Arudchelvan Yamini, Nishimura Yukio, Tokuda Nobuko, Sawada Tomoo, Ueyama Yoshiya, Fukumoto Tetsuo
Department of Oral and Maxillofacial Surgery, Yamaguchi University School of Medicine, Ube, Japan.
Anat Rec A Discov Mol Cell Evol Biol. 2003 Sep;274(1):798-806. doi: 10.1002/ar.a.10081.
Previous studies have concentrated on elucidating the subcellular localization of major histocompatibility (MHC) class II molecules mainly in B cells, macrophages, and dendritic cells. Despite very rich cell-surface expression of MHC class II molecules by cortical thymic epithelial cells (cTECs), little is known regarding the expression of these molecules by cTECs at the subcellular level. In the present study we focused on the identification and characterization of MHC class II compartments (MIICs) in cTECs in situ by immunogold electron microscopy (IEM). We found that MHC class II molecules were located exclusively in the cytoplasmic vacuoles, and we identified these MHC class II molecule-containing cytoplasmic vacuoles as MIICs in cTECs. These MIICs were immunopositive for early endosomal, late endosomal, and lysosomal markers. Moreover, in these MIICs, MHC class II molecules were colocalized with cathepsin L, H2-DM, class II-associated invariant chain (Ii), and class II-associated invariant chain peptide (CLIP). Similarly, Ii molecules were colocalized with endosomal and lysosomal markers, cathepsin L, and H2-DM in the vacuoles. Taken together, these results suggest that MIICs in cTECs represent conventional endocytic compartments. The colocalization of MHC class II molecule or Ii with cathepsin L and H2-DM in the MIICs suggests that MIICs in cTECs may be sites of Ii degradation and peptide loading.
以往的研究主要集中在阐明主要组织相容性复合体（MHC）II类分子在B细胞、巨噬细胞和树突状细胞中的亚细胞定位。尽管皮质胸腺上皮细胞（cTECs）表面的MHC II类分子表达非常丰富，但关于这些分子在cTECs亚细胞水平的表达情况却知之甚少。在本研究中，我们通过免疫金电子显微镜（IEM），重点对原位cTECs中的MHC II类区室（MIICs）进行了鉴定和表征。我们发现MHC II类分子仅位于细胞质空泡中，并将这些含有MHC II类分子的细胞质空泡鉴定为cTECs中的MIICs。这些MIICs对早期内体、晚期内体和溶酶体标记物呈免疫阳性。此外，在这些MIICs中，MHC II类分子与组织蛋白酶L、H2-DM、II类相关恒定链（Ii）和II类相关恒定链肽（CLIP）共定位。同样，Ii分子在空泡中与内体和溶酶体标记物、组织蛋白酶L和H2-DM共定位。综上所述，这些结果表明cTECs中的MIICs代表传统的内吞区室。MIICs中MHC II类分子或Ii与组织蛋白酶L和H2-DM的共定位表明，cTECs中的MIICs可能是Ii降解和肽装载的位点。
