The initial morphologic alteration in rabbit polymorphonuclear leucocytes exposed to streptolysin is rapid and extensive lysis of cytoplasmic granules. The granules appear to rupture directly into the cell sap. Within a few minutes following degranulation, the leucocyte rounds up, filamentous processes appear on the cell membrane, the cytoplasm liquefies, and finally the nuclear lobes swell and fuse.

Streptolysin O causes these changes in intact leucocytes when added in concentrations only slightly higher than those required for release of hydrolases from isolated liver lysosomes, and furthermore exerts its action on granulocytes promptly. On the other hand streptolysin S acts on white cells only after a 15 to 30 minute delay, and the levels necessary to disrupt granules in leucocytes are considerably higher than those which act on lysosome suspensions.

Exposure of rabbit alveolar macrophages to streptolysin O also results in lysis of granules, soon followed by alterations in the cytoplasm and membrane.

The observations are in accord with the hypothesis that streptolysins penetrate the leucocyte membrane and bring about lysis of granules. Autolytic enzymes released from the granules might then be responsible for the subsequent damage seen in various other cell structures.

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