NOT PROPER MAMMALS - IMMUNITY IN MONOTREMES AND MARSUPIALS

Immune systems and responses in Monotremata and Marsupialia are review ed. The Monotremata (Prototheria) are egg-laying mammals. Few studies have been carried out on monotremes. The structure of the lymph nodule s of Tachyglossus aculeatus is unusual, and the occurrence of IgG in t his species is noteworthy: IgG has not yet been found in any non-mamma l. A number of Marsupialia (Metatheria) species have been used as immu nological models. Generally immune responses are somewhat slower and l ess accentuated than in placental (eutherian) mammals. Of interest is the presence of cervical and thoracic thymuses in several marsupials. Marsupials are born very immature and possess rather rudimentary immun e responses at birth: the neonate may provide a helpful model for immu ne ontogenesis. Marsupials have a full repertoire of immunoglobulin cl asses. MHC Class II (but not Class I) gene polymorphism may be limited . Studies using molecular biology techniques are awaited to elucidate the structural organization of the immune components and to determine similarities and differences between marsupials' and other animals' im mune systems.