Selectivity of the major histocompatibility complex class II presentation pathway of cortical thymic epithelial cell lines.

Major histocompatibility complex (MHC) restriction of the immune response is established during positive selection of T cells in the thymus. This occurs mainly through interactions of T cell receptor of developing thymocytes with MHC/peptide ligands on cortical thymic epithelial cells (TEC). An ongoing controversy concerns the origin and the role of peptides involved in the positive selection of thymocytes. Evidence provided here shows that processing of MHC class II complexes in cortical TEC differs from that of medullary TEC. Removal of the invariant chain associated with MHC class II complexes was rapid and complete in medullary TEC which present peptides from both exogenous and cytosolic origin. In cortical TEC, a large fraction of class II dimers remained associated with a 10-12-kDa fragment of invariant chain (Ii). Incomplete removal of Ii correlated with the inability of cortical TEC to present peptides from exogenous origin. However, presentation of peptides from cytosolic proteins by cortical TEC remained possible. Thus, most peptides from exogenous proteins may be excluded from participating in positive selection of CD4+ T cells by a mechanism limiting Ii breakdown.

Modulation of HLA class II antigen expression by transfection of sense and antisense DR alpha cDNA.

In the human there are three isotypic forms of MHC class II gene products (HLA-DR, -DQ, and -DP). The isotype-matched alpha-beta dimers are predominant but isotype-mismatched dimers can also be expressed (DR alpha-DQ beta). Here it is shown that the expression of the DR alpha-DQ beta dimer can be correlated to a high ratio of DR alpha/DR beta mRNA. The DR alpha chain expression was modulated by transfection of a sense and antisense DR alpha cDNA. Overexpression of DR alpha promoted the appearance of the DR alpha-DQ beta dimer. On the other hand, pre-existing DR alpha-DQ beta dimer expression was suppressed after antisense DR alpha cDNA transfection. Therefore, imbalanced expression of the alpha and beta chain from a given isotype could lead to the modification of HLA class II phenotype.

HLA DR, DQ, and DP antigen expression in rheumatoid synovial cells: a biochemical and quantitative study.

Because an increased expression of HLA class II antigens appears to be a central feature in local lesions of rheumatoid arthritis (RA), we have developed specific tools to quantify Ia expression in RA at both the protein and mRNA levels. An original dot immunobinding assay and a quick blot hybridization with chain-specific HLA class II probes allowed quantification of HLA DR antigens and chain transcripts on small-size samples of adherent synovial lining cells (ASLC) from normal individuals or RA patients. These methods associated with Western blot techniques detecting class II and beta-chain expression showed that ASLC from RA patients freshly put in short-term culture expressed greater amounts of class II transcripts and proteins than ASLC from controls. Class II proteins and mRNA rapidly disappeared in culture. Recombinant interferon-gamma (rIFN-gamma) induced their re-expression. A study of the kinetics and levels of the HLA-D products showed similar patterns of activation in RA patients and controls. A qualitative analysis of HLA class II antigens synthesized in ASLC after rIFN-gamma induction was performed by two-dimensional gel electrophoresis. It revealed a normal pattern for alpha- and beta-chains in ASLC from normal and RA patients, thus eliminating the possibility that abnormal protein structure of Ia antigen expressed on ASLC is responsible for the activation of T cell immune responses in RA. Nevertheless, the invariant chain exhibited a particular pattern in ASLC with additional basic spots, and this might interfere with transport and glycosylation of HLA class II antigens in such cells.

Construction of chain- and locus-specific HLA class II DNA probes. Study of HLA-class II transcripts in leukemias.

In addition to their role in the immune response, MHC class II antigens may be considered as differentiation markers on hemopoietic cells. To study expression of class II genes at the mRNA level in leukemias representing various stages of lymphoid and myeloid differentiation, we constructed chain- and locus-specific HLA class II DNA probes. As the genes encoding the DR, DQ, and DP beta-chains display a strong sequence homology in the second extracellular and transmembrane domains, we used probes derived from the less conserved 3' untranslated regions. For the more divergent alpha-chain genes, DNA fragments derived from the coding portion were obtained from cDNA clones. All probes were designed to minimize background due to AT- or GC-rich segments and subcloned into pUC plasmids. Their lack of cross-hybridization was demonstrated in Southern blot experiments under moderately stringent conditions. Northern blot analysis of RNA from 15 patients with acute lymphoblastic and myeloblastic leukemias, chronic lymphoid and hairy cell leukemias showed that most patients expressed variable amounts of class II transcripts, some lacked all class II mRNA, and only two patients had a dissociated expression of class II genes, with lack of DQ and presence of DR and DP mRNA. This study reveals a vast heterogeneity of MHC class II gene expression in leukemias, as previously demonstrated at the protein level. The availability of these highly specific DNA probes should prove useful in extensive studies directed at better defining HLA class II gene expression during hemopoietic differentiation in physiologic and pathologic states.

New class I in man: serological and molecular characterization.

New class I antigens in linkage disequilibrium with HLA-A antigen are demonstrated in PHA T and EBV preferential target cells using human alloantisera. These new antigens are defined as class I antigens by immunoprecipitation of a 41-12 k dimer. The molecule is shown to be distinct from the HLA-A, -B, -C molecule and in particular from the A3 molecule as in sequential immunoprecipitations, the depletion of the HLA-A, -B, -C molecule or A3 molecule (44-12 k) has no effect on the new molecule (41-12 k). Being present on the PHA T cells and lymphoblast lines, these antigens are considered as new epitopes involved in the the cell activation process.

Changes in the patterns of protein phosphorylation associated with granulocytic and monocytic-induced differentiation of HL-60 cells.

Using two-dimensional gel electrophoresis we have analyzed the pattern of phosphorylated proteins in HL-60 leukemia cells and changes associated with their differentiation into granulocyte and monocyte-like cells. In undifferentiated cells 18 spots with MW ranging from 110 to 17, kDa were individualized with high resolution and reproducibility. Myelocytic differentiation induced by dimethyl sulfoxide (DMSO) and retinoic acid (RA) resulted in a decrease of the overall phosphorylation, the disappearance of two proteins of 42 and 17 kDa, and the appearance of one new acidic protein of 46-48 kDa. These changes seem to be specifically related to this differentiation pathway since they are not found in two HL-60 subclones resistant to DMSO or RA-induced differentiation. Monocytic differentiation induced by 1,25-dihydroxyvitamin D3 [1,25 (OH)2D3] and the combination of RA + 1-B-D-arabinofuranosyl cytosine (Ara-C) was associated with the appearance of 2 proteins of 68 kDa and 2 proteins of 80 kDa located in the acidic region of the gel. The protein of 17 kDa, when disappeared completely in granulocytic-like cells was present in monocytic cells, this suggesting that its phosphorylation state may be involved in the control of the differentiation pathway of HL-60 cells. Data concerning the effect of phorbol myristate acetate (PMA) and histamine on the level of phosphorylation of various proteins in HL-60 cells have also been obtained and discussed. Our results show that the myelocytic and monocytic phenotypes are characterized by a specific pattern of phosphoproteins involving both phosphorylation and dephosphorylation reactions.

Structure, biosynthesis, and polymorphism of chicken MHC class II (B-L) antigens and associated molecules.

Chicken MHC class II (B-L) antigens were immunoprecipitated by the monoclonal antibody TaP1 from inbred chicken splenic leukocytes and a lymphoblastoid B cell line (RP9), and were studied by two dimensional gel electrophoresis. B-L antigens are composed of one alpha and one beta chain that are noncovalently bound at the cell surface. In all haplotypes studied, a single acidic 34,000 dalton non-polymorphic chain was observed, whereas two polymorphic chains could be distinguished, differing in both pH and m.w. The alpha-beta heterodimer is associated during its maturation in the cytoplasm with several basic invariant molecules with m.w. ranging from 30,000 to 42,000 daltons. Treatment of cells with tunicamycin and treatment of immunoprecipitated molecules with several glycosidases revealed a complex process of maturation for all of these molecules. The alpha and beta chains undergo a N-glycosylation of complex type, whereas the invariant molecules bear N-linked high mannose glycans, and perhaps also O-linked glycans in the RP9 lymphoblastoid line. Overall, the B-L antigens appear very similar to the HLA-DR and I-E antigens.

Analysis of HLA-DR antigen glycosylation by serial lectin affinity chromatography.

The structure of the N-linked oligosaccharides of HLA-DR molecules from an HLA-DR homozygous B-lymphoblastoid cell line (CA) was characterized by serial lectin affinity analysis. Glycans lectin affinity profile were obtained for the HLA-DR complex and separated alpha- and beta-chains. Two structurally distinct glycosylation patterns were detected for the alpha-chain species, the alpha 1 with high-mannose- and complex-type oligosaccharides and alpha 2 with a complex-type one. In contrast, the beta-chain species contains only complex-type oligosaccharides. Further oligosaccharide heterogeneity is found for each alpha 1-, alpha 2- and beta-chain described. In contrast to murine and guinea-pig Ia antigens, no significant amount of glycopeptides with biantennary structure was found in HLA-DR.

Hybrid HLA-DC antigens provide molecular evidence for gene trans-complementation.

In the mouse there are hybrid determinants for the immune region (Ir) of the genome which contribute to the diversity of class II (Ia) antigens of the major histocompatibility complex (MHC) and provide a molecular basis for Ir gene complementation. In man, two prominent families of Ia molecule, HLA-DR and HLA-DC (or DS), have been identified which are respectively homologous to the murine I-E (E alpha, E beta) and I-A (A alpha, A beta) antigens. Whereas DR antigens consist of a constant alpha-chain and an extremely polymorphic beta-chain, both the alpha and beta subunits of DC antigens are structurally variable when different alleles are compared. The marked differences in the structure of the alpha- and beta-chains of HLA-DC molecules result in electrophoretic variants which allow the haplotype of origin of each subunit to be identified by two-dimensional gel electrophoresis. We report here that gene trans-complementation occurs in cells heterozygous for the HLA-D region, resulting in the expression of hybrid HLA-DC molecules in addition to the parental forms. Generation of new HLA-D region hybrid molecules contributes to the qualitative diversity of human MHC class II antigens and has important functional implications in immune regulation.

Differential expression of HLA-DR and HLA-DC/DS molecules in a patient with hairy cell leukemia: restoration of HLA-DC/DS expression by (12-0-tetradecanoyl phorbol-13-acetate), 5 azacytidine, and sodium butyrate.

Biosynthesis and molecular structure of major histocompatibility complex (MHC) class II antigens of DR2/DR7 hairy cells were analyzed by two-dimensional polyacrylamide-gel electrophoresis (2D-PAGE). Two anti-human Ia monoclonal antibodies (mAb) were used to immunoprecipitate DR and DR-linked DC/DS molecules. Monoclonal antibody VI 15 C recognizes DR (I-E-like) molecules and CA 2.06 precipitates DR and DR-linked DC/DS (I-A-like) molecules in DR7 allotypes. Studies were performed on a pure population of hairy cells before and after culture with phorbol ester: 12-O-tetradecanoyl phorbol-13-acetate (TPA), 5 azacytidine (5 Aza), sodium butyrate (NA-BU), and phytohemagglutinin (PHA-P). Before any treatment, hairy cells expressed and synthesized DR antigens: DR alpha and beta subunits appeared both qualitatively and quantitatively normal by 2D-PAGE profile. In contrast, the hairy cells failed to express and synthesized any DC/DS molecule. The lack of DC/DS molecular expression was restored after culture in presence of TPA, sodium butyrate, and 5 azacytidine, but not after PHA-P treatment. Differential molecular expression of MHC class II antigens in leukemic cells provides a model to define further discrete stages of hemopoietic differentiation and study the role of these molecules in the cellular interactions occurring during differentiation.