Cinemicrography and electron microscopy suggested that leukotoxic Streptococcus pyogenes killed polymorphonuclear neutrophils (PMN) by inducing intracytoplasmic rupture of the PMN granules. To further study the relationship between granule rupture and the mode of action of the streptococcal leukotoxin, PMN degranulation was experimentally altered. Exocytosis of PMN granule contents was blocked with 80 mM tetraethylammonium chloride, 2 mM dibutyryl cyclic adenosine monophosphate, or 2 mM magnesium ethylene glycol-bis(beta-aminoethyl ether)-N,N-tetraacetate in calcium-free medium. This treatment did not prevent the granules from firing into the cytoplasm of the PMN, nor did it significantly diminish leukotoxicity. Degranulating the PMN before exposure to the leukotoxic streptococci did partially block leukotoxicity if both the specific and the primary granules were released with either 5 microM calcium ionophore A23187 or 10% zymosan-activated serum plus 5 micrograms of cytochalasin B per ml. Leukotoxic streptococci stimulated intracytoplasmic rupture of granules, and this granule lysis contributed significantly to the ability of these streptococci to kill PMN.
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