The immune response to Haemophilus ducreyi resembles a delayed-type hypersensitivity reaction throughout experimental infection of human subjects

Previous work in 3 subjects infected for 2 weeks indicated that experimental infection with Haemophilus ducreyi recruits CD4 cells to the skin at the pustular stage of disease. In order to describe the kinetics of the host response, 23 subjects were infected at 2 sites with a stan-dardized dose of H. ducreyi. Subjects were biopsied 1 or 4 days after inoculation or when they developed a painful pustular lesion (days 7±14). Papules and pustules contained a pre-dominant T cell in®ltrate that consisted of CD45RO and CD4 cells of the ab lineage. Both papules and pustules contained mixed or T helper 1 type cytokine mRNA and interleukin-8 and tumor necrosis factor-a mRNA. Although the subjects had no history of chancroid, their immune responses resembled delayed-type hypersensitivity reactions that occurred within 24 h of inoculation and persisted throughout the course of experimental infection. Haemophilus ducreyi is the etiologic agent of the genital ulcer disease chancroid, which facilitates the transmission of human immunode®ciency virus type 1 [1±4]. Development of an effec-tive H. ducreyi vaccine may lower the incidence of chancroid and human immunode®ciency virus type 1 infection in area