Missing the target: DNAk is a dominant epitope in the humoral immune response of channel catfish (Ictalurus punctatus) to Flavobacterium columnare

Authors: Lange, Miles; Beck, Benjamin; Brown, Jason; Farmer, Bradley; Barnett, Louis - Matt; Webster, Carl

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2016
Publication Date: 4/1/2016
Publication URL: https://handle.nal.usda.gov/10113/5268871
Citation: Lange, M.D., Beck, B.H., Brown, J.D., Farmer, B.D., Barnett, L.M., Webster, C.D. 2016. Missing the target: DNAk is a dominant epitope in the humoral immune response of channel catfish (Ictalurus punctatus) to Flavobacterium columnare. Fish and Shellfish Immunology. 51:170-179.

Interpretive Summary: Flavobacterium columnare, the causative agent of columnaris disease produces substantial mortality worldwide among numerous freshwater farmed finfish species. As aquaculture production continues to increase the frequency of columnaris disease will only continue to rise. Add to this an increase in regulation of licensed therapeutants and resistance to antibiotics means that alternative methods of disease protection will be required. In the present study we sought to compare the humoral immune response in two groups of channel catfish that had survived a Flavobacterium columnare challenge. We identified consistent antibody responses that were made against the same bacterial protein in some of the individual naïve catfish as well as the individual immunized catfish. Our data would suggest that this protein represents a dominant target in the catfish antibody response to columnaris disease. We will design additional studies to test the protective capability of this antibody response to columnaris in the channel catfish.

Technical Abstract: Vaccination remains a viable alternative for bacterial disease protection in fish; however additional work is required to understand the mechanisms of adaptive immunity in the channel catfish. To assess the humoral immune response to Flavobacterium columnare; a group of channel catfish were first immunized with F. columnare LV-359-01 cultured in iron-depleted media, before being challenged with wild type F. columnare LV-359-01. The extent of serum and skin IgM antibodies made against F. columnare proteins varied from low to high responders in both control and immunized fish. Western blot analyses of individuals from both groups showed that the majority of antibodies generated were to the same 70 kDa extracellular protein, which was subsequently identified to be the bacterial chaperonin protein DNAk. Antibodies generated were cross reactive to DNAk proteins found in other gram negative bacteria. Our data suggests that DNAk is the dominant antigen in the channel catfish B-cell response to F. columnare.