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Role of neutrophil degranulation in streptococcal leukotoxicity
Abstract:
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.
Insights
Leukotoxic Streptococcus pyogenes kill immune cells by causing internal granule rupture. Blocking granule release did not stop this, but pre-emptively releasing granules partially protected the cells from bacterial toxins.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Leukotoxic Streptococcus pyogenes are known to kill polymorphonuclear neutrophils (PMN).
- Previous observations suggested intracytoplasmic rupture of PMN granules is involved in this killing mechanism.
Purpose of the Study:
- To investigate the role of PMN granule rupture in the cytotoxic mechanism of leukotoxic Streptococcus pyogenes.
- To determine if altering PMN degranulation affects susceptibility to streptococcal leukotoxin.
Main Methods:
- PMN degranulation was inhibited using tetraethylammonium chloride, dibutyryl cyclic adenosine monophosphate, or magnesium ethylene glycol-bis(beta-aminoethyl ether)-N,N-tetraacetate.
- PMN were degranulated prior to exposure to leukotoxic streptococci using calcium ionophore A23187 or zymosan-activated serum with cytochalasin B.
- Cinemicrography and electron microscopy were used to observe PMN granule behavior.
Main Results:
- Inhibiting exocytosis of PMN granule contents did not prevent intracytoplasmic granule firing or significantly reduce leukotoxicity.
- Pre-emptive degranulation of PMN, releasing both specific and primary granules, partially blocked leukotoxicity.
- Leukotoxic streptococci were confirmed to induce intracytoplasmic granule rupture.
Conclusions:
- Intracytoplasmic granule rupture induced by leukotoxic Streptococcus pyogenes is a significant factor in PMN killing.
- The ability of PMN to release granule contents externally is not the sole determinant of their susceptibility to this toxin.
- Targeting intracytoplasmic granule lysis may offer a strategy against Streptococcus pyogenes infections.