Nucleotide sequence of mutant I-A beta bm12 gene is evidence for genetic exchange between mouse immune response genes

Shared epitopes among HLA class II alleles: gene conversion, common ancestry and balancing selection

The extent and pattern of HLA class II sequence polymorphism raise a variety of evolutionary questions, notably those concerning the genetic mechanisms for generating diversity, the rate of change and the nature of the selection pressure maintaining this variation. Phylogenetic analysis of primate MHC class II sequences suggests that the allelic lineages are ancient, having diverged long before separation of the hominoid species. For the beta-chain loci, however, considerable allelic diversification within these lineages has occurred after speciation. The striking patchwork pattern of polymorphism with different alleles containing common sequence motifs can be accounted for by common ancestry, by gene conversion or by convergent evolution, depending on the location of the shared epitope.

Contribution of T-cell receptor-contacting and peptide-binding residues of the class II molecule HLA-DR4 Dw10 to serologic and antigen-specific T-cell recognition

The relative contributions of putative T-cell receptor (TCR)-contacting and peptide-binding residues of a major histocompatibility complex (MHC) class II restriction element to serologic and antigen-specific T-cell recognition were investigated by site-specific mutagenesis. Amino acids 70 and 71 in the DR beta 1 domain of DR4 Dw10 are uniquely differnet from the other Dw subtypes of DR4. Residue 70 is predicted to be located at the membrane-distal surface of the class II molecule, where it may influence T-cell recognition by a direct interaction with a TCR. Residue 71 is predicted to form part of the antigen-binding groove where its influence on T-cell recognition may be mediated indirectly via an effect on peptide binding. Transfected murine L cells were produced expressing the products of DR4 Dw10B genes in which the codons for residues 70 and 71 had been mutated towards DR4 Dw14. Support for the predicted orientations of beta-chain residues 70 and 71 was lent by the observation that only residue 70 plays an important role in the formation of a serologic determinant. Mutation of this residue was sufficient to produce recovery of recognition by a human monoclonal antibody, NI, which has specificity for all the DR4 subtypes with the exception of DR4 Dw10. The human T-cell clone HA1.7, specific for influenza virus hemagglutinin (HA) peptide 307-319 and restricted by DR1 Dw1, exhibits degeneracy of MHC restriction on the DR4 Dw subtypes with the exception of DR4 Dw10.(ABSTRACT TRUNCATED AT 250 WORDS)

Evolution of the rat kallikrein gene family: gene conversion leads to functional diversity

Kallikrein-like simple serine proteases are encoded by closely related members of a gene family in several mammalian species. Molecular cloning and genomic Southern blot analysis after conventional and pulsed-field gel electrophoresis indicate that the rat kallikrein gene family comprises 15-20 members, probably closely linked at a single locus. Determination of the nucleotide sequences of the rGK-3, -4, and -6 genes here completes sequence data for a total of nine rat kallikrein family members. Comparison of the rat gene sequences to each other and to those of human and mouse kallikrein family genes reveals patterns of relatedness indicative of concerted evolution. Analysis of nucleotide sequence variants in kallikrein family members shows that most sequence variants are shared by multiple family members; the patterns of shared variants are complex and indicate multiple short gene conversions between family members. Sequence exchanges between family members generate novel assortments of variants in amino acid coding regions that may affect substrate specificity and thereby contribute to the diversity of enzyme activity. Furthermore, small sequence exchanges also may play a role in generating the diverse patterns of tissue-specific expression of rat family members. These analyses indicate an important role for gene conversion in the evolution of the functional diversity of these duplicated genes.

HLA class II antigens and DNA restriction fragment length polymorphism in myasthenia gravis in Japan

Human leukocyte phenotypes and genes in the HLA class II regions were studied in 46 Japanese patients with myasthenia gravis. When the HLA phenotypes of the patients with myasthenia gravis were compared with the controls, an increased frequency of HLA-DRw53 was observed in females less than 30 years of age. The genomic DNAs of the HLA-DRw53-positive patients and DRw53-positive controls were analyzed by using four complementary DNA probes for HLA class II genes. With DQB complementary DNA as the probe, a higher incidence of the 6.5-kb or 8.2-kb BamHI fragment was observed in the patients (76.0%) compared with the controls (19.0%). In contrast, no significant difference was observed between patients and controls when complementary DNAs for DRB, DQA, and DPB were used as probes. These results indicate that the genetic background of Japanese females with early-onset myasthenia gravis is different from other patients with myasthenia gravis, and that DQB genes can greatly influence the onset of myasthenia gravis.

Genetic recombination in the alpha 2 domain of the E alpha chain yields an Ed molecule with altered T cell activation

We have used a novel T cell selection strategy to isolate a mutant of an H-2d/f murine macrophage line defective in its ability to present antigen to some Ed-restricted helper T cells. This mutant has an amino acid substitution in the alpha 2 domain of the Ed molecule. The mutation changes the sequence at codon 177 from ACC to CAC, which results in a threonine to histidine substitution and appears to be the first in vitro mutation to have arisen by genetic recombination. Even though the mutation is distal to the proposed antigen-binding groove, it affects antigen presentation, presumably by altering the scaffolding for the antigen-binding groove. This type of mutant might not be readily isolated using other selection techniques.

Experimental induction of systemic lupus erythematosus by recognition of foreign Ia

A chronic GVH reaction induced in normal mice results in a syndrome that closely resembles SLE. In this study, we compared the autoimmune GVH syndrome induced in parent (C57BL/6Kh [B6] and B6.C-H-2bm12 [bm12]) and F1 [( B6 x bm12]F1) mice by transfer of parental spleen cells. A majority of the mice in all groups developed autoantibodies to chromatin and erythrocytes, and some of the mice also produced anti-dsDNA antibodies. The predominant isotype of the anti-chromatin autoantibodies was found to be IgG2a, although high levels of IgG2b antibodies were also present. Autoantibody production was in general more intense and more prevalent in parent----F1 hybrid combinations, compared to parent----parent infusions. No influence of host or graft gender was observed. These studies show that a chronic GVH reaction can be induced by both parent----parent and parent----hybrid combinations.

Structures on the I-A molecule predisposing for susceptibility to type II collagen-induced autoimmune arthritis

The susceptibility to type II collagen (CII)-induced arthritis (CIA) in mice is profoundly influenced by major histocompatibility complex (MHC) class II genes in the H-2 region. Analyses of MHC-congenic strains on the B10 background show that only strains developing an anti-CII antibody response after immunization with autologous CII develop arthritis after induction with CII from various species. The susceptible haplotypes have been found to be H-2q, H-2r, H-2w3 and H-2w17. In addition, these haplotypes respond to different patterns of CII derived from various species suggesting that T cell receptors and CII peptides interact. In contrast, certain haplotypes closely related to H-2q, such as the H-2p and H-2w5 haplotypes, are resistant to induction of CIA and are nonresponders to CII. We have earlier shown that a critical structure on the I-A beta molecule determines the susceptibility differences between the p and q haplotypes. We have now determined the structure of exon 2 of the A beta as well as some of the A alpha genes of the remaining haplotypes in the p, q and r families. The sequences show similarities between the CIA-susceptible haplotypes in the A beta C-terminal part and the A alpha N-terminal part of the first domains forming a large part of the antigenic peptide-binding site. Among the wild mouse-derived haplotypes, the w5 haplotype showed an A beta sequence identical to that of the p haplotype consistent with its nonresponder nature to CII immunization. These findings suggest that (a) structures shared between different class II molecules are of importance for the susceptibility to disease in mouse strains and (b) most likely recognition of different CII peptides is important for development of disease.

Functional and molecular characterization of I-A kappa beta mutants is consistent with the predicted three dimensional structure of class II MHC molecules

Class II MHC (Ia) molecules have been shown to be critical as restriction elements in the T helper/inducer cell recognition of antigen. Efforts to determine the role of allelic variation in MHC restricted antigen presentation have included the use of serologically selected mutants to correlate structural variations in Class II molecules with changes in the antigen presenting function of Ia bearing cells. Such studies have revealed that serologically selected mutations tend to occur in a single immunodominant region and that even a single amino acid substitution can alter T cell recognition of Ia molecules. We report here the characterization of two more serologically selected Class II A beta chain mutations. Each is due to a single base change which alters a single amino acid. One of these mutations is in the third hypervariable region (amino acid 64--glutamine to arginine) and alters the antigen presenting function. The second mutation at amino acid 48, though a relatively non-conservative change (arginine to cysteine), has no effect on APC phenotype. Such a result would be predicted based on comparisons made with the proposed three dimensional crystallographic structure of Class I molecules and models proposed for Class II molecules based on Class I structure. The amino acid change at position 48 is in a portion of the molecule that is most likely unavailable to bind antigen or interact with T cell receptor whereas the mutation at amino acid 64 is on an exposed face of the alpha helix, a region which could affect interaction with either antigen and/or the T cell receptor.

Polymorphic DQ alpha and DQ beta interactions dictate HLA class II determinants of allo-recognition

18 transfected cell lines were generated that expressed distinct DQ molecules related to the serologically defined HLA-DQw3 specificity. These transfectants were constructed using site-directed mutagenesis to introduce nucleotide substitutions into DQ3.2 beta cDNA, followed by retrovirus-mediated gene expression of the mutagenized genes in human B cell lines with different endogenous DQ alpha chains. The capacity of particular class II dimers to stimulate alloreactive T cell clones was investigated. T cell activation was found to be dependent on both DQ alpha and DQ beta chains. In some cases, single amino acid substitutions at codons 13, 26, 45, or 57 of the DQ beta chain were sufficient to dramatically alter T cell reactivity; T cell recognition of these substitutions, however, was strongly influenced by the alpha chain polymorphisms present in the stimulatory class II dimer. Both gain and loss of major serologic and cellular specificities associated with specific DQw3+ alleles were observed with a limited array of site-directed substitutions.

Adoptive immunotherapy is suppressed in C57BL/6J and B6.C-H-2bm12 mice following recognition of congenic class II MHC antigen determinants

In previous reports, we have shown that adoptive transfer of tumor-sensitized T (immune) cells to tumor-bearing mice that have received a prior injection of cyclophosphamide (CY) results in the induction of permanent tumor regression in syngeneic strains. It has also been shown that adoptive immunotherapy results in an increased expression of class II MHC antigens (Ia) by macrophages at the tumor site and in the peritoneal cavity and is associated with expansion of CD4+ and CD8+ T cells at the site of tumor regression. In this report, we use the Ia mutant strain, B6.C-H-2bm12, and congenic C57BL/6J (B6) mice to determine the relative importance of Ia expression in regulating amplification of immune responses following adoptive immunotherapy and to test the hypothesis that recognition of congenic Ia determinants will result in the induction of suppressor mechanisms that down-regulate active immunity. The data indicated that the adoptive transfer of immune congenic T cells (B6 immune cells into CY-treated tumor-bearing bm12 mice and vice-versa) down-regulated active immunity, while the transfer of syngeneic immune cells resulted in permanent tumor regression. By using radiation-chimeric mice, it was shown that down-regulation was associated with incompatibility of the transferred immune T cells and bone-marrow-derived cells (putatively expressing the Ia haplotype of donor-derived macrophages) and the appearance of long-lived splenic suppressor cells. Suppression per se was shown to be induced in response to the Ia difference between the two strains and not in response to the MCA/76-9 sarcoma, which appears to be one of the few tumors that can induce active immunity in both the syngeneic and congenic strains without obvious subsequent down-regulation by suppression.

Transgenic HLA-DR alpha faithfully reconstitutes IE-controlled immune functions and induces cross-tolerance to E alpha in E alpha 0 mutant mice

We have constructed transgenic mice that express the human class II MHC molecule HLA-DR alpha on a genetic background in which the equivalent endogenous gene, H-2 IE alpha, is not expressed. In these mice, DR alpha complemented the E beta chain such that tissue-specific expression of an interspecies hybrid DR alpha-E beta heterodimer was obtained. Despite 25% amino acid differences between DR alpha and E alpha, immune responsiveness to IE-controlled antigens, clonal deletion of IE-reactive T cells, and alloantigenicity were quantitatively and qualitatively indistinguishable in IE-positive mice and in mice that had integrated at least four copies of the transgene. These results demonstrate a remarkable degree of structural, regulatory, and functional conservation. They also suggest that tolerance induction involves only discrete portions of MHC molecules.

A cellular and functional split in the DRw8 haplotype is due to a single amino acid replacement (DR beta ser 57- asp 57)

The single DR beta chain gene of the DRw8 haplotype has been suggested to carry both the DRw8 and the DRw52 epitopes. Cellular typing has shown that the DRw8 haplotype can be split into three subtypes, Dw8.1, Dw8.2, and Dw8.3, presumably due to a polymorphism in the DRw8 beta chain. Furthermore, Dw8.1 and Dw8.2 cells present influenza virus antigen to different T-cell clones. In the present study, DRw8/Dw8.2 beta chain cDNA was cloned and characterized. A comparison of this sequence with a partial DRw8/Dw8.1 beta chain gene suggested that the DRw8 split is due to a single amino acid replacement of ser57-asp57 caused by three nucleotide substitutions in the same codon. In most DR haplotypes, two expressed DR beta chain genes exist. Comparing the nucleotide sequence of the single beta gene in the DRw8 haplotype to those of other DR beta genes revealed that the DRw8 beta gene sequence is most closely related to the DRB1 genes of the DR3, 5, and w6 haplotypes. However, the comparisons also showed that it was not possible from sequence similarities to divide the DR beta genes into two or more distinct allelic series.

A novel MHC class II epitope expressed in thymic medulla but not cortex

The repertoire of receptors expressed by peripheral T cells is the result of two selective events that occur during intrathymic development. Positive selection expands cells able to recognize foreign peptides presented by self MHC molecules, and negative selection eliminates cells reactive to self MHC molecules and associated self peptides. Chimaera studies suggest that, at least in the case of T cells recognizing MHC class II, interaction with thymic cortical epithelial cells is responsible for the former, whereas thymic medullary cells, of bone marrow origin, mediate the latter. This view of thymic development is supported by recent morphometric analyses, showing that autoreactive cells are found in thymic cortex but not medulla. Although numerous studies have shown that MHC class II molecules are expressed in both sites, none provides any explanation for the differential selection of T cells that is observed. Here, we describe a novel MHC class II epitope which is found on cells in thymic medulla but not cortex. The antibody to this epitope reacts with about 10% of class II molecules on B cells and may be recognizing a self peptide-MHC complex. These results provide the first evidence for differential expression of class II epitopes in different tissues and are compatible with the hypothesis that different ligands, rather than different affinity thresholds for the same ligand, are involved in positive and negative selection of the T-cell repertoire.

HLA-DR molecules on all cells are electrophoretically unique

Previous SDS-PAGE studies of autologous clonal ALL and normal B cell lines indicated that HLA-DR molecules on leukemic cells have an extra beta chain band. We now show that these results are not an artifact of cell lines, EBV transformation, or cell growth in culture. Leukemic cells from four ALL patients were surface labeled with 125I and their HLA-DR molecules compared with those on autologous normal peripheral blood B cells. The electrophoretic patterns of HLA-DR molecules on these in vivo cell populations are identical to those on the corresponding cell lines. Moreover, EBV-transformation does not alter the electrophoretic appearance of HLA-DR molecules on normal tonsil B cells. Cell lines can now be used to study the chemical basis for these electrophoretic differences.

Microrecombinations generate sequence diversity in the murine major histocompatibility complex: analysis of the Kbm3, Kbm4, Kbm10, and Kbm11 mutants

The mechanism that generates spontaneous mutants of the Kb histocompatibility gene was analyzed. Nucleotide sequence analysis of four mutant genes (Kbm3, Kbm4, Kbm10, and Kbm11) revealed that each mutant K gene contains clustered, multiple nucleotide substitutions. Hybridization analyses of parental B6 genomic DNA and cloned class I genes with mutant-specific oligonucleotide probes, followed by sequence analyses, have identified major histocompatibility complex class I genes in the K, D, and Tla regions (K1, Db, and T5, respectively) that contain the exact sequences as substituted into mutant Kb genes. These data provide evidence for the hypothesis that the mutant Kb genes are generated by a microrecombination (gene conversion) mechanism that results in the transfer of small DNA segments from class I genes of all four regions of the major histocompatibility complex (K, D, Qa, and Tla) to Kb. Many of the nucleotides substituted into the mutant Kb genes were identical to those found in other naturally occurring K alleles such as Kd. Thus, we propose that the accumulation of microrecombination products within the K genes of a mouse population is responsible for the high sequence diversity among H-2 alleles.

Genetic control of T cell responsiveness to the Friend murine leukemia virus envelope antigen. Identification of class II loci of the H-2 as immune response genes

T cells primed specifically for the envelope glycoprotein of Friend murine leukemia helper virus (F-MuLV) were prepared by immunizing mice with a recombinant vaccinia virus that expressed the entire env gene of F-MuLV. Significant proliferative responses of F-MuLV envelope-specific, H-2a/b T cells were observed when the T cells were stimulated with antigen-pulsed peritoneal exudate cells (PEC) having the b allele at the K, A beta, A alpha, and E beta loci of the H-2. On the other hand, PEC having only the kappa allele at these loci did not induce the envelope-specific T cell proliferation, even when the PEC had the b allele at the E alpha, S, or D loci. F-MuLV envelope-specific proliferation of H-2a/b T cells under the stimulation of antigen-pulsed, H-2a/b PEC was specifically blocked with anti-I-Ab and anti-I-Ek mAbs but not with anti-Kb, anti-Kk, or anti-I-Ak mAbs. Moreover, (B10.MBR x A/WySn)F1 mice that have the b allele only at the K locus but not in I-A subregion were nonresponders to the envelope glycoprotein, and the bm12 mutation at the A beta locus completely abolished the T cell responsiveness to this antigen. These results indicate that proliferative T cells recognize a limited number of epitopes on F-MuLV envelope protein in the context of I-Ab, hybrid I-Ak/b, and/or hybrid I-Ek/b class II MHC molecules but fail to recognize the same envelope protein in the context of I-Ak or I-Ek molecules. This influence of the H-2I region on T cell recognition of the envelope glycoprotein appeared to control in vivo induction of protective immunity against Friend virus complex after immunization with the vaccinia-F-MuLV env vaccine. Thus, these results provide, for the first time, direct evidence for Ir gene-controlled responder/nonresponder phenotypes influencing the immune response to a pathogenic virus of mice.

Microrecombinations generate sequence diversity in the murine major histocompatibility complex: analysis of the Kbm3, Kbm4, Kbm10, and Kbm11 mutants

The mechanism that generates spontaneous mutants of the Kb histocompatibility gene was analyzed. Nucleotide sequence analysis of four mutant genes (Kbm3, Kbm4, Kbm10, and Kbm11) revealed that each mutant K gene contains clustered, multiple nucleotide substitutions. Hybridization analyses of parental B6 genomic DNA and cloned class I genes with mutant-specific oligonucleotide probes, followed by sequence analyses, have identified major histocompatibility complex class I genes in the K, D, and Tla regions (K1, Db, and T5, respectively) that contain the exact sequences as substituted into mutant Kb genes. These data provide evidence for the hypothesis that the mutant Kb genes are generated by a microrecombination (gene conversion) mechanism that results in the transfer of small DNA segments from class I genes of all four regions of the major histocompatibility complex (K, D, Qa, and Tla) to Kb. Many of the nucleotides substituted into the mutant Kb genes were identical to those found in other naturally occurring K alleles such as Kd. Thus, we propose that the accumulation of microrecombination products within the K genes of a mouse population is responsible for the high sequence diversity among H-2 alleles.

MHC polymorphism pre-dating speciation

Two features distinguish the polymorphism of the major histocompatibility complex (MHC) loci from that of other loci: its high diversity and the large genetic distance between MHC alleles. More than 100 alleles exist in natural populations in the mouse at each of the functional class I and class II alleles, all alleles occurring at frequencies that cannot be explained by recurrent mutations. Some of the alleles differ by approximately 70 nucleotides in the coding region alone and some of the products of the allelic genes differ by more than 50 amino acids. It has generally been assumed that these differences accumulated after species inception. Here, we present evidence for an alternative explanation of the origin of MHC polymorphism: a large part of the MHC polymorphism pre-dates speciation and is passed on from species to species. We describe allelic differences that must have arisen before the separation of mice and rats from a common ancestor more than 10 million years ago.

A molecular basis for MHC class II--associated autoimmunity

Class II major histocompatibility (MHC) molecules have an immunoregulatory role. These cell-surface glycoproteins present fragments of protein antigens (or peptides) to thymus-derived lymphocytes (T cells). Nucleotide sequence polymorphism in the genes that encode the class II MHC products determines the specificity of the immune response and is correlated with the development of autoimmune diseases. This study identifies certain class II polymorphic amino acid residues that are strongly associated with susceptibility to insulin-dependent diabetes mellitus, rheumatoid arthritis, and pemphigus vulgaris. These findings implicate particular class II MHC isotypes in susceptibility to each disease and suggest new prophylactic and therapeutic strategies.

Intergenic exchange maintains identity between two human lambda light chain immunoglobulin gene intron sequences

Evidence for gene conversion or unequal double crossover in the human lambda light chain immunoglobulin locus is presented. The high level of J2C2-J3C3 intron cross-hybridization, the identity of the J lambda and J lambda 3 coding and intron sequences, the presence of multiple base differences between the C lambda 2 and C lambda 3 coding regions, and the presence of both the unconverted and converted alleles in the normal gene pool, suggest that a recombinational event has resulted in the conversion of the J lambda 2 coding and intron sequences to those of J lambda 3 and its flanking sequences. Intergenic exchanges, such as the one described here, may provide a mechanism to maintain sequence homogeneity and functionality among the duplicated members of the human lambda gene family.

A specific nucleotide sequence defines a functional T-cell recognition epitope shared by diverse HLA-DR specificities

An oligonucleotide probe that distinguishes the HLA-DR4, Dw14 allele from other HLA-DR4-associated class II genes was used to identify a common nucleotide sequence shared between the DR beta 1 locus encoding HLA-DR1 (Dw1), Dw16, and DRw10 haplotypes. The presence of this nucleotide sequence correlated with the ability of these haplotypes to stimulate an alloreactive proliferative T-cell clone (clone 14B) raised against a Dw14+ stimulator cell. Alleles of DR beta 1 that differ by one specific nucleotide variation at codon 71 neither hybridize to the Dw14-specific oligonucleotide nor stimulate clone 14B. These data demonstrate the presence of a shared epitope present on serologically distinct DR alleles that is recognized as a specific allodeterminant by a single T-cell clone.

Linkage relationships in the bovine MHC region. High recombination frequency between class II subregions

Class II genes of the bovine major histocompatibility complex (MHC) have been investigated by Southern blot analysis using human DNA probes. Previous studies revealed the presence of bovine DO beta, DQ alpha, DQ beta, DR alpha, and DR beta genes, and restriction fragment length polymorphisms for each of these genes were documented. In the present study, the presence of three additional class II genes, designated DZ alpha, DY alpha, and DY beta, are reported. DZ alpha was assumed to correspond to the human DZ alpha gene while the other two were designated DY because their relationship to human class II genes could not be firmly established. The linkage relationships among bovine class II genes and two additional loci, TCP1B and C4, were investigated by family segregation analysis and analysis of linkage disequilibrium. The results clearly indicated that all these loci belong to the same linkage group. This linkage group is divided into two subregions separated by a fairly high recombination frequency. One region includes the C4, DQ alpha, DQ beta, DR alpha, and DR beta loci and the other one is composed of the DO beta, DY alpha, DY beta, and TCP1B loci. No recombinant was observed within any of these subregions and there was a strong or fairly strong linkage disequilibrium between loci within groups. In contrast, as many as five recombinants among three different families were detected in the interval between these subregions giving a recombination frequency estimate of 0.17 +/- 0.07. The fairly high recombination frequency observed between class II genes in cattle is strikingly different from the corresponding recombination estimates in man and mouse. The finding implies either a much larger molecular distance between some of the bovine class II genes or alternatively the presence of a recombinational "hot spot" in the bovine class II region.

Identification of an immunodominant region on the I-A beta chain using site-directed mutagenesis and DNA-mediated gene transfer

To identify which polymorphic residues determine the allospecific antibody binding sites on A beta polypeptides, mutant Ak beta genes were constructed encoding single or multiple amino acids of the d allele at 14 polymorphic positions in the beta 1 domain. Cell lines expressing these genes were analyzed by quantitative immunofluorescence using 16 mAbs reactive to Ak beta or Ad beta. Substitution of d allele residues at positions 63 and 65-67 in the Ak beta polypeptide resulted in the loss of binding of all Ak beta-reactive antibodies and the gain of binding of most Ad beta-reactive antibodies. Two Ad beta-reactive mAbs bound to the mutant Ak beta polypeptide containing d allele-characteristic residue at position 40. In contrast, substitution of the other polymorphic residues in the NH2-terminal and COOH-terminal regions of the beta 1 domain did not alter antibody binding.

Characterization of the MHC class II region in cattle. The number of DQ genes varies between haplotypes

The organization of the major histocompatibility complex (MHC) class II region in cattle was investigated by Southern blot analysis using human probes corresponding to DO, DP, DQ, and DR genes. Exon-specific probes were also employed to facilitate the assessment of the number of different bovine class II genes. The results indicated the presence of single DO beta and DR alpha genes, at least three DR beta genes, while the number of DQ genes was found to vary between MHC haplotypes. Four DQ haplotypes, DQ alpha 1 beta 1 to DQ alpha 2 beta 4, possessed a single DQ alpha and a single DQ beta gene whereas both these genes were duplicated in eight other haplotypes, DQ alpha 3 beta 5 to DQ alpha 9 beta 12. No firm evidence for the presence of bovine DP genes was obtained. The same human probes were also used to investigate the genetic polymorphism of bovine class II genes. DQ alpha, DQ beta, DR alpha, DR beta, and DO beta restriction fragment length polymorphisms (RFLPs) were resolved and in particular the DQ restriction fragment patterns were highly polymorphic. Comparison of the present result with the current knowledge of the class II region in other mammalian species suggested that the DO, DP, DQ, DR, and DZ subdivision of the class II region was established already in the ancestor of mammals. The DP genes appear to be the least conserved class II genes among mammalian species and may have been lost in cattle. The degree of polymorphism of different class II genes, as revealed by RFLP analyses, shows striking similarities between species.

DNA sequence analysis of I-Ak beta mutants reveals serologically immunodominant region

We have produced a series of in vitro serologically selected cell lines that express mutant I-Ak molecules. In this report we describe the DNA sequence analysis of the Ak beta gene of four cell lines that express serologically altered Ak beta polypeptides in association with wild-type Ak alpha polypeptides. Each of the major serologic epitopes on the Ak beta polypeptide has been altered in one or more of the four mutants. In addition, the four mutants exhibit a broad spectrum of functional defects when used to stimulate a panel of T hybridomas of various specificities. The DNA sequence analysis revealed that each mutant had sustained a single nucleotide substitution resulting in a single amino acid substitution. All four independent substitutions occurred within or near the third of the four variable regions defined in the beta 1 domain of the A beta polypeptide by allelic comparisons. These data strongly suggest that the third variable region is the major determinant of alloantigenicity on the Ak beta polypeptide.

Molecular analysis of antigen recognition by insulin-specific T-cell hybridomas from B6 wild-type and bm12 mutant mice

Molecular analysis of the heterodimeric T-cell antigen receptor of insulin-specific class II-restricted T-cell hybridomas (THys) derived from C57BL/6 (B6) wild-type and B6.C-H-2bm12 (bm12) mutant mice revealed that such T cells use a diverse V gene repertoire. Analysis of three THys that use related V genes, however, showed a number of novel features. Two THys that share major histocompatibility complex restriction use V alpha genes that are 98.6% homologous. Two THys sharing the same antigen fine specificity use a particular germ line V beta D beta J beta combination. A 21-base-pair deletion in the 5' segment of the J beta gene occurs in one THy, suggesting a novel mechanism for generating diversity in T-cell antigen receptor beta genes. The first amino acid encoded by N sequences at the V-D junction is conserved in a pair of T cells which recognize identical antigenic epitopes. The implications of these findings for the structural mechanisms underlying major histocompatibility complex-restricted antigen-specific T-cell recognition are discussed.

Functional diversity of Ia epitopes on macrophages

A panel of monoclonal antibodies directed against various epitopes of mouse Iak was used to block functions mediated by Iak on CBA/J macrophages in two different assay systems. The first system was the recently described proliferation inhibition of an H-2k T cell clone (8.1.11.2) by a combination of CBA/J (nonactivated) macrophages and anti-Iak (Kedar, I. et al. J. Immunol. 1986. 136: 3166). The second system was the well known macrophage cytotoxicity induced by interferon against various transformed cells. We found that anti-Iak antibodies directed against serological specificity number 2 (on the alpha chain of IA) blocked the proliferative stimulus of the macrophage Iak for the 8.1.11.2 T cell clone. Both an IgG and an IgM antibody with this specificity were effective, whereas seven other anti-Iak (including several for other specificities on the alpha chain of IA) were not. Conversely, two different monoclonal anti-Iak antibodies directed against serological specificity number 17 (on the beta chain of IA) inhibited the cytolytic activity of the activated macrophages for the 8.1.11.2 T cell clone as well as the P815 (H-2d) mastocytoma as target, whereas four other antibodies were ineffective in this regard. In addition to providing evidence that Ia may participate in the cytolytic activity of activated macrophages, these studies demonstrate that different epitopes of Iak on macrophages are differentially involved in different biological functions.

Multiple T cell antigenic determinants identified within a limited region of the horse cytochrome c molecule

The antigen fine specificity of T cell hybridomas recognizing the horse apocytochrome c fragment 1-65, restricted to the I-Ab molecule, was determined to gain some insight into the molecular nature of T cell antigenic peptides. Two major groups of clones specific for distinct subsites, namely residues 1-38 and 39-65, could be identified. Hybridomas recognizing the latter determinant were further tested with different horse cytochrome c peptides and analogues. This analysis revealed the presence of at least two epitopes encompassed by residues 47-53 and 48-53. Furthermore, clones specific for the amino acid sequence 48-53 showed considerable heterogeneity in respect to the antigen concentration required to obtain 50% of the maximal interleukin 2 secretion. Most prominent was the heteroclitic response towards tuna cytochrome c which differs at positions 44, 46 and 47 from the horse cytochrome c molecule in the relevant region. Comparison of the conformation of the sequence 43-46 between the two cytochrome c suggests that this segment, which forms a 3(10) bend, may be important in maintaining the proper structure of the antigenic determinant. Moreover, the variations up to 180-fold in the concentrations of the cross-reacting cytochrome c and peptides required for stimulation were not always correlated with the maximal interleukin 2 secretion they induced. This indicates that the biological response, that is supposed to be an indication of the affinity of the T cell receptor for its ligand, is not necessarily a function of the antigen concentration.

Functional polymorphisms among HLA-DR4+ DR beta chains associated with limited peptide diversity

Tryptic peptide map analysis by high-pressure liquid chromatography of DR4- associated DR beta chains revealed limited structural variation within DR beta polypeptides. Comparison of 3H-leucine-labelled tryptic peptide maps of Dw4 and Dw14 homozygous cells identified distinct peaks corresponding to Dw4 and Dw14-associated DR beta polypeptides. HPLC analysis of cell line 256, heterozygous for two DR4-related specificities, Dw4 and Dw14, displayed both peptides, corresponding to the variable Dw4 and Dw14 chromatograms. This observation was confirmed using a deletion mutant cell line derived from 256 lacking Dw4-associated class II genes. The observed peptide variation correlated precisely with predicted nucleotide-derived amino acid sequences implicating amino acids 66-71 of the DR beta chain as contributing to HLA-D structural and functional polymorphisms.

Molecular analysis of antigen recognition by insulin-specific T-cell hybridomas from B6 wild-type and bm12 mutant mice

Molecular analysis of the heterodimeric T-cell antigen receptor of insulin-specific class II-restricted T-cell hybridomas (THys) derived from C57BL/6 (B6) wild-type and B6.C-H-2bm12 (bm12) mutant mice revealed that such T cells use a diverse V gene repertoire. Analysis of three THys that use related V genes, however, showed a number of novel features. Two THys that share major histocompatibility complex restriction use V alpha genes that are 98.6% homologous. Two THys sharing the same antigen fine specificity use a particular germ line V beta D beta J beta combination. A 21-base-pair deletion in the 5' segment of the J beta gene occurs in one THy, suggesting a novel mechanism for generating diversity in T-cell antigen receptor beta genes. The first amino acid encoded by N sequences at the V-D junction is conserved in a pair of T cells which recognize identical antigenic epitopes. The implications of these findings for the structural mechanisms underlying major histocompatibility complex-restricted antigen-specific T-cell recognition are discussed.

Thymic immune response gene function in radiation chimeras reconstituted with purified hemopoietic stem cells

Thymectomized (C57BL/6[B6] X bm1)F1 mice and thymectomized (B6 X bm12)F1 mice were engrafted with neonatal parental thymus of either B6 type [H-2b mouse, Sendai virus cytotoxic T cell (Tc) responder] or bm1 type (H-2Kb mutant, Sendai virus Tc nonresponder) and B6 type (H-Y Tc responder) or bm12 type (H-2 I-Ab mutant, H-Y Tc nonresponder), respectively. All mice were irradiated and reconstituted with highly purified syngeneic pluripotent hemopoietic stem cells. All types of thymus engraftment resulted in a restored T cell immunocompetence. The Tc reaction to Sendai virus in (B6 X bm1)F1 mice engrafted with both responder type B6 and nonresponder, type bm1 neonatal thymus allowed maturation of Sendai-specific, H-2Kb-restricted Tc. For the Tc reaction to H-Y, only responder type B6 thymus restored the Tc response, whereas this was not achieved with nonresponder type bm12 thymuses. We conclude from this study that in this radiation stem cell chimera system the radioresistant component of the thymus dictates major histocompatibility complex (MHC) specificity and immune response phenotype of T cells restricted to class II MHC molecules but not of T cells restricted to class I MHC molecules.

The azobenzenearsonate conjugate of poly-glutamic-lysine-tyrosine will induce tyrosine-azobenzenearsonate-specific T-cell responses and clones in nonresponder mice

Mice of the H-2b haplotype are low responders to ABA-tyr. However, when they were immunized with ABA coupled to poly-GLT15 for which they are nonresponders, they developed strong proliferative responses to ABA-tyr in draining lymph node cells. Clones derived from these cells were highly reactive to ABA-tyr although the original mice were not. No evidence was found to indicate that suppression played a role in the failure to respond to ABA-tyr. Characterization of two clones showed an absolute specificity for the arsonic acid group and the Azo linkage. Alterations in the terminal amino acid residues produced varying changes in reactivity which could not be ascribed unequivocally to an effect on epitope or agretope.

A single base mutation in an I-A alpha-chain gene alters T-cell recognition

The interaction between the clonally selected T-cell antigen receptor, antigen, and Ia molecule is poorly understood at the molecular level. A cell line bearing an altered I-Ak alpha-chain (Ak alpha) molecule has been examined in order to provide more information about the relationship between Ia structure and function. The cell line, 3J9, was derived from the TA3 B-cell hybridoma through a series of negative and positive immunoselection steps. The 3J9 mutant lacked the binding site recognized by the Ak alpha-specific monoclonal antibody 39J and failed to present antigen to two T-cell hybridomas out of a large panel of I-Ak-restricted T-cell hybridomas examined. Sequence analysis of the mutant Ak alpha gene showed a single base transition (G----A) that resulted in a glutamic acid to lysine substitution at amino acid 75 of the alpha 1 domain. This mutation confirms the importance of amino acid 75 in the expression of the Ia.19 epitope, demonstrates the involvement of this region in the presentation of antigen to specific T cells, and provides a further example of the multiple functional domains on the Ia molecule that are involved in antigen presentation.

Interaction between Kb and Q4 gene sequences generates the Kbm6 mutation

Genetic interaction as a mechanism for the generation of mutations is suggested by recurrent, multiple nucleotide substitutions that are identical to nucleotide sequences elsewhere in the genome. We have sequenced the mutant K gene from the bm6 mouse, which is one of a series of eight closely related, yet independently occurring mutants known collectively as the "bg series." Two changes from the Kb gene are found, positioned 15 nucleotides apart: an A-to-T change and a T-to-C change in the codons corresponding to amino acids 116 and 121, resulting in Tyr-to-Phe and Cys-to-Arg substitutions, respectively. Hybridization analysis with an oligonucleotide specific for the altered Kbm6 sequence identifies one donor gene, Q4, located in the Qa region of the H-2 complex. The two altered nucleotides that differentiate Kbm6 and Kb are present in Q4 in a region where Kb and Q4 are otherwise identical for 95 nucleotides, delineating the maximum genetic transfer between the two genes. Because the Kbm6 mutation arose in an homozygous mouse these data indicate that the Q4 gene contains the only donor sequence and demonstrates that Q-region gene sequences can interact with the Kb gene to generate variant K molecules.

Mutations of class II MHC molecules

It remains unclear how the tertiary interaction of T-cell receptor, la molecule and foreign antigen results in the extensive diversity of the helper T cell repertoire. Here Laurie Glimcher and Irwin Griffith focus on what has been learned about the relationship between structure and function of the la molecule from the use of mouse strains with mutations in the genes coding for these glycoproteins.

Alloreactivity of an OVA-specific T-cell clone. I. Stimulation by class II MHC and novel non-MHC B-cell determinants

A T-cell clone (Ly1-03) derived from BALB/cBy mice, though highly specific for OVA/Ad, reacted to allogeneic spleen cells of 6 of 12 H-2 haplotypes tested. The reactivity to each particular H-2 haplotype required the expression of a non-major histocompatibility complex (MHC) gene product present on the B cells of certain strains of mice. All the alloreactive responses were MHC restricted and were inhibited by class II-specific and L3T4-specific monoclonal antibodies. The non-MHC gene product, X, is a new lymphocyte-stimulating determinant that is not expressed in mice with the xid defect. We favor a model that proposes two independent sites (or receptors) for X and the class II molecule. Contrary to previous models for alloreactivity, the anti-MHC site is not directed to a polymorphic receptor for self-class II epitope on the foreign class II molecule, but rather to a conserved determinant present on both self- and allo-class II molecules. If there is only one antigen receptor on the T-cell clone Ly1-03, then anti-X receptor must bind to a cross-reactive determinant found on immunogenic OVA and the non-MHC coded gene product expressed on the cell surface membrane. We further postulate that class II plus "X" recognition may be a general rule for alloreactive as well as autoreactive responses. Thus, both allo-class II and allo-class I reactive T cells are similar in that both bind a non-MHC coded gene product prior to activation.

Host immune response and pathological expression in malaria: possible implications for malaria vaccines

Recent progress in parasite immunobiology has led to the identification of several plasmodial antigens representing the target of the protective antibody response of the infected host. As a consequence, some of these antigens have been envisaged as potential malaria vaccines in man. However, in spite of these achievements, the fine mechanisms which lead to the development of a state of partial protective immunity or to the triggering of immunopathology during malaria infection are not yet fully understood. Thus, it may be appropriate to evaluate the relative importance of individual host immune responsiveness to parasite epitopes involved in the induction of immunity, or of some immunologically mediated adverse reactions such as glomerulonephritis, anaemia, thrombocytopenia, and cerebral syndrome.

Evolutionary and genetic implications of sequence variation in two nonallelic HLA-DR beta-chain cDNA sequences

Most HLA haplotypes carry two expressed DR beta-chain genes; in the DR4 haplotype, the polymorphic locus has been called DR beta 1 and the apparently nonpolymorphic locus has been called DR beta 2. We have isolated nearly full-length DR beta-chain cDNA clones representing each of these two loci from a cell line homozygous for DR4 and Dw4. The clones have been sequenced and the sequences compared with published DR beta cDNA sequences derived from other haplotypes. A comparison of our sequences with other published cDNA sequences did not allow assignment of these other sequences to either the beta 1 or beta 2 locus. Comparison of our DR4 beta 1 sequence with DR beta 1 sequences isolated from other DR4-positive cells suggests that the alleles of DR4 beta 1 may have recently diverged from a common ancestor. The apparent lack of polymorphism of DR beta 2 may in part be a reflection of this recent divergence.

Sequence analysis of the human major histocompatibility gene SX alpha

The DP subregion of the human major histocompatibility complex contains two closely linked gene pairs, DP alpha, DP beta and SX alpha, SX beta. The exon-intron organization and the complete DNA sequence of the SX alpha gene are reported here. There are several mutations within the SX alpha gene which strongly suggest that it is a pseudogene. These include two frameshift mutations, one in the alpha 1 domain and the other in the cytoplasmic domain. A 5' splice site mutation at the end of the alpha 1 exon also exists. DNA sequence homology between DP alpha and SX alpha suggests that these genes arose through a gene duplication event.