Induction of Suicidal Erythrocyte Death by Listeriolysin from Listeria monocytogenes
Listeriolysin, the secreted cytolysin of the facultative intracellular bacterium Listeria monocytogenes, is its major virulence factor. Previously, non-lytic concentrations of listeriolysin were shown to induce Ca2+-permeable nonselective cation channels in human embryonic kidney cells. In erythrocytes, Ca2+ entry is followed by activation of K+ channels resulting in K+-exit as well as by membrane scrambling resulting in phosphatidylserine exposure at the cell surface. Phosphatidylserine-exposing erythrocytes are recognized by macrophages, engulfed, degraded and thus cleared from circulating blood. Phosphatidylserine exposure is a key event of eryptosis, the suicidal death of erythrocytes. The present study utilized patch-clamp technique, Fluo3-fluorescence, and annexin V-binding in FACS analysis to determine the effect of listeriolysin on cell membrane conductance, cytosolic free Ca2+ concentration, and phosphatidylserine exposure, respectively. Within 30 minutes, exposure of human peripheral blood erythrocytes to low concentrations of listeriolysin (which were non-hemolytic for the majority of cells) induced a Ca2+-permeable cation conductance in the erythrocyte cell membrane, increased cytosolic Ca2+ concentration, and triggered annexin V-binding. Increase of extracellular K+ concentration blunted, but did not prevent, listeriolysin-induced annexin V-binding. In conclusion, listeriolysin triggers suicidal death of erythrocytes, an effect at least partially due to depletion of intracellular K+. Listeriolysin induced suicidal erythrocyte death could well contribute to the pathophysiology of L. monocytogenes infection.