A monoclonal antibody with broad anti-HLA-DR activity fails to bind to DRw11/Dw5: possible effect of a unique polymorphism on the beta 1 domain alpha-helix

Allele-specific variation in the degeneracy of major histocompatibility complex (MHC) restriction

The role of peptides in determining immune responses for both allorecognition and antigen-specific recognition has been clearly documented. The importance of different regions of the major histocompatibility complex (MHC) class II molecule in contributing to recognition has been demonstrated by studies involving site-directed mutagenesis and exon shuffling. These studies have indicated that the N-terminal region of the MHC class II molecule has a role to play in contributing to the T-cell receptor (TCR)-MHC-peptide interaction. Variation in the importance of different regions of the MHC class II molecule may be dependent on different aspects of this interaction, such as restriction specificity and affinity of the responding T-cell clone, and the nature of the bound peptide. We demonstrate here that the degree of T-cell degeneracy may be allele dependent. Thus, a series of exon-shuffled molecules were generated by shuffling the first and second variable region of a particular DR beta 1 molecule with the third variable region of a different DR beta 1 molecule. A panel of transfectants, which expressed these hybrid molecules, was then generated and used as antigen-presenting cells (APCs). A panel of peptide-specific T-cell clones was generated using the native HLA-DR molecules as the restricting elements. For the majority of restricting alleles, HLA-DRB5*0101, HLA-DRB1*1101, and HLA-DRB1*0701, all three variable regions were required for recognition. The exception to this observation was HLA-DRB1*0401, which was degenerate. Such degeneracy may facilitate the breakdown of self-tolerance through the cross-reactive recognition of other alleles in DR4/DR"x" heterozygotes. Such an observation as this may contribute to our understanding of the etiopathology of rheumatoid arthritis, an autoimmune disease strongly associated with HLA-DRB1*0401.

Quantitative but not qualitative variation in MHC class II alters CD4 interaction and influences T cell repertoire formation

The influence of the interaction between CD4 and MHC class II molecules on selection of the T cell repertoire was studied in transgenic mice expressing human or human/mouse hybrid MHC class II beta chains. Either wild-type DR beta chains (DR1 beta) or hybrid beta chains comprising the beta1 domain of DR and the beta2, transmembrane, and intracytoplasmic domains of I-E (DRbeta 1Ebeta2) were introduced into and expressed in transgenic mice as a heterodimer with endogenous I-E alpha. Mice expressing low levels of DR1beta:I-E alpha or those expressing low or higher levels of the hybrid DRbeta 1Ebeta2:I-E alpha were studied. Immunization with a suboptimal dose of influenza nucleoprotein peptide exposed a fivefold lower frequency of DR-restricted, peptide-specific, IL-2-secreting T cells in the mice with low-level expression of DRbeta1 Ebeta2:I-E alpha when compared to mice expressing the same molecule at higher levels. The frequency in DRbeta wild-type mice was only twofold lower than that measured in mice with comparable levels of expression of DRbeta 1Ebeta2. These results suggest that positive selection is sensitive to quantitative variation in MHC class II density, unmasked when antigen is limiting, but is relatively insensitive to qualitative variation in the MHC class II: CD4 interaction.

Definition of sites on HLA-DR1 involved in the T cell response to staphylococcal enterotoxins E and C2

We have exploited the relative inefficiency of interaction between staphylococcal enterotoxins, SEE or SEC2, and H-2Ek compared to HLA-DR1 molecules to deduce which regions of the major histocompatibility complex (MHC) class II molecule are involved in the T cell response to these superantigens. Transfectants expressing hybrid DR/H-2E MHC class II molecules were used to present SEE to the T cell receptor V beta 8.1-expressing Jurkat cell line, and SEC2 to human peripheral blood T cells. For SEE, the critical region of the class II molecule for T cell reactivity and for binding was the beta 1 domain alpha-helix. The functional data were corroborated by measurements of direct binding. Sequence comparison between DR and H-2E raised the possibility that the glutamic acid at position 84 in the beta chain of H-2Ek, in place of glycine was responsible for the observed functional effects. This suggestion was supported by the finding that DQw2 (glutamine at 84) transfectants supported the SEE response much more efficiently than DQw6 that has glutamic acid at this position. In addition, amino acid substitutions at either position 36 or 39 in the DR alpha 1 domain abolished T cell reactivity without any obvious alteration in binding. For SEC2, use of transfectants expressing exon-shuffled alpha and beta chain genes showed that replacement of the alpha 1, alpha 2 and beta 1 domains with H-2E sequence inhibited the presentation of SEC2. Similarly, the substitutions at positions 36 and 39 in the alpha 1 domain abolished the T cell response to SEC2. Taken together, these data may be best explained by a model in which these two toxins have primary binding sites on the beta 1 domain (SEE) and the alpha 1 and alpha 2 domains (SEC2), but by virtue of a secondary binding site on the opposite surface of the class II molecule, cross-link two adjacent DR molecules. Such cross-linking may be important in the induction of T cell reactivity.

HLA-DR alpha chain residues located on the outer loops are involved in nonpolymorphic and polymorphic antibody-binding epitopes

The structure-function relationships of the HLA-DR alpha chain have been analyzed by identifying DR alpha residues involved in several nonpolymorphic and polymorphic antibody epitopes. Antibody binding to transfectants expressing a WT or mutant DR alpha chain with the WT DR(beta 1*0701) chain was analyzed. Our results indicate that residues 18, 36, and 39 located on the outer loops of the DR alpha chain are critical for one or more of the epitopes recognized by the SG157, Q2/70, L243, LB3.1, D1-12, and CL413 mAbs. Similar results were obtained when the DR alpha position 18 and 39 mutants were expressed with other DR beta 1 alleles. Furthermore, residues 15 and 18 of the DR alpha chain were shown to be involved in the epitopes of two polymorphic mAbs, HU-26 and I-2, whose epitopes also include residue 4 of the corresponding DR beta chains. In addition to their involvement in antibody-binding epitopes, residues in this region on the outer surface of the DR alpha chain have also been shown to be involved in superantigen binding and presentation and T-cell recognition of foreign antigen, emphasizing the functional importance of DR alpha-chain residues located outside of the peptide-binding groove.

Critical role of HLA-DR beta 1 residue 58 in multiple polymorphic epitopes recognized by xenogeneic and allogeneic antibodies

In a previous study, we identified glutamic acid at position 58 in DR (beta 1*1101) as critical for the epitopes recognized by the DRw11-specific mAb GS88.2, as well as the I-LR1 mAb that recognizes a polymorphic epitope on DR(alpha,beta 1*1101) and some DP molecules. The purpose of this study was to determine whether other polymorphic residues contribute to these epitopes and whether DR beta glutamic acid or alanine 58 and DP beta glutamic acid 56, the analogous position in DP beta, contribute to epitopes recognized by other anti-class-II mAb and allosera. Site-directed mutagenesis and transfection were used to produce cells bearing wild-type or mutant class II molecules that were analyzed with mAbs by flow cytometry and with human allosera by absorption and subsequent microcytotoxicity assays. These studies demonstrate that the residue at DR beta position 58 plays a central role in at least three different mAb epitopes and an epitope recognized by anti-DRw11 allosera. Substitution of glutamic acid for alanine at position 58 of eight DR beta chains caused gain of binding of four mAbs to all of the mutant molecules, except DR(alpha,beta 4*0101). These data suggest that the side chains of DR beta 58 and DP beta 56 point outward from the alpha-helix and directly contact antibody.

Diverse locations of amino acids in HLA-DR beta chains involved in polymorphic antibody binding epitopes on DR(alpha, beta 1*0101), DR(alpha, beta 1*1101), and DR(alpha,beta 3*0202) molecules

In a previous study, we used transfectants expressing hybrid HLA-DR(beta 1*0403)/DR(beta 1*0701) chains to map sequences involved in polymorphic antibody binding epitopes on DR(alpha, beta 1*0403) or DR(alpha, beta 1*0701) molecules. Amino acids 1-40 of the beta 1 domain were found to make the major contributions to most of the antibody binding epitopes studied. To begin to localize sequences that contribute to polymorphic antibody epitopes on DR(alpha,beta 1*0101), DR(alpha,beta 1*1101) and DR(alpha,beta 3*0202) molecules, we used indirect immunofluorescence and flow cytometry to assess the binding of mAb to transfectants expressing hybrid DR(beta 1*0101)/DR(beta 1*1101) or DR(beta 1*1101)/DR(beta 3*0202) chains that divide the DR beta chain into three segments: amino acids 1-40, 41-97, and the beta 2 domain. The results indicate that amino acids 41-97 of the beta 1 domain on DR(beta 1*0101), DR(beta 1*1101), or DR(beta 3*0202) are critical in most of the epitopes, including those recognized by human antibodies MP4 and MP12, and mouse mAb GS88.2, I-LR1, 21r5, and 7.3.19.1, whereas amino acids 1-40 of DR(beta 1*1101) are critical in the epitope recognized by the MCS-7 mAb, and both segments 1-40 and 41-97 of DR(beta 1*1101) are important in the epitopes recognized by the I-LR2 and UL-52 mAbs. Based on these data and comparison of DR beta allelic protein sequences, the residues that may play critical roles in these antibody binding epitopes are predicted.

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)