The lipooligosaccharide (LOS) of Haemophilus ducreyi contains a major glycoform that is immunochemically identical to paragloboside, a glycosphingolipid precursor of major human blood group antigens. We recently identified the gene responsible for the glucosyltransferase activity and constructed an isogenic mutant (35000glu-) deficient in this activity. 35000glu-makes an LOS that consists only of the heptose trisaccharide core and 2-keto-deoxyoctulosonic acid (KDO). For this study, the mutant was reconstructed in the 35000HP (human passaged [HP]) background. Five human subjects were inoculated with 35000HP and 35000HPglu-in a dose-response trial. The pustule formation rates were 40% (95% confidence interval [CI], 13.7 to 72.6%) at 10 sites for 35000HP and 46.7% (95% CI, 24.8 to 69.9%) at 15 sites for 35000HPglu-. The histopathology and recovery rates of H. ducreyi from surface cultures and biopsies obtained from mutant and parent sites were similar. These results indicate that the expression of glycoforms with sugar moieties extending beyond the heptose trisaccharide core is not required for pustule formation by H. ducreyi in humans.Haemophilus ducreyi causes the genital ulcer disease chancroid. Structural and immunochemical analyses have demonstrated that the principal glycoform of H. ducreyi lipooligosaccharide (LOS) shares common epitopes with the LOS of other mucosal pathogens, such as Neisseria gonorrhoeae, Neisseria meningitidis, and Haemophilus influenzae (12,20,26,27,36). The major oligosaccharide structure of H. ducreyi LOS (Gal1-4-GlcNAc1-3Gal1-4Hep␣1-6Glc1-4Hep␣1-5KDO) contains a terminal lactosamine (Gal1-4-GlcNAc) and is similar in structure to paragloboside (Gal1-4GlcNAc1-3Gal1-4Glc), a precursor of the major human blood group antigens, I and i (11,12,19,26). The terminal N-acetyllactosamine of the major glycoform of H. ducreyi LOS is modified by sialic acid, much like the mature human I and i antigens (26). The LOS is thought to help H. ducreyi evade the host immune response by mimicking human antigens or by facilitating adherence to and/or invasion of host cells by binding to human cell surface receptors for glycosphingolipids or sialic acid.Several lines of evidence suggest that H. ducreyi LOS plays a role in the pathogenesis of chancroid. Injection of purified LOS causes intradermal inflammation in experimental animal models (13). Purified LOS induces interleukin-8 (IL-8) expression from keratinocytes in vitro and may stimulate an inflammatory response that leads to lesion formation (46). Mutants whose LOS consisted only of 2-keto-deoxyoctulosonic acid (KDO) or KDO and heptose were attenuated in the temperature-dependent rabbit model of infection, but these mutants also had altered outer membrane protein (OMP) profiles (5, 6). A mutant with a disruption in the D-glycero-Dmanno-heptosyltransferase gene exhibited reduced adherence and invasion of human keratinocytes in vitro (19). However, the D-glycero-D-manno-heptosyltransferase mutant and a sialyltransferase mutant were virulent in the...
