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Haemophilus ducreyi is the etiologic agent of chancroid, a sexually transmitted genital ulcer disease. Keratinocytes are likely the first cell type encountered by H. ducreyi upon infection of human skin; thus, the interaction between H. ducreyi and keratinocytes is probably important for the ability of H. ducreyi to establish infection. We have used the HaCaT keratinocyte cell line grown in monolayers and in cocultures with HS27 fibroblasts to investigate H. ducreyi interactions with keratinocytes and the host-cell response to H. ducreyi infection. Using quantitative adherence and gentamicin protection assays, we determined that approximately 13% of H. ducreyi adhered to HaCaT cell monolayers, while only a small proportion (0.0052%) was intracellular. By transmission electron microscopy, we observed numerous H. ducreyi organisms adherent to but rarely within HaCaT cells cocultured with fibroblasts. Both live H. ducreyi and purified H. ducreyi lipooligosaccharide (LOS) induced significant interleukin 8 (IL-8) expression from HaCaT cell-HS27 cell cocultures. However, the level of IL-8 expression in response to LOS alone was not as pronounced. H. ducreyi LOS was a more potent inducer of IL-8 from cocultures than Escherichia coli lipopolysaccharide (LPS) at the same concentration, suggesting a unique effect of H. ducreyi LOS on cocultures. Neither live H. ducreyi nor purified H. ducreyi LOS or E. coli LPS induced tumor necrosis factor alpha expression from cocultures. H. ducreyi induced drastically different cytokine profiles from cocultures than from HS27 or HaCaT cells cultured separately. IL-8 expression by skin cells in response to H. ducreyi infection in vivo may be responsible for the massive influx of polymorphonuclear leukocytes and other inflammatory cells to the site of infection. This influx of inflammatory cells may be partly responsible for the tissue destruction characteristic of chancroid.

Examination of Early Interactions between Haemophilus ducreyi and Host Cells by Using Cocultured HaCaT Keratinocytes and Foreskin Fibroblasts