Structural polymorphism of human DR antigens

Antigen Targeting to Human HLA Class II Molecules Increases Efficacy of DNA Vaccination

It has been difficult to translate promising results from DNA vaccination in mice to larger animals and humans. Previously, DNA vaccines encoding proteins that target Ag to MHC class II (MHC-II) molecules on APCs have been shown to induce rapid, enhanced, and long-lasting Ag-specific Ab titers in mice. In this study, we describe two novel DNA vaccines that as proteins target HLA class II (HLA-II) molecules. These vaccine proteins cross-react with MHC-II molecules in several species of larger mammals. When tested in ferrets and pigs, a single DNA delivery with low doses of the HLA-II-targeted vaccines resulted in rapid and increased Ab responses. Importantly, painless intradermal jet delivery of DNA was as effective as delivery by needle injection followed by electroporation. As an indication that the vaccines could also be useful for human application, HLA-II-targeted vaccine proteins were found to increase human CD4⁺ T cell responses by a factor of ×10³ in vitro. Thus, targeting of Ag to MHC-II molecules may represent an attractive strategy for increasing efficacy of DNA vaccines in larger animals and humans.

Identification of B-L antigens on reticular epithelial cells of the bursa of Fabricius

We have established two monoclonal antibodies against B-L antigens (chicken Ia-like antigens). The specificity of the antibodies for B-L antigens was determined by two criteria, the cellular expression and the molecular structure of antigens with which they reacted. They reacted with antigens expressed on bursacytes, Con A-blast thymocytes, macrophages, and MDCC MSB1, but not with thymocytes and erythrocytes. In molecular basis, they recognized 64,000 dalton glycoprotein consisting of two polypeptides, 35,000 and 32,000 dalton, which bound non-covalently. To investigate the distribution of B-L antigens on non-lymphoid cells of the bursa of Fabricius, which were thought to play important roles in the differentiation of B cells, anti-B-L antigen and anti-chicken immunoglobulin (Ig) monoclonal antibodies were used. B-L antigen-positive cells were detected in both cortical and medullary areas, whereas Ig-positive lymphoid cells were confined to the medullary areas of normal chicken bursal follicles. In the bursal follicles of cyclophosphamide (CY)-treated chickens, lymphoid cells were depleted but epithelial cells remained intact. And B-L antigen-positive but Ig-negative cells were easily detected in the medullary areas of almost all follicles. These cells were identified to be reticular epithelial cells (REp cells) from the result of their keratin expression.

DR5-associated DC molecules carry three different allospecificities

Antiserum 8w670 which had been classified as anti-DR5 in the Workshop analysis was found by the direct binding test to react with about 40% of Ia molecules in an Ia preparation from LG38 cells (DR5,5) that was deleted of DR molecules and DR-like molecules we call BR and enriched in DC molecules by pretreatment with a rabbit antiserum raised against alpha-subunits of DR and BR molecules. The specificity involved in the binding reaction was shown by the binding inhibition assay to be present in 100% of DR5-positive cases (53 out of 53) and 8w13-positive cases (2 out of 2) and in 23% of DR4-positive cases (4 out of 17). This association pattern did not correspond to any of the known supertypic specificities including the DC beta 4 and DC alpha 3, both of which had been found on DR5-associated DC molecules. Yet sequential binding analysis revealed that the 8w670-defined specificity was indeed present on the same molecules carrying DC beta 4 and DC alpha 3 specificities. This specificity was designated DC5.

Genomic hybridization with class II transplantation antigen cDNA probes as a complementary technique in tissue typing

Hybridizations of HLA-DR and DC transplantation antigen beta chain cDNA probes to restriction enzyme digested genomic DNA were examined in regard to their potential in tissue typing. DNA from cells, typed by cellular techniques to be homozygous for the specificities Dw 1 to 8, gives rise to unique fragment patterns for each specificity. Hybridizations to DNA from unrelated individuals serologically typed to be DR identical occasionally reveal genetic differences in the class II antigen region, notably with the DC beta cDNA probe. In contrast, hybridizations to DNA from monozygotic twins displayed completely identical patterns with both types of probes. From these data it seems reasonable to conclude that genomic hybridizations with class II antigen probes will be useful in the definition of new class II antigen loci and alleles, in determination of paternity, in studies of class II antigen linked diseases and as a complementary method in conventional tissue typing.

Delineation of serologically distinct monomorphic determinants of human MHC class II antigens: evidence of heterogeneity in their topographical distribution

Three monoclonal antibodies (mAbs), FMC4, FMC14 and FMC15, which react with invariant sites of major histocompatibility complex (MHC) class II (Ia-like) molecules were studied in various serological assays. Sequential immunodepletion experiments show that all three epitopes are present on the same class II molecules. However, a minor subset may exist which does not express epitope 15. In competitive binding assays, using several different B-lymphoblastoid cell lines (B-LCLs), e.g. BRISTOL-8 8392, B-85, RAJI, 8866, CESS-B and LD-B, FMC4 did not block the binding of FMC14, or FMC15, and vice versa. In contrast, mutual inhibition was observed between FMC14 and FMC15. Furthermore, pairwise combinations of saturating amounts of FMC4 + FMC14 and FMC4 + FMC15 gave additive binding whilst FMC14 + FMC15 did not. These results demonstrate that epitopes 4 and 14/15 are spatially distinct; 14 and 15 on the other hand appear to be spatially related. However, contrary to this partial and reciprocal inhibition was consistently observed between FMC4 and FMC14 on two other LCLs, namely DAUDI and BALM-2. Furthermore, on certain cells, FMC14 and FMC15 show markedly disparate binding. Taken together, these observations indicate that the juxtaposition of certain epitopes on class II antigens can vary according to the cell type. This demonstrates a hitherto unreported heterogeneity of antigenic determinants and of their topographical distribution on the class II molecule.

Analysis of the structural heterogeneity and polymorphism of human Ia antigens. Four distinct subsets of molecules are coexpressed in the Ia pool of both DR1,1 homozygous and DR3,W6 heterozygous B cell lines

Four monoclonal antibodies reacting with distinct human Ia antigenic determinants have been used to demonstrate the coexpression of four distinct subsets, NG1, NG2, H40+-3/4+, and DC1 H40--3/4+, in the Ia pool of DR heterozygous or homozygous B cell lines. By two-dimensional peptide mapping the four subsets within the same Ia pool displayed structurally different beta as well as alpha subunits. The beta chain of the NG1 subset was shown to display considerable structural polymorphism when analyzed in two cell lines with distinct DR but similar DC phenotype, LG2 (DR1,1-DC1) and Raji (DR3, W6-DC1). In contrast, the beta chains of NG2, DC1 H40+-3/4+, and DC1 H40--3/4+ subsets of LG2 cells were shown to be very similar to their homologous Raji cell counterparts, thus indicating a relatively low structural polymorphism. Furthermore, the alpha chains of either one of the four subsets expressed in LG2 cells displayed very high structural similarities to the homologous counterparts in the Raji Ia pool, thus suggesting a relatively low polymorphism for the large Ia subunits described in this study. A striking feature deduced from this study was the selective subunit association of the distinct alpha-beta heterodimers.

Both alpha and beta chains of HLA-DC class II histocompatibility antigens display extensive polymorphism in their amino-terminal domains

At least three class II antigens, all composed of an alpha and a beta subunit, are encoded in the human major histocompatibility complex, i.e., DR, DC and SB. Two cDNA clones, encoding a DC alpha and a DC beta chain, respectively, were isolated from a cDNA library of the lymphoblastoid cell line Raji (DR3,w6). The two polypeptides predicted from the nucleotide sequences of these clones are each composed of a signal peptide, two extracellular domains, a hydrophobic transmembrane region and a short cytoplasmic tail. Comparison of the DC alpha sequence with two previously published partial sequences shows that the majority of the differences is located in the amino-terminal domain. The differences are not randomly distributed; a cluster of replacements is present in the central portion of the amino-terminal domain. Likewise, the allelic polymorphism of the DC beta chains occurs preferentially in the amino-terminal domain, where three minor clusters of replacements can be discerned. The non-random distribution of the variability of DC alpha and beta chains may be due to phenotypic selection against replacement substitutions in the second domains of the polypeptides.

Electrophoretic analysis of human HLA-DR antigens from HLA-DR4 homozygous cell lines: correlation between beta-chain diversity and HLA-D

Two-dimensional gel electrophoresis of immunoprecipitated human HLA-DR antigens from cells expressing the HLA-DR4 haplotype shows distinct clustering of beta-chain patterns. Six unique electrophoretic variants were observed among 17 HLA-DR4 homozygous cell lines (HCL) analyzed. These patterns correlate precisely with the HLA-D phenotype of the HCL donor as determined by reactivity in mixed lymphocyte culture. All DR4 HCL that belong to one of the well-defined HLA-D antigen groups (Dw4, Dw10, LD "40", LD "DYT", LD "KT2", or LD "TAS") have identical DR beta-chain patterns; DR4 HCL belonging to different HLA-D antigen groups do not. The concordance of the functional expression in mixed lymphocyte culture of a specific D phenotype with a distinct DR beta-chain pattern on gel analysis provides a direct structural basis for understanding the genetic control of HLA-D polymorphisms; HLA-D specificities as revealed by T-cell recognition in mixed lymphocyte culture thus might be accounted for by DR beta-chain polymorphisms. The extent of this beta-chain diversity within a single DR haplotype may aid in understanding variations in Ia-regulated functions, such as Ir gene control and certain disease susceptibilities.

The heavy chain of human B-cell alloantigen HLA-DS has a variable N-terminal region and a constant immunoglobulin-like region

The HLA-D region of the major histocompatibility complex (MHC) of man encodes polymorphic glycoproteins found predominantly on the cell surfaces of B cells and macrophages. These proteins mediate interactions, required for the induction of immune responses, among cells of the immune system and consequently are referred to as Ia (immune-response associated). Two families of Ia molecules, DR and DS (also known as DC), have been defined, the former analogous to the I-E (ref. 1) and the latter to the I-A molecules of the murine MHC. Both DR and DS molecules consist of two noncovalently associated polypeptide chains with molecular weights of 33,000 and 28,000, designated alpha and beta, respectively. The polymorphism of DR molecules is due to structural variation in the small subunit, DR beta, with the large subunit, DR alpha, being constant in structure. In contrast, both subunits DS alpha and DS beta are structurally variable when DS allotypes are compared. We have now isolated a cDNA clone from a DR7 cell line that contains the entire coding sequence for the DS alpha subunit and have compared its predicted amino acid sequence with that previously deduced from a DS alpha cDNA clone isolated from a DR4,w6 cell line. This comparison reveals that 10 of 11 amino acid differences are located within the alpha 1 (N-terminal) domain and that the alpha 2 or immunoglobulin-like domains are identical.

Detection of HLA-D/DR-related DNA polymorphism in HLA-D homozygous typing cells

Sequences of different sizes are generated when DNA from homozygous HLA-Dw/DR typing cells are digested with restriction endonuclease and analyzed by hybridization with a HLA-D region class II antigen beta-chain cDNA probe. The patterns of hybridization were highly polymorphic but one endonuclease, BamHI, defined sequences unique to all HLA-Dw/DR specificities 1-8 except HLA-Dw/DR 2 and 6; however, these two specificities were resolved with the enzyme EcoRI. Digestion with other endonucleases such as Pst I results in patterns of restriction fragments that differ between homozygous typing cells of the same HLA-Dw/DR specificity. HLA-D region beta-chain probes permit HLA-D region genotyping at the DNA level and may allow detection of genes controlling the association of HLA specificities with a wide variety of diseases.

Microfingerprinting analysis of human Ia molecules favours a three loci model

Alpha subunits from DC1 Ia molecules, when compared with DR alpha subunits, are shown to possess distinctive features revealed by differences in microfingerprinting patterns after peptic digestion. Alpha chains from BR4X7 molecules differ from DC1 alpha chains and are more similar to DR alpha chains. Since DC1 and BR4X7 beta chains (which carry the HLA-controlled alloantigenic determinants) associate with different alpha subunits, it is considered unlikely that they are controlled by alleles at the same locus. The proposed model implies the existence of three tightly linked HLA loci controlling the beta subunits of DR, DC and BR molecules respectively.

Human B cell variants immunoselected against a single Ia antigen subset have lost expression of several Ia antigen subsets

Two monoclonal antibodies, D1-12 and BT 2.2, recognizing two distinct subsets of human Ia molecules, NG1 and NG2, respectively, present in all individuals irrespective of their HLA-DR phenotype, have been used to immunoselect cell variants from the lymphoblastoid cell line Raji. Results showed that, irrespective of the monoclonal antibody used for immunoselection, the cell variants analyzed in this study had lost the expression of both D1-12-and BT 2.2-specific antigenic determinants. Moreover, the expression of antigenic determinants specific for a third family of Ia molecules, the DC-1 subset, were also lost in the cell variants. In contrast, expression of HLA A, B, and C common structures, as recognized by the W6.32 monoclonal antibody, as well as expression of surface immunoglobulins, were not affected. Possible mechanisms inducing such a coordinate loss of expression of several families of human Ia molecules are discussed.

HLA-DR products are a subset of human Ia antigens

Human Ia antigens are polymorphic cell-surface sialoglycoproteins which have restricted tissue distribution. They are bimolecular complexes of 34,000 (alpha) and 28,000 (beta) molecular weight and most of the polymorphism is found in the smaller polypeptides. They are involved in the initiation of immune responses and particular Ia antigens are associated with increased susceptibility to certain diseases. They are also the major barrier to human allogeneic tissue transplantation. Whereas serological analysis and mixed lymphocyte typing have defined three polymorphic families of Ia antigens, HLA-DR, -DC and -SB, protein sequencing results and studies with monoclonal antibodies indicate that the complexity is much greater. Thus the HLA-DR and DC specificities as defined by alloantisera, could represent groups of antigens which are controlled by HLA genes in linkage disequilibrium. Here, we have used a monoclonal antibody specific for HLA-DR2 to show that this determinant is carried by molecules which are distinct from those of the DC series and which represent 30% of the Ia antigens expressed on the cell surface of an HLA homozygous line PGF.

Human class II major histocompatibility antigen beta-chains are derived from at least three loci

Class II antigens of the major histocompatibility complex (MHC) consist of two glycosylated, membrane-integrated polypeptide chains. These cell surface-expressed molecules are involved in several immunobiological events involving cell-cell interactions, most of which seem to require that genetically identical class II antigens, or other molecules controlled by the same region of the MHC, are expressed on the interacting cells. The extensive genetic polymorphism of the class II antigens has rendered analyses in the human system of the number of non-allelic species of class II antigens difficult, although several laboratories have reported the existence of at least two types of human class II antigens. Here we present the results of experiments using restriction enzyme digestions and separation of DNA from individuals homozygous for the MHC followed by hybridization to human class II antigen alpha- and beta-chain cDNA probes. While the alpha-chain probe gave only a single hybridization band, the various beta-chain probes revealed a more complex pattern that is consistent with the existence of at least three separate beta-chain genes or pseudogenes in the human MHC.

N-terminal amino acid sequences of the alpha and beta chains of HLA-DR1 and HLA-DR2 antigens

The N-terminal amino acid sequences of the alpha and beta chains of HLA-DR1 and HLA-DR2 antigens were obtained with subnanomole quantities of material by using a gas-liquid solid-phase sequencer. A comparison of the N-terminal amino acid sequences of HLA-DR1 and HLA-DR2 alpha chains revealed no differences. However, in the first 35 N-terminal residues of the beta chains from HLA-DR1 and HLA-DR2 antigens, two regions of variability are readily apparent, each comprising about six amino acids. Conceivably one or both of these variability regions may be responsible for the serologically defined polymorphism of HLA-DR alloantigens.

A biochemical analysis of the secregation of HLA-DR heavy and light chains in a family studied by two-dimensional gel electrophoresis

Previous studies in our laboratory using primed lymphocyte typing (PLT) in an informative family have led to the identification of four traits and two regions, separable by recombination within the HLA-DR system. In the present study, we analysed the heterogeneity of HLA-DR antigens among members of this family as a first step towards defining the molecular entities responsible for the observed cellular reactivities. Cell lines of various genotypes derived from the members of this family were labelled biosynthetically with 35S-methionine. The total glycoproteins and immunoprecipitates prepared with two monoclonal anti-HLA-DR antibodies, two monoclonal anti-mouse Ia antibodies cross-reactive with HLA-DR, and a rabbit anti-HLA-DR (anti-p27,33) antiserum were fractionated by two-dimensional gel electrophoresis. In agreement with previous results, HLA-DR light chains were clearly polymorphic whereas the heavy chains looked rather monomorphic. The light chain subunits either segregated with one haplotype, or were shared by some but not all haplotypes or were common to all haplotypes. Whereas the haplotype-specific polypeptides correlated best with HLA-DR3 and HLA-DR5 specificities, the shared subunits may have corresponded to the cross-reactivities observed by PLT. Comparison of the patterns obtained with the various monoclonal antibodies and with the rabbit antiserum revealed that each monoclonal antibody bound a subset of HLA-DR light chains, all of which were present in the anti-p27,33 precipitates. This rabbit antiserum and one of the monoclonal antibodies immunoprecipitated a set of heavy chains not bound by the other 3 antibodies. Since overlapping pools of light chains were present in all five immunoprecipitates, these results suggest that different heavy chains may associate with the same light chains.

The distribution of DR5, MT2, and MB3 specificities on human Ia subsets

Human Ia molecules were isolated from cells of LG-38, an HLA-homozygous lymphoid cell line of DR5 specificity. Three Ia subsets could be distinguished and separated by using specific alloantisera and a monoclonal antibody with polymorphic reactivity. These subsets carried the specificities DR5 and MT2, MT2 alone and MB3 alone. The structure of the three molecular species was analyzed by microfingerprinting. The subset carrying only MT2 was similar, in both the component alpha and beta chains, to the major subset carrying DR5 and MT2, whereas the subset carrying MB3 was distinct in both chains from the other two subsets. These data are compatible with our previous findings obtained for the products of two Ia loci closely linked to the DR locus and provisionally called DC and BR; they also support the conclusion that the subset carrying only MT2 is an allelic product of the BR locus, whereas the MB3 subset is an allelic product of the DC locus. MT2 appears to be a shared specificity of DR and BR loci products.

Expression of T-lymphoblast-encoded HLA-DR antigens on human T-B lymphoblast hybrids

The mode of expression of novel HLA-DR antigens on hybrids of human T and B lymphoblastoid cell lines (LCL) was examined by several approaches. In each case, the results indicated that the novel antigens are T-LCL-encoded. First, hybrids of sublines of the T-LCL CEM with three different B-LCL express indistinguishable sets of novel HLA-DR antigens. Second, the novel HLA-DR and MT specificities of WI-L2 x HSB (a hybrid of a subline of the T-LCL HSB and the B-LCL WI-L2) match those of SB, a B-LCL derived from the same individual as HSB. Finally, an immunoselected variant of SB x CEM.1 (a hybrid of a subline of CEM and SB) lacking one copy of chromosome 6 and one of the hybrid's novel HLA-DR specificities also lacks a class I antigen known to be encoded by CEM.

Isolation of distinct cDNA clones encoding HLA-DR beta chains by use of an expression assay

cDNA clones encoding different human Ia antigen beta chains were isolated by use of a complementation-expression assay in Xenopus oocytes. The assay was based on two previous findings. First, oocytes injected with mRNA from a human B-cell line express HLA-DR antigen. The three intracellular DR chains are assembled in oocytes and can be immunoprecipitated with anti-DR monoclonal antibodies. Second, we have isolated cDNA clones encoding DR alpha and intermediate chains. In order to identify beta-chain cDNA clones, mRNA was hybrid-selected with pools of cDNA clones, mixed with mRNA for the alpha and intermediate chains, and injected into oocytes. We isolated two distinct clones that could select DR beta-chain mRNA as demonstrated by assembly of the translation product with DR alpha chains and immunoprecipitation with DR-specific monoclonal antibodies. One clone is specific for a beta chain of the DR locus. The other clone, much weaker in its ability to select DR mRNA, encodes another Ia-like beta chain. Full-length cDNA clones corresponding to the DR and Ia-like beta chains were isolated and compared. Cross-hybridization was detectable in the coding regions but not in the 3' untranslated regions. Distinct RNAs homologous to the DR and the Ia-like beta-chain clones were present in B cells but were undetectable in three T-cell lines.

Isolation of cDNA clones encoding HLA-DR alpha chains

HLA-DR antigens, the human equivalent of mouse Ia antigens, are multimeric surface glycoproteins characterized by a high degree of allelic polymorphism. They are expressed specifically on macrophages and lymphocytes and they play a key role in the regulation of the immune response. We have investigated this complex genetic system by a direct study of the genes involved through molecular cloning. This paper deals with the cloning, in plasmids, of full-length cDNA sequences for the HLA-DR alpha chain from the human B-cell line Raji. The approach relies on a translation assay of mRNA injected into frog oocytes and recognition of translation products by polyclonal and monoclonal antibodies. After enrichment of specific mRNA and cloning of cDNA, plasmid clones were analyzed by hybridization-selection of mRNA and translation in oocytes. A clone was identified and used to screen a cDNA library from which several full-length HLA-DR alpha chain plasmids were isolated. DNA sequence determination of one such clone confirmed its identity and also established the amino acid sequence of the NH2-terminal signal sequence of HLA-DR alpha chains. The translation product of HLA-DR alpha chain mRNA purified by hybridization-selection gives a single alpha chain spot on two-dimensional gels, whereas the alpha chain released from the alpha/beta HLA-DR complex gives about seven distinct spots. Finally, the results of analysis of genomic DNA by Southern blotting are compatible with the existence of a single nonpolymorphic alpha chain gene and indicate extensive cross-hybridization with a homologous gene in mouse DNA.

Peptide map comparisons of similar serologically defined HLA-DR antigens isolated from different lymphoblastoid cell lines

In these studies, we have examined the possibility that DR subtypes, closely related to each other in structure, compose the major DR allotypic groups. The structures of DR molecules, isolated from pairs of cell lines that had the same serologically defined HLA-DR type, were compared by peptide mapping. HLA-DR molecules isolated from pairs of cell lines in which both members were either DR1, DR2, or DR7 were identical. However, DR molecules isolated from cell lines LG-29 (DR5) and LG-38 (DR5) displayed two distinct differences in their small (beta) subunits. This number of differences, two of 15 peptides or 15%, is much fewer than is observed between DR allotypes (approximately 50%) and suggests that at least two subtypes exist within the DR5 allotype family.

Direct demonstration of an HLA-DR allotypic determinant on the low molecular weight (beta) subunit using a mouse monoclonal antibody specific for DR3

A murine monoclonal antibody directed against a human B cell surface antigen with the characteristics of HLA-DR is described. The antigen detected is tightly linked to HLA and is correlated with the alloantigen HLA-Dw/DR3. Reactivity with a fraction of Dw/DRw6 cells is also observed. The determinant recognized by this antibody has been shown to be present on the smaller molecular weight beta subunit of the HLA-DR antigen.

Membrane insertion and oligomeric assembly of HLA-DR histocompatibility antigens

HLA-DR histocompatibility antigens are assembled in the endoplasmic reticulum. This assembly has been studied in vitro and in vivo. Three polypeptides are involved in forming the oligomeric structure of HLA-DR antigens, DR alpha chains (molecular weight 35,000), DR beta chains (molecular weight 29,000) and DR gamma chains (molecular weight 33,000). They are cotranslationally inserted into the membrane of the endoplasmic reticulum, and all span the membrane. The size of the cytoplasmic portion of DR alpha and DR beta is about 500- 1000 daltons, whereas that of the DR gamma chain is about 3000 daltons. Oligomeric assembly of DR alpha, DR beta and DR gamma chains occurs shortly after their synthesis in the endoplasmic reticulum. DR gamma chains are synthesized in excess of DR alpha and DR beta chains, and hence in the endoplasmic reticulum they are found either in a complex with DR alpha and DR beta or in a free form. Free DR gamma chains remain in the endoplasmic reticulum, whereas DR gamma chains present in the oligomeric complex with DR alpha and DR beta undergo intracellular transport. Their molecular weight increases during transport, probably because of the addition of complex sugars in the Golgi complex. This is followed by the detachment of DR gamma chains from the oligomeric complex and the appearance of DR alpha and DR beta chains on the cell surface. Whether any DR gamma chains appear on the cell surface is uncertain.

Demonstration of two distinct light chains in HLA-DR-associated antigens by two-dimensional gel electrophoresis

The polypeptide composition of HLA-DR-associated antigens was analyzed by two-dimensional nonequilibrium pH gradient electrophoresis (NEPHGE)/sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE). Glycoprotein fractions from B lymphoblastoid cell lines homozygous for the DR antigen were used as antigen source. The HLA-DR-associated antigens were isolated by immunoprecipitation using a monoclonal anti-DR antibody, TDR31.1. Two polypeptides corresponding in molecular weight to the HLA-DR-associated antigen beta chain were detected. These polypeptides were shown to be different molecules on the basis of their separation on NEPHGE/SDS-PAGE analysis, their rates of turnover relative to the other polypeptides of the HLA-DR-associated antigens, and their noncoordinate alteration in position on NEPHGE/SDS-PAGE two-dimensional analysis of different cell lines. Of the two beta polypeptides, only one was invariant in position on NEPHGE/SDS-PAGE analyses of cell lines homozygous for the same DR specificity. It appears therefore that the position of one of these beta polypeptides correlates with DR specificity, while the other beta polypeptide exhibits positional variation on NEPHGE/SDS-PAGE analysis, indicative of polymorphism at a second HLA-DR-associated locus.

Isolation and identification of a cDNA clone corresponding to an HLA-DR antigen beta chain

The HLA-D locus in the major histocompatibility complex controls the expression of the genetically polymorphic HLA-DR antigens. mRNA coding for the beta chains of these antigens was partially purified from the human lymphoblastoid cell line Raji. The mRNA was copied into double-stranded cDNA and cloned in Escherichia coli. One clone, pDR-beta-1, obtained by hybrid selection, carries a 1070-base-pair insert comprising all of the coding region except the signal sequence and a substantial portion of the untranslated region. To identify pDR-beta-1, highly purified HLA-DR antigen beta chains derived from Raji cells were subjected to NH2-terminal amino acid sequence determination. This sequence displayed extensive homology with that deduced from the nucleotide sequence at the 5' end of the pDR-beta-1 coding region. Taken together, the amino acid and nucleotide sequences strongly argue in favor of Raji cells containing at least two beta-chain loci.

Control of HLA-DR antigen gene expression at the pretranslational level: comparison of an HLA-DR-positive B lymphoblastoid cell line and its HLA-DR-negative variant

An HLA-DR-positive human B lymphoblastoid cell line, T5-1, and its HLA-DR negative variant, 6.1.6, were studied to elucidate mechanisms resulting in the nonexpression of HLA-DR genes in 6.1.6. The cell lines were labeled with 35S-methionine in vivo, their proteins immunoprecipitated with a monoclonal HLA-DR-specific antibody, and their two-dimensional gel electrophoresis patterns compared. The T5-1 map showed DR-antigen heavy and light chains, while the 6.1.6 map showed neither chain. When the cells were labeled in the presence of tunicamycin, the two-dimensional map of T5-1 showed nonglycosylated heavy and light chains of DR antigen while that of 6.1.6 did not. RNA was extracted from T5-1 and 6.1.6 cells and translated in rabbit reticulocyte lysates. Two-dimensional gel analysis of the immunoprecipitated proteins from T5-1 revealed spots which were identified as HLA-DR light chain and I invariant on the basis of their precipitation by monoclonal and specific allo- and heteroantibodies, and their molecular weight and pI values. These spots were absent in the 6.1.6 maps, indicating that 6.1.6 has no detectable translatable messenger RNA for HLA-DR light chains. The addition of dog pancreas microsomes to the T5-1 cell-free translation mixture resulted in an increase in the molecular weight of the precursor HLA-DR proteins consistent with glycosylation. Together with earlier cell fusion studies showing that DR structural genes were intact in 6.1.6, these data suggested that the lesion in 6.1.6 is an alteration in a regulatory element required for transcription of DR genes or mRNA processing.

Translation and assembly of HLA-DR antigens in Xenopus oocytes injected with mRNA from a human B-cell line

HLA-DR antigens are polymorphic cell surface glycoproteins, expressed primarily in B lymphocytes and macrophages, which are thought to play an important role in the immune response. Two polypeptide chains, alpha and beta, are associated at the cell surface, and a third chain associates with alpha and beta intracellularly. RNA isolated from the human B-cell line Raji was injected in Xenopus laevis oocytes. Immunoprecipitates of translation products with several monoclonal antibodies revealed the presence of HLA-DR antigens similar to those synthesized in Raji cells. One monoclonal antibody was able to bind the beta chain after dissociation of the three polypeptide chains with detergent. The presence of all three chains was confirmed by two-dimensional gel electrophoresis. The glycosylation pattern of the three chains was identical to that observed in vivo, as evidenced in studies using tunicamycin, an inhibitor of N-linked glycosylation. The presence of alpha chains assembled with beta chains in equimolar ratio was further demonstrated by amino-terminal sequencing. An RNA fraction enriched for the three mRNAs, encoding alpha, beta, and intracellular chains, was isolated. This translation-assembly system and the availability of monoclonal antibodies make it possible to assay for mRNA encoding specific molecules among the multiple human Ia-like antigens.

Distribution of antigenic determinants recognized by three monoclonal antibodies (Q2/70, Q5/6 and Q5/13) on human Ia-like alloantigens and on their subunits

The distribution of antigenic determinants recognized by the anti-Ia-like antigen monoclonal antibodies (MoAb) Q2/70, Q5/6 and Q5/13 on molecules coded for by the DR locus and by non-DR loci was investigated using a binding assay with 125I-labeled Ia-like antigens isolated from four B lymphoid cell lines. The determinants reacting with the MoAb Q2/70 and Q5/13 are expressed on all DR alloantigens tested and on BR4X7 specificities, while those reacting with the MoAb Q5/6 are not detectable on DRw7 and BR4X7 molecules. None of the monoclonal antibodies reacted with DC1 molecules. The MoAb Q5/6 and Q5/13 reacted with the isolated beta subunit of the Ia-like antigenic complex, while the MoAb Q2/70 did not react with the isolated chains.

Binding of one monoclonal antibody to human Ia molecules can be enhanced by a second monoclonal antibody

A monoclonal anti-human Ia antibody, PTF 29, was tested for its ability to bind purified, 125I-labeled human Ia preparations. It was found that the binding level increases considerably in the presence of a second monoclonal antibody. Experimental conditions were selected under which only the binding of PTF 29 and not the binding of the second antibody could be determined. Under these conditions, it was found that "helped" PTF 29 binding has higher affinity and is exerted on a molecular subset different from that bound by PTF 29 alone. This phenomenon, while not easily accommodated in the present conceptual framework of the human Ia system, appears in itself interesting and may have more general implications.

Human B-cell alloantigens DC1, MT1, and LB12 are identical to each other but distinct from the HLA-DR antigen

Some human B-lymphoblastoid cell lines are shown to express at least two types of Ia-like antigens. One antigen is defined by alloantisera to HLA-DR, and the other antigen is defined by alloantisera and a monoclonal antibody to the specificities DC1, MT1 (MB1), and LB12, which are in linkage disequilibrium with HLA-DR. The subunits of the DC1 molecule differ from those of the DR molecule. The light chains of both molecules are structurally polymorphic.

Analysis of HLA-DR polymorphism by two-dimensional peptide mapping

Two-dimensional peptide mapping was used to study the polymorphism of DR antigens, membrane glycoproteins composed of two chains, alpha and beta, and encoded by the human major histocompatibility complex (MHC). Four DR antigens were purified by immunoabsorption from four human lymphoblastoid cell lines homozygous at the DR locus. After labeling with 125I, alpha and beta chains were separated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate and digested with pepsin. Comparison of the peptide maps showed a marked degree of polymorphism among beta chains: only 43% of peptides were common to all four chains and 15-21% of the spots were unique to a given chain. By contrast, only a limited variability was observed among alpha chains. Homology was 75% for the four chains and the percentage of unique peptides was very low. DR7 did not possess even a single unique peptide. The limited variability among alpha chains and the lack of "private" peptides in one of them point to the conclusion that the beta chain is the unique carrier of the alloantigenic specificities. Higher homology within the known crossreactive groups was not observed, suggesting that the determinants responsible for crossreactivity are on different molecules. From a genetic point of view, because beta chains show allele-associated polymorphism, they are likely to be MHC encoded, whereas the minor differences among alpha chains do not allow a similar conclusion. The available data point to an analogy between these DR antigens and the mouse I-E/C antigens.

Serological, functional, and immunochemical characterization of a monoclonal antibody (MoAb Q2/70) to human Ia-like antigens

Serological and immunochemical studies showed that monoclonal antibody Q2/70 (MoAb Q2/70), produced by the hybridoma technique, is specific for human Ia-like antigens. This antibody recognizes an antigenic determinant which is different from those defining the serologic polymorphism of Ia-like antigens, and is expressed on subsets of human Ia-like molecules and on lymphoid cells from other species. MoAb Q2/70 inhibits unidirectional MLRs* between allogenic human lymphocytes, but not between murine and human lymphocytes. In ADCC* assays. MoAb Q2/70 mediates lysis of cultured human B lymphoid cells RPMI 4098, effected by murine splenocytes. The antibody is suitable to isolate immunologically functional B lymphocytes from human peripheral blood.

Polymorphism of human B-cell alloantigens: evidence for three loci within the HLA system

The B-cell alloantigens of an HLA-DR3-homozygous, MB2-homozygous, MT2-positive lymphoblastoid cell line were studied by two-dimensional gel electrophoresis. Analysis of gel patterns suggested assignment of the HLA-DR3 determinant to the larger (35,000-dalton) subunit (alpha) of the B-cell alloantigen. MB2 was found to be either a determinant on the small (27,000 dalton) subunit (beta) or a crossreactive determinant(s) on the HLA-DR3 alpha subunit and an additional alpha subunit. MT2 was found to be a determinant on Ia antigen-like molecules distinct from those carrying the MB and HLA-DR determinants. The results are consistent with the existence in the major histocompatibility complex of at least three loci encoding B-cell alloantigens.

A novel molecule expressing HLA-DR antigenic determinants

Our previous studies suggested that the polymorphism of HLA-DR antigens (the human equivalent of murine I-E antigens) was a result of structural variation in the small (beta) subunit. In order to more accurately define this polymorphism we have expanded these studies to include HLA-DR antigens isolated with monoclonal cells derived from genotypically HLA-homozygous DRw2, DR2w5, and DRw7 lymphoblastoid cells derived from offspring of consanguineous relationships. Our results indicate the large (alpha) subunits of DRw2 and DRw7 antigens are nearly identical, while their beta subunits show many differences. In contrast, both the alpha and beta subunits of the DRw5 antigen differ strikingly from the respective subunits of the DRw2 and DRw7 antigens. The significance of the variability of the DRw5 alpha subunit is in question at this point. One intriguing possibility is that DRw5 actually represents the human counterpart of the mouse I-A subregion antigen and that the monoclonal antibody is reacting with a determinant which is shared by the human equivalents of murine I-A and I-E antigens.

Small subunit of I-A subregion antigens determines the allospecificity recognized by a monoclonal antibody

The murine major histocompatibility complex (MHC) codes for three groups of identifiable cell-surface proteins, the K, D molecules, the I-A subregion antigens and the I-E subregion antigens. All three groups of molecules display a high degree of serologically detectable polymorphism and consist of two noncovalently associated polypeptides. Amino acid sequence and peptide comparisons among allotypes of K, D and I-E molecules reveals that one polypeptide is relatively constant, whereas the other is highly variable. Thus, it is likely that only one of the two polypeptides, the variable component, determines the antigenic specificities recognized by alloantisera. In contrast to the K, D anad I-E molecules, both subunits of I-A molecules display substantial structural differences when comparisons among allotypes are made. Therefore, we have investigated whether one or both subunits of I-A molecules determine their alloantigenic specificities. Our results, presented here, indicate that only one of the two subunits determines a particular allospecificity recognized by a monoclonal antibody.

Monoclonal antibodies to HLA--DRw determinants

Two monoclonal antibodies recognizing HLA-DRw (human la) antigens were produced. The DA2 antibody binds a monomorphic determinant, common to all specificities and Genox3.53 antibody binds to a cross-reacting site on the HLA-DRw1,2 and 6 specificities. Both antibodies are IgG1 and show complement dependent cytotoxicity only in the presence of rabbit anti-mouse IgG serum. Specificity of both antibodies for the HLA-DRw molecule was shown by inhibition of antibody binding by preincubation of antibody with detergent solubilized Ia from JY (HLA-DRw4,6) cells and by preincubation of target cells with F(ab')2 fragments of a rabbit anti-la serum. DA2 antibody reacted with all cells of human B cell origin tested and with peripheral blood lymphocytes of several primate species tested. Genox3.53 antibody bound only to human cells expressing HLA-DRw1,2 or 6 antigens, giving a negative reaction with all primates tested. Genox3.53 antibody detected a split in the HLA-DRw6 specificity, showing reduced binding to the Daudi cell (HLA-DRw6) in comparison with binding to several other cell lines typed as HLA-DRw6, under saturating conditions. This low reactivity with Daudi was confirmed by absorption experiments. The ratio of DA2 binding to Genox3.53 binding to homozygous and heterozygous cell lines under saturation conditions was compared. Results suggested that, on some cell lines, DA2 might be reacting with a second population of human Ia antigens in addition to the HLA-DRw antigens. When a mixture of saturating concentrations of DA2 and Genox3.53 antibodies was tested for binding to cells under saturating conditions, the number of counts bound suggested the antibodies could bind simultaneously. Direct binding experiments showed that when each antibody was iodinated, its binding was not inhibited by preincubation with the other antibody, confirming that the DA2 and Genox3.53 determinants are distinct on the Ia molecule.

Molecular identification of human Ia antigens coded for by a gene locus closely linked to HLA-DR locus

Human Ia(-like) specificities controlled by gene loci other than HLA-DR were searched for at the molecular level in cells of human B-cell-type cell lines which carry two established DR specificities. Chevalier cells of DRw3 and 7 and U698M cells of DRw2 and 4 were used. Their Ia molecules were partially purified, radioiodinated and analyzed for Ia specificities by the direct binding and sequential binding assays with a selected panel of human Ia alloantisera. It was possible in both the cell lines to define a third subset of Ia molecules carrying a new specificity in addition to two Ia subsets carrying the established DR specificities. The new specificity was detected by putative anti-DRw4 and anti-DRw7 antisera and was closely associated with DRw4 and DRw7 at population level. It was thus designated provisionally as BR4X7. These results suggest that the BR4X7 specificity is coded for by a separate Ia locus closely linked to HLA-DR locus. The determinant(s) responsible for BR4X7 was located on the small subunit of Ia molecules.