INDUCIBLE IMMUNITY WITH A PILUS PREPARATION BOOSTER VACCINATION IN ANANIMAL-MODEL OF HAEMOPHILUS-DUCREYI INFECTION AND DISEASE

Using the temperature-dependent rabbit model of Haemophilus ducreyi in fection as a quantitative virulence assay, we tested the abilities of two bacterial antigen preparations to induce protection against subseq uent infection and disease, Lipooligosaccharide (LOS) and a pilus prep aration were purified from H. ducreyi 35000 and were used in a booster immunization procedure. The serologic response to each immunogen was monitored by enzyme immunoassay. H. ducreyi virulence was assayed by i ntraepithelial inoculation and subsequent measurement of disease for h omologous strain 35000 or clinical isolate RO-34. LOS and the pilus pr eparation induced humoral responses. The kinetics of the LOS antibody response suggest a type 1 T-independent response, whereas the pilus pr eparation induced an anamnestic response. An inoculum of 10(5) CFU of H. ducreyi 35000 or RO-34 consistently produced ulcerative chancroidal lesions in naive rabbit controls, Immunization with LOS did not modif y the virulence of H. ducreyi 35000. Immunization with the strain 3500 0 pilus preparation significantly reduced the severity of disease and the duration of infection and disease compared with controls, with eit her homologous or heterologous strain infection, The histology of lesi ons from pilus preparation-vaccinated rabbits compared with that of le sions from controls revealed accelerated lymphoid cell recruitment, mo re prominent plasma cell infiltrate, and reduction in subsequent histi ocytic infiltration. We conclude that both LOS and the pilus preparati on are immunogenic and that the latter induces homologous and heterolo gous strain protection in this animal model of infection and disease.