Whole blood culture Heparinized blood was mixed with an equal volume of culture medium (RPMI 1640 supplemented with 25 mM HEPES (2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid), 100 U/ml penicillin, 100 µg/ml streptomycin) and 1 ml aliquots were transferred into loosely sealed round-bottom polypropylene tubes (Greiner, Germany). Whole blood cultures were kept at 37 oC and 5 % CO2 for the indicated time periods. Thereafter, cell-free plasma/RPMI samples were obtained by centrifugation and stored at -70oC until assessment of cytokine concentrations by enzyme linked immunosorbent essay (ELISA). Experiments were started within 60 min of blood withdrawal. Thus, the whole blood cultures consisted of the whole range of white blood cells as well as erythrocytes. Except for determination of IL-1β release, cultures were either kept as unstimulated control or stimulated with LPS (10 or 100 ng/ml), or with the combination of IL-1β plus TNF-α (50 ng/ml each) for 24h. For determination of IL-1β release, cells were kept as unstimulated control or were stimulated with Toll-like receptor 4 ligand LPS (100 ng/ml) for altogether 5h. For efficient release of IL-1β from activated cultures, LPS was combined with ATP (2 mM) which was added during the last 2h of the 5h stimulation period in order to achieve activation of the purinoreceptor P2X7.