REGULATION AND FUNCTION OF THE CD4 GENE

成熟的T淋巴细胞可根据其分化程度分为两个亚群。 表达两种细胞表面糖蛋白CD 4或CD 8中的任一种。 不 识别II类主要组织相容性复合体（MHC）的细胞 蛋白质通常表达CD 4并且是辅助物或诱导物，而那些 识别I类MHC蛋白通常表达CD 8并且是细胞毒性的（或 可能是抑制剂）。 CD 4已被证明在以下方面发挥重要作用： 增强T细胞对抗原的应答以及在T细胞的选择中 在胸腺发育过程中 此应用程序的目标是定义 CD 4是通过什么机制来实现这两种功能的？ A CD4-CD8-，Kb 将使用应答性T细胞杂交瘤来确定CD 4是否可以 增强对I类MHC蛋白质的反应，如果是这样，是否会发生这种情况， 仅仅通过粘附或者也通过信号转导。 的作用 酪氨酸激酶p56 lck在CD 4介导的抗原应答增强中的作用 将使用野生型和突变型p56 lck的转染进行检查 在II类限制性抗原依赖性T细胞杂交瘤中。 相互作用 将检测CD 4和组成型活性形式的p56 lck之间的关系， 确定它们的影响是否是相加的，两者是否相关， 以及CD 4和/或T细胞受体（TCR）的交联对 蛋白质缔合，底物和抗原的酪氨酸磷酸化 应答 TCR相关p59 fyn酪氨酸激酶在CD-4中的作用 介导的抗原应答刺激也将使用 突变体和野生型p59 fyn构建体。 （二）以双？ 阳性胸腺细胞变成CD 4单阳性，如果他们有II类 限制性TCR，或CD 8，如果他们有一个I类限制性TCR，将被 探讨了 这将通过交配表达一种 嵌合CD 8/CD 4构建体与I类特异性TCR转基因小鼠的结合， II类缺陷小鼠 还将使用同源重组 以产生其中内源性CD 8 α基因被替换为 具有CD 4跨膜区和胞质尾区的CD 8 α，或 用反向构建体替换内源性CD 4基因。

Mature T lymphocytes can be divided into two subsets based upon their expression of either of two cell surface glycoproteins, CD4 or CD8. T cells that recognize class II major histocompatibility complex (MHC) proteins generally express CD4 and are helper or inducer, while those that recognize class I MHC proteins generally express CD8 and are cytotoxic (or possibly suppressor). CD4 has been shown to play important roles in enhancing T cell responses to antigen and in the selection of T cells during thymic development. The goal of this application is to define the mechanisms by which CD4 accomplishes these two functions. A CD4-CD8-, Kb responsive T cell hybridoma will be used to determine whether CD4 can enhance responses to class I MHC proteins, and if so, whether this occurs merely by adhesion or also by signal transduction. The role of the tyrosine kinase p56lck in CD4-mediated enhancement of antigen responses will be examined using transfection of wild-type and mutant forms of p56lck in a class II restricted, antigen dependent T cell hybridoma. Interactions between CD4 and a constitutively active form of p56lck will be examined to determine whether their effects are additive, whether the two associate, and the effects of cross-linking of CD4 and/or the T cell receptor (TCR) on protein associations, tyrosine phosphorylation of substrates and antigen responses. The role of the TCR-associated p59fyn tyrosine kinase in CD-4 mediated stimulation of antigen responses will also be assessed using mutant and wild-type p59fyn constructs. The mechanism(s) by which double- positive thymocytes become single positive for CD4 if they have a class II restricted TCR, or CD8 if they have a class I restricted TCR will be explored. this will be done both by mating transgenic mice expressing a chimeric CD8/CD4 construct to a class I specific TCR transgenic mouse and to a class II deficient mouse. Homologous recombination will also be used to generate mice in which the endogenous CD8alpha gene is replaced with CD8alpha having a CD4 transmembrane region and cytoplasmic tail, or the endogenous CD4 gene is replaced with the reverse construct.