An examination of the immunological function of the thymus of a marsupial

Abstract

An account was given of investigations carried out with Professor Waring and Dr Mohan Yadav of the Department of Zoology, of work on the Rottnest Island Quokka (<i>Setonix brachyurus</i>). The function of the thymus glands of the quokka was being studied because (1) this marsupial possessed two pairs of thymus glands, a large superficial thymus located bilaterally in the neck and a thoracic thymus, and (2) thymectomy could be attempted at a stage in ontogenetic development far earlier than could be attempted with eutherians. The response of intact superficially thymectomized and totally thymectomized quokkas to sheep's red blood cells (SRBC), <i>S. adelaide</i> fiagella and OX174 was studied, together with some homograft reactions. Observations showed that total thymectomy inhibited the response of the pouch young to all 3 antigens, provided the superficial thymus was removed before day 5 and the thoracic thymus before day 20 of pouch life. Towards the end of pouch life at about 150 days, totally thymectomized animals returned to competence and would produce antibodies to SRBC in the same manner as intact animals. The view was expressed that the two sets of thymus glands did not serve different functions, but were programmed to operate at different times; the superficial thymus before the thoracic thymus. Insufficient evidence was available to explain the return to immunological competence or the need for herbivore marsupials like the quokka to have relatively large superficial thymus glands during the early stages of pouch life.