BINDING, OLIGOMERIZATION, AND PORE FORMATION BY STREPTOLYSIN-O IN ERYTHROCYTES AND FIBROBLAST MEMBRANES - DETECTION OF NONLYTIC POLYMERS

Streptolysin O (SLO) is a representative of the family of cholesterol- binding cytolysins that form large pores in target cell membranes, Agg regation of the toxin to polymeric structures is required for pore for mation, However, it is not known whether, vice versa, polymers may und er certain circumstances remain nonfunctional, and whether this might be the cause underlying the relative resistance of certain cells towar ds toxin action, In the present study, we applied radioiodinated, func tionally active SLO to human, rabbit, and mouse erythrocytes and to hu man fibroblasts and keratinocytes, Binding and polymerization were qua ntified and correlated with membrane damage, At low toxin concentratio ns, human and rabbit but not mouse erythrocytes were lysed, but bindin g and polymerization of SLO were essentially identical in all cases. N onlytic polymers were also detected on human fibroblasts and keratinoc ytes treated with subcytotoxic concentrations of SLO, and quantitative estimates indicated that nonpermeabilized cells could carry hundreds of polymers on their surface, When applied at low concentrations to fi broblasts, much of the toxin remained in monomer form and was subseque ntly shed from the cells, This was shown by monitoring the fate of rad ioiodinated toxin and also by using a sensitive cell enzyme-linked imm unosorbent assay that permitted immunological detection of surface-exp osed SLO. Thus, relative resistance of cells towards the permeabilizin g action of SLO may be due to their ability to tolerate formation of a limited number of SLO polymers and to shedding of nonoligomerized tox in from their surface.