Neutrophil degranulation induced by Haemophilus ducreyi

Haemophilus ducreyi is the causative bacterium of genital ulcers, which are collectively known as chancroid. Little is known about the cytotoxicity of H. ducreyi. The virulent strains are relatively resistant to phagocytosis and apoptosis by neutrophils. Therefore, experiments were designed to examine whether neutrophil degranulation caused by H. ducrey would provide insights into the virulence mechanisms through which cellular damage is affected by the organism. Clinical isolates of eight strains of H. ducreyi and the culture strain type CIP542 (Collection Institute Pasteur) were incubated with neutrophils harvested from human donor blood. The release by the organism of lysosomal enzymes from intracellular granules of neutrophils was indicative of degranulation. The results showed that H. ducreyi triggered the release of lysosomal enzymes from human neutrophils, and that the magnitude of the release was dependent both on the ratio of bacteria to neutrophils and the duration of incubation. In vitro experiments involving HeLa cells were designed to determine the manner in which H. ducreyi initiated the process of degranulation. The morphological changes associated with degranulation were visualized by confocal and transmission electron microscopy. This is the first report that describes degranulation of neutrophils induced by H. ducreyi which causes chancroid infection.