Histological Development of the Immune Tissues of a Marsupial, the Red‐Tailed Phascogale (Phascogale calura)

Abstract

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.

Red‐tailed phascogales: A review of their biology and importance as model marsupial species

“…Marsupials give birth to less developed young compared with eutherian mammals at birth, and their immune tissues are not yet mature (Borthwick et al, 2014; Old & Deane, 2000). Phascogales, are not unlike other marsupials in this regard as Borthwick and Old (2016) described immune tissue development of phascogales from birth to adulthood, and are likely highly reliant on maternal milk for their survival (Stannard et al, 2020). The pattern of immune tissue development (Table 2) follows that of other mammals including eutherians, however, the majority of development appeared post birth in the red‐tailed phascogale like other marsupials (Baker et al, 1999; Old & Deane, 2003, Old et al, 2003a,b; 2004a,b).…”

“…Much has already been investigated in terms of immune system development in the phascogale, including the development of the thymus, bone marrow, liver, spleen, lymph nodes, and some mucosal‐associated lymphatic tissues (Borthwick & Old, 2016; Borthwick et al, 2019), thus enabling more in‐depth studies in the future. The thymus is the first immune tissue to histologically mature in the red‐tailed phascogale, as it is in other marsupials (Basden et al, 1997; Old et al, 2003a).…”

“…The thymus is the first immune tissue to histologically mature in the red‐tailed phascogale, as it is in other marsupials (Basden et al, 1997; Old et al, 2003a). It is initially visible as two distinct lobes on Day 1 postpartum, however, it quickly develops and is mature in appearance within 2 weeks after birth, at which stage the thymus has differentiated into well‐defined medullary and cortical areas (Borthwick & Old, 2016). Hassall's corpuscles can also be observed at this stage (Borthwick & Old, 2016).…”

“…It is initially visible as two distinct lobes on Day 1 postpartum, however, it quickly develops and is mature in appearance within 2 weeks after birth, at which stage the thymus has differentiated into well‐defined medullary and cortical areas (Borthwick & Old, 2016). Hassall's corpuscles can also be observed at this stage (Borthwick & Old, 2016). Expression of CD3ε, CD4, TCRδ, and TCRμ were detected on Day 1 postpartum in the thymus, whilst the remaining genes isolated by Borthwick et al (2018) were expressed from Day 3 postpartum.…”

An Examination of the Development and Localization of Key Immune Cells in Developing Pouch Young of the Red‐Tailed Phascogale (Phascogale calura)

“…The red-tailed phascogale and many other Dasyurid species are classified as endangered. The histological development of the immune tissues of the phascogale has previously been examined, and like other marsupial species the immune tissues of this species develop and reach histological maturity during the pouch-bound phase of life (Borthwick and Old, 2016). Histological immunosenesence has also been examined in the phascogale (Letendre et al, 2018).…”