Investigations Of Cytotoxic Leukocytes In The Nurse Shark

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Microbiology and Immunology


Nurse shark (Ginglymostoma cirraturm) peripheral blood leuckocytes were shown to possess spontaneous cytolytic activity toward xenogeneic red blood cell targets when the environmental temperature fell below 23(DEGREES). When leukocytes were fractionated on glass bead columns, the adherent cells were found to possess this activity. Unfractionated leukocytes from sharks held above 23(DEGREES) had no spontaneous cytotoxicity. However, if glass adherent leukocytes were isolated at temperatures above 23(DEGREES), they were shown to have spontaneous activity, demonstrating the continual presence of the effector cell. The effector cell was demonstrated to be plastic adherent and phagocytic. This cell was determined to be either a granulocyte or a macrophage. The glass adherent, effector cells were shown to function best in vitro at 23(DEGREES), the environmental temperature at which their effect is observed. Glass nonadherent leukocytes were demonstrated to have an inhibitory effect on spontaneous cytotoxicity. This was not due to effector cell dilution and required viable cells in the inhibiting cell population. These regulatory glass nonadherent leukocytes must be in close association with the glass adherent cells in order to mediate inhibition. Thus, the nurse shark, a phylogenetically primitive vertebrate, was shown to have cellular regulation of a cytotoxic response. This regulatory cell may be controlled by temperature.Glass adherent shark leukocytes were also found to possess another cytotoxic activity which required the presence of shark plasma, which contains natural antibody to the target cell. In contrast to spontaneous cytotoxicity, these effector cells are not phagocytic. The activity present in shark plasma could be reduced by adsorption with target cells. Shark 19s immunoglobulin was shown to induce a similar cytotoxic response and may be the plasma component responsible for this cytotoxicity. The immunoglobulin was shown to adhere better to the shark leukocytes than to the target cell.Shark leukocytes, therefore, can mediate at least two cytotoxic reactions. These reactions are mediated by different cell populations. The spontaneous cytotoxic reaction is mediated by phagocytic cells, whereas the plasma induced response is not. Both of these cytotoxic reactions have the potential to function in vivo and provide the shark with an effective immunosurveillance system.


Biology, Microbiology

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