Dual effects of pertussis toxin on murine neutrophils in vivo

Abstract

Pertussis toxin (Ptx) has been employed as an adjuvant by many investigators to augment various types of cell-mediated and humoral immune responses. Recent work from our laboratory indicates that the exacerbation of delayed-type hypersensitivity (DTH) and contact hypersensitivity (CH) responses observed in Ptxtreated mice may be mediated by an absolute increase in the number of circulating neutrophils capable of migrating into tissue sites of antigen challenge. The purpose of the present study was to analyze the effects of Ptx on neutrophils and neutrophil function in vivo. Evidence is presented here suggesting that Ptx has both direct and indirect effects on neutrophils following its in vivo administration to normal mice. Mature neutrophils that are directly exposed to the actions of Ptx in vivo exhibit a marked reduction in their ability to extravasate into tissue sites of inflammation. These findings are consistent with those that have been reported following the exposure of isolated neutrophils to the effects of Ptx in vitro (i.e., that Ptx has an inhibitory effect on many of the functional capabilities of isolated neutrophils). Moreover, we have also determined that Ptx can affect the kinetics of neutrophil production indirectly through its ability to stimulate granulopoiesis. Ptx-exposed mice develop a protracted peripheral blood neutrophilia following toxin administration. Although the mechanism(s) involved in stimulating increased neutrophil production is presently unclear, both dexamethasone and indomethacin (cyclooxygenase pathway inhibitors) are able to function synergistically with Ptx to produce a markedly enhanced neutrophilia in exposed mice. We propose that the capacity of Ptx to augment CH and DTH responses and act as a potent adjuvant may relate, in part, to its ability to alter the rate of neutrophil production in vivo.