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Research Project: Pathogen Characterization, Host Immune Response and Development of Strategies to Reduce Losses to Disease in Aquaculture

Location: Aquatic Animal Health Research

Title: Analysis of agglutinants elicited by antiserum of channel catfish immunized with extracellular proteins of virulent Aeromonas hydrophila

item Zhang, Dunhua
item Xu, Dehai
item Beck, Benjamin

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2018
Publication Date: 3/1/2019
Citation: Zhang, D., Xu, D., Beck, B.H. 2019. Analysis of agglutinants elicited by antiserum of channel catfish immunized with extracellular proteins of virulent Aeromonas hydrophila. Fish and Shellfish Immunology. 86:223-229.

Interpretive Summary: The emergence of new virulent Aeromonas hydrophila (vAh) strains is of concern in aquaculture industries since the bacteria are capable of causing high mortality of warm-water fishes worldwide. In the Southeastern United States, a severe outbreak of motile Aeromonas septicemia (MAS) caused by vAh was reported in 2009 in catfish farms; the disease has since resulted in the loss of millions of pounds of market-size catfish annually. The mechanism that leads to the development of MAS, however, is still largely unknown. Prevention and control of MAS remain to be a challenging issue in aquaculture. Prophylactic vaccination against vAh is under investigation as this strategy has been shown to be efficacious for many infectious fish diseases. Previously, we demonstrated that channel catfish developed immunity against vAh infection after immunization of the pathogen’s extracellular proteins (ECP) and serum from ECP-immunized fish was able to recognize specific proteins in the vAh ECP (via immunoblotting assay) and aggregated vAh cells (causing agglutination). In this study, we analyzed and characterized agglutinants of ECP and cells of vAh, elicited by anti-ECP serum to reveal the versatility of vAh antigens and catfish Ig M.

Technical Abstract: Channel catfish developed immunity against infection of virulent Aeromonas hydrophila (vAh) after immunization with the pathogen’s extracellular proteins (ECP). Anti-ECP fish serum (antiserum) exhibited a high agglutination titer against cells of vAh. Agglutinants of ECP and cells of vAh, elicited by antiserum, were analyzed by SDS-PAGE and mass spectrometry in this report. Five fish proteins were identified in ECP agglutinants, including two innate immunity associated proteins (serotransferrin and rhamnose-binding lectin), two immunoglobulin M (IgM) molecules (IgM heavy chain and light chain) and a constitutively-produced protein (warm temperature acclimation protein). More than 68 vAh proteins in ECP were recognized and caused to aggregate by IgM in the antiserum. IgM was isolated from vAh cell agglutinants; the native IgM was shown to form a tetramer that was responsible for bacterial agglutination. Immunoblotting analysis indicated that the isolated native IgM was able to recognize some proteins in ECP, such as aerolysin and hemolysin (in the form of a high molecular weight heterologous polymer). Gene expression analysis by quantitative PCR showed that fish immunized with vAh ECP had more transcripts of genes coding for IgM, serotransferrin and rhamnose binding lectin than mock-immunized fish. Both innate and antibody-mediated immune responses in serum and expressed genes contributed to fish immunity upon immunization with ECP.