Graduate Thesis Or Dissertation
 

Glucocorticoid regulation of salmonid B lymphocytes

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  • The in vitro effects of cortisol in regulating salmonid B cell functions were investigated. B cells at three distinct stages of differentiation were examined for cortisol sensitivity. B lymphocyte responses were examined 1) during the early stage of the precursor, 2) during the intermediate stage of differentiation associated with clonal proliferation, and 3) at the stage of terminal differentiation associated with antibody secretion. The effect on B cell precursors was assessed by limiting dilution analysis, clonal proliferation by limiting dilution analysis and mitogenic stimulation, and antibody secretion by the induction of plaque-forming cells (PFC). Physiological levels of cortisol inhibited, in a dose-dependent fashion, the proliferative and antibody-secreting responses of splenic and pronephric-derived lymphocytes. Cortisol-mediated cytolysis of the lymphocytes was not responsible for this inhibition. Organ-dependent differences in cortisol sensitivity were observed with pronephric- and splenic-derived lymphocytes. Pronephric lymphocytes were sensitive to cortisol only at an early stage of differentiation, whereas splenic lymphocytes were sensitive at all stages. Preincubation of splenic lymphocytes with cortisol increased their sensitivity to later additions of cortisol, whereas no such increase occurred with pronephric lymphocytes. Cortisol-induced suppression of pronephric lymphocytes was reversible. Proliferative and antibody-producing cell (APC) responses in cortisol-suppressed cultures were fully restored by addition of leukocyte-derived conditioned medium (CM-L). The active material in CM-L was found to range in molecular weight from 10 to 18 kd. Recombinant bovine and human interleukins restored the proliferative phases of B cell differentiation formerly suppressed by cortisol. Studies also revealed that: 1) two cells (B and adherent) are required for TNP-LPS responses and 2) pronephric lymphocytes can be physically separated into surface Ig+ and Ig- populations which appear to be functionally distinct.
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