[show abstract][hide abstract] ABSTRACT: The non-classical major histocompatibility complex (MHC) class I molecule CD1d presents lipid antigens to invariant natural killer T (iNKT) cells, which are an important part of the innate immune system. CD1d/iNKT systems are highly conserved in evolution, and cross-species reactivity has been suggested to be a common feature of different animals based on research in humans and mice. However, we found that CD1d from the tree shrew (Tupaia belangeri), a close evolutionary relative of primates, failed to stimulate human iNKT cells, despite being more homologous to human CD1d than that of mouse. Sequence comparison and molecular modelling showed that two of the key amino acid residues in human CD1d proposed to be in direct contact with T-cell receptors were mutated in tree shrew CD1d. Substitution of one of the residues, but not the other, with the human residue enabled tree shrew CD1d to regain the ability to present lipid antigen to human iNKT cells. These results indicate that CD1d/iNKT recognition is species-specific, and that cross-species reactivity may be less common than currently proposed. Also, a naturally occurring CD1d mutation(s) that confers inability to stimulate iNKT cell function may have implications for future studies on CD1d/iNKT-associated diseases.
[show abstract][hide abstract] ABSTRACT: Tree shrews (Tupaia Belangeri ) are phenogenetically close to humans and primates and generally recognized as a prominent small animal model for studies of heptitis virus type B (HBV). Isolating and culturing tree shrew hepatocytes is the first key step toward the cellular model of HBV infection in vitro. Due to the lack of details in previous reports, establishing the model has been a matter of arbitary experiences. In this study, we validated the superiority of perfusion over mechanic dispersion for hepatocyte separation and isolation. Subsequent cultures showed that dimethyl sulphoxide (DMSO) could suppress the growth of fibroblast-like cells and maintain the hepatocytes in the differentiated status. Furthermore, hepatocyte growth factor (HGF) and epidermal growth factor (EGF) could sustain growth and survival of the hepatocytes in the long-term culture. The combination of DMSO and HGF/EGF could maintain the hepatocytes in a longer and more stable differentiated status with clear trend to form liver sinus-like structures. Following this detailed method as a laboratory routine would permit plentiful starting material for study of HBV infection in vitro and drug-screening, as well as studies on hepatitis viruses type C and D, and herpes simplex virus.
Zoological Research (ISSN: 0254-5853) Vol 30 Num 1. 01/2009;