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PubMed1998

Matrix-assisted laser desorption ionization/mass spectrometry mapping of human immunodeficiency virus-gp120 epitopes recognized by a limited polyclonal antibody.

In this study we have applied epitope excision and epitope extraction strategies, combined with matrix assisted laser desorption/ionization mass spectrometry, to determine the fine structure of epitopes recognized by a polyclonal antibody to human immunodeficiency virus envelope glycoprotein gp120. This is the first application of this approach to epitope mapping on a large, heavily glycosylated protein. In the epitope excision method, gp120 in the native form is first bound to the antibody immobilized on sepharose beads and cleaved with endoproteinase enzymes. In the epitope extraction method, the gp120 was first proteolytically cleaved and then allowed to react with the immobilized antibody. The fragments that remain bound to the antibody, after repeated washing to remove the unbound peptides, contain the antigenic region that is recognized by the antibody, and the bound peptides in both methods can be characterized by direct analysis of the immobilized antibody by matrix assisted laser desorption ionization/mass spectrometry. In this study we have carried out epitope excision and extraction experiments with three different enzymes and have identified residues 472-478 as a major epitope. In addition, antigenic regions containing minor epitopes have also been identified.

Amino Acid Sequence↗
PubMed1996

Mass spectrometric mapping of protein epitope structures of myocardial infarct markers myoglobin and troponin T.

Monoclonal antibodies are widely used analytical tools in biochemical research. The knowledge of their corresponding epitopes is of major interest. One possible approach for epitope characterization is the application of protein antigen proteolysis in combination with mass spectrometric peptide mapping analysis. Two complementary analytical strategies were applied: (a) limited proteolysis of antibody-bound antigen followed by removal of nonbound peptides and detachment of the antigenic peptides (epitope excision) and (b) enzymatic digest of the antigen followed by extraction of the antigenic peptides with the antibody and detachment of antigenic peptides after removal of nonbinding fragments (epitope extraction). In the few examples published so far, immobilized antibodies were used for these studies. In this study we present a method for characterization of the epitope sequences without prior immobilization of the monoclonal antibody. The separation of nonepitope peptides from antibody-bound peptides was carried out by ultrafiltration. The epitope and nonepitope fractions were analyzed by MALDI-MS without further purification, and the epitope sequences were identified. The method was developed using a model system consisting of the synthetic C-terminal cyanogen bromide fragment CB3 of myoglobin and the commercial monoclonal anti-myoglobin MG1. In further investigations the epitope sequence of a synthetic 32 amino acid peptide derived from heart muscle protein troponin T toward a monoclonal antibody MAb-M7, which was raised against the intact protein, was characterized. With this approach the epitope binding site of this antibody was determined, and selective shielding of potential cleavage sites in the immune complex could be observed. Furthermore, statements about the three-dimensional structure of the bound antigen were made.

Amino Acid Sequence↗
PubMed2000

Characteristics of haemopoietic progenitor cells related to CD34 epitope class expression.

Haemopoietic progenitor cells (HPCs) express the CD34 molecule, a heavily glycosylated transmembrane protein displaying three main classes of epitopes. The CD34 epitope class expression may vary between different subsets of HPCs. The aim of this study was to characterise the subsets of HPCs expressing CD34 class II and III epitopes. The cells were studied for coexpression of activation-, lineage- and adhesion-associated molecules, and their clonogenic ability and morphological features were examined. CD34+ HPCs expressing class III epitopes outnumbered those expressing class II. Class III expressing HPCs were enriched for CFU-GM and BFU-E and cells coexpressing CD13, CD33, c-kit and CD71 compared to class II expressing HPCs. CD34+ cells exclusively expressing class III epitopes uniformly displayed CD13 and CD33; they had a high clonogenic capacity and morphological characteristics of promyelocytes and myelocytes. The data show that class III epitopes are distributed more broadly on CD34+ HPCs than are class II epitopes, and that lack of class II epitopes is confined to CD34+ HPCs at a late stage of myeloid differentiation. The higher number of class III expressing HPCs coexpressing c-kit and CD71 suggests that these cells exhibit a higher proliferative or differential potential than do HPCs expressing class II epitopes.

Antigens, CD34↗
PubMed1999

Identification of isoform-specific T-cell epitopes in the major timothy grass pollen allergen, Phl p 5.

BACKGROUND: The involvement of CD4+ T cells in the pathophysiology of atopic disease is well established. OBJECTIVE: To gain further insight into the activation requirements for allergen-specific T cells, we characterized epitope specificity, HLA restriction and T-cell receptor (TCR) usage for T cells specific to Phl p 5, the group 5 major allergen of the grass Phleum pratense. METHODS: To identify the T-cell epitopes of Phl p 5, three Phl p 5-specific T-cell lines (TCLs) and 15 T-cell clones (TCCs) generated from the peripheral blood of three grass-allergic patients were tested with recombinant truncated Phl p 5a fragments and synthetic Phl p 5b peptides representing these two different recombinant Phl p 5 isoallergens. Additional activation experiments with HLA-subtyped antigen-presenting cells and flow cytometry analysis with TCR V-specific mAb were performed to further characterize the activation requirements for Phl p 5-specific TCCs. RESULTS: At least nine distinct T-cell specificities were identified and the T-cell epitopes recognized differed considerably among the three patients. Most of the epitopes found were isoform-specific, whereas three epitopes were shared between Phl p 5a and 5b. Several human leucocyte antigen (HLA) class II molecules were involved in the recognition of Phl p 5. Different HLA restriction specificities were even found among TCCs specific to the same epitope region. All TCCs were TCR-alpha/beta positive, and an overrepresentation of TCR Vbeta 3.1+ clones among TCCs specific to Phl p 5 appear to exists as 31% (4/13) of the TCCs expressed TCR Vbeta 3.1 (compared with 5% TCR Vbeta 3.1+ T cells in human peripheral blood) with no correlation with epitope specificity or HLA restriction. CONCLUSION: The T-cell reactivity of the three grass-allergic patients investigated shows that isoallergen-specific T-cell epitopes are found throughout the peptide backbone of Phl p 5a and Phl p 5b, and dominant T-cell epitopes of Phl p 5 were not identified. This indicates that a mixture of at least full-length rPhl p 5a and rPhl p 5b may be required to target the total Phl p 5-specific T-cell response of atopic patients.

Allergens↗
PubMed1998

Differential activation requirements associated with stimulation of T cells via different epitopes of CD3.

A panel of monoclonal antibodies directed to different epitopes of porcine CD3 were employed to investigate stimulation requirements of porcine T lymphocytes. It was found that epitope specificity was an important property of the anti-CD3 antibodies that determined the requirements for T-cell proliferation. Thus, T-cell proliferation induced by triggering different CD3 epitopes showed three different requirements: (a) proliferation induced by the most insensitive epitope required both epitope ligation and some unknown additional signal(s); (b) proliferation induced by the most common epitopes only required epitope ligation, either by monocytes or by immobilization; (c) proliferation induced by the most sensitive epitope required neither epitope ligation nor participation of antigen-presenting cells (APC). These findings may help to explain the previous confusion over the requirements for T-cell activation through the CD3 pathway. Finally, the above conclusions apply only to alpha beta T cells, as porcine gamma delta T cells, either in bulk culture or isolated, did not proliferate in response to anti-CD3 stimulation. Therefore, the mechanism underlying gamma delta T-cell activation may be different from that of alpha beta T cells.

Animals↗
PubMed1998

The role of the different CD34 epitopes in detection and positive selection of CD34+ bone marrow and peripheral blood stem cells.

Positive selection of CD34+ cells is an attractive approach to reduce tumour cell contamination in bone marrow (BM) and peripheral blood progenitor cell (PBPC) autografts in malignancies not expressing CD34. All current selection methods use monoclonal antibodies (MoAbs) specific for the class I or class II CD34 epitopes, while for detection most investigators use class III MoAbs. Since the distribution of the different CD34 epitopes on haematopoietic progenitors differs, we studied their significance in CD34+ selection procedures. Testing MoAbs against class I, II and III CD34 epitopes on normal BM we observed that +/- 23% of class III positive cells was class I negative. A higher expression of the class III epitope compared with classes I or II was observed on the KG1 cell line, whereas no differences in binding capability were found. The class III epitope anti-CD34, 561, was compared with the class I epitope anti-CD34, BI-3C5, both coupled to M450 Dynabeads. The yield of CD34+ cells obtained with the 561 beads was 1.7% of the mononuclear cells versus 0.95% using the class I epitope, a 1.95-fold increase (1.3-2.7), whereas the purity was similar (96% in both cases). The absolute number of CD34+ cells was therefore twofold higher after 561 selection, including cells with a more mature phenotype. In single cell assay comparable numbers of highly proliferative progenitors but higher numbers of differentiated colonies per phenotypic subfraction were measured. In conclusion, M450 beads coated with the 561 anti-class III CD34 epitope are more efficient in isolating CD34+ cells from bone marrow, probably due to a broader distribution of the class III epitope.

Antibodies, Monoclonal↗
PubMed2002

Large-scale computational identification of HIV T-cell epitopes.

Bioinformatics-driven T-cell epitope-identification methods can enhance vaccine target selection significantly. We evaluated three unrelated computational methods to screen Pol, Gag and Env sequences extracted from the Los Alamos HIV database for HLA-A*0201 and HLA-B*3501 T-cell epitope candidates. The hidden Markov model predicted 389 HLA-B*3501-restricted candidates from 374 HIV-1 and 97 HIV-2 sequences. The artificial neural network (ANN) model, and Bioinformatics and Molecular Analysis Section (BIMAS) quantitative matrix predictions for A*0201 yielded 1122 HIV-1 and 548 HIV-2 candidates. The overall sequence coverage of the predicted A*0201 T-cell epitopes was 2.7% (HIV-1)and 3.0% (HIV-2). HLA-B*3501-predicted epitopes covered 0.9% (HIV-1) and 1.4% (HIV-2) of the total sequence. Comparison of 890 ANN- and 397 BIMAS-derived HIV-1 A*0201- restricted epitope candidates showed that only 13-19% of the predicted and 26% of the experimentally confirmed T-cell epitopes were captured by both methods. Extrapolating these results, we estimated that at least 247 predicted HIV-1 epitopes are yet to be discovered as active A*0201-restricted T-cell epitopes. Adequate comparison and combined usage of various predictive bioinformatics methods, rather than uncritical use of any single prediction method, will enable cost-effective and efficient T-cell epitope screening.

Computational Biology↗
PubMed2002

B-cell epitopes as a screening instrument for persistent cow's milk allergy.

BACKGROUND: Cow's milk is one of the most common causes of food allergy in the first years of life. We recently defined IgE-binding epitopes of all 6 major cow's milk proteins (alpha(s1)-, alpha(s2)-, beta-, and kappa-casein; alpha-lactalbumin; and beta-lactoglobulin) and had some evidence suggesting that IgE antibodies from patients with persistent cow's milk allergy (CMA) recognize different epitopes on cow's milk proteins than do those from patients who were likely to outgrow their allergy. OBJECTIVE: In this study we sought to assess whether recognition of IgE antibodies of certain epitopes of cow's milk proteins would clearly separate the patients with life-long CMA from those who will become clinically tolerant to cow's milk. METHODS: According to the known IgE-binding regions of cow's milk proteins, 25 decapeptides of alpha(s1)-casein, alpha(s2)-casein, kappa-casein, alpha-lactalbumin, and beta-lactoglobulin, comprising the core epitopes, were synthesized on a cellulose-derivatized membrane. Sera from 10 patients with persistent CMA and 10 patients who subsequently outgrew their milk allergy were used to investigate the differences in epitope recognition. RESULTS: Five IgE-binding epitopes (2 on alpha(s1)-casein, 1 on alpha(s2)-casein, and 2 on kappa-casein) were not recognized by any of the patients with transient CMA but showed binding by the majority of the patients with persistent allergy. The presence of IgE antibodies against at least 1 of 3 epitopes (amino acid [AA] 123-132 on alpha(s1)-casein, AA 171-180 on alpha(s2)-casein, and AA 155-164 on kappa-casein) identified all patients with persistent CMA. CONCLUSIONS: The presence of IgE antibodies to distinct allergenic epitopes of cow's milk proteins can be used as a marker of persistent CMA. Prospective studies are needed to investigate the usefulness of these informative epitopes in predicting life-long CMA in young children.

Adolescent↗
PubMed2004

Peptide mapping of a novel discontinuous epitope of the major surface adhesin from Streptococcus mutans.

Guy's 13 is a mouse monoclonal antibody that specifically recognizes the major cell-surface adhesion protein SA I/II of Streptococcus mutans, one of the major causative agents of dental caries. Passive immunization with Guy's 13 prevents bacterial colonization in humans. To help elucidate the mechanism of prevention of colonization conferred by this antibody, the SA I/II epitope recognized by Guy's 13 was investigated. It was previously established that the epitope is conformational, being assembled from two non-contiguous regions of SA I/II. In the current study, using recombinant fragments of SA I/II and, ultimately, synthetic peptides, the discontinuous epitope was localized to residues 170-218 and 956-969. This work describes the mapping of a novel discontinuous epitope that requires an interaction between each determinant in order for epitope assembly and recognition by antibody to take place. Guy's 13 binds to the assembled epitope but not to these individual epitope fragments. The assembled epitope results from the interaction between the individual antigenic determinants and can be formed by mixing together determinants present on separate polypeptide chains. The data are consistent with one of the epitope fragments adopting a polyproline II-like helical conformation.

Adhesins, Bacterial↗
PubMed1993

Epitope-specific enhancement of antigen presentation by invariant chain.

The MHC class II-associated invariant chain (Ii) is involved in the intracellular sorting of class II molecules to the endocytic pathway where peptides from processed exogenous antigens are bound, and thereby Ii is thought to enhance antigen presentation. Here we demonstrate that presentation of only one out of five epitopes of a given antigen is augmented by Ii. We have compared the presentation of five different epitopes derived from hen egg white lysozyme (HEL) to Ak-restricted T hybridomas by rat-2 fibroblasts transfected with A alpha k and A beta k (RKK) and RKK cells supertransfected with the mouse invariant chain (RKKI). Only the presentation of the HEL epitope 46-61 was enhanced whereas the presentation of the HEL epitopes 25-43, 34-45, 112-124, and 116-129 was unchanged or even slightly diminished in RKKI cells. The presentation of the epitopes 25-43 and 34-45 was virtually insensitive to the lysosomotropic reagent chloroquine. Brefeldin A (BFA), which inhibits protein egress from the endoplasmic reticulum, blocked the presentation of all epitopes tested in RKKI cells. In contrast, in Ii-negative RKK cells only the presentation of the epitope HEL(46-61) was inhibited by BFA and the presentation of the epitopes 25-43 and 34-45 was only slightly impaired. These findings suggest that Ii may target class II molecules to selected endosomal subcompartments involved in the processing of different peptides derived from an endocytosed antigen. As a result, the enhancement of the class II-restricted presentation in Ii expressing cells appears to be epitope specific rather than antigen specific.

Animals↗
PubMed1994

Higher autoantibody levels and recognition of a linear NH2-terminal epitope in the autoantigen GAD65, distinguish stiff-man syndrome from insulin-dependent diabetes mellitus.

The smaller form of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD65) is a major autoantigen in two human diseases that affect its principal sites of expression. Thus, destruction of pancreatic beta cells, which results in insulin-dependent diabetes mellitus (IDDM), and impairment of GABA-ergic synaptic transmission in Stiff-Man syndrome (SMS) are both characterized by circulating autoantibodies to GAD65. Anti-GAD65 autoantibodies in IDDM are predominantly directed to conformational epitopes. Here we report the characterization of humoral autoimmune responses to GAD65 in 35 SMS patients, of whom 13 (37%) also had IDDM. All SMS patients immunoprecipitated native GAD65 and the main titers were orders of magnitude higher than in IDDM patients. Furthermore, in contrast to the situation in IDDM, autoantibodies in 35 of 35 (100%) of SMS patients recognized denatured GAD65 on Western blots. Two major patterns of epitope specificity were identified on Western blots. The first pattern, detected in 25 of 35 SMS patients (71%), of whom 11 had IDDM (44%), was predominantly reactive with a linear NH2-terminal epitope residing in the first eight amino acids of GAD65. Nine of nine individuals who were HLA-haplotyped in this group carried an IDDM susceptibility haplotype and HLA-DR3, DQw2 was particularly abundant. The second pattern, detected in 10 of 35 patients (29%) of whom two had IDDM (20%), included reactivity with the NH2-terminal epitope plus strong reactivity with one or more additional epitope(s) residing COOH-terminal to amino acid 101. The second epitope pattern may represent epitope spreading in the GAD65 molecule, but may also include some cases of epitope recognition associated with IDDM resistant HLA-haplotypes. The principal NH2-terminal linear epitope in GAD65 distinguishes the reactivity of SMS and IDDM autoantibodies and may be a determinant of pathogenicity for GABA-ergic neurons. The greater magnitude and distinct specificity of the humoral response to GAD65 in SMS may reflect a biased involvement of the T helper cell type 2 (Th2) subset of CD4+ T cells and antibody responses, whereas IDDM is likely mediated by the Th1 subset of CD4+ T cells and cytotoxic T cell responses.

Adult↗
PubMed2000

DM determines the cryptic and immunodominant fate of T cell epitopes.

The ability of the immune system to focus T cell responses against a select number of potential epitopes of a complex antigen is termed immunodominance. Epitopes that trigger potent T cell activation, after in vivo priming, are classified as immunodominant. By contrast, determinants that fail to elicit any response are called cryptic. DM, a major histocompatibility complex (MHC) heterodimer, plays a pivotal role in the presentation of MHC class II-restricted epitopes by catalyzing the exchange of class II-associated invariant chain peptide with the antigen-derived peptides within the MHC class II binding groove. Using L cells transfected with genes for MHC class II, invariant chain, and DM, we have studied the contribution of DM in the presentation of two cryptic (peptide 11-25 and peptide 20-35) and one dominant (peptide 106-116) epitope of hen egg white lysozyme (HEL). Cells lacking DM heterodimers efficiently display the determinants HEL 11-25 and HEL 20-35 to T cells. Strikingly, however, cells expressing DM are severely compromised in their ability to present the cryptic HEL 11-25/A(d) and 20-35/A(d) epitopes. DM-mediated antagonism of HEL 11-25/A(d) and 20-35/A(d) presentation could thus be central to 11-25/A(d) and 20-35/A(d) being cryptic epitopes in the HEL system. Interestingly, the display of the immunodominant epitope of HEL, 106-116/E(d), and of a dominant epitope of sperm whale myoglobin (SWM), 102-118/A(d), is entirely dependent on the expression of DM. Thus, cells lacking DM molecules are unable to efficiently express HEL 106-116/E(d) and SWM 102-118/A(d) determinants. We conclude that the DM heterodimers direct the immunodominant and cryptic fate of antigenic epitopes in vivo.

Animals↗
PubMed1994

Serial deletion mapping by competition ELISA assay: characterization of a linear epitope in the V3 loop of HIV-1.

Precise epitope mapping and characterization is important for development of a subunit vaccine. To identify epitopes in the principal neutralizing determinant (PND) within the V3 loop of human immunodeficiency virus type 1 (HIV-1), sera were screened in a direct ELISA assay with a coating peptide consisting of IHIGPGRAF, a specific sequence commonly found in the loop, linked at the C terminus to GAGAAK, a nonspecific hexapeptide. Epitope mapping experiments revealed that a competition ELISA assay using IGPGRAFGAGAAK as coating peptide was superior to a direct ELISA assay for epitope definition and characterization. The competing peptides contained only specific sequences and were serially deleted of single amino acids first at the N terminus and then at the C terminus. Study of the most highly reactive serum identified in the initial screening identified the epitope (the shortest peptide with the most potent inhibitory activity) as IGPGRAF. Deletion of a single amino acid from the C terminus of the epitope resulted in complete loss of activity as competing peptide. In contrast, single amino acid deletions of three N-terminal amino acids resulted in a stepwise 2700-fold reduction in affinity. RAF was the shortest peptide with inhibitory activity. Additional studies are needed, especially with regard to choice of coating peptide, to establish the general utility of the described epitope mapping procedure. However, the above method, termed serial deletion mapping, may be useful for defining and characterizing linear epitopes and thus may be particularly informative in investigating the multiple overlapping epitopes of the PND.

Amino Acid Sequence↗
PubMed1992

Biochemical characterization of 25 distinct carcinoembryonic antigen (CEA) epitopes recognized by 57 monoclonal antibodies and categorized into seven groups in terms of domain structure of the CEA molecule.

The chemical nature of 25 distinct carcinoembryonic antigen (CEA) epitopes, which were recognized by 57 different monoclonal antibodies and categorized into 7 groups (Groups A to G) in terms of domain structure of the CEA molecule, was analyzed and the findings obtained were compared with the results of our previous studies using recombinant CEA proteins. All 21 epitopes of Groups A to F defined by 48 MAbs were resistant to periodate oxidation and were to a greater or lesser extent retained after deglycosylation of CEA, indicating that they are all protein in nature. The 21 epitopes were detected in recombinant CEA proteins expressed in Chinese hamster ovary (CHO) cells. Seven of the 21 epitopes of protein nature were partially or completely sensitive to reduction and alkylation of CEA and not detected or only slightly revealed in the recombinant CEA proteins expressed in E. coli, indicating that those epitopes are dependent on the tertiary structure of the peptide chain, which is formed by disulfide bonds. All 4 epitopes of Group G defined by 9 MAbs were sensitive to mild periodate oxidation and deglycosylation, but resistant to reduction and alkylation and to digestion with pepsin or pronase, indicating that those 4 epitopes are carbohydrate in nature. Although none of the 4 epitopes of Group G were detected in the recombinant CEA proteins expressed in E. coli, two were detected in those expressed in CHO cells. The biochemical studies reported here thus provide information as to the nature of the epitopes on the CEA molecule and help form the basis for selecting the anti-CEA MAbs for use in biological study and potential clinical applications of CEA.

Animals↗
PubMed1989

A neutralizing epitope of human immunodeficiency virus type 1 has homologous amino acid sequences with the active site of inter-alpha-trypsin inhibitor.

A neutralizing epitope (epitope beta) of the HTLV-IIIB strain of HIV-1 was mapped to 24 amino acids of an external envelope glycoprotein (gp120) using a neutralizing monoclonal antibody (0.5 beta) and hetero-antisera against synthetic peptides encoding gp120. Proteins that have homologous sequences with epitope beta were sought from a databank of protein sequences to assess biological features of epitope beta. The results showed that epitope beta was found to have homologous sequences to inter-alpha-trypsin inhibitor (ITI). The homologous region of ITI included the active site of the protein. Synthesized peptides including epitope beta were good substrates for trypsin, because these peptides inhibited trypsin activities in a competitive manner (Ki = 24.5 microM). Human urinary trypsin inhibitor (UTI), a protein indistinguishable from ITI, as well as synthetic peptides including epitope beta inhibited syncytium formation caused by the LAV-1-infected CCRF-CEM and uninfected Molt-4 cells in a dose-dependent manner (0.1-1 mM). These findings suggest that epitope beta of HIV-1 could be substrate of protease upon HIV-1 infection and also suggest that protease inhibitory activity of epitope beta may play a role in the pathophysiology of HIV-1-infected individuals.

Alpha-Globulins↗
PubMed2000

Differential expression of alpha-GAL epitopes (Galalpha1-3Galbeta1-4GlcNAc-R) on pig and mouse organs.

BACKGROUND: Expression of the alpha-gal epitope in mice can be completely eliminated by disruption of the alpha1,3 galactosyltransferase gene. As an initial step for assessing the feasibility of this approach in the pig, it was of interest to compare the expression of alpha-gal epitopes in pig and mouse organs. METHODS: Membranes from pig and mouse organ homogenates were analyzed for alpha-gal epitope expression by Western blots, enzyme-linked immunosorbent assay (ELISA), immunostaining of tissues, and ELISA inhibition assay. RESULTS: Immunostaining of Western blots with human anti-Gal detected alpha-gal epitopes on glycoproteins from pig organs but not on glycoproteins from the corresponding mouse organs. ELISA with membrane homogenates and immunostaining of tissue sections demonstrated a much higher binding of human anti-Gal to alpha-gal epitopes on pig membranes than on mouse membranes. ELISA inhibition assay with monoclonal anti-Gal indicated that alpha-gal epitope expression in pig organs is up to 500-fold higher than in mouse organs. CONCLUSION: Expression of alpha-gal epitopes in pig organs is many fold higher than in mouse organs. The abundance of these epitopes in pigs raises the question of whether pigs can properly develop without expression of alpha-gal epitopes.

Animals↗
PubMed2000

Epitope analysis of HLA class I donor specific antibodies in sensitized renal transplant recipients.

OBJECTIVE: The goal of this study was to evaluate the epitope specificity of donor-specific HLA class I antibodies detected in the serum of alloimmunized from a previous renal graft patients. METHOD: A total of 410 serum samples from 87 patients who had lost a previous graft, were collected every 4 months during a 2-year follow-up period. All recipients and donors were typed for class I HLA-antigens by a standard lymphocytotoxicity technique. To define the specificities of the HLA class I antibodies, two techniques were used in parallel: the antihuman globulin augmented CDC (AHG-CDC) technique and an ELISA technique. The mismatched HLA-antigens and the detected HLA class I antibodies were categorized as intra-cross-reactive group mismatches (intra-CREGs-MMs) and other-CREG-MMs. For each sensitized patient actual and at risk epitope specificities were defined. RESULTS: Thirty-eight patients (43.7%) had developed IgG HLA class I-specific antibodies with stable specificities against mismatched alloantigens from the previous graft. A total of 60 antibody reactivity patterns and 82 specificities against private and public epitope were recognized. Patients with only intra-CREGs-MMs produced HLA class I-specific antibodies less frequently than patients with only other-CREG-MMs, although the difference was nearly statistically significant (P=0.053). All HLA class I donor-specific antibodies were considered to have specificities against the private epitopes of the mismatched graft HLA-antigens. In the cases where HLA class I alloreactivity was spreading to more than one donor antigens, we considered that the detected antibodies had specificities against the private and the shared between the alloantigens epitope(s). No epitope-specific antibodies were detected against shared epitopes between the mismatched alloantigens and the HLA-antigens of the patients. In 11/38 cases (28.9%) HLA class I alloreactivity spreading to non-graft antigens was detected. These antibodies were directed against HLA-antigens that share epitope(s) and have strong serological reactivity with the immunogenic alloantigens. CONCLUSION: Our data show that a small number of private and public alloepitopes seem to be responsible for antibody production in patients sensitized from a previous graft. A detailed description of these HLA-epitopes, in the context of clinical graft complications, may lead to an improved organ allocation strategy.

Antibody Specificity↗
PubMed2003

Cross-reactive CD8+ T cell epitopes identified in US adolescent minorities.

Vaccines designed to bring forth CD8+ T cell responses in different racial and ethnic groups will require inclusion of T cell epitopes presented by various MHC class I molecules. This study was designed to identify new CD8+ T cell epitopes in HIV-infected African American and Hispanic youth as well as to determine the frequency of responses to both novel and previously described HIV-1 epitopes in a cohort of racially and ethnically diverse individuals. We found 8 MHC class I-restricted CD8+ T cell epitopes that had not been previously described, another 8 epitopes that were restricted by class I alleles not previously associated with these epitopes, and 8 additional epitopes that have been described previously. In a larger cohort, we demonstrated that 11 (69%) of these 16 newly described immunogens were recognized by individuals of different race or ethnicity. Most HIV-1-specific CD8+ T cell epitopes identified were either novel or restricted by alternative MHC class I alleles. Frequent recognition of several of these CTL epitopes in persons of diverse racial backgrounds bodes well for the development of a broadly reactive HIV-1 vaccine.

AIDS Vaccines↗