INDUCTION OF ADHERENCE AND DEGRANULATION OF POLYMORPHONUCLEAR LEUKOCYTES - A NEW EXPRESSION OF THE INVASIVE PHENOTYPE OF SHIGELLA-FLEXNERI

In the present study, the ability of Shigella flexneri to activate pol ymorphonuclear neutrophils (PMN) was examined, The invasive serotype 5 strain M90T induced strong PMN adherence, which was dependent on both the multiplicity of infection and the duration of incubation, When te sted under the same experimental conditions, the noninvasive strain BS 176 (cured of the 220-kb virulence plasmid) was less efficient, Indeed , incubation of PMN for 2 h with either M90T or BS176 (multiplicity of infection, 100) induced 51.8% +/- 10.5% and 15.2% +/- 4.2% adherence, respectively (n = 3; P < 0.05). Stronger PMN activation by M90T was c onfirmed by evaluating PMN degranulation induced by the two strains. W hereas M90T triggered significant PMN secretion, BS176 did not. M90T s trains with mutations in ipa genes were then analyzed. When PMN were i ncubated with these mutants, their activation was of the same intensit y as that obtained with BS176. These data provide the first evidence f or PMN activation induced by S. flexneri, a process which appears to b e mediated by Ipa invasins.