Duncan Louise G, Nair Sham V, Deane Elizabeth M
Department of Biological Sciences, Division of Environmental and Life Sciences, Macquarie University, NSW, Australia.
Vet Immunol Immunopathol. 2009 May 15;129(1-2):14-27. doi: 10.1016/j.vetimm.2008.12.003. Epub 2008 Dec 6.
In eutherian mammals, CD8 is a key receptor of cytotoxic T cells and plays a pivotal role in the recognition and elimination of infected host cells by cell-mediated cytotoxicity. Here, we report the molecular cloning and expression analysis of CD8alpha and CD8beta cDNAs in two marsupial species, the gray short-tailed opossum and the tammar wallaby. The opossum and tammar CD8 sequences share a high degree of amino acid identity of 63% (CD8alpha) and 57% (CD8beta) to each other as well as 36-45% (CD8alpha) and 38-41% (CD8beta) with their eutherian counterparts. In addition, many of the signature features of eutherian CD8alpha and CD8beta are preserved in both marsupials including the two invariant cysteines that form the intra-chain disulphide bond in the extracellular IgSfV domain and the two hinge region cysteines involved in dimerisation between the two subunits. The p56(lck) binding motif in the cytoplasmic tail of the CD8alpha subunit is also conserved. Interestingly, the opossum CD8alpha and the tammar CD8beta sequences have a truncated cytoplasmic tail. RT-PCR analysis of CD8alpha and CD8beta transcripts in the tissues of the adult opossum and tammar showed broad tissue expression with a high level of expression observed in the lymphoid tissues of both marsupials. Furthermore, RT-PCR analysis of CD8alpha and CD8beta transcripts in the immune tissues of tammar young over the first 120 days of pouch life revealed a pattern of expression analogous to the maturation of the lymphoid tissues. This is the first report confirming the presence of CD8 in the tissues of a marsupial and will provide the tools to further analyse T cell subsets in this unique group of mammals.
在真兽类哺乳动物中，CD8是细胞毒性T细胞的关键受体，在通过细胞介导的细胞毒性识别和清除受感染宿主细胞的过程中发挥着关键作用。在此，我们报告了两种有袋类动物——灰短尾负鼠和帚尾袋鼩中CD8α和CD8β cDNA的分子克隆及表达分析。负鼠和帚尾袋鼩的CD8序列彼此之间具有63%（CD8α）和57%（CD8β）的高度氨基酸同一性，与它们的真兽类对应序列分别具有36 - 45%（CD8α）和38 - 41%（CD8β）的氨基酸同一性。此外，真兽类CD8α和CD8β的许多标志性特征在这两种有袋类动物中都得以保留，包括在细胞外IgSfV结构域中形成链内二硫键的两个不变半胱氨酸，以及参与两个亚基之间二聚化的两个铰链区半胱氨酸。CD8α亚基细胞质尾部的p56(lck)结合基序也保守存在。有趣的是，负鼠的CD8α和帚尾袋鼩的CD8β序列具有截短的细胞质尾部。对成年负鼠和帚尾袋鼩组织中CD8α和CD8β转录本的RT-PCR分析显示，其在广泛的组织中表达，在这两种有袋类动物的淋巴组织中均观察到高水平表达。此外，对帚尾袋鼩幼崽育幼袋生活前120天免疫组织中CD8α和CD8β转录本的RT-PCR分析揭示了一种与淋巴组织成熟类似的表达模式。这是首次证实有袋类动物组织中存在CD8的报告，将为进一步分析这一独特哺乳动物群体中的T细胞亚群提供工具。
