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Infection and Immunity, December 2003, p. 6971-6977, Vol. 71, No. 12
0019-9567/03/$08.00+0 DOI: 10.1128/IAI.71.12.6971-6977.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Robert A. Fulcher,1 Lani R. San Mateo,1,
Paul E. Orndorff,2 and Thomas H. Kawula1*
Department of Microbiology and Immunology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599,1 Department of Microbiology, Pathology and Parasitology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina 276062
Received 24 July 2003/ Returned for modification 26 August 2003/ Accepted 10 September 2003
Haemophilus ducreyi is the etiologic agent of the sexually transmitted genital ulcer disease chancroid. Neither naturally occurring chancroid nor experimental infection with H. ducreyi results in protective immunity. Likewise, a single inoculation of H. ducreyi does not protect pigs against subsequent infection. Accordingly, we used the swine model of chancroid infection to examine the impact of multiple inoculations on a host's immune response. After three successive inoculations with H. ducreyi, pigs developed a modestly protective immune response evidenced by the decreased recovery of viable bacteria from lesions. All lesions biopsied 2 days after the first and second inoculations contained viable H. ducreyi cells, yet only 55% of the lesions biopsied 2 days after the third inoculation did. Nearly 90% of the lesions biopsied 7 days after the first inoculation contained viable H. ducreyi cells, but this percentage dropped to only 16% after the third inoculation. Between the first and third inoculations, the average recovery of CFU from lesions decreased approximately 100-fold. The reduced recovery of bacteria corresponded directly with a fivefold increase in H. ducreyi-specific antibody titers and the emergence of bactericidal activity. These immune sera were protective when administered to naïve pigs prior to challenge with H. ducreyi. These data suggest that pigs mount an effective humoral immune response to H. ducreyi after multiple exposures to the organism.
Present address: Groton Laboratories, Pfizer Inc., Groton, Conn.
Present address: Centocor, Inc., Malvern, Pa.
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