SP816
TRANSIENT SUPPRESSION OF PRO-INFLAMMATORY T-CELL SUBSETS AFTER LPS CHALLENGE IN A HUMAN, EXPERIMENTAL ENDOTOXINAEMIA MODEL Free

INTRODUCTION AND AIMS: Systemic inflammatory response syndrome (SIRS) is a multifactorial inflammatory response of an organism to infection or endotoxins, e.g. lipopolysaccharides (LPS). Two different overlapping phases of the immune response, a pro- and anti-inflammatory phase, can be observed in SIRS. SIRS patients are more prone to secondary infections and the underlying mechanisms are not completely understood. T-cells provide pro- and anti-inflammatory functions. Pro-inflammatory T-cell subsets are functional characterized by their mediators e.g. interleukin (IL)-2, interleukin (IL)-17A and interferon-γ (IFN-γ). Regulatory T-cells (Tregs^IL-10+) have a pivotal role in immune regulation via limiting pro-inflammatory conditions by producing interleukin (IL)-10, which is the most important anti-inflammatory cytokine expressed by various cells. The aim of this study is to investigate the T-cell response during the anti-inflammatory phase of SIRS in the human endotoxinaemia model.

METHODS: In a crossover designed placebo-controlled study, 20 healthy male volunteers received an intravenous injection of either LPS (0.8ng/kg body weight) or a placebo (saline 0.9%). Quantification of CD3⁺/CD4⁺/CD8⁺T-cells and intracellular cytokines was done by flow cytometry at baseline and 3 hours after LPS/placebo injection. Complete blood cell counts were obtained with an automated hematology analyzer and cytokines were quantified by ELISA.

RESULTS: Circulating leukocytes were significantly increased 3 hours after LPS injection (p<.0001) with a maximum rise of neutrophils after 6 hours (p<.0001). CD3⁺/CD4⁺/CD8⁺T-cells showed a significant decrease after LPS injection (p<.0001). Intracellular pro-inflammatory T-cell cytokine production such as IFN-γ, IL-2 and IL-17A from T helper cells (TH, CD3⁺/CD8^-) significantly decreased comparing baseline before LPS injection and three hours after LPS challenge (IFN-γ of TH: 17.03% vs. 5,02%, p=.0001; IL-2 and IL-17A production of TH: 41.55% vs. 37.17%, p=.0024; 1.15% vs. 0.63%, p=.0005). The frequency of Tregs^IL-10+ was unchanged (0.83% vs. 0.71%, p=.18). However, the systemic IL-10 level increased significantly after LPS administration (0.57 pg/ml vs. 16.66 pg/ml, p=.0005). The suppressive effect was transient with full recovery of pro-inflammatory T-cell function after 72h.

CONCLUSIONS: The circulating pro-inflammatory T-cell compartments diminished transiently after LPS application most likely due to the increase of IL-10. The IL-10 level sharply increased potentially secreted by highly activated Tregs^IL-10+. IL-10 may have a pivotal role in immunoparalysis during the anti-inflammatory phase of SIRS by suppression of the pro-inflammatory T-cell response and might cause a higher susceptibility of secondary infections.