Contact-dependent haemolytic activity was observed with cells of HRv and HRa, but not with those of BCG and . Culture filtrates of all these strains did not exhibit any haemolytic activity. HRv was subsequently used for the isolation of haemolysin. Haemolytic activity was retained in the cell debris even after sonication of the cells and treatment with Tween 80 and lysozyme. Solubilisation of haemolysin was possible only after the cell debris was washed with ethanol 70% and then treated with Tween 80 0.1%. The haemolysin thus obtained showed a micellar M of >200 000 by gelfiltration on Sephadex G-200 and a subunit M of 66 000 by SDS-PAGE. It was sensitive to trypsin but stable when heated at 60C for 10 min. Polyclonal serum raised in rabbits against the haemolysin neutralised the haemolytic activity. The N-terminal amino-acid sequence of the 66-kDa subunit of haemolysin showed identity with TB66, the 66-kDa secretory protein of , and 30% homology with the haemolysin A precursor of . Phosphatidylglycerol inhibited lysis of sheep erythrocytes by the haemolysin and is probably the receptor for the haemolysin. Haemolysin not only lysed erythrocytes, but was also cytotoxic to human lung cells. It appears that, among the members of the complex, the cell-bound contact-dependent haemolysin/cytolysin is restricted to and it may be associated with the pathogenesis of .


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