Feasibility of vaccination for chancroid: Sero-immunology and virulence assay in an experimental model of infection.

Because of the well established epidemiologic and biologic interactions between human immunodeficiency virus (HIV) transmission and genital ulcer disease, measures to control chancroid could have a significant impact on the epidemic of HIV. I developed an IgG and IgM antibody serologic enzyme linked immunosorbent assay (ELISA) using pooled sera from clinically and microbiologically proven cases of chancroid as positive controls, and pooled sera from normal individuals without a history of sexually transmitted diseases as negative controls. Cross reactivity was minimized by absorption of serum samples with a sorbent prepared from three other Haemophilus species. Performance of the ELISA was enhanced in the period of early convalescence from acute primary chancroid and was not diminished in the presence of HIV coinfection, reflecting the tempo of the natural serologic response to and acute infection. I also developed an inhibition ELISA to determine antigenicity of potential vaccine candidates in human H. ducreyi infection, using lipooligosaccharide (LOS) as the test antigen. In a panel of 10 sera from cases of primary natural H. ducreyi infection reactive to H. ducreyi 35000 soluble antigen, only 4 samples were identified with reaction to H. ducreyi 35000 LOS. Inhibition ELISA confirmed that pre-adsorption with LOS substantially diminished reactivity of these sera to LOS but not to soluble antigen. Using the ELISA to detect immunogenicity by measuring the serologic response to vaccine candidates in rabbits, we further tested the feasibility of three bacterial antigen preparations to induce protective immunity against infection and disease. LOS carbohydrate and a pilus preparation were purified from H. ducreyi 35000 and used in a booster immunization procedure. Virulence was assayed by intra-epithelial challenge and measurement of disease for homologous strain 35000 or the virulent clinical isolate RO-34. LOS and the pilus preparation both induced humoral responses to the corresponding antigen, but the carbohydrate preparation did not. Immunization with LOS or carbohydrate did not modify virulence of infection with H. ducreyi 35000. Immunization with the strain 35000 pilus preparation significantly reduced the severity of disease, and the duration of infection and disease compared with controls. I conducted passive immunization experiments, and characterized the inflammatory infiltrate of chancroidal lesions. Naive rabbits were passively immunized with 24 or 48 mg of purified polyclonal IgG intravenously and 24 hours after infusion, challenged with the homologous strain 35000. No significant difference in disease resulting from infection with the homologous strain was observed. I then comparatively evaluated the serial immunohistology of lesions produced by infectious challenge with the homologous strain in sham-immunized or rabbits immunized with the pilus preparation. Flow cytometric analysis of rabbit peripheral blood leucocytes with CD5 and CD4 rabbit lymphocyte markers prior to infectious challenge revealed two T lymphocyte populations: CD5+CD4+ and CD5+CD4$-$. Pilus preparation vaccinee lesions showed significant quantitative acceleration and increase in T lymphocyte infiltration, and similar early increased recruitment of the CD4+ T lymphocyte subset preceding early lesion sterilization and early healing without ulceration. (Abstract shortened by UMI.