Reactions and crossreactions of a rabbit anti-H2 antigen serum

Cis association of Ly49A with MHC class I restricts natural killer cell inhibition

Natural killer (NK) cell function is negatively regulated by inhibitory receptors interacting with major histocompatibility complex class I molecules expressed on target cells. Here we show that the inhibitory Ly49A NK cell receptor not only binds to its H-2D(d) ligand expressed on potential target cells (in trans) but also is constitutively associated with H-2D(d) in cis (on the same cell). Cis association and trans interaction occur through the same binding site. Consequently, cis association restricts the number of Ly49A receptors available for binding of H-2D(d) on target cells and reduces NK cell inhibition through Ly49A. By lowering the threshold at which NK cell activation exceeds NK cell inhibition, cis interaction allows optimal discrimination of normal and abnormal host cells.

The assembly of H2-Kb class I molecules translated in vitro requires oxidized glutathione and peptide

Association of the mouse major histocompatibility complex (MHC) class I heavy chain H2-Kb with mouse beta 2-microglobulin (beta 2m) was studied in an in vitro translation system. Formation of stable class I complexes was found to be dependent on the presence of presentable peptides and oxidized glutathione, which promotes the formation of disulfide bridges. Translocation of peptides into microsomes was demonstrated by showing that a radioiodinated peptide containing an N-glycosylation acceptor site became glycosylated. Class I complex formation was observed only when heavy chains and beta 2m were translated simultaneously, and thus occurs in the microsomes and not after their solubilization. However, peptide binding takes place only after solubilization of the microsomes. The class I complexes translated in vitro show the same specificity and length preference for peptides as their counterparts in RMA-S cells. Assembly of in vitro translated class I complexes was found to occur also in the absence of peptides, resulting in the formation of unstable molecules that are stabilized by incubation with peptides.

Role of histocompatibility antigen gene and protooncogene expressions in intracerebral tumorigenicity of mouse neuroblastoma

The role of N-myc, c-src, and major histocompatibility complex (MHC, H-2 in the mouse) class I antigen gene expressions in dimethyl sulfoxide (DMSO)-induced differentiation and intracerebral tumorigenicity was examined using a mouse MNB85 neuroblastoma cell line. A fluorescence-activated cell sorter disclosed cell-surface MHC enhancement by DMSO, causing an increase in cytotoxic T-lymphocyte sensitivity. Southern blot analysis verified a single copy of the proto-oncogenes and MHC deoxyribonucleic acids in both untreated and DMSO-treated MNB85 cells. Northern blot analysis indicated that DMSO treatment induced a decrease in N-myc and an increase in c-src and MHC messenger ribonucleic acids. Nuclear run-off transcription assay revealed down-regulation of N-myc at a posttranscriptional level, contrasted with primary up-regulation of c-src at a transcriptional level. Immunoprecipitation after treatment with enzyme endo-beta-N-acetyl-glycoseamidase H proved that the terminal glycosylation of MHC heavy-chain gene products normally occurs in the Golgi apparatus of MNB85 cells. Intracerebral tumorigenicity assay showed that cells highly MHC-expressed by DMSO were less tumorigenic than untreated cells in association with DMSO-augmented cytotoxic T-lymphocyte susceptibility. These results suggest that proto-oncogenes may be linked to cellular differentiation, while cell-surface MHC gene expression influences intracerebral immunosurveillance.

Empty and peptide-containing conformers of class I major histocompatibility complex molecules expressed in Drosophila melanogaster cells

Transfected Drosophila melanogaster cells can express large quantities of class I major histocompatibility complex molecules. Such molecules lack endogenous peptides because the Drosophila cells are devoid of proteins necessary for intracellular peptide loading. The empty molecules are efficiently expressed on the cell surface and can acquire extracellular peptides. The conformation and stability of empty murine class I molecules are determined by the source of beta 2-microglobulin. All beta 2-microglobulin-induced conformers of empty heavy chains seem to be unified in a common rigid conformation on peptide binding.

Translocation of peptides through microsomal membranes is a rapid process and promotes assembly of HLA-B27 heavy chain and beta 2-microglobulin translated in vitro

We have translated major histocompatibility complex (MHC) class I heavy chains and human beta 2-microglobulin in vitro in the presence of microsomal membranes and a peptide from the nucleoprotein of influenza A. This peptide stimulates assembly of HLA-B27 heavy chain and beta 2-microglobulin about fivefold. By modifying this peptide to contain biotin at its amino terminus, we could precipitate HLA-B27 heavy chains with immobilized streptavidin, thereby directly demonstrating class I heavy chain-peptide association under close to physiological conditions. The biotin-modified peptide stimulates assembly to the same extent as the unmodified peptide. Both peptides bind to the same site on the HLA-B27 molecule. Immediately after synthesis of the HLA-B27 heavy chain has been completed, it assembles with beta 2-microglobulin and peptide. These interactions occur in the lumen of the microsomes (endoplasmic reticulum), demonstrating that the peptide must cross the microsomal membrane in order to promote assembly. The transfer of peptide across the microsomal membrane is a rapid process, as peptide binding to heavy chain-beta 2-microglobulin complexes is observed in less than 1 min after addition of peptide. By using microsomes deficient of beta 2-microglobulin (from Daudi cells), we find a strict requirement of beta 2-microglobulin for detection of peptide interaction with the MHC class I heavy chain. Furthermore, we show that heavy chain interaction with beta 2-microglobulin is likely to precede peptide binding. Biotin-modified peptides are likely to become a valuable tool in studying MHC antigen interaction and assembly.

High-resolution one-dimensional isoelectric focusing of mouse MHC class I antigens. Identification of natural and experimentally induced class I antigens

A method is described for a biochemical comparison of mouse class I antigens utilizing antisera with a monomorphic pattern of reaction and high-resolution one-dimensional isoelectric focusing (1D-IEF). The most commonly occurring and studied H-2K and D alleles were identified in a comparison of over 40 mouse strains. By comparing H-2 mutant mouse strains, cell lines transfected with defined class I genes, or mice transgenic for a mouse class I gene and H-2 recombinant mouse strains, unambiguous identification of class I alleles was possible. The complex pattern presented by H-2-heterozygous mice was readily resolved into the contribution by the individual parental alleles. The H-2b bm series of mutants was analyzed, and for those mutants where a charge difference was predicted based on their known sequence, a change in isoelectric point (IEP) was indeed observed. Based on analysis by IEF, the bm8 mutant may contain (an) amino acid substitution(s) in addition to those reported. The present method further appears useful in elucidating defects in class I antigen synthesis and post-translational modifications, as these cannot be easily characterized when using surface staining with monoclonal antibodies (mAbs).

Empty MHC class I molecules come out in the cold

Major histocompatibility complex (MHC) class I molecules present antigen by transporting peptides from intracellularly degraded proteins to the cell surface for scrutiny by cytotoxic T cells. Recent work suggests that peptide binding may be required for efficient assembly and intracellular transport of MHC class I molecules, but it is not clear whether class I molecules can ever assemble in the absence of peptide. We report here that culture of the murine lymphoma mutant cell line RMA-S at reduced temperature (19-33 degrees C) promotes assembly, and results in a high level of cell surface expression of H-2/beta 2-microglobulin complexes that do not present endogenous antigens, and are labile at 37 degrees C. They can be stabilized at 37 degrees C by exposure to specific peptides known to interact with H-2Kb or Db. Our findings suggest that, in the absence of peptides, class I molecules can assemble but are unstable at body temperature. The induction of such molecules at reduced temperature opens new ways to analyse the nature of MHC class I peptide interactions at the cell surface.

Requirements for the association of adenovirus type 2 E3/19K wild-type and mutant proteins with HLA antigens

The E3/19K protein of human adenovirus type 2 is a resident of the endoplasmic reticulum (ER). Immediately after synthesis, it associates with major histocompatibility complex class I antigens and prevents their intracellular transport and cell surface expression. We have generated several C-terminal deletion mutants of the E3/19K protein that are preterminated at various positions on both sides of the membrane-spanning segment of the protein. One of these mutants is terminated at the luminal side of the membrane (M310), and two are terminated in the hydrophobic segment (M374 and M392), whereas mutant M621 is terminated on the cytoplasmic side of the ER membrane. The M310, M374, and M392 mutants are soluble proteins. They do not associate with HLA antigens in transfected 293 cells, and they are, to some extent, secreted into the medium. The M621 mutant protein is integrated in the ER membrane, associates immediately after its synthesis with HLA antigens, and exits from the ER. By using either an in vitro translation system supplemented with microsomes or overexpression in insect cells, we showed that M374 and E3/19K are able to associate with HLA antigens. These results indicate that the conformation of the luminal part of the E3/19K protein is not grossly altered by the mutations. Rapid transport of the M374 mutant out of the ER and partial degradation of this protein may prevent the interaction with HLA class I antigens in transfected 293 cells.

Molecular complexity of Qa-2 antigens demonstrated by two-dimensional gel electrophoresis

Biosynthetically labelled Qa-2 antigens were isolated from mouse spleen cells by immunoprecipitation with anti-Qa-2 antisera. When newly synthesized Qa-2 molecules from several different inbred strains were analysed by two-dimensional (2D) gel electrophoresis; four different phenotypes were observed that differed in the number of polypeptides present. The ability to distinguish Qa-2+ phenotypes was used to map the recombination points in two congenic strains, B6.Tlaa and A.Tlab. No alternative Qa-2-like polypeptides were detected in B6.K1 (Qa-2-) cells using a polyspecific rabbit antiserum against mouse class I antigens, but a new molecule was detected in BALB/cBy (Qa-2-) cells. Pulse-chase and surface-labelling experiments showed that some, but not all, of the newly synthesized Qa-2 precursor forms are processed to mature cell surface molecules.

Beta 2-microglobulin is not required for cell surface expression of the murine class I histocompatibility antigen H-2Db or of a truncated H-2Db

beta 2-Microglobulin (beta 2m) has been thought essential for transport of all major histocompatibility complex class I antigens to the cell surface. Here, we show that the mouse class I antigen H-2Db is expressed at the cell surface even when there is no beta 2m present within the cell. This was established by transfecting the H-2Db gene into the R1E cell line, which lacks beta 2m. The conformation of the Db antigen expressed by the R1E transfectant is very different from that of the native molecule. This Db antigen is not recognized by Db-allospecific and Db-restricted cytotoxic T lymphocytes or by most monoclonal antibodies to the native Db. We show further that a deletion construct of the Db gene, which consists of exon 1 linked to exons 4-8, expresses a truncated Db antigen lacking domains 1 and 2 [Db-(1 + 2)] at the cell surface after transfection into the R1E line. Previous biochemical and crystallographic data have indicated that domain 3 is associated with beta 2m; unexpectedly, Db-(1 + 2) does not associate with beta 2m when the mouse beta 2mb gene is transfected into the R1E transfectant expressing the truncated Db. This suggests that interactions with domains 1 and 2 are important for the paired association of domain 3 and beta 2m in the native Db antigen.

Distribution of the major histocompatibility complex antigens in human and rat kidney

We have compared the distribution of the major histocompatibility complex (MHC) antigens in human and rat kidney using monospecific antisera to class I and II antigens of the MHC. FITC/TRITC double immunofluorescence was used to demonstrate these antigens in frozen sections and the Staphylococcus aureus Cowan I rosette assay on the cell surface. In both species, the MHC antigens were prominently present on the passenger leukocytes. Immunofluorescence analysis of human kidney demonstrated that the class I, beta 2-microglobulin (beta 2m), and class II antigens were present in the vascular endothelial cells and class I antigens in the renal tubular cells. The Staphylococcus assay demonstrated that these antigens were also exposed on the respective cell surfaces. In clear contrast, in the rat, class I, the beta 2m, and class II antigens were absent from the kidney vascular endothelium of large vessels and intertubular capillaries; however, large amounts of class II antigens were seen inside the proximal renal tubular cells. The Staphylococcus assay indicated that none or very little of these antigens were exposed on the kidney parenchymal cell surface. These differences may explain why rat renal transplants are relatively non-immunogenic and easily accepted, whereas human renal transplant recipients must be immunosuppressed ad infinitum.

Recycling of transferrin receptors in A431 cells is inhibited during mitosis

There is a marked reduction in the number of surface transferrin receptors as A431 cells enter mitosis which persists until telophase when receptors reappear to a level that exceeds the original interphase value. This is most simply explained by assuming that recycling of receptors back to the cell surface is inhibited as cells enter mitosis but that internalisation continues for a short while, causing surface receptor depletion. In telophase recycling would resume before internalisation giving a temporary excess of surface transferrin receptors.

Cytolytic T cells recognize the two amino-terminal domains of H-2 K antigens in tandem in influenza A infected cells

We have genetically engineered three alleles of the K locus of the major histocompatibility complex (MHC) of the mouse. These novel hybrid H-2K genes were introduced into mouse 1T 22-6 cells (H-2q), and their products were shown to be expressed on the cell surface. The hybrid H-2 K antigens were examined for their ability to function as restricting elements for cytotoxic T lymphocytes during influenza A infection. Both the alpha 1 and alpha 2 domains of the Kd antigen were required for T cell recognition. This implies an important role for "conformational determinants" on H-2 antigens acting as restricting elements. The cytoplasmic domain of the Kb antigen is not phenotypically important for recognition by T cells.

Murine H-2Dd-reactive monoclonal antibodies recognize shared antigenic determinant(s) on human HLA-B7 or HLA-B27 molecules or both

We have evaluated the serological relationships between the murine H-2Dd and human HLA molecules using four H-2Dd-reactive monoclonal antibodies (mAbs) produced in the A.BY (KbIbDb) anti-A.TL (KsIkDd) combination. In the mouse, these reagents exhibited three distinct reactivity patterns: Dd, Ks, and H-2u (mAb 81.L); Dd, H-2p, and H-2u (mAb 81.R); and Dd, Kd, H-2p, H-2u, and H-2v (mAbs 97.G and 97.H). Sequential immunoprecipitation and cross-competitive mAb binding experiments revealed that these mAbs recognized determinants in two spatially distinct polymorphic domains on the H-2Dd molecule of B10.A(5R) cells (defined by mAbs 81.L and 81.R, 97.H, and 97.G, respectively). MAbs 81.R, 97.G, and 97.H, but not 81.L, also defined an HLA-linked polymorphism in the human, the main characteristics of which can be summarized as follows: (i) on B lymphoblastoid cell lines, mAbs 81.R and 97.H bound to cells expressing the HLA-B7, HL-B27 or Bw40 cross-reacting specificities, (ii) on peripheral blood lymphocyte (PBL) panel mAb 81.R exerted C dependent cytotoxicity to 118 of 400 cells tested, including almost all HLA-B7 or HLA-B27 cells or both (r: 0.952), (iii) the expression of the 81.R cross-reacting determinant segregated in an informative family with the parental haplotype carrying the HLA-B7 allele, and (iv) mAbs 81.R, 97.G, and 97.H recognized topologically related determinants on the same class I molecule(s) of the human B lymphoblastoid cells JY (HLA-A2,2, -B7,7). These data support the view that some, but not all H-2Dd allotopes have been conserved throughout evolution and are associated in the human with the HLA-B7, -B27 cross-reacting specificities.

Expression of major histocompatibility antigens on pancreatic islet cells

Insulin-dependent diabetes mellitus is often accompanied by manifestations of autoimmunity and is frequently associated with certain HLA haplotypes, predominantly DR3 and DR4. Because the major histocompatibility antigens are important determinants of the immune response in various tissues, we have investigated their expression on the pancreatic islet cells. Human, mouse, or rat islets of Langerhans, as well as lymphocytes or other differentiated cells, were biosynthetically labeled with radioactive amino acids, lysed in detergent, and immunoprecipitated with several antisera specific for major histocompatibility antigenic groups. The immunoprecipitates were analyzed by NaDodSo4/polyacrylamide gel electrophoresis under reducing conditions followed by autoradiography. The major histocompatibility antigens corresponding to the H-2 K,D molecules in mice, the H1-A in rats, and the HLA-A, -B, and -C in humans were precipitated from both islet and lymphocyte lysates and were accompanied by beta 2-microglobulin. Binding of H-2 antibodies to islet cells was also confirmed by a radioligand assay using 125I-labeled protein A and by indirect immunofluorescence. Analyses in the fluorescence-activated cell sorter revealed that greater than 95% of the cells in the beta-cell-rich fraction were fluorescent, providing further evidence that the pancreatic beta cells express the major histocompatibility antigens. Monoclonal antibodies or mouse alloantisera against HLA-DR or Ia antigens did not react with labeled pancreatic islet cell proteins.

cDNA clone coding for part of a mouse H-2d major histocompatibility antigen

mRNA coding for mouse major transplantation antigens of the d haplotype was partially purified, copied into double-stranded cDNA, and cloned in Escherichia coli. Clones were selected by their ability to hybridize specifically with mRNA coding for H-2K, D, or L antigens. One of these clones, pH-2d-1, carries a 1200-base-pair insert, comprising the noncoding region, including poly(A) at the 3' end and part of the coding region. A partial sequence of the latter region showed extensive homology with the known amino acid sequences of H-2Kb,Kk, and HLA-B7 antigens. From this comparison, it appears that the coding region extends from amino acid 133 in the second domain, through the third domain, to the cytoplasmic COOH-terminal region. A stretch of 24 hydrophobic or uncharged residues, located 31 amino acids from the COOH-terminal end, could represent the segment that spans the membrane. This is followed on the cytoplasmic side of the membrane by a cluster of basic amino acids and a possible phosphorylation site on a threonine residue.

Hormonal regulation of the expression of Ia antigens on mammary gland epithelium

Guinea pig and mouse mammary gland epithelial cells express Ia antigen-like molecules that react specifically with a rabbit anti-Ia antigen antiserum. The murine Ia antigen-like molecules were shown to share alloantigenic determinants with regular spleen cell Ia antigens. The expression of the mammary gland Ia antigens is under hormonal control, i.e. the Ia antigen expression is induced by pregnancy and lactation and can also be induced by the exogenous administration of lactotropic hormones.

Isolation and partial characterization of a murine cell surface glycoprotein with affinity for exogenously added beta 2-microglubulin

Exogenously added beta 2-microglobulin (beta 2m) binds to a variety of murine cell types. The 'receptor' for beta 2m has been isolated. The purified 'receptor' comprised a 48,000-dalton chain and occasionally a 25,000-dalton component. Direct crosslinking of beta 2m to the receptor on intact cells gave rise to a single 60,000-dalton beta 2m-'receptor' complex. The molecular characteristics of the 'receptor' were considerably changed on binding beta 2m. The size of the beta 2m-'receptor' complex was increased partly due to enhanced binding of deoxycholate. The 'receptor' was less easily degraded by proteases when beta 2m was bound then when free. The solubilized 'receptor' reacted with a heteroantiserum raised against H-2K and D antigens but did not exhibit any alloantigenic determinants shared with H-2K, D or Ia antigens.

Demonstration of a murine cell surface component with affinity for exogenous beta 2-microglobulin

Murine and human beta 2-microglobulin (beta 2m) bind to various types of mouse cells. The binding is saturable and displays a single association constant of about 1 x 10(9) liter/mol. The binding of beta 2m to splenocytes was not affected by a variety of metabolic inhibitors but was temperature-dependent. It is suggested that the beta 2m "receptor" exhibits a temperature-dependent conformational change since the "receptor", whether integrated into the membrane or solubilized by the detergent Triton X-100, binds beta 2m poorly at low temperatures. Spleen T and B lymphocytes display more binding sites than thymocytes, kidney, liver and brain cells. The relative amounts of the beta 2m-binding "receptor" on these cell types are strongly correlated to the relative amounts of H-2 antigens. This correlation is also obvious for the teratocarcinoma cell line F9, which lacks both beta 2m "receptor" and H-2 antigens, but spermatozoa, which express very small amounts of H-2 antigens, have an appreciable amount of the beta 2m "receptor". The latter observation, together with the fact that alloantisera directed against H-2 K and D antigens do not measurably affect the binding of beta 2m to the "receptor", may argue against the notion that the beta 2m "receptor" represents H-2 antigens which have lost their endogenous beta 2m. Normal mouse serum contains a component which inhibits the binding of beta 2m to splenocytes. It is likely that this serum protein is identical to a newly discovered H-2 antigen-like glycoprotein. The beta 2m "receptor" appears to be under the control of the major histocompatibility complex as splenocytes of the H-2f haplotype bind considerably more beta 2m than splenocytes of other haplotypes.

Radioimmunoassay determinations of murine beta 2-microglobulin and an H-2 antigen-like serum component

Normal mouse serum contains H-2 antigen-like components. One such protein consists of a 40 000 dalton chain and beta 2-microglobulin (beta 2m) and the other component contains the two H-2 antigen-like subunits and, in addition, two larger polypeptide chains with apparent molecular weights (mol. wt.) of 65 000 and 80 000. Radioimmunoassay procedures specific for the H-2 antigen-like chain and beta 2m, respectively, have been developed. Whereas free beta 2m and beta 2m associated with other polypeptide chains reacted identically in the beta 2m radioimmunoassay, the two serum forms of the H-2 antigen-like chain displayed different reactivities in the heavy-chain assay. The low mol. wt. protein complex, comprising the 40 000 dalton chain and beta 2m, inhibited in the heavy-chain assay identically with the standard. However, the high mol. wt. complex containing the H-2 antigen-like chain gave rise to a biphasic inhibition profile. This was apparently due to some antigenic determinants of the 40 000 dalton chain being buried by the 65 000 and 80 000 dalton chains. Inhibition curves parallel with the standard were, however, obtained on dissociation of the high mol. wt. protein complex with sodium dodecyl sulfate. Thus, by subjecting serum to the ionic detergent-sensitive radioimmunoassay, procedures for the two H-2 antigen-like chains could be developed. The serum levels of the H-2 antigen-like chain and of beta 2m vary with the age of the animal, and adult levels are recorded only at 6 to 7 weeks of age. The serum concentrations of the two proteins are strongly correlated. The H-2 haplotype appears to partly regulate the serum levels of the two proteins. Mice of the H-2f haplotype contain about 40-fold lower levels of the H-2 antigen-like chain than do mice of other strains.

Distribution of Ia-antigen-like molecules on non-lymphoid tissues

Ia-antigen-like molecules are expressed on cells within several different non-lymphoid tissues of the guinea-pig. In indirect immunofluorescence analyses anti-Ia-antigen antibodies stained epithelial cells lining the intestinal tract, the bile ducts, the respiratory tract and the urinary tract. The rabbit antibodies against Ia antigens also stained the cells of the parotid and the submandibular glands. Evidence was also obtained suggesting that the reticuloepithelial cells of the thymus, like the Kupffer cells of the liver, express Ia-antigen-like molecules. In several cases indirect immunoprecipitation analyses and SDS-polyacrylamide gel electrophoresis confirmed the immunofluorescence studies inasmuch as Ia-antigen-like subunits with apparent molecular weights of 26,000 and 34,000 could be isolated from the non-lymphoid organs.