Circulating cell-free DNA (cfDNA) may be involved in immune response regulation. We studied the variations in abundance of telomeric sequences in plasma and serum in young healthy volunteers and the ability of cfDNA contained in these samples to co-activate the TNF-α m RNA expression in monocytes. We performed qPCR to determine relative telomere length (T/S ratios) in plasma, serum and whole blood of 36 volunteers. Using paired samples of plasma and serum and DNase treatment, we analysed the contribution of cfDNA to the co-activation of TNF-α mRNA expression in THP1 monocytic cell line. We found significant differences between paired plasma and serum samples in relative T/S ratios (median 1.38 ± 1.1 vs. 0.86 ± 0.25, respectively) and in total amounts of cfDNA and in estimated total amounts of telomeres which were significantly higher in serum than in plasma. TNF-α mRNA expression in THP1 cells increased significantly after DNase treatment of all samples used for stimulation. The highest TNF-α mRNA expressions were observed after stimulation with DNase treated serum samples. Our results suggest that the different content of telomeric sequences in plasma and serum may contribute to the tuning of immune response. Further studies of this interesting phenomenon are needed.

Department of Anthropology and Human Genetics Faculty of Science Charles University Vinicna 7 128 43 Prague Czech Republic

Department of Biology and Medical Genetics 1st Faculty of Medicine Charles University and General Faculty Hospital Prague Albertov 4 128 00 Prague Czech Republic

Department of Histology and Embryology 1st Faculty of Medicine Charles University Albertov 4 128 00 Prague Czech Republic

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Monitoring of telomere dynamics in peripheral blood leukocytes in relation to colorectal cancer patients' outcomes

Cell-free DNA in plasma as an essential immune system regulator