Graduate Thesis Or Dissertation
 

Modulation of respiratory burst activity of trout (Oncorhynchus mykiss) phagocytic cells

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  • In a comparison of the mammalian and fish immune systems many similarities and differences are found. While most of the differences occur in the acquired or lymphoid arm of immunity, the nonlymphoid immune systems of fish and mammals share many similarities. For instance, both animal groups use phagocytic neutrophils and macrophages as effector cells. The functions of these cells are crucial to the health of the organism as they provide the first line of cellular defense against invading pathogens. One of these functions is the production of bactericidal superoxide radicals (respiratory burst) which serves as a defensive mechanism shared by fish and mammalian phagocytic cells. This thesis examines the nature and the modulation of the respiratory burst by rainbow trout pronephric phagocytic cells. This organ contains two populations of phagocytic cells which can be separated into adherent and nonadherent subpopulations each of which shares functional characteristics with their mammalian homologues, macrophages and neutrophils. On a per cell basis, the fish adherent cells produce less PMA-stimulated superoxide than the nonadherent cells. The respiratory burst of the nonadherent cells is diminished by in vitro conditions of cell crowding and adherence and occurs at temperature ranges higher than the physiological maintenance temperature of the fish. In rainbow trout the respiratory burst is also modulated by in vitro exposure to lipopolysaccharide (LPS), a component of the cell wall of gram negative bacteria. Incubation of mixed adherent and nonadherent cells for 24 hours in the presence of LPS enhances the respiratory burst of the nonadherent pronephric phagocytes. Incubation for 72 hours diminishes the response due, at least partly, to an LPS-induced increased adherence of 'nonadherent' cells removing them from the PMA-reactive population. Alteration of nonadherent cell function is mediated through adherent cells as evidenced by the ability of LPS-treated adherent cells and their supernatants to simulate LPS effects on nonadherent cells. The respiratory burst of trout phagocytic cells is also modulated by stress. Brief suspension of fish out of the water resulted in diminished superoxide production by nonadherent cells assayed one hour later. In vitro incubation of nonadherent cells for 72 hours with 10⁻⁶ M dexamethasone, a synthetic stress hormone, also diminished the respiratory burst.
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