Interferon gamma levels are reduced by adenosine 5'-triphosphate in lipopolysaccharide-stimulated whole human blood

Introduction

Extracellular release of ATP is an important modulator of immune response. ATP plasma concentration is increased in sepsis [1]. IFNγ plays a critical role in host defense by promoting Th1 phenotype and bacterial clearance. Low IFNγ levels are associated with the Th2 phenotype consistent with critical illness anergy [2]. It has been reported that 100 and 300 mM ATP increased LPS/PHA-stimulated IL-10 secretion in human blood [3]. Higher IL-10/IFNγ ratio shifts the immune phenotype from Th1 to Th2 response. We studied the effect of ATP on LPS-stimulated IL-10 and IFNγ secretion in a standardized ex-vivo whole human blood culture.

Methods

Venous blood from 10 healthy volunteers was drawn into tubes containing 10 ng LPS/ml (ILCSÒ; EDI GmBH, Reutlingen, Germany) and incubated with or without 100 mM ATP, respectively, at 37°C for 24 hours. The supernates were separated and frozen at -20°C. Cytokine levels were analysed on a robotic workstation (epMotion 5075; Eppendorf AG, Hamburg, Germany) in duplicate using the ELISA Cytokine kit (Luminex; Biosource Int., Camarillo, CA, USA).

Results

Added ATP reduced the mean concentration of IFNγ in LPS-stimulated blood from 1,206 ± 1,667 pg/ml to 140 ± 128 pg/ml; P = 0.006. There was no consistent effect of ATP on IL-10 secretion in our study (21.6 ± 16.9 pg/ml to 17.2 ± 18.8 pg/ml). Interestingly, three subjects of Indian/Indonesian origin had IL-10 levels below the assay detection limit. The mean IL-10/IFNγ ratio was increased from 0.05 ± 0.04 to 0.16 ± 0.09 in the remaining Caucasian subjects (P = 0.015). See Figure 1.

Figure 1

(abstract P5)

Conclusion

Our results suggest an immunosuppressive effect of extracellular ATP that is evident by the decrease of IFNγ and therefore the relative shift of the immune response towards Th2 phenotype. Although this may represent a self-protective mechanism, it may contribute to critical illness anergy.