Molecular analysis of the HLA-D region has uncovered a complex array of related genes encompassing a minimum of 6 alpha and 7 beta chain sequences. A high level of polymorphism is characteristic of the DQ alpha and beta genes, as well as DR beta. The DP genes, both alpha and beta, are also polymorphic, though to a lesser extent. The genes fit into the previously established loci: DP, DQ and DR, except for a newly-discovered sequence, DZ alpha, which is approximately equally related to all of the other alpha chain genes. Analysis of the polymorphism and evolution of the HLA-D region, by examination of the sequences, calls for several independent duplication events in the generation of this family of genes.

Several cDNA clones containing the EpsteinBarr virus BamHI fragment H rightward open reading frame 1 (BHRF1) have been recovered from the tightly latent lymphoblastoid cell line IB4. These clones contain the 5' leader exons encoded in the major internal repeat 1 and the viral BamHI fragment Y, identified in the rightwardly transcribed viral mRNAs associated with the latent viral life cycle. In addition, a cDNA clone containing BHRF1 from the Burkitt lymphoma cell line Jjoye was also recovered and exhibits a distinctive splicing pattern. In vitro transcription and translation of BHIRF1, followed by iminmunoprecipitation with EpsteinBarr virus-positive human sera, indicates that this viral antigen is expressed during infection. RNA blot analyses with a wide panel of lymphoblastoid and Burkitt Iymphoma cell lines revealed a complex pattern of transcription. Hybridization data obtained with several probes is presented.

The HLA class II antigens are a highly polymorphic family of dimeric cell-surface glycoproteins, expressed predominantly on the surface of immunocompetent cells. They are intimately involved with the induction of the T-cell response to extrinsic antigen and are important predisposing factors for a wide spectrum of autoimmune diseases. We describe here the expression of a class II product from the HLA-DP (new WHO nomenclature, formerly SB) subregion after transfer of cloned genes into mouse fibroblasts. The transfected DP antigen is recognized by several HLA class II monoclonal antibodies and, though present in a mouse cell background, is able to function in the presentation of influenza antigen to cloned DP-restricted human T lymphocytes.

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Mouse L cells transfected with human HLA-DP (DPw4) a and f3 genes were used to make monoclonal antibodies in C3H mice. A polymorphic antibody, DPl1. Alloantisera, mainly produced by fetal maternal stimulation, were the original basis for the definition of the HLA-DR and -DQ region products and their polymorphism. It is clear that most of the serologically detected variation is in the DR and DQ 83 chains. The DP specificities were identified by cellular typing techniques and there is, so far, no corresponding serological identification. One monoclonal antibody, IRL1, has been identified, which appears to react preferentially to DPw2 and DPw3 (4). Monoclonal antibodies that are monomorphic have made a major contribution to the biochemical analysis of the HLA-D region products (5, 6), but useful polymorphic antibodies have been harder to obtain (7). A wider range of polymorphic HLA-D monoclonal antibodies, particularly for the definition of HLA-DP types, would be extremely useful both for serological typing and for biochemical and functional studies.The production by transfection of mouse L cells expressing a single human HLA-D region product, in this case HLA-DP (8), provides the basis for a novel approach to making anti-HLA class II monoclonal antibodies. If an HLA-DPexpressing L-cell transfectant is used to immunize C3H mice, the strain from which L cells were derived, then the only product the mice should react to, apart from L-cell-specific determinants, is HLA-DP. This principle is an extension of that used to make human-specific antisera (9) and monoclonal antibodies (10) by immunizing mice with human-mouse somatic cell hybrids containing a single human chromosome. In this paper, we describe the recognition of polymorphic specificities on L-cell DP transfectants and the use of these transfectants to make a polymorphic monoclonal anti-DP antibody with, surprisingly, specificity for the a chain of DPw4 and to an apparently lesser extent, DPw2.