• harbor seal;
  • Phoca vitulina;
  • captivity;
  • peripheral blood;
  • mononuclear leucocytes;
  • mitogenic reactivity;
  • lymphocyte transformation test;
  • E-rosettes;
  • age;
  • immunology;
  • hematology


Peripheral blood was collected from 13 captive seals (12 harbor seals and 1 gray seal) of various ages to study different immunological and hematological parameters. In vitro mitogenic reactivity of blood lymphocytes was measured by means of a microculture lymphocyte transformation test (LTT). After stimulation with different doses of the mitogens concanavalin A (Con A) and pokeweed mitogen (PWM), all examined seals showed significant proliferative responses to each mitogen. Furthermore, mitogenic reactivity significantly decreased with animal age suggesting this parameter of seal lymphocyte function is age-related. The present experiments support that the LTT is a suitable tool to monitor the functional capacity of seal lymphocytes. By means of the erythrocyte-rosette (E:-rosette) test it was demonstrated that a subpopulation of mononuclear seal bloosd leucocytes formed rosettes with sheep red blood cells (Srbc). This observation indicates that the phenomenon probably represents a marker for T lymphocytes in the seal as in several other mammalian species. Furthermore, the percentage of Srbc rosette-forming cells decreased with the age of the animals. Total blood leucocyte counts and differential leucocyte counts were determined by light microscopy. The number of leucocytes varied considerably among individual animals. Parallel to a significant decline of the percentage of lymphocytes with age, a corresponding increase in the percentage of neutrophils was demonstrated. In all of the seals, the percentages of monocytes and eosinophils were found to be low with only minor individual variation. The LTT and the E-rosette test are suggested as potential tools to elucidate immunological disorders in the seal.