Upregulation of cytokine mRNA in circulating leukocytes during human endotoxemia

Endotoxemia induces pronounced changes in leukocyte count and enhances the release of many cytokines. However, the molecular regulation of this cytokine release is poorly characterized in humans. The time course of mRNA expression of 24 cytokines in circulating leukocytes was studied in a well-standardized model of human endotoxemia (2 ng/kg). Real-time polymerase chain reaction (RT-PCR) was used to quantify the lipopolysaccharide (LPS)-inducible mRNA levels of leukocytes from 16 healthy volunteers in a randomized, placebo-controlled trial. Baseline mRNA levels of interleukins including IL-1α, IL-3, IL-5, IL-6, IL-12p40, IL-13, IL-15, IL-17, granulocyte colony-stimulating factor (G-CSF) and granulocyte monocyte CSF (GM-CSF) were below detectable levels in normal blood of the healthy participants. After 2 h, LPS infusion increased median mRNA levels of IL-1α by >1100-fold and IL-1β and IL-8 by 33-fold and 46-fold, respectively. In contrast, levels of tumor necrosis factor (TNF-α) and IL-10 mRNA increased by only 7-fold, whereas changes in mRNA expression of other cytokines showed either a more than two fold increase or were undetectable. In vitro incubation of whole blood with 50 pg/mL LPS for 2 h enhanced transcription levels of IL-1α mRNA by >10,000-fold, IL-6 and IL-12p40 by >1000-fold, IL-1β by 400-fold, TNF-α by 100-fold, IL-8, IL-18, interferon γ (IFN-γ) and G-CSF by >10-25-fold, and IL-10, IL-12p35, TNF-β, and IL-13 by 10-25-fold. Only half of the 24 evaluated cytokines were expressed at the mRNA level in circulating leukocytes under basal conditions and after an LPS challenge. Only IL-1α, IL-1β, IL-10, IL-8, and TNF-α were upregulated in the circulating leukocytes, whereas several other cytokines (including IL-6 and G-CSF), were expressed on the mRNA level following in vitro incubation of blood with LPS. In addition, IL-1α and IL-1β might be potential diagnostic targets in inflammatory diseases.