Generation of antistreptolysin O activity in contaminated sera

Abstract

THE ability to lyse erythrocytes of reduced streptolysin O, produced by strains of Lancefield's group A streptococci apparently results from attachment to membrane cholesterol. Cholesterol in aqueous emulsion will inhibit streptolysin activity at concentrations of about 1.0 µg ml⁻¹ (ref. 1). Sera contaminated with bacteria can occasionally give false positive tests for anti-streptolysin antibody but the underlying mechanism has never been defined. We have excluded the possibility that bacterial contamination leads to release of free cholesterol from either ester-bound or protein-bound cholesterol by showing that (1) cholesterol added to contaminated sera showing positive antistreptolysin activity is bound to the same extent as in normal serum, and (2) that ultrafiltrates of such contaminated sera do not contain free cholesterol. Therefore it seemed likely that bacteria in serum might release proteolytic enzymes which would cleave the streptolysin molecule. But the studies reported here indicate that the system is more complex.