RELATIVE IMMUNOCOMPETENCE OF THE NEWBORN HARBOR SEAL, PHOCA-VITULINA

The immune system of many mammalian species is not fully developed at birth, with newborns obtaining temporary immunological protection from maternal antibodies. Little is known of the immune system of the harb our seal, and developmental aspects of its immune system have not been systematically studied. We collected blood and milk samples from nine free-ranging mother-pup pairs throughout the lactation period on Sabl e Island, Canada, in an effort to characterise developmental aspects o f the immune system of this newborn pinniped. Pup lymphocytes responde d stronger to the mitogens concanavalin A, phytohaemagglutinin, and po keweed mitogen than the lymphocytes of their mothers. In contrast to n ewborn cats and dogs, newborn seal pups developed high specific antibo dy responses after immunisation with an inactivated rabies vaccine. Ci rculating levels of total IgG in newborn pups were low (3% of maternal levels), but increased rapidly after colostrum intake (to 65% of mate rnal levels after 15 days). A similar pattern of increase in pup serum was observed for phocine distemper virus specific antibodies which ha d been detected in the serum and milk of mothers, suggesting that the transfer of colostral antibodies is an important feature of temporary protection for the pup. We speculate that the relative immunocompetenc e of the harbour seal at birth reflects an adaptation to its relativel y short nursing period and limited maternal care.