Haemophilus ducreyi Activates Human NK Cells through Interactions with Macrophages and Dendritic Cells

Abstract

The role of natural killer (NK) cells in the host response to Haemophilus ducreyi is unclear. In pustules obtained from infected human volunteers, there was an enrichment of CD56bright NK cells bearing the activation markers CD69 and HLA-DR compared to peripheral blood. To study the mechanism by which H. ducreyi activated NK cells, we used peripheral blood mononuclear cells from uninfected volunteers. H. ducreyi activated NK cells only in the presence of antigen presenting cells. H. ducreyi-infected monocytes and monocyte-derived macrophages activated NK cells in a contact- and IL-18-dependent manner, while monocyte-derived dendritic cells induced NK activation through soluble IL-12. More lesional NK cells produced IFN-γ in response to IL-12 and IL-18 than peripheral blood NK cells. We conclude that NK cells are recruited to experimental lesions and likely are activated by infected macrophages and dendritic cells. IFN-γ produced by lesional NK cells may facilitate phagocytosis of H. ducreyi.