The class II genes of the rat MHC

Genes that encode class II Ag from the MHC of the rat, the RT1 region, have been isolated as a series of cosmid clones. The cosmids define two clusters, each of which contains three identifiable sequences; one homologous to alpha-chain and two to beta-chain genes. Both the serologically identified rat class II Ag have been expressed in mouse L cell fibroblasts after the introduction of each alpha-chain gene along with a beta-chain gene from the same cluster. There are substantial homologies to the I region of the mouse H-2 complex in the presence, location, orientation, and expression of the six identified sequences from the rat RT1, supporting the view that the overall organization of the two gene complexes has remained conserved since the species separated.     

Human MHC class II molecules as differentiation markers

DA6.231 and DA6.164 are mouse monoclonal antibodies that immunoprecipitate HLA-DR-like p34,29 glycoprotein dimers from surface- and metabolically-labeled cells. On lymphoblastoid cell lines the distribution of the 231 epitope is completely nonpolymorphic, while the 164 epitope is present on all cells except on those that are DR7 homozygous. Binding-inhibition studies show that the 231 and 164 epitopes are spatially close to each other when present on the same molecule. The mutual inhibition pattern and the absence of the 164 epitope from the 231⁺ cells of a few leukemia patients suggest, however, that 231 and 164 epitopes are not invariably present together. Most DR-positive cells possess 231^– 164⁺ and 231⁺ 164^– class 11 molecules in approximately a 2:1 ratio. This has been confirmed by immune depletion studies. Thus DA6.231 appears to define a supralocus epitope. The 164 epitope may be a marker for a subset of class 11 molecules exhibiting differential expression on various cell types immortalized by malignant transformation.     

An immunohistochemical study of human pituicytes demonstrating frequent expression of MHC class II antigens and macrophage markers

Using a panel of antibodies (Abs) and a lectin, normal human adult pituicytes were studied in neurohypophyses obtained from 29 patients at antopsy. The pituicytes reacted frequently with Abs against major histocompatibility complex (MHC) class II antigens (Ags), macrophage markers (KP.1, PG.M1, LN-5), an anti-vimentin Ab and a biotinylated lectinRicinus communis agglutinin (RCA-1). The number of pituicytes immunostained for these reagents varied, with the notable exception of vimentin. MHC class II Abs (LN-3, CR3.43)-positive pituicytes were numerous in approximately half. Microscopically, MHC class II Ag was found in pituicytes of various shapes, and were identified in macrophage-typed pituicytes by electron microscopic immunohistochemistry. Glial fibrillary acidic protein was found in only a small number of pituicytes and was absent in cells labeled with MHC class II Abs or macrophage markers. The results indicate that the immunophenotype of human pituicytes is distinct from other glial cells of the central nervous system, with a considerable number of cells expressing MHC class II Ags and macrophage markers.     

Regulation of MHC class II gene expression by the class II transactivator

MHC class II molecules are pivotal for the adaptive immune system, because they guide the development and activation of CD4+ T helper cells. Fulfilling these functions requires that the genes encoding MHC class II molecules are transcribed according to a strict cell-type-specific and quantitatively modulated pattern. This complex gene-expression profile is controlled almost exclusively by a single master regulatory factor, which is known as the class II transactivator. As we discuss here, differential activation of the three independent promoters that drive expression of the gene encoding the class II transactivator ultimately determines the exquisitely regulated pattern of MHC class II gene expression.     

Bone marrow-derived mesenchymal stem cells differentiation into tubular epithelial-like cells in vitro

The possibility of differentiating bone marrow‐derived mesenchymal stem cells (BMSCs) into tubular epithelial‐like cells is explored in vitro. Purified BMSCs from Sprague–Dawley rats were obtained by density gradient centrifugation. Third generation BMSCs were divided into six groups and were cultured under different conditions. The expression of alkaline phosphatase and cytokeratin (CK)‐18 protein was detected through staining and immunocytochemistry, respectively, and the expression of E‐cadherin proteins was recorded through immunofluorescence. Some cells in ischemia/reperfusion (I/R), all‐trans retinoic acid (ATRA), epidermal growth factor (EGF) and bone morphogenetic protein‐7 (BMP‐7) groups turned positive, whereas the positive cells in the combined group significantly increased compared with the other groups. Compared with the control group, the positive expression rates of CK‐18 in the I/R, ATRA, EGF, BMP‐7 and the combined group were 11·50% ± 3·84%, 27·40% ± 2·70%, 29·60% ± 4·51%, 26·80% ± 5·00% and 44·00% ± 3·16%, respectively, and CK‐18 mRNA expression in the combined group was obviously higher than that in the other groups (P < 0·01). Immunofluorescence detection showed that E‐cadherin expression was not detectable in the control group, whereas the positive expression rates of E‐cadherin in the I/R, ATRA, EGF, BMP‐7 and the combined group were 6·75% ± 2·13%, 16·40% ± 2·69%, 18·25% ± 3·50%, 16·06% ± 2·00% and 30·26% ± 5·16%, respectively. The addition of ATRA, EGF and BMP‐7 induces BMSCs differentiation into tubular epithelial‐like cells in stimulated acute renal failure microenvironment in vitro. Copyright © 2011 John Wiley & Sons, Ltd.     

Human cytomegalovirus disrupts constitutive MHC class II expression

CD8(+) and CD4(+) T lymphocytes are important in controlling human CMV (HCMV) infection, but the virus has evolved protean mechanisms to inhibit MHC-based Ag presentation and escape T lymphocyte immunosurveillance. Herein, the interaction of HCMV with the MHC class II Ag presentation pathway was investigated in cells stably transfected with class II transactivator. Flow cytometry experiments demonstrate that HCMV infection decreases cell-surface MHC class II expression. HCMV down-regulates MHC class II surface expression without a significant effect on class II RNA or steady-state protein levels. SDS-stability and confocal microscopy experiments demonstrate normal levels of steady-state peptide-loaded class II molecules in infected cells and that class II molecules reach late endosomal and HLA-DM positive peptide-loading compartments. However, MHC class II positive vesicles are retained in an abnormal perinuclear distribution. Finally, experiments with a mutant HCMV strain demonstrate that this novel mechanism of decreased MHC class II expression is not mediated by one of the known HCMV immunomodulatory genes. These defects in MHC class II expression combined with previously identified CMV strategies for decreasing MHC class I expression enables infected cells to evade T lymphocyte immunosurveillance.     

MHC II类分子表达调控的研究进展

MHCII类分子提呈经过加工的抗原给CD4 T淋巴细胞 ,在诱发免疫反应中起重要作用。MHCII类分子不正常表达会引起严重的免疫缺陷疾病 ,如裸淋巴细胞综合征 (BLS)等。目前已识别出四种不同的MHCII调控基因。这些基因分别编码RFXANK、RFX5、RFXAP和CIITA。其中 ,前三个是RFX复合物的亚基 ,RFX是一种结合于所有MHCII类基因启动子上的泛式表达的因子。CIITA是MHCII类分子表达的主要调控因子 ,其严密调控的表达模式决定了MHCII类分子表达的细胞特异性 ,及能否被诱导且在何种水平上表达。本文着重介绍近年来国内外对MHCII类分子表达及其调控研究的新进展