Flow cytometric cellular analyses on the developmental, activation, and proliferation states of B cells in rainbow trout (81.3)

Abstract

Abstract Teleosts, including rainbow trout, provide an important animal model for the immunologist as they lack bone marrow and lymph nodes and utilize the kidney, spleen, and blood as immune organs. The developmental, activation, and proliferation stages of trout B cells and the location of these processes within the immune tissues are not well defined. Expression patterns of B cell transcription factors can be used as markers to investigate the B cell stages. In this study, the transcription factors Pax5 and XbpI, as well as RAG1, total IgM, secreted IgM, and BrdU incorporation were used as markers in trout B cells. Pax5 is expressed in early B cell development through the plasmablast stage, but is absent from plasma cells. In contrast, XbpI is induced in activated B cells and is expressed throughout plasmablast and plasma cell stages. Trout immune cells were LPS-activated in culture, fixed and permeabilized, and stained cells were analyzed by flow cytometry. Preliminary data suggests that each of the immune organs contains a plasmablast (Pax5+/XbpI+/total IgM+/ BrdU+) population either prior to, or upon LPS activation in culture. In the spleen, most of such cells are present at day 4, while blood has most plasmablasts on day 2. Both anterior and posterior kidney contain relatively high frequencies of plasmablasts immediately after isolation, but frequencies decrease upon culturing. This study supports the concept that flow cytometric analysis can be used to determine the location and differentiation state of B cells within the immune organs of the rainbow trout. This research was funded by a grant from the NIH.