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Title: IMMUNE AND HISTOPATHOLOGIC RESPONSES AMONG DNA-VACCINATED HYBRID STRIPED BASS MORONE SAXATILIS X M. CHRYSOPS AFTER ACUTE MYCOBACTERIUM MARINUM INFECTION

Author
item Pasnik, David
item SMITH, STEPHEN - VMRCVM

Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2006
Publication Date: 11/21/2006
Citation: Pasnik, D.J., Smith, S.A. 2006. Immune and histopathologic responses among dna-vaccinated hybrid striped bass morone saxatilis x m. chrysops after acute mycobacterium marinum infection. Diseases of Aquatic Organisms vol 73, no 1:33-41.

Interpretive Summary: Mycobacterium marinum is well-recognized as a primary agent of fish mycobacteriosis. These bacteria can then cause development of internal granulomas which may subsequently lead to organ malfunction or death. The immune and histopathologic responses among fish 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 x M. chrysops) were injected intramuscularly with 25 µg or 50 µg DNA plasmid and developed significant specific protective responses after live bacterial challenge 120 days after vaccination. Both vaccine groups demonstrated increased survival, reduced splenic bacterial counts, and reduced granuloma formation compared to the control groups 14 days after challenge with M. marinum. The vaccine groups also developed more rapidly and significantly increased antibody and lymphoproliferative responses post-challenge over those of the 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 µg and 50 µg vaccination groups, and these groups eventually experienced increased mortalities, splenic bacterial counts, and granuloma formation within 28 days after challenge comparable to those of the control groups at 14 days after challenge. Therefore, vaccination of hybrid striped bass with a DNA vaccine encoding the M. marinum Ag85A gene provided limited duration of protection against high-dose M. marinum challenge.

Technical Abstract: The post-challenge immune and histopathologic responses among fish 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 x M. chrysops) were injected intramuscularly with 25 µg or 50 µg DNA plasmid and developed significant specific protective responses after 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 x 105 cfu M. marinum g-1 body weight of fish. The vaccine groups also developed more rapidly and significantly increased antibody and lymphoproliferative responses post-challenge over those of the 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 µg and 50 µg vaccination groups, and these groups eventually experienced increased mortalities, splenic bacterial counts, and granuloma formation within 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 high-dose M. marinum challenge.