Effect of Interleukin-29 on Interferon-alpha Secretion by Peripheral Blood Mononuclear Cells

Abstract

Objective: The effect of interleukin (IL)-29, a new therapeutic agent similar to type I interferons (IFNs), on IFN-alpha secretion of human plasmacytoid dendritic cells (pDCs) has not been studied. Therefore, in this study, we aimed to clarify the effect of IL-29 on IFN-alpha secretion of pDCs using human peripheral blood mononuclear cells (PBMCs) in the presence of cytosine-phosphate-guanosinemotif-containing oligodeoxy nucleotides (CpG). Materials and Methods: In this experimental and prospective study, PBMCs were obtained from 11 healthy volunteers and divided into four culture conditions: I. control, II. CpG treatment, III. IL-29 treatment and IV. CpG plus IL-29 treatment. The amount of IFN-alpha secretion was measured from each culture supernatant by flow cytometry using the flow-cytomix apparatus (eBioscience, Vienna, Austria). Fractional IFN-alpha production of the cultured PBMCs was measured by intracellular staining using the cytomics FC 500 system (Beckman Coulter, Brea, CA, USA) with CXP Software. Results: The mean +/- standard deviation (SD) of supernatant IFN-alpha secretion per pDC/mu L was 5.7 +/- 9.3 pg/mL/count/mu L for condition I, 1071.5 +/- 1026.6 pg/mL/count/mu L for condition II, 14.1 +/- 21.1 pg/mL/count/mu L for condition III, and 1913.9 +/- 1525.9 pg/mL/count/mu L for condition IV. There were statistically significant differences between conditions I and II as well as betweenconditions II and IV. Intracellular IFN-alpha production was only detectable in the pDC fraction from one culture; the production amount was similar between the cells treated with CpG and those treated with CpG plus IL-29. Natural killer (NK) cell production of IFN-alpha was observed in two out of three cultures and one culture showed IFN-alpha production in the monocyte fraction. Conclusion: IL-29 alone did not show any effect on IFN-alpha secretion of PBMCs. However, the addition of CpG along with IL-29 enhanced IFN-alpha secretion of PBMCs. Given that pDCs are the major secretors of IFN-alpha in peripheral blood, this result has suggested the possibility that IL-29 has an enhancing effect in human pDC IFN-alpha secretion. Although the supernatant IFN-alpha secretion was not directly correlated with pDCs's intracellular IFN-alpha production in this study, prolonged incubation of pDC and other PB subsets with CpG or IL-29 for over 4 hours could be applied in future studies. These studies would help to elucidate the mechanism of action of IL-29 in human pDCs associated with viral infections.