Autopsy data from cases of streptococcal toxic shock demonstrate accumulation of polymorphonuclear leukocytes (PMNL) within lung and soft tissue microvasculature. Because of the increased prevalence of streptococcal pyrogenic exotoxin A (SPEA)-producing strains associated with streptococcal toxic shock syndrome, experiments were done to determine whether SPEA or streptolysin O (SLO, a thiol-activated cytolysin produced by all group A streptococci) could stimulate PMNL-dependent adherence mechanisms in vitro. SPEA (0.01-10 micrograms/5.5 x 10(6) PMNL) only modestly enhanced PMNL adherence over the entire range of concentrations tested. In contrast, SLO-induced PMNL binding was highly dose dependent (maximal binding, 55.1 +/- 1.6% at 0.5 hemolytic units/5.5 x 10(6) PMNL) and was mediated by CD11/CD18 adherence glycoprotein.