[The Role of Vitamin D3 on the Immune Responses of Monocytes]

The active form of vitamin D (Vit D), 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3), is important for cell functions and immunity, as well as its role in bone metabolism. Monocytes/macrophages initiate innate immune response, and is considered to be the cell that first comes into contact with the pathogen. They play effective roles in innate immune and inflammatory responses by intercellular relations and inflammatory mediator secretion. Human THP-1 leukemia cells are frequently used for the in vitro determination of the signal pathways, and the functions of monocyte/macrophages. Nuclear factor-kappa B (NF-κB) are complex networks of signaling pathways that regulate many important cellular behaviors, especially in inflammation, cell death, cell differentiation or proliferation. Midkine (MK) is a cytokine and growth factor that is one of the regulators of inflammatory processes, immune cell functions, proliferation and autoimmunity. The effects of Vit D3 on inflammation and MK secretion in hyperglycemia is still unknown. In this study, it was aimed to determine the dose-dependent effects of Vit D3 on the lipopolysaccharide (LPS) stimulated pro/ anti-inflammatory cytokine, NF-κB and MK responses of THP-1 monocyte cells under normo and hyperglycemic conditions. For this purpose, THP-1 monocyte cells stimulated with LPS (Escherichia coli, 0111, 1 μg/ml) under normoglycemic (glucose 100 mg/dl)/hyperglycemic (glucose 500 mg/dl) conditions, were incubated for 24 hours in the presence and absence of 10-50-100 IU/ml Vit D3. MK, TNF-α, IL-8, IL-10 cytokine levels in the supernatants collected from the wells at the end of the incubation periods, and NF-κB levels in the obtained cell lysates were detected by ELISA method. LPS stimulation induced higher levels of TNF-α, IL-8 and MK responses in hyperglycemic conditions. IL-10 secretions were found to be decreased under hyperglycemia. Vit D3 modulates TNF-α, IL-10 and MK secretions in hyperglycemic conditions. The MK and TNF-α levels were determined to be correlated with NF-κB and IL-10. The results obtained in the study showed that Vit D3 can play a role in immune modulation by regulating NF-κB and cytokine/ chemokine-like molecule MK suppression and proinflammatory/anti-inflammatory cytokine balance. The mechanism of the action of Vit D3 under different conditions should be examined in detail.