Introduction

While the mammalian body may be said to be a hotel for millions of potential pathogens, it is the warm, moist tissues of all mammals that can provide the breeding ground. To combat the effects of invading, replicating pathogens, evolution has provided the immunolymphatic system. This system is essential for survival in the day-to-day life of marsupials.

Because the lymphatic arm and the immune arm of the system cannot be easily seen and because these are difficult to dissect, particularly in marsupials, this system has been rather neglected in the past. Studies of the marsupial immunolymphatic system have concentrated on few species and general statements are made based on these. Such a selective approach is, however, the way in which most biological systems are studied. The marsupial immune system is now the focus of a number of intensive studies worldwide. Because the neonatal marsupial is immature at birth, i.e. altricial, and because organogenesis occurs in the pouch, the pouch young provide a unique and accessible model for studies of the development of the mammalian immunolymphatic system. Old and Deane (2000) have reviewed the development of immunological protection in pouch young, and make the point that the pouch provides an environment which is particularly challenging.

The immunolymphatic system encompasses lymphatic vessels and immune system tissues. These tissue include the tonsils, adenoids, lymph nodes, thymus gland, Peyer's patches and spleen. As well, there are tissues collectively known as the mucosa-associated lymphoid tissues (MALT).