The effects of exotoxin A (EXA) from on polymorphonuclear leucocytes (PMNLs) were studied in a mouse model and PA103, which produced EXA, was 20 times more virulent for normal mice than was its EXA-deficient mutant, PA103-29. EXA was detected in the plasma of mice infected with PA103, and its presence correlated with increasing numbers of bacteria in the blood and internal organs. A monoclonal antibody (MAb) against EXA prevented the death of the mice if it was given simultaneously with, or 2 h before, infection with strain PA 103. The number of PMNLs in murine blood decreased by 50% within 30 min of intravenous injection of EXA, but this decrease was prevented by simultaneous or prior injection of MAb to the toxin. EXA inhibited in-vitro phagocytosis and killing of by human and murine PMNLs and decreased the number of the PMNLs by between 60 and 68%. Collectively, these results not only confirm that EXA. is toxic , but also suggest that this toxin accelerates the growth of virulent in mice.


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