O, a thiol-activated cytolysin, which creates membrane holes on eukaryotic cells. One specific type of cytolysin is the "Cholesterol-dependent cytolysin" (CDC). The term "Cytolysin" is then introduced by Bernheimer to replace "Hemolysin". Membrane-damaging toxins exhibit hemolysin or cytolysin activity "in vitro". The Thiol-activated Cholesterol-dependent Cytolysin (CDC) family (TC# 1.C.12) is a member of the MACPF superfamily. Finally, the formed cytolysin clusters penetrate target cells' membranes and form membrane pores.