Current knowledge of the development of the marsupial immune system, particularly in the context of lymphoid tissue development and the appearance of lymphocytes, has been examined and limitations identified. While primary lymphoid tissues like the thymus have been extensively studied, secondary lymphoid tissues such as the spleen and lymph nodes have been examined to a lesser extent, partly due to the difficulty of macroscopically identifying these structures, particularly in very small neonates. In addition, little research has been conducted on the mucosal-associated lymphoid tissues; tissues that directly trap antigens and play an important role in the maturity of adaptive immune responses. Research on the development of the marsupial immune tissues to date serves as a solid foundation for further research, particularly on the mechanisms behind the development of the immune system of marsupials. With the recent sequencing and annotation of whole marsupial genomes, the current wealth of sequence data will be essential in the development of marsupial specific reagents, including antibodies, that are required to widen our specific knowledge of the complex marsupial immune system and its development.

Red-tailed phascogale (Phascogale calura) pouch young at birth were relatively underdeveloped in comparison with their eutherian counterparts, and the lymphoid tissues of the immune system were found to be histologically immature. The phascogale thymus rapidly developed in the first few days of pouch life and was quickly populated with lymphocytes. By the end of pouch life, involution of the thymus was underway. The bone marrow started to develop in the early stage of pouch life, although adipocytes and megakaryocytes were not observed until slightly later. The liver was hematopoietic from birth and reached histological maturity toward the end of pouch life. The lymph nodes were difficult to detect macroscopically because of their small size, but were easily identified microscopically later in pouch life, particularly in the mesentery, and these lymph nodes exhibited germinal centers by the end of pouch life. The early spleen was predominately mesenchymal, but exhibited some erythropoiesis. Follicles with well-developed germinal centers were not observed until the latest stage of pouch life. Although intraepithelial lymphocytes were detected in the intestines early in pouch life, the discrete lymphoid aggregates and Peyer's patches characteristic of the gut-associated lymphoid tissue (GALT) were not detected until later in pouch life. This is the first report of histological development in phascogale pouch young, as well as the first report of the thymus, bone marrow, and lymph nodes in this dasyurid species at any age. Anat Rec, 299:207-219, 2016. V C 2015 Wiley Periodicals, Inc.

This paper reports successful breeding by 4-year-old female red-tailed phascogales (Phascogale calura) and that they can survive until at least 5 years of age in captivity, whilst males can survive until at least 2 years of age in captivity. These findings have implications for captive breeding programs, providing evidence that older females can be successfully bred. In the longer term we hope these findings may aid conservation efforts of this endangered dasyurid.

Cells expressing the surface markers CD3, CD4, CD79b, IgM, MHC class II, and ModoUG (nonclassical MHC class I) were detected in red-tailed phascogale tissues using immunohistochemistry, and the appearance and localization of cells observed here was consistent with previous observations in other marsupial species. CD3 + cells were first detected at one day postpartum (dpp) in the thymus, followed by ModoUG + cells at 5-7 dpp in the thymus and lymph nodes. CD79b + cells were first detected at 12-14 dpp in bone marrow, spleen, and lymph nodes. IgM + cells were first detected at 12-14 dpp in thymus, bone marrow, spleen, and lymph nodes. MHC class II + cells were first detected at 12-14 dpp in thymus, bone marrow, and lymph nodes. CD4 + cells were detected in adult thymus and spleen only. The presence of the mature immune cell populations and their localization to characteristic T and B cell zones in mature lymphoid tissues with normal histological structure indicates that red-tailed phascogales develop immunocompetence by the end of pouch life.

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