The effects of purified toxin A in vitro on the shape and function of polymorphonuclear leukocytes (PMNL) were examined. Toxin A induced changes in adherent PMNL shape from a compact spherical or pyramidal shape to a thin and rope-like shape. This change in shape was accompanied by rearrangement of the F-actin cytoskeleton into aggregates. Toxin A-treated PMNL exhibited increased adherence and expressed less L-selectin and more Mac-1, compared with untreated PMNL. In contrast to these proinflammatory actions, toxin A impaired both directed and non-directed PMNL migration in response to N-formylmethionylleucylphenylalanine. In addition, toxin A decreased the oxidative activity of adherent PMNL stimulated by recombinant human tumor necrosis factor-alpha. These effects could be explained by toxin A-induced glucosylation of the signaling small-size guanine 5'-triphosphate-binding proteins of the Rho family in human PMNL.