Target cell range of Haemophilus ducreyi hemolysin and its involvement in invasion of human epithelial cells

Haemophilus ducreyi, the causative agent of chancroid, produces a hemolysin , whose role in virulence is not well defined. To assess the possible role of hemolysin in pathogenesis, we evaluated its target cell range by using w ild-type H. ducreyi 35000, nonhemolytic mutants with the hemolysin structur al gene deleted, and isogenic strains expressing different amounts of hemol ytic activity, The cytotoxicity of the various cell types was assessed by q uantitating the release of lactate dehydrogenase into culture supernatants as a measure of cell lysis. In these experiments, human foreskin fibroblast s, human foreskin epithelial cells, and, to a lesser extent, HEp-2 cells we re lysed by H. ducreyi hemolysin. Hemolysin also lysed human blood mononucl ear cells and immune system cell lines including U937 macrophage-like cells , T lymphocytes, and B lymphocytes. In contrast, human polymorphonuclear le ukocytes were not sensitive to hemolysin under the conditions tested. We al so analyzed the effect of hemolysin on invasion of human epithelial cells a nd found that H, ducreyi strains expressing cloned hemolysin genes showed a 10-fold increase in invasion compared to the control strain. These data su pport the hypothesis that the H, ducreyi hemolysin is important in the path ogenesis of chancroid and may contribute to ulcer formation, invasion of ep ithelial cells, and evasion of the immune response.