Haemophilus ducreyi Associates with Phagocytes, Collagen, and Fibrin and Remains Extracellular throughout Infection of Human Volunteers

Abstract

In a previous study, Haemophilus ducreyi was found in the pustule and dermis of samples obtained at the clinical end point in the human model of infection. To understand the kinetics of localization, we examined infected sites at 0, 24, and 48 h after inoculation and at the clinical end point. Immediately after inoculation, bacteria were found predominantly in the dermis but also in the epidermis. Few bacteria were detectable at 24 h; however, by 48 h, bacteria were readily seen in the pustule and dermis. H. ducreyi was associated with polymorphonuclear leukocytes and macrophages in the pustule and at its base, but was not associated with T cells, Langerhans' cells, or fibroblasts. H. ducreyi colocalized with collagen and fibrin but not laminin or fibronectin. Association with phagocytes, collagen, and fibrin was seen as early as 48 h and persisted at the pustular stage of disease. Optical sectioning by confocal microscopy and transmission electron microscopy both failed to demonstrate intracellular H. ducreyi. These data identify collagen and fibrin as potentially important targets of adherence in vivo and strongly suggest that H. ducreyi remains extracellular throughout infection and survives by resisting phagocytic killing in vivo.

Haemophilus ducreyi-Induced Interleukin-10 Promotes a Mixed M1 and M2 Activation Program in Human Macrophages

“…Internalized H. ducreyi cells were very sensitive to phagocytic killing by all groups of macrophages, and fewer than 5% of the ingested bacteria survived in macrophages 7 h postinfection. This result is consistent with the previously published study showing that H. ducreyi cells associate with macrophages but are not found intracellularly during human infections (6).…”

“…Experimental pustules and natural ulcers are identical histologically and represent immunological failure. In pustules and ulcers, H. ducreyi colocalizes with macrophages and neutrophils but resists phagocytosis and phagocytic killing and replicates extracellularly (6,7). H. ducreyi secretes two antiphagocytic proteins, LspA1 and LspA2, which inhibit Fc receptor-mediated uptake by macrophage-and neutrophil-like cell lines in vitro (50); a mutant lacking LspA1 and LspA2 expression is attenuated in human volunteers (20).…”

Inhibition of Phagocytosis byHaemophilus ducreyiRequires Expression of the LspA1 and LspA2 Proteins

“…This organism has been shown to attach to extracellular matrix components in vitro, including type I and type III collagen, fibronectin, and laminin (9), and to colocalize with collagen and fibrin in infected sites in human volunteers (8). Several studies have indicated that H. ducreyi can attach to or invade human epithelial cell lines, fibroblasts (2,32,33,54), or keratinocytes (14,24,29) in vitro, although a recent study in the human model for experimental chancroid indicated that, at least through the pustular stage of disease, H. ducreyi apparently remains extracellular (8). It has been suggested that H. ducreyi survives in vivo by resisting phagocytic killing (49), and two other laboratories recently confirmed that H. ducreyi can resist phagocytosis in vitro (1,58).…”

A Superoxide Dismutase C Mutant of Haemophilus ducreyi Is Virulent in Human Volunteers

“…Throughout the papular and pustular stages of experimental infection, H. ducreyi is surrounded by professional phagocytes but remains extracellular (5,6). In vitro, H. ducreyi adheres to the human macrophage-like cell line U-937 but resists phagocytosis (41).…”