DAO 73:33-41 (2006)  -  doi:10.3354/dao073033

Immune and histopathologic responses of DNA-vaccinated hybrid striped bass Morone saxatilis × M. chrysops after acute Mycobacterium marinum infection

David J. Pasnik1,2, Stephen A. Smith1,*

1Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine (VMRCVM),Virginia-Polytechnic Institute and State University (VPI&SU), Duck Pond Drive, Blacksburg, Virginia 24061, USA
2Present address: Aquatic Animal Health Research Laboratory, United States Department of Agriculture, Agricultural Research Service, Chestertown, Maryland 21620, USA
*Corresponding author. Email:

ABSTRACT: The post-challenge immune and histopathologic responses of hybrid striped bass vaccinated with a DNA vaccine encoding the Mycobacterium marinum Ag85A gene and subsequently challenged with M. marinum were investigated. Juvenile hybrid striped bass Morone saxatilis × M. chrysops were injected intramuscularly with 25 or 50 µg DNA plasmid and developed significant specific protective responses to live bacterial challenge 120 d post-vaccination. Both vaccine groups demonstrated increased survival, reduced splenic bacterial counts, and reduced granuloma formation compared to the control groups 14 d after challenge with approximately 8 × 105 cfu M. marinum g–1 fish body wt. The vaccine groups also developed more rapidly and significantly increased antibody and lymphoproliferative responses post-challenge compared to control groups, and these post-challenge immune responses appear to be vital against M. marinum infection in vaccinated hybrid striped bass. No significant differences in immune responses were recognized between the 25 and 50 µg vaccination groups, and these groups eventually experienced mortalities, splenic bacterial counts, and granuloma formation 28 d post-challenge comparable to those of the control groups at 14 d post-challenge. Therefore, vaccination of hybrid striped bass with a DNA vaccine encoding the M. marinum Ag85A gene provided significant but limited duration of protection against an acute high-dose M. marinum challenge.

KEY WORDS: Immunity · DNA · Vaccine · Mycobacterium marinum · Fish · Striped bass · Morone spp.

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