Identification of HLA-DR alpha chain residues critical for binding of the toxic shock syndrome toxin superantigen.

Staphylococcal toxic shock syndrome toxin 1 (TSST-1) binds to major histocompatibility complex class II molecules, and the toxin-class II complexes induce proliferation of T cells expressing V beta 2 sequences. To define the residues involved in TSST-1 binding, a set of transfectants expressing 21 HLA-DR alpha chain mutants were analyzed for their abilities to bind and present TSST-1 and to present an antigenic peptide. Mutations at DR alpha positions 36 and 39 markedly decreased the ability of the DR7 molecule to bind and present TSST-1 but did not affect the ability to present an antigenic peptide. These data indicate that DR alpha residues 36 and 39, predicted to be located on an outer loop, are important in the formation of the TSST-1 binding site on DR molecules.

The role of polymorphic HLA-DR beta chain residues in presentation of viral antigens to T cells.

The relative importance of 11 polymorphic positions in the HLA-DR7 beta 1 chain in T cell recognition of foreign antigens was investigated using transfectants expressing mutant DR7 beta 1 chains as APC for five rabies virus-specific T cell clones. The results indicate that multiple amino acids, located in both the beta-strands and alpha-helix of DR7 beta 1 in the model of a class II molecule, are involved in DR7-restricted T cell recognition of these antigens. Many of the substitutions appeared to reduce the affinity of an antigenic peptide for the mutant DR7 molecules but did not prevent binding. The heterogeneity of responses of the three G-specific T cell clones to presentation of the G11.3 peptide by several of the mutant DR7 molecules indicates that the T cell receptor (TCR) of each these clones requires a different view of the G11.3/DR7 complex and raises the possibility that the G11.3 peptide may bind to the DR7 molecule in more than one conformation.

The complexity of HLA-DS molecules. A homozygous cell line expresses multiple HLA-DS alpha chains.

Ia molecules expressed by an HLA-DRw6 homozygous cell line were immunoprecipitated with anti-Ia allosera and monoclonal antibodies and analyzed by 2-D gel electrophoresis. The DRw6 homozygous cell line was shown to express two DS beta chains; this observation extends our previous finding that a DR5 homozygous cell line expresses two DS beta chains and suggests that the expression of at least two DS beta chains by DR homozygous cell lines is a generalized phenomenon. The data presented here document for the first time that a DR homozygous cell line expresses at least two DS alpha chains. Therefore, this cell line expresses at least two DS molecules with the potential for the expression of four DS molecules. In agreement with previous reports, the cell line was shown to express two DR beta chains and one DR alpha chain that combine to form two DR molecules. The molecular specificities of two MB1 allosera and two MB1 -like monoclonal antibodies were also compared in these studies. Both MB1 allosera isolated a single DS molecule, while the MB1 -like monoclonal antibodies isolated at least two DS molecules. Therefore, these studies document for the first time that anti-Ia reagents which are specific for the MB1 or MB1 -like determinants in population studies do not recognize the same Ia molecules in immunochemical studies. The data presented here for the expression of at least two DS alpha chains and the location of the MB1 allodeterminant on only one of multiple DS molecules are in agreement with recent studies at the gene level.

Peptide binding specificity of HLA-DR4 molecules: correlation with rheumatoid arthritis association.

We have investigated whether sequence 67 to 74 shared by beta chains of rheumatoid arthritis (RA)-associated HLA-DR molecules imparts a specific pattern of peptide binding. The peptide binding specificity of the RA-associated molecules, DRB1*0401, DRB1*0404, and the closely related, RA nonassociated DRB1*0402 was, therefore, determined using designer peptide libraries. The effect of single key residues was tested with site-directed mutants of DRB1*0401. The results have demonstrated striking differences between RA-linked and unlinked DR allotypes in selecting the portion of peptides that interacts with the 67-74 area. Most differences were associated with a single amino acid exchange at position 71 of the DR beta chain, and affected the charge of residues potentially contacting position 71. The observed binding patterns permitted an accurate prediction of natural protein derived peptide sequences that bind selectively to RA-associated DR molecules. Thus, the 67-74 region, in particular position 71, induces changes of binding specificity that correlate with the genetic linkage of RA susceptibility. These findings should facilitate the identification of autoantigenic peptides involved in the pathogenesis of RA.

An HLA-DR5 homozygous cell line expresses two DS (I-A-like) molecules.

Previous studies have indicated that LLA-DR homozygous cell lines express two DR molecules but only a single DS (I-A-like) molecule. This report demonstrates that an HLA-DR5 homozygous cell line expresses at least two distinct DS molecules. These two DS molecules are formed by the association of a single DS alpha chain with either of two DS beta chains. Four distinct Ia molecules have now been identified from this DR5 homozygous cell line.

Pocket 4 of the HLA-DR(alpha,beta 1*0401) molecule is a major determinant of T cells recognition of peptide.

To investigate the functional roles of individual HLA-DR residues in T cell recognition, transfectants expressing wild-type or mutant DR(alpha,beta 1*0401) molecules with single amino acid substitutions at 14 polymorphic positions of the DR beta 1*0401 chain or 19 positions of the DR alpha chain were used as antigen-presenting cells for five T cell clones specific for the influenza hemagglutinin peptide, HA307-19. Of the six polymorphic positions in the DR beta floor that were examined, mutations at only two positions eliminated T cell recognition: positions 13 (four clones) and 28 (one clone). In contrast, individual mutations at DR beta positions 70, 71, 78, and 86 on the alpha helix eliminated recognition by each of the clones, and mutations at positions 74 and 67 eliminated recognition by four and two clones, respectively. Most of the DR alpha mutations had minimal or no effect on most of the clones, although one clone was very sensitive to changes in the DR alpha chain, with loss of recognition in response to 10 mutants. Mutants that abrogated recognition by all of the clones were assessed for peptide binding, and only the beta 86 mutation drastically decreased peptide binding. Single amino acid substitutions at polymorphic positions in the central part of the DR beta alpha helix disrupted T cell recognition much more frequently than substitutions in the floor, suggesting that DR beta residues on the alpha helix make relatively greater contributions than those in the floor to the ability of the DR(alpha,beta 1*0401) molecule to present HA307-19. The data indicate that DR beta residues 13, 70, 71, 74, and 78, which are located in pocket 4 of the peptide binding site in the crystal structure of the DR1 molecule, exert a major and disproportionate influence on the outcome of T cell recognition, compared with other polymorphic residues.

Mice deficient in IL-1beta manifest impaired contact hypersensitivity to trinitrochlorobenzone.

Mice rendered deficient in IL-1 beta by gene targeting in embryonic stem cells develop and grow normally in a protected laboratory environment. Endotoxin-stimulated peritoneal macrophages from IL-1beta-deficient mice showed normal synthesis and cellular release of IL-1alpha after treatment with 5 mM ATP demonstrating that IL-1beta is not necessary for expression and release of the IL-1alpha isoform. Mice deficient in IL-1beta showed unaltered sensitivity to endotoxic shock, with or without pretreatment with D-galactosamine. In contrast, IL-1beta-deficient mice showed defective contact hypersensitivity responses to topically applied trinitrochlorobenzene (TNCB). This defect could be overcome either by application of very high doses of sensitizing antigen, or by local intradermal injection of recombinant IL-1beta immediately before antigen application. These data demonstrate an essential role for IL-1beta in contact hypersensitivity and suggest that IL-1beta acts early during the sensitization phase of response. They suggest an important role for IL-1beta in initiation of the host of response at the epidermal barrier.

Demonstration of a third structurally distinct human Ia beta chain by two-dimensional gel electrophoresis.

Previous studies have indicated that HLA-DR homozygous cell lines express two Ia alpha and Ia beta chains that combine to form at least two Ia molecules. This report demonstrates by two-dimensional gel electrophoresis the existence of a third structurally distinct human Ia beta chain on DR2 and DR5 cell lines. This suggests that at least five separate genes control the expression of Ia molecules on HLA-DR homozygous cell lines.

Structural identity of human histocompatibility leukocyte antigen-B27 molecules from patients with ankylosing spondylitis and normal individuals.

Although the association between human histocompatibility leukocyte antigen (HLA) B27 and ankylosing spondylitis is the prototype of HLA-disease association, the mechanism underlying these associations has not been determined. We have investigated the possibility that the B27 molecules from patients with ankylosing spondylitis are different from those of normals, and only the "different" molecules predispose the individual to disease. Biosynthetically radiolabeled HLA-B27 molecules from patients with ankylosing spondylitis and normal individuals were compared by two-dimensional gel electrophoresis and tryptic peptide mapping with high pressure liquid chromatography. Extensive charge heterogeneity in the 45,000-dalton heavy chain was detected when B27 molecules were analyzed by two-dimensional gel electrophoresis; the charge heterogeneity was reduced, but not eliminated, when the B27 molecules were treated with neuraminidase to remove sialic acid residues before analysis. No structural difference in the B27 molecules from an ankylosing spondylitis patient and a normal individual were detected by two-dimensional gel electrophoresis. Analysis of [(3)H]leucine-labeled and [(3)H]arginine-labeled tryptic peptides and chymotryptic peptides of the trypsin insoluble material by reverse-phase high pressure liquid chromatography revealed identity of the B27 molecules from ankylosing spondylitis patients and normal individuals. These studies indicate that development of akylosing spondylitis in only some B27 positive individuals is not attributable to those individuals possessing variant B27 molecules.

Collagen-induced arthritis in the BB rat. Prevention of disease by treatment with CTLA-4-Ig.

Antigen-specific T cell activation requires two independent signalling events, one mediated through T cell receptor engagement by the antigen-presenting cell-expressed peptide/class II major histocompatibility complex, and the second through the cognate interactions of costimulatory molecules expressed on the T cell and antigen-presenting cell. There is evidence from in vitro and in vivo experimental systems suggesting that the CD28/B7 costimulatory pathway is crucial for induction of maximal T cell proliferation and T helper-B cell collaboration for IgG production. This pathway can be blocked by CTLA-4-Ig, a soluble form of CTLA-4 which binds with high avidity to the CD28 ligands, B7-1 and B7-2. Here, we show that CTLA-4-Ig treatment prevents clinical and histological manifestations of disease in a collagen-induced arthritis model of rheumatoid arthritis in the diabetes resistant BB/Wor rat, when therapy is initiated before immunization with bovine type II collagen (BIIC). Anti-BIIC antibody titers are reduced in CTLA-4-Ig-treated rats compared to diseased control animals. Histologically, joints from CTLA-4-Ig-treated animals show no histological abnormalities, in contrast to control antibody-treated animals, which show complete erosion of the articular cartilage and bone. Despite the efficacy of CTLA-4-Ig in preventing clinical and histological signs of arthritis and reducing antibody responses to BIIC, delayed type hypersensitivity responses to collagen 18 d or more after CTLA-4-Ig treatment ends are similar in CTLA-4-Ig-treated and untreated rats, suggesting that the prolonged disease suppression observed does not result from induction of T cell anergy.

Long-term inhibition of murine experimental autoimmune encephalomyelitis using CTLA-4-Fc supports a key role for CD28 costimulation.

T cell activation involves not only recognition of antigen presented by the MHC, but also nonspecific interactions termed "costimulation." The costimulatory molecules B7-1 and B7-2 are ligands on antigen-presenting cells for the CD28 and CTLA-4 receptors on T cells. Previously, a fusion protein consisting of human CTLA-4 linked to human Fc was shown to bind B7-1 and B7-2 with high avidity and to prevent specific T cell activation. Here we investigated the effects of a recombinant fusion protein consisting of the extracellular domain of human CTLA-4 bound to mouse IgG2a Fc (CTLA-4-Fc) upon experimental autoimmune encephalomyelitis, a T cell-mediated disease that serves as a model for multiple sclerosis. CTLA-4-Fc prevented experimental autoimmune encephalomyelitis in 26 of 28 CTLA-4-Fc-treated mice (median maximum score 0), whereas 28 of 30 mice treated with control mouse IgG2a developed disease (median maximum score 2.75). Less inflammation and virtually no demyelination or axonal loss occurred in CTLA-4-Fc-treated compared with control-treated mice. Activated splenocytes from CTLA-4-Fc-treated mice were able to transfer disease adoptively to naive recipients. These results indicate a key role for the B7/CD28 system in the development of actively induced murine experimental autoimmune encephalomyelitis, suggesting an area of investigation with therapeutic potential for multiple sclerosis.

Negative and positive regulation of human leukocyte antigen class I gene transcription in K562 leukemia cells.

The mechanism of transcriptional activation of human leukocyte antigen class I genes by gamma interferon and 5-azacytidine was studied in K562 human leukemia cells. Nuclear run-on transcription assays with various protein and RNA synthesis inhibitors yield evidence for both stimulation of a positive regulatory factor and inhibition of an mRNA that codes for a labile repressor. A novel mechanism is proposed to explain how 5-azacytidine can activate repressed genes without affecting DNA methylation.

Gamma interferon and 5-azacytidine cause transcriptional elevation of class I major histocompatibility complex gene expression in K562 leukemia cells in the absence of differentiation.

We studied the effects of gamma interferon (IFN-gamma) on HLA class I gene expression, differentiation, and proliferative capacity of K562 human leukemia cells. In the uninduced state, K562 cells show little or no class I gene expression but actively express the erythroid-specific gamma-globin gene as well as genes associated with cell proliferation, including the transferrin receptor, c-myc, and alpha-actin genes At both the surface protein and mRNA levels, IFN-gamma induces class I and beta 2-microglobulin gene expression, but does not alter the expression of the gamma-globin, transferrin receptor, c-myc, or alpha-actin genes. A 10-fold maximal induction of both class I surface protein and mRNA occurs at 48 h and is reversible upon withdrawal of IFN-gamma from the culture medium. In vitro nuclear run-on transcription assays were performed to directly establish that IFN-gamma exerts an early effect at the level of transcription, with maximal transcription rates occurring within 4 h. The difference between the time course of transcription induction and that of mRNA accumulation suggests that the regulation of class I gene expression in this human leukemic cell line also involves posttranscriptional mechanisms. Measurements of cell proliferation rates and cell cycle distribution, as well as the reversibility of the effects of IFN-gamma, demonstrate that the selective induction of class I genes in these cells occurs in the absence of differentiation.

Functional activity of staphylococcal enterotoxin A requires interactions with both the alpha and beta chains of HLA-DR.

The staphylococcal enterotoxins, SEA and SEE, bind one zinc atom per molecule of protein. The presence of this metal atom enhances the binding of the toxins to MHC class II molecules, presumably through an interaction with histidine 81 of the beta chain. L cell transfectants expressing HLA-DR1 and HLA-DR7 molecules, with mutations in either the alpha1 or beta1 domains, were tested for their ability to bind SEA and present it to T cells. Cells expressing DR1 molecules with alanine at positions 77, 78, 80, 83, 84 and 85, or serine at position 79 could all bind SEA and present it to either polyclonal or monoclonal T cells. Most point mutations within the alpha-helical portion of the DR7 beta chain had no effect on binding and presentation. However, substitution of histidine 81 with alanine, glutamate, or aspartate, abrogated SEA binding as well as T cell stimulation by the superantigen. This effect was also observed when the non-polymorphic aspartate, at position 76 was changed to alanine. Mutation of the asparagine at position 82 had an intermediate effect. Point mutations of the DR alpha chain had little effect on binding of SEA as determined by a flow cytometric assay. However, mutation of lysine at position 39 of the alpha chain and, to a lesser extent methionine at position 36, markedly decreased the ability of SEA to stimulate toxin-responsive mouse T cell hybridomas. Finally, the monoclonal antibody, L243 binds to the alpha chain of HLA-DR, and was able to block T cell activation by SEA without blocking SEA binding. These data support the model whereby HLA-DR has two binding sites for SEA. A low affinity site, present on the alpha chain, is required for T cell stimulation by the superantigen, but is insufficient to mediate toxin binding. High affinity binding of HLA-DR to SEA occurs solely through residues on the beta chain, including both histidine 81 and aspartate 76.

Heterogeneous MHC II restriction pattern of autoreactive desmoglein 3 specific T cell responses in pemphigus vulgaris patients and normals.

Pemphigus vulgaris is a life threatening bullous autoimmune disease of the skin mediated by autoantibodies against desmoglein 3 (Dsg3) on epidermal keratinocytes. Pemphigus vulgaris patients exhibit T cell responses against Dsg3 that may serve as a target to modulate the production of pathogenic autoantibodies. Healthy carriers of major histocompatibility complex class II alleles identical or similar to those that are highly prevalent in pemphigus vulgaris, namely DRbeta1*0402 and DRbeta1*1401, also mount T cell responses against Dsg3. We thus wanted to determine whether these prevalent major histocompatibility complex class II alleles restricted Dsg3 specific T cell responses. A CD4+ T cell line from the DRbeta1*0402+ patient PV9 was stimulated by Dsg3 with DRbeta1*0402+ L cells as antigen-presenting cells. A CD4+ T cell line and six CD4+ T cell clones from the DR11/14+ patient PV8, and six CD4+ T cell clones from the DR11+ healthy donor C6, required DR11/ DQbeta1*0301+ peripheral blood mononuclear cells but not DR11+ L cells as antigen-presenting cells and were strongly inhibited by anti-DQ antibodies, indicating that they were restricted by HLA-DQbeta1*0301. A CD4+ T cell line and three T cell clones from the DR11+ healthy donor C11 were differentially stimulated by Dsg3 with L cells expressing one of several DR11 alleles. T cell recognition of Dsg3 was thus not only restricted by the pemphigus vulgaris associated DRbeta1*0402 allele, but also by several DR11 alleles, some of which are highly homologous to DRbeta1*0402, and by HLA-DQbeta1*0301.

CTLA-4-Fc treatment of ongoing EAE improves recovery, but has no effect upon relapse rate. Implications for the mechanisms involved in disease perpetuation.

Several laboratories including ours have shown that T cell co-stimulation mediated through B7-1 or B7-2 is critical to the initiation of EAE. The role of T cell co-stimulation in ongoing EAE is less clear. In the present study, 32 mice with established EAE were randomly assigned to receive treatment with either CTLA-4-Fc or control Ig. Mice were followed daily by clinical scoring for 2 months post-immunization. A significant improvement in the degree of recovery following the acute episode and following relapses of EAE was observed in those mice randomized to CTLA-4-Fc treatment. Full clinical remission occurred twice as often in the CTLA-4-Fc group as in those mice receiving placebo, whereas placebo-treated mice were more likely to develop a stable prolonged neurologic deficit. Serial clinical scoring revealed no effect of CTLA-4-Fc upon relapse rate, with greater than 80% of the mice in each group displaying at least one clinical EAE relapse. In that the activation of memory T cells is relatively independent of T cell co-stimulation, these results indicate that development of chronic disease is associated with the activation of naive T cells and the recruitment of the latter cells into the disease process. Blocking B7 molecules may be beneficial in the treatment of established CNS inflammatory demyelinating diseases such as multiple sclerosis.

HPRT mutant T-cell lines from multiple sclerosis patients recognize myelin proteolipid protein peptides.

Mutation of the hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene in a T-cell is believed to be an indication that the T-cell has been activated and has proliferated in vivo. HPRT mutant T-cell lines were generated from peripheral blood mononuclear cells from patients with MS and control subjects. More lines were isolated from the MS patients than from the control subjects. Using stringent criteria for recognition, none of the lines from MS-affected or control subjects recognized intact myelin basic protein (MBP) or myelin proteolipid protein (PLP) molecules. Using stringent criteria, two of the 10 MS patients harbored mutant lines each recognizing distinct PLP peptides (PLP peptide 40-60 recognized by 3 lines from one patient and PLP peptide 178-191 recognized by 2 lines from the other patient). A single line recognizing PLP peptide 89-106 was derived from 1 of 7 normal controls. HPRT mutant lines recognizing multiple epitopes of PLP which spanned much of the molecule could be isolated from MS patients, and to a lesser extent, normal subjects.

The molecular specificities of DS-specific reagents: an MB3-like monoclonal antibody isolates two DS molecules.

HLA-DS molecules are the human homologues of murine I-A molecules. The molecular specificities of four anti-DS reagents were examined by two-dimensional gel electrophoresis in light of the recent evidence that HLA-DR homozygous cell lines express at least two DS molecules. Each of the DS-specific reagents, including the IVD12 monoclonal antibody which defines an MB3-like determinant, isolated at least two DS molecules from a DR5 homozygous cell line. Because previous studies of this cell line documented that anti-MB3 allosera isolated only one DS molecule, these data indicate that there is heterogeneity of the molecular specificities of anti-Ia reagents that are specific for the MB3 allodeterminant or the MB3-like determinant in population studies.

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.

Identification of amino acids in HLA-DPw4b beta and -DR5 beta 1 chains that are involved in antibody binding epitopes using site-directed mutagenesis and DNA-mediated gene transfer.

Based on comparisons of the amino acid sequences of the beta chains of HLA class II molecules that do or do not bind the I-LR1 monoclonal antibody, we predicted that glutamic acid 56 of I-LR1-positive DPw2, DPw3, and DPw4b beta chains and the analogous glutamic acid 58 of I-LR1-positive DR5 beta 1 chains are involved in the I-LR1 epitope. Site-directed mutagenesis of DPw4b beta and DR5 beta 1 cDNAs was used to change the codons for glutamic acid 56 in DPw4b beta and glutamic acid 58 in DR5 beta 1 to the codon for alanine found in I-LR1-negative beta chains. Transfectants expressing wild-type DPw4b beta chains or DR5 beta 1 chains bind the I-LR1 monoclonal antibody, whereas transfectants expressing the mutant DPw4b beta or DR5 beta 1 chains do not bind I-LR1. Therefore, DPw4b beta glutamic acid 56 and DR5 beta 1 glutamic acid 58 are involved in the epitope recognized by the I-LR1 monoclonal antibody. Interestingly, the DR5 beta 1 glutamic acid----alanine 58 substitution also causes the loss of binding of two DR5-specific monoclonal antibodies to DR5 beta 1 molecules. Because the sequences of amino acids 36 to 64 of the DPw4b beta chain and 38 to 66 of the DR5 beta 1 chain are identical, these data raise some interesting issues about the formation of antibody epitopes on class II molecules.