INVARIANT CHAIN AND ANTIGEN PRESENTATION

主要组织相容性复合体(MHC)分子负责 用于将抗原呈递给T细胞。两个结构相似的 第一类和第二类分子已经进化出结合槽 可以容纳各种多肽抗原。而给定的MHC 分子可能只能结合宇宙的一小部分 抗原肽，存在多种等位和等位形式的 I类和II类分子确定该物种有能力 现有的大多数抗原中。然而，相似的I类和II类分子 与多肽结合有关，它们呈现不同的多肽 起源于活体。因此，I类分子主要与 由第I类产生的蛋白质衍生的多肽-表达 细胞，而II类分子通常从 外源蛋白质，这些蛋白质已经通过 内吞作用。造成这种两极分化的机制很差。 可以理解，但一个促成因素是不变链(II)。这 内质网中与II类链相关的分子 (Er)并防止多肽与II类分子结合。运输后 到后高尔基隔室，II被释放，II类分子 能够获得多肽。因此，II可能是最重要的单曲 负责外源肽的II类结合的因子。 为了完成它的任务，II被赋予了结构主题 将不同形式的分子作用于不同的亚细胞 车厢。这些目标信号的确切性质将是 下定决心。亚细胞分离分析和形态分析 分析将揭示不同形式的非法入境者在 细胞到达它们的目的地。这些分析将揭示班级 II分子获得多肽。这些信息将是无价的 设计新的疫苗，并应该阐明自我分子是如何 可能会引起自身免疫反应。

The major histocompatibility complex (MHC) molecules are responsible for the presentation of antigens to T cells. Two structurally similar types of molecules, class I and class II, have evolved binding grooves that can accommodate a variety of peptidic antigens. While a given MHC molecule may only be able to bind a subfraction of the universe of antigenic peptides, the existence of multiple iso- and allelic forms of the class I and II molecules ascertain that the species has the capacity of present most antigens. However similar class I and class II molecules are with regard to peptide binding, they present peptides of different origins in vivo. Thus, class I molecules primarily associate with peptides derived from proteins manufactured by the class I-expressing cell while the class II molecules usually obtain their peptides from exogenous proteins, which have been imported into the cell by endocytosis. The mechanisms responsible for this dichotomy are poorly understood but one contributing factor is the invariant chain (Ii). This molecule associates with class II chains in the endoplasmic reticulum (ER) and prevents peptide binding to class II molecules. After transport to a post-Golgi compartment, Ii is released and the class II molecules are able to acquire peptides. Thus, Ii may be the most important single factor responsible for the class II binding of exogenous peptides. To accomplish its task, Ii is endowed with structural motifs that targets various forms of the molecules to different subcellular compartments. The precise nature of these targeting signals will be determined. Subcellular fractionation analyses and morphological analyses will reveal which routes the various forms of Ii take in the cell to reach their destinations. These analyses will reveal where class II molecules obtain peptides. Such information will be invaluable in designing novel vaccines and should shed light on how self-molecules might give rise to auto-immune reactions.