Ratnofsky S E, Peterson A, Greenstein J L, Burakoff S J
Dana-Farber Cancer Institute, Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115.
J Exp Med. 1987 Dec 1;166(6):1747-57. doi: 10.1084/jem.166.6.1747.
In general, the human CD8 molecule is expressed on T cells specific for HLA class I molecules. Studies designed to delineate the function and to define the ligand of the CD8 molecule have been complicated by the fact that the presumptive ligand for CD8 is on the HLA class I molecule, the same molecule encoding the ligand for the antigen-specific T cell receptor. The ability to express genes in cells other than their natural host has produced a new technology with which to approach CD8 functional studies. The insertion of a cDNA clone for CD8 in a defective retroviral vector has allowed the transfer of CD8 by infection with the resulting defective retrovirus. CD8 was then expressed in an HLA class II-specific T cell, thus separating the ligand requirements of the TCR and CD8. By this approach, the human CD8 molecule was expressed in a murine T cell hybridoma specific for human class II antigens. The resulting CD8+ hybridomas demonstrated a 10-fold increase in IL-2 production over the parent cell line when stimulated with JY, a human B lymphoblastoid cell line expressing both class I and II HLA antigens, demonstrating that expression of CD8 increases T cell activation. mAbs directed against the CD8 molecule inhibited the response of CD8+ hybridomas to JY, supporting the conclusion that the CD8 molecule was fractional. The role of CD8 as a receptor for class I MHC antigens was addressed by stimulation with a cell line expressing HLA-DR antigens, but lacking the expression of HLA class I antigens (Daudi). Stimulation of the CD8+ hybridomas by Daudi did not result in increased IL-2 production. The response to Daudi was unaltered by the addition of anti-CD8 mAb, in contrast to the ability of anti-CD8 mAb to block JY stimulation. Furthermore, mAbs directed against the class I antigens present on JY cells were able to block the enhanced response of the CD8+ hybridomas to JY. These data support the hypothesis that HLA class I molecules are the ligands involved in the CD8-dependent enhancement of T cell activation.
一般来说，人类CD8分子在对HLA I类分子具有特异性的T细胞上表达。旨在阐明CD8分子功能并确定其配体的研究因以下事实而变得复杂：CD8的假定配体存在于HLA I类分子上，而该分子正是编码抗原特异性T细胞受体配体的同一分子。在细胞而非其天然宿主中表达基因的能力产生了一种用于进行CD8功能研究的新技术。将CD8的cDNA克隆插入缺陷型逆转录病毒载体中，通过用产生的缺陷型逆转录病毒感染实现了CD8的转移。然后，CD8在HLA II类特异性T细胞中表达，从而将T细胞受体（TCR）和CD8的配体需求分开。通过这种方法，人类CD8分子在对人类II类抗原具有特异性的小鼠T细胞杂交瘤中得以表达。当用JY（一种表达I类和II类HLA抗原的人类B淋巴母细胞系）刺激时，产生的CD8 +杂交瘤与亲代细胞系相比，IL - 2产量增加了10倍，表明CD8的表达增强了T细胞活化。针对CD8分子的单克隆抗体（mAb）抑制了CD8 +杂交瘤对JY的反应，支持了CD8分子起作用的结论。通过用表达HLA - DR抗原但缺乏HLA I类抗原表达的细胞系（Daudi）进行刺激，研究了CD8作为I类MHC抗原受体的作用。Daudi对CD8 +杂交瘤的刺激并未导致IL - 2产量增加。与抗CD8 mAb阻断JY刺激的能力相反，添加抗CD8 mAb对Daudi的反应没有影响。此外，针对JY细胞上存在的I类抗原的mAb能够阻断CD8 +杂交瘤对JY的增强反应。这些数据支持了以下假设：HLA I类分子是参与CD8依赖性T细胞活化增强的配体。
