Inter-individual and intra-individual variability in TNF-alpha production by human peripheral blood cells in vitro

Background: Two assays-isolated peripheral blood mononuclear cells (PBMC) and a whole blood assay (WBA)-are commonly used to study TNF-alpha production by an individual in order to distinguish between high and low cytokine producers. We assessed the reliability and reproducibility of these assays. Methods: The PBMC assays (n=5) were performed weekly over a period of 6 weeks and the WBAs (n=4) weekly over a 4-week period. Polymethylmethacrylate particles (approx. 6 X 102 particles/cell) and optimal concentrations of endotoxin (6.25 and 12.5 ng/ml) were used as the stimulatory agents in PBMC and WBAs, respectively. TNF-alpha production was measured by ELISA. Results: There was a high degree of both intra- and inter-individual variability of TNF-alpha secretion, with unpredictable changes in the amount of the cytokine produced by cells from the same donor. This variability could not be eliminated by correcting for cell numbers. Conclusion: The PBMC and WBA models of TNF-alpha production by human peripheral blood cells cannot be used for the evaluation of inter-individual variability in cytokine secretion due to the high intra-individual variability observed. In the case of PBMC this is partly due to differences in the confluency of the cells between individuals. (c) 2005 Elsevier Ltd. All rights reserved.