Background: Interleukin 24 (IL-24) is expressed at different levels in a variety of tumor tissues and matched normal tissues and is regarded as a potential tumor biomarker as its expression levels in tumor tissues are associated with tumor patient prognosis. At present, the expression level of IL-24 in healthy human peripheral blood is unknown.
Methods: In this study, 1940 blood samples were collected using different processing methods from healthy donors. ELISA was used to detect IL-24 concentrations.
Results: The results showed that processing methods had the greatest influence on test results, with the highest IL24 concentration in EDTA plasma and the lowest in sodium citrate plasma. Lengths of storage time at 4°C had no obvious effect on IL-24 test results, and IL-24 in peripheral blood was stable for 15 days. IL-24 concentration in the sera of healthy donors showed no associations with age, blood glucose, hemoglobin, total cholesterol, carcinoembryonic antigen, absolute lymphocyte counts, alpha fetoprotein, white blood cells, thyroid stimulating hormone, or cereal third transaminase. We also confirmed that IL-24 expression level in the blood of healthy subjects was positively correlated with pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-α), and interleukin 6 (IL-6), but negatively correlated with anti-inflammatory cytokine, IL-10.
Conclusions: We observed that sample processing methods influence the detection of IL-24 levels as EDTA plasma had the highest IL-24 concentration, and citric acid sodium, the lowest. Age, gender, and physical and chemical indicators were not related to IL-24 concentrations. We confirmed the IL-24 concentration was positively related to IL-6 and TNF-α and negatively to IL-10.