cluster of differentiation (CD) 44v6, CD133 and ATP‑binding cassette transporter G2 (ABCG2) expressing populations in adherent tumor cell culture conditions. Furthermore, a similar trend was observed in cells pretreated with these cytokines grown in sphere forming culture conditions. Similar to previous studies, TNFα treatment increased the proportion of epidermal growth factor receptor (EGFR) expressing cells in adherent culture, and this data was further supported by the results of the sphere formation assay, in which the subculture with a high proportion of EGFR expressing cells exhibited the most efficient sphere forming ability. However, the proportion of vascular endothelial growth factor receptor 1 (VEGFR1) expressing cells did not increase upon treatment with these cytokines individually or in combination. This data was subsequently supported by the results of the wound healing assay in which cytokine treatment did not increase the migration of cells. The MTT cell proli­feration and cytotoxicity assay revealed that TNFα + TGFβ‑1 treatment significantly increased cell proliferation and daunorubicin resistance, but not gemcitabine resistance. In conclusion, the data of the current study provide a mechanistic association between TNFα, TGFβ‑1 and the CSC properties of MiaPaCa‑2 cells. In addition, it suggests that targeting TNFα and TGFβ‑1 is beneficial for improving the therapeutic efficacy of treatments for patients with PC.