On the prenatal initiation of T cell development in the opossum Monodelphis domestica

Abstract

Thymus dependent lymphocytes (T cells) are a critical cell lineage in the adaptive immune system of all jawed vertebrates. In eutherian mammals the initiation of T cell development takes place prenatally and the offspring of many species are born relatively immuno-competent. Marsupials, in contrast, are born in a comparatively altricial state and with a less well developed immune system. As such, marsupials are valuable models for studying the peri- and postnatal initiation of immune system development in mammals. Previous results supported a lack of prenatal T cell development in a variety of marsupial species. In the gray short-tailed opossum, Monodelphis domestica, however, there was evidence that αβT cells were present on postnatal day 1 and likely initiated development prenatally. Demonstrated here is the presence of CD3ε+ lymphocytes in late stage embryos at a site in the upper thoracic cavity, the site of an early developing thymus. CD3ε+ cells were evident as early as 48 hours prior to parturition. In day 14 embryos, where there is clear organogenesis, CD3ε+ cells were only found at the site of the early thymus, consistent with no extra-thymic sites of T cell development in the opossum. There was no evidence of prenatal B cell marker (CD79b) expression consistent with prior analyses supporting B cell lymphopoiesis being delayed relative to T cells. These observations are the first evidence of prenatal T cell lineage commitment in any marsupial.

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

“…The first immune cells detected were CD3ε + lymphocytes within the thymus at 1 dpp, indicating that T cells mature in the thymus rapidly after birth, and development of these cells could likely be initiated during the prenatal stage (Hansen and Miller, 2017). This pattern of T cell development is also similar to the common brushtail possum, where CD3ε + cells were detected in the thoracic thymus at two dpp (Baker et al, 1999).…”

Surfing on the waves of the human γδ T cell ontogenic sea

“…As this observation is based on RT‐PCR experiments, we do not know yet the abundance of the different T cell subsets in the opossum thymus (depicted by dotted lines). CD3ε+ cells that have been detected in the thymus of opossums at 48‐24h prior to birth, based on the previously described PCR results, might belong to the αβ T cell lineage 212 (depicted by dotted lines before partum). A more extreme exception is represented by the squamata lineage (squamates), as this family of reptiles has been reported to have lost the TCR γ and δ loci during evolution 8 .…”

Epigenetic clock and methylation studies in marsupials: opossums, Tasmanian devils, kangaroos, and wallabies

“…Comparisons of postnatal development in these species also discovered some potentially biologically relevant differences, including a strong association of age and CpGs located near immune system-related genes in opossums but not mouse. In contrast to placentals, much of the development of the adaptive immune system occurs after birth in marsupials [ 73 , 74 ]; for example, opossum newborns do not begin to produce their own antibodies until a week or more after their birth [ 75 ]. As a result, newborn marsupials must navigate the ex-utero world and its potentially pathogenic microorganisms with only their innate immune system active [ 76 ].…”