The Immunological Responses of Marsupials

Abstract

Recent work on the immune responses of marsupials is reviewed, with emphasis on cellular immune responses of the macropod marsupial Setonix brachyurus (quokka). Adult marsupials show immunological responses broadly comparable to those of eutherian mammals. However, two immunological mechanisms have evolved to protect the immunologically immature neonate: namely, the passive transfer of antibody and the rapid maturation of immune competence. Thymectomy in marsupials causes a marked lymphocytic depletion of the lymph nodes and spleen, and, in the quokka, a transient abolition of the humoral immune response to SRBC and depression of the response to other antigens. The blood leucocyte response to phytohemagglutinin (PHA) in vitro is also depressed. Although a wasting syndrome does not occur in the quokka, neonatally thymectomized animals have a markedly reduced lifespan. Thymus grafts in either intact or neonatally thymectomized pouch young persist, and in the latter case, fully reconstitute the in vitro leucocyte response to PHA. However, a concomitant restoration of the hemolytic antibody response was not achieved. A high level of lymphocyte chimaerism was found in the grafted animals. These results are discussed with reference to the specificity of cell-cell cooperation in the antibody response, and the possible implication of thymic humoral factors.