Classification of microbial, plant and animal cytolysins based on their membrane-damaging effects of human fibroblasts.

38 cytolytic agents of mainly microbial origin were investigated with respect to membrane-damaging activity on human diploid fibroblasts. Increased plasma membrane permeability was measured as leakage of three defined cytoplasmic markers of various sizes: alpha-aminoisobutyric acid, uridine nucleotides and ribosomal RNA. The relative leakages of these markers, caused by different concentrations of the various cytolysins, yielded a leakage pattern for each substance. Five distinct types of leakage patterns were obtained. These were transformed into numerical expressions by calculating the ratios between the amounts of cytolysin needed to release 50% of the nucleotide and ribosomal RNA markers and the amounts required to release 50% of the alpha-aminoisobutyric acid marker (ED50 ratios). A classification of the cytolysins into five groups was arrived at on the basis of the different types of leakage patterns with the aid of reference cytolysins with well-known mechanisms of membrane interaction. These groups comprised: (1) detergent-like agents, (2) agents interacting with only certain constituents of the cell membrane, (3) agents interacting with specific receptor molecules in the membrane, (4) agents inducing small functional holes of a definable size, and (5) agents inducing only a very limited increase in plasma membrane permeability. The system may be useful for characterization and differentiation of new cytolytic agents of various sources as it divides membrane-damaging agents into separate groups on the basis of their principal function on intact human cells.