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Title: B cell signatures of BCWD-resistant and susceptible lines of rainbow trout: a shift towards more EBF-expressing progenitors and fewer mature B cells in resistant animals

item ZWOLLO, PATTY - College Of William & Mary
item RAY, JOCELYN - College Of William & Mary
item SESSITO, MICHAEL - College Of William & Mary
item KIEMAN, ELIZABETH - College Of William & Mary
item Wiens, Gregory - Greg
item KAATTARI, STEPHEN - Virginia Institute Of Marine Science
item ST. JACQUES, BRITTANY - College Of William & Mary
item EPP, LIDIA - College Of William & Mary

Submitted to: Developmental and Comparative Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2014
Publication Date: 8/4/2014
Citation: Zwollo, P., Ray, J., Sessito, M., Kieman, E., Wiens, G.D., Kaattari, S., St. Jacques, B., Epp, L. 2014. B cell signatures of BCWD-resistant and susceptible lines of rainbow trout: a shift towards more EBF-expressing progenitors and fewer mature B cells in resistant animals. Developmental and Comparative Immunology. 4:48(1):1-12. DOI: 10.1016/j.dci.2014.07.018.

Interpretive Summary: The increased availability of disease resistant animals is a priority for aquaculture producers. Since 2005, scientists at the National Center for Cool and Cold Water Aquaculture have selectively bred rainbow trout for improved resistance against an important aquaculture pathogen, Flavobacterium psychrophilum. This pathogen causes bacterial cold water disease which is prevalent at many locations in the U.S. We have utilized family-based selective breeding to improve disease resistance and developed a new rainbow trout line, designated ARS-Fp-R. In addition, we maintain a susceptible line having a similar genetic background for comparison, designated ARS-Fp-S. While breeding efforts have increased specific disease resistance; it is unclear whether we have also changed cell populations within the immune system. B lymphocytes are important immune cells that produce antibodies necessary for removal of pathogens. We investigated whether the two lines exhibit differences in developing and mature B lymphocytes by developing new reagents to identify and measure different stages of immune cell development in rainbow trout blood and tissues. We found that there were more developing immune cells but fewer mature, antibody producing B cells in the resistant line as compared to the susceptible line. At present, we do not understand whether these differences are directly or indirectly related to bacterial cold water disease resistance.

Technical Abstract: Bacterial Cold Water Disease (BCWD) is a chronic disease of rainbow trout, and is caused by the gram-negative bacterium Flavobacterium psychrophilum (Fp), a common aquaculture pathogen. The National Center for Cool and Cold Water Aquaculture has bred two genetic lines of rainbow trout: a line of Fp-resistant trout (ARS-Fp-R or R-line trout) and a line of susceptible trout (ARS-Fp-S, or Sline). Little is known about how phenotypic selection alters immune response parameters or how such changes relate to genetic disease resistance. Herein, we quantify interindividual variation in the distribution and abundance of B cell populations (B cell signatures) and examine differences between genetic lines of naive animals. There are limited trout-specific cell surface markers currently available to resolve B cell subpopulations and thus we developed an alternative approach based on detection of differentially expressed transcription factors and intracellular cytokines. B cell signatures were compared between R-line and S-line trout by flow cytometry using antibodies against transcription factors Early B cell Factor-1 (EBF1) and paired domain box protein Pax5, the pro-inflammatory cytokine IL-1ß, and the immunoglobulin heavy chain mu. R-line trout had higher percentages of EBF+ B myeloid/ progenitor and pre-B cells in PBL,anterior and posterior kidney tissues compared to S-line trout. The opposite pattern was detected in more mature B cell populations: R-line trout had lower percentages of both IgM+ mature B cells and IgM-secreting cells in anterior kidney and PBL compared to S-line trout. In vitro LPS-activation studies of PBL and spleen cell cultures revealed no significant induction differences between R-line and S-line trout. Together, our findings suggest that selective resistance to BCWD may be associated with shifts in naive animal developmental lineage commitment that result in decreased B lymphopoiesis and increased myelopoiesis in BCWD resistant trout relative to susceptible trout.