Polymorphic B-cell determinants in man

An overview of the restriction fragment length polymorphism of the HLA-D region: its application to individual D-, DR- typing by computerized analyses

HLA-D/DR alleles as defined by cellular and serological typing can also be identified by biochemical methods. The Southern blot technique provides an additional typing facility which can be applied to DNA obtained from any source of nucleated cells. The polymorphism revealed by Southern blot analyses, the so-called restriction fragment length polymorphism (RFLP), depends upon the restriction enzyme and cDNA probes used. To identify HLA-DR specificities a protocol was developed based on the use of the results of southern blot analyses with several restriction enzymes and cDNA probes within a panel of HLA-D/DR homozygous cells representing the DR1 to DRw8 alleles. First, hybridizations with the 3' untranslated sequence of the DR beta cDNA probe, after digestion of the DNA with PvuII (PvuII-DR beta 3') allows the selective identification of DR1, DR2 and DRw8; DR3, DR5 and DRw6 are found as one group as well as DR4 and DR7 as another. Second, TaqI-DQ alpha hybridization allows the splitting of DRw6-Dw18, DRw6-Dw19 and DRw6-Dw9 from the DR3, DR5 and DRw6 group. The other alleles DR3, DR4, DR5, DRw6-Dw16 and DR7 are revealed by dehybridization and rehybridization of the blot with a DR beta cDNA probe. This protocol was used to test whether in a panel of 30 randomly chosen individuals the HLA-DR typing could be performed. The results were highly concordant to the serotyping. Furthermore by adding the Pst-DR beta and TaqI-DQ alpha RFLPs, most of the MLC defined Dw specificities could also be identified. An overview of the specific fragments described here has been summarized in matrices which can be used as references for DNA-typing in computerized analyses.

Polymorphisms within the HLA-DRw6 haplotype. II. Protein charge heterogeneity reflects MLC subtyping of HLA-DRw6 homozygous cells

We have analyzed the HLA class II gene products from HLA-DRw6 homozygous cells. Epstein-Barr virus-transformed B-cell lines were internally labeled with [35S]-methionine. An NP-40 lysate of the cells was subjected to immunoprecipitation, first with a DRw52-like-specific monoclonal antibody and subsequently with a DR-specific framework antibody. The DR region-encoded gene products were analyzed by one-dimensional gel isoelectric focusing and two-dimensional gel electrophoresis. It is shown that DRw6 homozygous cell lines contain at least two nonallelic DR beta chains, one carrying a DRw52 determinant and one DRw52-negative population. Both chains appear to be polymorphic between the cellularly defined subtypes of DRw6. The determinant responsible for the differential mixed lymphocyte culture reactivity of Dw18 and Dw19 cells resides on the DRw52-positive population, whereas the Dw6-Dw9 differences are attributed to determinants on both populations of DR light chains. The Dw16-derived DRw52+ chain much resembles the Dw18 DRw52+ light chain whereas there is a clear-cut difference between these two subtypes in the DRw52- population. We conclude that, for DRw6 homozygous cells, the cellularly recognized D determinants are probably located on DR-encoded molecules, both DRw52+ and DRw52-, and that charge shift of these chains is at least partly responsible for differential recognition of these cells in mixed lymphocyte cultures.

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.

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.

H-2U: a new region at the D end of the murine MHC

A new genetic region, mapping within the H-2 complex, has been serologically defined with several alloantisera raised in mice which differ at the D region. When these antisera were absorbed to remove H-2D antibodies, residual antibody activity remained that reacted in a strain-specific manner, and the antigens involved mapped to a new genetic region between the S and D regions. Two allelic variants relating to the d and k haplotypes have been defined by genetic mapping studies. This new region has been designated H-2U and the antigens it controls appear to resemble Ia antigens in their cellular distribution and molecular weight. The new antigen is primarily expressed on B cells, and is carried on protein molecules having approximate molecular weights of 36 000 and 60 000 daltons and resembling the alpha and alpha--beta chain dimer characteristic of Ia antigens.

Demonstration of structural polymorphism among HLA-DR light chains by two-dimensional gel electrophoresis

Human HLA-DR antigens were immunoprecipitated from Nonidet P-40 extracts of [35S]methionine-labeled B lymphoblastoid cell lines and compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and isoelectric focusing (IEF). Two-dimensional (2-D) gel analyses, combining SDS-PAGE in the first dimension and IEF in the second dimension, revealed that the heavy (alpha) and light (beta) chains of each DRw specificity displays microheterogeneity of charge. However, the pattern of the heavy chain did not vary among different DRw specificities. In contrast, the light chains of different DRw types varied both in apparent size and charge distribution. Removal of sialic acids with neuraminidase or inhibition of glycosylation with tunicamycin reduced the microheterogeneity of both DR subunits. However, the heavy and light chains each still focused as two major bands, suggesting that other post-translational modifications contribute to the microheterogeneity or that there are two nonallelic DR-like molecules. After treatment with either neuraminidase or tunicamycin, the DR light chains, but not the heavy chains, were still structurally polymorphic. The DR light chains of serologically cross-reactive specificities displayed similar 2-D gel patterns suggesting that the structural polymorphism of the DR light chains is the basis for the serologically detected polymorphism of the HLA-DR antigens. Two additional polypeptides were observed in immunoprecipitates of DR antigens. These proteins, designated M1 and M2, both had a basic isoelectric point and were invariant among different cell lines. The protein M1 may be intracellular because it can not be immunoprecipitated from the cell surface.