AUTHOR=Lange Miles D. , Abernathy Jason , Farmer Bradley D. 

TITLE=Evaluation of a Recombinant Flavobacterium columnare DnaK Protein Vaccine as a Means of Protection Against Columnaris Disease in Channel Catfish (Ictalurus punctatus)

JOURNAL=Frontiers in Immunology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2019.01175

DOI=10.3389/fimmu.2019.01175

ISSN=1664-3224

ABSTRACT=<p><italic>Flavobacterium columnare</italic> causes substantial losses among cultured finfish species. The Gram-negative bacterium is an opportunistic pathogen that manifests as biofilms on the host's mucosal surfaces as the disease progresses. We previously demonstrated that the dominant mucosal IgM antibody response to <italic>F. columnare</italic> is to the chaperone protein DnaK that is found in the extracellular fraction. To establish the efficacy of using recombinant protein technology to develop a new vaccine against columnaris disease, we are reporting on two consecutive years of vaccine trials using a recombinant <italic>F. columnare</italic> DnaK protein (rDnaK). In year one, three groups of channel catfish (<italic>n</italic> = 300) were immunized by bath immersion with a live attenuated <italic>F. columnare</italic> isolate, rDnaK or sham immunized. After 6 weeks, an <italic>F. columnare</italic> laboratory challenge showed a significant increase in survival (&gt;30%) in both the live attenuated and rDnaK vaccines when compared to the non-immunized control. A rDnaK-specific ELISA revealed significant levels of mucosal IgM antibodies in the skin of catfish immunized with rDnaK at 4- and 6-weeks post immunization. In the second year, three groups of channel catfish (<italic>n</italic> = 300) were bath immunized with rDnaK alone or with rDnaK after a brief osmotic shock or sham immunized. After 6 weeks a laboratory challenge with <italic>F. columnare</italic> was conducted and showed a significant increase in survival in the rDnaK (&gt; 25%) and in rDnaK with osmotic shock (&gt;35%) groups when compared to the non-immunized control. The rDnaK-specific ELISA demonstrated significant levels of mucosal IgM antibodies in the skin of catfish groups immunized with rDnaK at 4- and 6-weeks post immunization. To further understand the processes which have conferred immune protection in the rDnaK group, we conducted RNA sequencing of skin samples from the non-immunized (<italic>n</italic> = 6) and rDnaK treated channel catfish at 1-week (<italic>n</italic> = 6) and 6 weeks (<italic>n</italic> = 6) post immunization. Significantly altered gene expression was identified and results will be discussed. Work to further enhance the catfish immune response to <italic>F. columnare</italic> rDnaK is underway as this protein remains a promising candidate for additional optimization and experimental trials in a production setting.</p>