Recognition by a murine monoclonal antibody of a unique epitope specific for the human alloantigen HLA-B8

HLA-DMA and -DMB genes are both required for MHC class II/peptide complex formation in antigen-presenting cells

Major histocompatibility complex (MHC) class II molecules are highly polymorphic cell-surface glycoproteins that present antigenic peptides to CD4+ T lymphocytes. The normal assembly of class II molecules with cognate peptides for antigen presentation requires an accessory function provided by a gene mapping to the class II region of the HLA complex. The isolation of somatic cell mutants of antigen-presenting cells (APC) has shown that at least one gene which maps between HLA-DP and HLA-DQ, provisionally designated c2p-1 (ref. 3), mediates this process. Here we describe a unique new mutant 2.2.93, which manifests defective formation of class II/peptide complexes like that described in c2p-1 mutants. We show that (1) mutant 2.2.93 contains a mutation in HLA-DMA, and a representative c2p-1 mutant, 9.5.3, contains a mutation in HLA-DMB; and (2) transfection and expression of DMA complementary DNA in 2.2.93, and DMB cDNA in 9.5.3, reverses their mutant phenotypes. These results show that HLA-DMA and -DMB, genes of previously unknown function mapping between HLA-DP and HLA-DQ, are required for the normal assembly of peptides with MHC class II molecules. They suggest that HLA-DMA and -DMB encode subunits of a functional heterodimer which is critical in the pathway of class II antigen presentation.

Generation of a human hybridoma producing a pure anti-HLA-A2 monoclonal antibody

We report the production and characterization of a human monoclonal IgM hybridoma antibody recognizing antigen HLA-A2. B lymphocytes obtained from the peripheral blood of a multiparous volunteer 1 week postpartum were transformed in vitro by Epstein-Barr virus, screened by a microlymphocytotoxicity assay, and electrofused with the heterohybridoma fusion partner, K6H6/B5. A specifically anti-A2 secreting hybridoma cell line. MBW1, was then identified and cloned. The cytotoxic IgM antibody produced showed complete correlation (r = 1.00) with the A2 antigen on a large panel of unrelated donors' lymphocytes, and no cross-reactivity with A28, Aw68, or Aw69 antigens was observed.

Conservation of HLA class I private epitopes in macaques

Fifty mouse monoclonal antibodies (mAb) specific for HLA class I epitopes were compared for their reactivity against two closely related nonhuman primate species, pigtailed macaques (Macaca nemestrina, Mn) and longtailed macaques (M. fascicularis, Mfl), which diverged from the hominoids 23-40 million years ago. An analysis of Nei's genetic identity (I) and distance (D) based on reactivity of all class I-specific mAb showed, as expected, that the macaques are more closely related to each other (I = 0.959) than to man (I = 0.782 for Mn and 0.859 for Mfl). However, there were clear differences in genetic similarity with respect to certain epitopes. Macaques were most different from each other and from man in expression of heterologous epitopes recognized by the mouse that are not polymorphic among humans. In contrast, the most polymorphic epitopes unique to single HLA alleles, so-called private epitopes, were present in all the species, and neither macaque species could be distinguished from humans, suggesting that certain class I private epitopes may be highly conserved in evolution.

A deletion mutant defines DQ beta variants with DR4 positive DQw3 positive haplotypes

We describe the production of an HLA deletion mutation by radiation mutagenesis of a DR4- and DQw3-homozygous, Dw4- and Dw14-heterozygous cell line designed to analyze polymorphisms associated with DR4 and DQw3. Southern blot analysis confirms a deletion of class I and class II genes on one haplotype. Variation in DQ beta alleles associated with DQw3 was previously described by characteristic RFLP patterns for a DQ beta bene. One pattern, which correlated precisely with A-10-83 monoclonal antibody reactivity (TA10), defined an allele which we call DQ"3.1". The mutant cell line has lost the polymorphic bands on Southern blots corresponding to the DQ"3.1" allele, while the intact Dw14 haplotype retains the alternate allele at DQ beta which is DQw-3 positive. TA10-negative. These data demonstrate the segregation of two DQw3 positive DQ beta allelic variants, both associated with DR4, which can be distinguished on the basis of both RFLP and monoclonal antibody reactivity.