The Genetic Control of Human Ia Alloantigens: A Three‐Loci Model Derived from the Immunochemical Analysis of ‘Supertypic’ Specificities

149

The HLA-D region (class II) genes determine cell-surface glycoproteins, which function in the immune response. The known products of these genes are heterodimers of an a and a /3 chain. There are at least three major sets of products coded for by the HLA-D region. These are HLA-DR (homologous to I-E of the mouse H-2 region), defined by conventional serological methods; DC or MT (homologous to mouse I-A), originally defined by the cross-reacting group that included DR1, -2, and -w6; and SB, the "secondary B" cell types defined by primed lymphocyte typing (for reviews, see refs. 1 and 2). A fourth product, closely related to DR and called BR, has also been proposed on the basis of immunochemical analysis (3). Unlike the HLA-A and -B loci, whose original antigens were rapidly "split" to yield more than 20 HLA-A and more than 40 HLA-B alleles, the list of HLA-DR alleles has not yet been greatly expanded. Studies by two-dimensional gel electrophoresis have shown that most of the serologically detected polymorphic variation is attributable to variation in the 83 chains of the DR and DC molecules (1, 4), and DNA probes for the ,B chains have revealed a high level of restriction fragment polymorphism (5, 6). In contrast, probes for the DRa-and SBa-chain genes detect little restriction-site polymorphism among unrelated individuals, while a probe for the DCa chain detects a high level of polymorphism (7,8). These results are consistent with the finding of sequence variation in regions of cDNA clones for DCa and the homologous I-A a chains in mouse (9, 10). In preliminary studies, the variation detected by the DCa probe appeared to be associated with certain patterns of allelic variation in HLA-DR (7,8). The other three class II a-chain genes described previously showed little restriction enzyme polymorphism (7,11).In this paper we describe two additional class II a-chain gene sequences, both on chromosome 6. We have also studied systematically the variation in restriction patterns in two genes as revealed by the DCa-chain probe. Using a panel of cell lines, that are for the most part homozygous for HLA-DR, there is a strong association, due to linkage disequilibrium, between the restriction patterns and the HLA-DR types. Within some DR types, even those that are serologically homogeneous, there is additional polymorphic variation detected at the DNA level for both the DCa and the related DXa genes. MATERIALS AND METHODSEnzymes and Other Reagents. Restriction enzymes were purchased from Cambridge Biotechnology Laboratories and New England Biolabs., radiochemicals were from the Radiochemical Centre, and DNA polymerase I was from Boehringer Mannheim.Cell Lines. All DNA samples were extracted from the lymphoblastoid lines shown in Table 2. Most of the cell lines behaved as homozygous typing cells in the mixed lymphocyte reaction, which detects mainly HLA-DR-associated determinants. The human-mouse hybrids used for assigning sequences to chromosome 6 contained a human X/6 translocation chromosome from the cell line G3.32.2 (7,...

mentioning

confidence: 99%

Six HLA-D region alpha-chain genes on human chromosome 6: polymorphisms and associations of DC alpha-related sequences with DR types.

Spielman¹,

Lee²,

Bodmer³

et al. 1984

149

“…No recombinational event between DQ and DR has yet been confirmed, suggesting a relatively low frequency of recombination. Biochemical studies (2,(12)(13)(14)(15)(16)(17)(18) and analysis of cDNA clones (19)(20)(21)(22)(23)(24)(25)(26) indicate that a majority of the Ia genes are expressed as products. Ia gene products belonging to the same group are highly related (greater than 95% protein homology) while those belonging to different groups are only approximately 60% related.…”

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confidence: 99%

Nucleotide sequence of an HLA-DQ alpha chain derived from a DRw9 cell line: genetic and evolutionary implications.

Moriuchi¹,

Moriuchi²,

Silver³

1985

Three families of human Ia molecules, DP, DQ, and DR, have previously been defined. A cDNA clone, pDSH-9.1, encoding the a chain of a DQ molecule derived from an HLA-DRw9 homozygous cell line has been isolated and sequenced. Comparison of the nucleotide and predicted protein sequence to those of other DQ a subunits reveals that DQ a subunits derived from DR4, -7, and -9 cells are very similar to each other but quite different from a DQ a subunit derived from a DRw6 cell line. These studies suggest that certain Ia haplotypes have a common evolutionary history. Furthermore, in the context of current serologic and biochemical knowledge, they suggest that the gene encoding the DQ a subunit is in strong linkage disequilibrium with the DR locus.The Ia region of the major histocompatibility complex (MHC) consists of a series of closely linked loci encoding cell surface molecules that regulate the immune response. These Ia molecules may be divided into three groups, DP (formerly known as SB) (1), DQ (formerly known as DS) (2), and DR (3), that are structurally distinct. Ia molecules consist of two subunits, a and ,3, with molecular weights of approximately 28,000 and 33,000. Within each group, DP, DQ, and DR, multiple a-and /8-chain gene loci have been described; at present seven P3 chain (two DP, two DQ, and three DR) and five a chain (two DP, two DQ, and one DR) gene loci have been identified (4-9). Although their precise genetic order is not yet known, the DP locus is known to be centromeric to both DQ and DR, which in turn are centromeric to the class I loci, HLA-A, -B, and -C (10). Recombinational analysis indicates that both DP and the class I loci are approximately 1 centimorgan from the DQ and DR loci (10,11). No recombinational event between DQ and DR has yet been confirmed, suggesting a relatively low frequency of recombination. Biochemical studies (2,(12)(13)(14)(15)(16)(17)(18) and analysis of cDNA clones (19)(20)(21)(22)(23)(24)(25)(26) indicate that a majority of the Ia genes are expressed as products. Ia gene products belonging to the same group are highly related (greater than 95% protein homology) while those belonging to different groups are only approximately 60% related.The Ia system is highly polymorphic. At least 11 alleles at the DR locus (designated numerically-i.e., DR1-DR11) have been defined serologically (27). Similarly, at least 6 alleles at the DQ locus and 6 at the DP locus have been defined biochemically and by cellular assays, respectively (27,28 (29). Similarly, cells typing as DR1, -2, and -6 frequently display the MB1 antigenic determinant (30).Although the molecular basis for these antigenic determinants is not known, in some instances, the gene products expressing them have been identified. Thus, MB1, which is expressed on Drl, -2, and -6 cells, and MB3, which is expressed on DR4 and DR5 cells, are both present on different allelic forms of DQ molecules (28,31,32). In other instances, the molecular assignment has been more controversial; MT3 has been localized to DR-like mol...

“…It is clear that the overall organization of the region is the same in these three haplotypes. An interesting point to note is that the supertypic specificity called MT2 (27) (Fig. 5).…”

Section: Discussionmentioning

confidence: 99%

Linkage map of three HLA-DR beta-chain genes: evidence for a recent duplication event.

Rollini¹,

Mach²,

Gorski³

1985

131

The predominant class II, or Ia, antigen of the human major histocompatibility complex is HLA-DR. It consists of an a and a 13 chain, the latter being responsible for the remarkable polymorphism of these Ia antigens. Studies with cloned genes had shown the existence of more than one DR 13-chain locus. We have isolated about 100 kilobases of the HLA-DR 13-chain gene region from a cosmid library generated from a consanguineous homozygous B-cell line of the DR3 haplotype. Three HLA-DR 13-chain genes have been characterized. They are arranged in a head-to-tail orientation. One of the genes lacks the region encoding the first domain of the DR 13 chain. The two other genes are transcribed, as shown by RNA blot hybridization analysis. A striking restriction site homology has been found within the DR 13-chain gene cluster, suggesting a recent duplication event involving at least 25 kilobases of DNA. Moreover, the molecular map of DR 13 chain genes cloned from B-cell lines of two other HLA-DR haplotypes shows extensive homology between alleles of a given DR 1-chain locus.The class II antigens of the major histocompatibility complex are highly polymorphic transmembrane glycoproteins, consisting of an a subunit and a p subunit. These molecules are located predominantly on the surface of macrophages and B cells. They play a key role in the control of the immune response, functioning in cell-cell interactions and antigen presentation to regulatory T lymphocytes. In the human major histocompatibility complex (HLA), the class II molecules have been mapped to the HLA-D region on chromosome 6. Three subregions have been defined, DP, DQ, and DR. The HLA-DR antigen is the predominant surface product and it is the p chain that is responsible for the DR polymorphism (for reviews, see refs. 1 and 2).The molecular organization of the HLA-D region has not yet been elucidated. The restriction map of the DP subregion is known. There are two DP a-and p-chain loci (3) found as a-p pairs with the a and p chain genes in a head-to-head orientation (4-6). The organization of the DQ and DR subregions is not known, although the genetic complexity of these subregions has been documented. There are two DQ a loci (7,8) and two DQ p loci (9, 10). The HLA-DR subregion has been shown to contain only one nonpolymorphic a-chain gene (11,12). Analysis of cDNA clones (13, 14) and genomic clones (10), as well as direct studies of cellular DNA by Southern blot hybridization (15), has allowed us to establish the existence of multiple DR p-chain loci.In this study, we report the characterization of overlapping cosmid clones containing DR p-chain genes isolated from a genomic library prepared from DNA of a HLA-homozygous individual. Three DR p-chain genes in a head-to-tail conformation have been aligned. Two of these genes are transcribed, while the third one appears to be truncated, lacking the first domain. Extensive restriction site homology between DR P-chain genes within the same haplotype has been observed, suggesting a recent duplication event. ...