Clostridium perfringens phospholipase C-induced platelet/leukocyte interactions impede neutrophil diapedesis.

Clostridium perfringens gas gangrene is a fulminant necrotizing infection in which inflammatory cells are notably absent from infected tissues but are often massed within adjacent vessels. It has been shown that C. perfringens phospholipase C (PLC) stimulates formation of large intravascular platelet/leukocyte complexes and that PLC-induced activation of platelet gpIIbIIIa plays a major role. In vivo, such aggregates contribute to microvascular thrombosis and ischaemic necrosis of tissue. However, the effects of adherent platelets on neutrophil diapedesis have not been established. The present work investigated (1) the contribution of platelet P-selectin (CD62P) to PLC-induced cellular complex formation and (2) the effects of platelet adhesion on neutrophil diapedesis. The effects of anti-gpIIbIIIa and anti-CD62P strategies on PLC-induced complex formation were measured by flow cytometry and followed by light microscopy. Both platelet gpIIbIIIa and CD62P contributed to the formation of platelet/leukocyte complexes. Specifically, gpIIbIIIa mediated the formation of large platelet/platelet aggregates that were tethered to the leukocyte principally via CD62P. Neutrophil diapedesis, quantified by a transendothelial cell migration assay and visualized by electron microscopy, was significantly reduced (>60%) by the adherence of large platelet aggregates. It was concluded that the absence of a tissue inflammatory response in C. perfringens gas gangrene is due, in part, to impaired neutrophil mobility caused by large aggregates of adherent platelets induced by PLC. Further, an adjunctive immunotherapeutic strategy targeting both gpIIbIIIa and CD62P may improve the tissue inflammatory response, prevent vascular occlusion, maintain tissue viability, and reduce the need for radical amputation in patients with clostridial gas gangrene.

Beta-adrenergic regulation of the eosinophil respiratory burst as detected by lucigenin-dependent luminescence.

Because beta-adrenoceptor agonists are commonly used in the treatment of disease states associated with eosinophil activation, beta-adrenergic regulation of the eosinophil respiratory burst (as monitored with lucigenin-dependent luminescence) was evaluated. Normodense, nonprimed eosinophils from healthy volunteer subjects were potently inhibited by very low concentrations of isoproterenol. The inhibitory concentration of 50% for isoproterenol was approximately 2 nmol/L. The beta-agonist was able to inhibit the eosinophil respiratory burst induced by receptor-mediated (chemotactic peptide) and nonreceptor-mediated (calcium ionophore and phorbol ester) stimuli. Thus beta-agonist inhibition was unlikely to be isolated to an effect at the receptor or G protein linkage. To determine whether cyclic adenosine 3',5' monophosphate (cAMP) may mediate beta-agonist effects, studies were performed with the type IV cAMP phosphodiesterase inhibitor Ro-201724. beta-Agonist inhibition of the respiratory burst was clearly synergistic with effects of Ro-201724. We conclude that beta-adrenoceptor agonists can regulate the eosinophil respiratory burst at least partially through an effect mediated by cAMP. Because regulation of the eosinophil by isoproterenol was observed at very low concentrations, these results may be relevant to pharmacologic effects of beta-agonists in disease states complicated by eosinophil activation during asthma.