Fig 2: Model of pore former induced lysis. A bacterial toxin inserts a large channel or pore into the erythrocyte membrane. ATP is immediately released through the pore and activates P2X receptors. The membrane insertion of the toxin also causes a steep rise in the intracellular Ca2+ concentration ([Ca2+]i), which results from Ca2+ passing through the pore itself and from activation of P2X receptors, which are non-selective cation channels permeable to Ca2+. The increase in [Ca2+]i activates the Ca2+-sensitive K+ channel KCa3.1 and Cl- channel TMEM16A, which results in K+ and Cl- efflux and cell shrinkage as obligated water follows. The cells will remain shrunken as long as the K+ efflux surpasses the Na+ influx via the toxin pore and the P2X receptors. Prolonged stimulation of P2X7 can activate pannexins, which will contribute to the Na+ influx. Eventually, the Na+ influx will exceed the K+ efflux and the cells will swell and eventually burst. Blockage of the P2X1 and P2X7 receptor has been proven as a protective measure for bacterial toxins, and for complement to carry out their toxicity. The model based on previous work [6, 14, 17, 30]

Fig 3: Haematocrit and haemoglobin levels and erythrocyte P2X receptor expression in patients infected with cytolysin-producing bacteria. a Change in haematocrit between Emergency Department (ER) and ICU admissions in patients with a positive blood culture result for cytolysin-producing bacteria and correlation with P2X1 receptor expression on erythrocytes. b Change in haemoglobin between ER and ICU admissions in patients with a positive blood culture result for cytolysin-producing bacteria and correlation with P2X1 receptor expression

Fig 4: Freeze-thaw - control experiments. a Whole blood drawn from healthy volunteers was incubated either with vehicle (Veh), 100 µM NF449 (P2X1 antagonist) or 100 µM A804598 (P2X7 antagonist) and frozen and stored for 3 weeks as whole blood at - 80 °C. After thawing, lysis was measured as absorbance of free haemoglobin in supernatant at 540 nm. n = 3, mean ± SEM. b Flow cytometry of thawed whole blood samples diluted 1000-fold, to ascertain equal distribution of blood cell sub-populations. Cells were identified by forward scatter FSC and side scatter SSC and quantified based on fixed regions. c Bar graph shows data presented as mean ± SEM, n = 3. ns, not significant