We have utilized the human monocytic cell line, THP‐1, and freshly isolated adherent human monocytes with the compounds pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disuphonic acid (PPADS), oxidized ATP, and 1‐(N,O‐bis{5‐isoquinolinesufonyll}‐N‐methyl‐L‐tyrosyl)‐4‐phenylpiperazine (KN‐62) to pharmacologically characterize the P2 receptor involved in ATP‐induced release of interleukin 1β (IL‐1β). We have also investigated the involvement of P2 receptors in lipopolysaccharide (LPS)‐induced IL‐1β release from both cell types.

ATP caused release of IL‐1β from LPS primed THP‐1 cells in both a time‐ and concentration‐dependent manner, with a minimal effective ATP concentration of 1 mM. Stimulation of cells with 5 mM ATP resulted in detectable concentrations of IL‐1β in cell supernatants within 30 min.

The ATP analogue benzoylbenzoyl ATP (DBATP), a P2X₇ receptor agonist, was approximately 10 fold more potent than ATP at eliciting IL‐1β release.

KN‐62 (1 μM), PPADS (100 μM) or oxidized ATP (100 uM) significantly inhibited 5 mM ATP‐induced IL‐1β release by 81, 90 and 66% respectively, but failed to significantly inhibit LPS‐induced IL‐1β release in both THP‐1 cells and in freshly isolated human monocytes.

In both THP‐1 cells and freshly isolated human monocytes, addition of the ATP degrading enzyme apyrase (0.4 U ml⁻¹) to cell supernatants prior to LPS activation failed to significantly inhibit the LPS‐induced IL‐1β release. In addition there was no correlation between extracellular ATP concentrations and IL‐1β release in THP‐1 cells when studied over a 6 h time period.

In conclusion our data confirm the involvement of P2X₇ receptors in ATP‐induced IL‐1β release in human monocytes. However no evidence was obtained which would support the involvement of either endogenous ATP release or P2X₇ receptor activation as the mechanism by which LPS‐induces IL‐1β release in either the THP‐1 cell line or in freshly isolated human monocytes.