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NMR study and comparison of the antigenic properties of a peptide recognized by two HIV-1 neutralizing antibodies.

Fab-peptide complexes formed between a 15 residue peptide derived from the HIV-1 gp120 V3 loop and two of its cognate monoclonal antibodies, 5023A and 5025A, were studied using isotope-edited solution nuclear magnetic resonance (NMR) techniques. Since these antibodies neutralize HIV-1 virus with different strain specificities, this study was conducted to better understand the nature of these differences. The amide proton and nitrogen NMR resonances of specific residues were used to monitor the backbone of this peptide in these complexes. Three central residues of this peptide ('RAF') were found to be strongly affected by binding to both antibodies. Several other peptide residues were affected by binding to antibody 5023A but not 5025A. The antibody epitopes mapped by NMR are similar to those obtained previously via PEPSCAN at higher pH. One main difference between the PEPSCAN and NMR determined epitopes for 5023A involved two glycine residues of the peptide. By NMR, one of these glycines was more dramatically affected by antibody binding than predicted by PEPSCAN, while the other was much less so.

Antibodies, Monoclonal↗

Antigen processing is predictable: From genes to T cell epitopes.

In order to induce a cellular immune response, antigens have to be processed in intracellular compartments, transported, and presented by HLA molecules prior to recognition by specific T cells. Many of the events that contribute to antigen processing have been thoroughly investigated during the past years and are now well understood, which lead to a number of prediction programs. "Reverse immunology" has been used for about 10 years in order to identify T cell epitopes from pathogens or tumor-associated antigens. The advantages and pitfalls of T cell epitope prediction compared to classical experimental procedures such as epitope mapping and cloning experiments have been discussed many times. In this presentation, a number of internet programs that offer help in T cell epitope prediction (or prediction of antigen processing) will be discussed in the light of transfusion medicine. Some databases are listing published HLA ligands and T cell epitopes, others offer epitope prediction for many HLA class I or class II restrictions. In addition, a number of established programs will be demonstrated which are freely accessible at no cost in the world wide web for the prediction of either HLA-peptide binding, proteasomal processing of antigens, or both. Epitope prediction and processing prediction programs will be applied to minor histocompatibility antigens (miHAgs) and compared. This reflects the actual possibilities and limitations of such computer-aided work not only in cellular immunology, but also in transplantation immunology.

Animals↗

Monoclonal antibodies to yeast poly(A) polymerase (PAP) provide evidence for association of PAP with cleavage factor I.

Purified yeast poly(A) polymerase (PAP) was used to produce monoclonal antibodies which recognize the enzyme in immunoblots. Epitope mapping using truncated forms of PAP and cyanogen bromide cleavage products revealed two classes of antibodies. One class (N-term) recognizes an epitope in the first 100 amino acids, and a second class (C-term) is specific for a determinant located in the last 20 amino acids of PAP. These C-terminal 20 amino acids can be removed without affecting the nonspecific poly(A) addition activity of the purified enzyme. Neither antibody inhibits the nonspecific poly(A) polymerase activity or the sequence-specific activity observed in processing extracts. The antibodies show species specificity and cannot recognize mammalian, Xenopus, or vaccinia PAP. The C-term antibodies can deplete PAP from yeast whole cell extracts, resulting in loss of poly(A) addition activity. This immunodepletion also causes a reduction in the cleavage activity which can be restored by addition of yeast cleavage factor I [CF I; Chen, J., & Moore, C. (1992) Mol. Cell Biol. 12, 3470-3481], a factor needed for both the cleavage and poly(A) addition reactions. This demonstrates that a complex of PAP and CF I exists in extracts in the absence of ATP or exogenous RNA substrate. The monoclonal antibodies against yeast PAP will be a useful tool for further study of factors required for yeast mRNA 3' end processing.

Antibodies, Monoclonal↗

A protective epitope of Moraxella catarrhalis is encoded by two different genes.

The high-molecular-weight UspA protein of Moraxella catarrhalis has been described as being both present on the surface of all M. catarrhalis disease isolates examined to date and a target for a monoclonal antibody (MAb 17C7) which enhanced pulmonary clearance of this organism in a mouse model system (M. E. Helminen et al., J. Infect. Dis. 170:867-872, 1994). A recombinant bacteriophage that formed plaques which bound MAb 17C7 was shown to contain a M. catarrhalis gene, designated uspA1, that encoded a protein with a calculated molecular weight of 88,271. Characterization of an isogenic uspA1 mutant revealed that elimination of expression of UspA1 did not eliminate the reactivity of M. catarrhalis with MAb 17C7. In addition, N-terminal amino acid analysis of internal peptides derived from native UspA protein and Southern blot analysis of M. catarrhalis chromosomal DNA suggested the existence of a second UspA-like protein. A combination of epitope mapping and ligation-based PCR methods identified a second M. catarrhalis gene, designated uspA2, which also encoded the MAb 17C7-reactive epitope. The UspA2 protein had a calculated molecular weight of 62,483. Both the isogenic uspA1 mutant and an isogenic uspA2 mutant possessed the ability to express a very-high-molecular-weight antigen that bound MAb 17C7. Southern blot analysis indicated that disease isolates of M. catarrhalis likely possess both uspA1 and uspA2 genes. Both UspA1 and UspA2 most closely resembled adhesins produced by other bacterial pathogens.

Amino Acid Sequence↗

CD4+ T-cell responses to Epstein-Barr virus (EBV) latent-cycle antigens and the recognition of EBV-transformed lymphoblastoid cell lines.

There is considerable interest in the potential of Epstein-Barr virus (EBV) latent antigen-specific CD4+ T cells to act as direct effectors controlling EBV-induced B lymphoproliferations. Such activity would require direct CD4+ T-cell recognition of latently infected cells through epitopes derived from endogenously expressed viral proteins and presented on the target cell surface in association with HLA class II molecules. It is therefore important to know how often these conditions are met. Here we provide CD4+ epitope maps for four EBV nuclear antigens, EBNA1, -2, -3A, and -3C, and establish CD4+ T-cell clones against 12 representative epitopes. For each epitope we identify the relevant HLA class II restricting allele and determine the efficiency with which epitope-specific effectors recognize the autologous EBV-transformed B-lymphoblastoid cell line (LCL). The level of recognition measured by gamma interferon release was consistent among clones to the same epitope but varied between epitopes, with values ranging from 0 to 35% of the maximum seen against the epitope peptide-loaded LCL. These epitope-specific differences, also apparent in short-term cytotoxicity and longer-term outgrowth assays on LCL targets, did not relate to the identity of the source antigen and could not be explained by the different functional avidities of the CD4+ clones; rather, they appeared to reflect different levels of epitope display at the LCL surface. Thus, while CD4+ T-cell responses are detectable against many epitopes in EBV latent proteins, only a minority of these responses are likely to have therapeutic potential as effectors directly recognizing latently infected target cells.

Antibody Specificity↗

Single amino acid residues in a synthetic peptide of influenza haemagglutinin, HA 1 177-199, distinguish I-Ad- and I-Ed-restricted T-cell epitopes.

A majority of Iad-restricted, CD4+ T-cell clones, derived from BALB/c mice infected with X31 (H3N2) influenza virus and specific for the HA 1 subunit of the viral haemagglutinin (HA), has previously been shown to recognize the synthetic peptide HA 1 177-199, corresponding to the primary amino acid sequence of a major antibody binding site. Here it is demonstrated that both I-Ad- and I-Ed-restricted T-cell clones recognize HA 1 177-199, and that inter- and intra-allelic differences in Iad-restricted recognition are defined by single amino acid residues. A panel of truncated HA 1 synthetic peptides defined three distinct but overlapping CD4+ epitopes within the common antigenic site (HA 1 177-199): two I-Ad-restricted epitopes mapped within HA 1 186-198 and HA 1 177-199, and peptide HA 1 178-195 identified an I-Ed-restricted epitope. Moreover, fine specificity differences in the recognition of synthetic peptides, truncated at the carboxy terminus of HA 1 177-199, identified residues HA 1 A 198 and HA 1 S 199 as being critical for defining inter- and intra-allelic differences, respectively, in the Iad-restricted T-cell recognition of HA.

Amino Acids↗

Identification and immunological characterization of the domain of Actinobacillus actinomycetemcomitans leukotoxin that determines its specificity for human target cells.

Although extensive amino acid homology exists among the various Repeats in ToXin (RTX) family of bacterial cytolysins, the cellular and species specificities remain unique for individual toxins (i.e. Actinobacillus actinomycetemcomitans leukotoxin (LtxA) kills human monomyelocytes while a related toxin, Pasteurella hemeolytica leukotoxin (LktA) kills bovine lymphoid cells). To determine the Ltx domain responsible for species specificity, ltxA/lktA chimeric toxin genes were expressed in tandem with the ltxC gene under control of the P lambda promoter. The ability of lysates to kill either HL-60 (human) or BL-3 (bovine) cells was assessed by trypan blue exclusion. The critical area required for the chimeric toxins to recognize human target cells is a 253-amino acid fragment (residue 688-941) that contains the GGXGXDX(L[I[V[W[Y[F)X repeats. A panel of 12 neutralizing anti-LtxA monoclonal antibodies also recognized specificities within the 253-amino acid fragment. Epitope mapping of the monoclonal antibody panel showed that all antibodies bound to one of three sites on the LtxA molecule. One monoclonal recognized epitope A which was composed of LtxA residues 698-709 (KLDYYYTNKGFK), six antibodies recognized epitope B, a peptide composed of residues 746-757 (LIYGYDGDDRLY), whereas the remaining five monoclonals recognized epitope C, which is composed of residues 926-937 (DRARLKRQFELQ).

Aggregatibacter actinomycetemcomitans↗

Antibodies against the C2 COOH-terminal region discriminate the active and latent forms of the multicatalytic proteinase complex.

The mouse cDNA homologues of the rat C2, C9, and C5 subunits of the multicatalytic proteinase have been cloned and expressed in bacteria. The respective recombinant proteins were purified and used to produce specific anti-subunit antibodies. Immunoblotting of two-dimensional gels of purified rat liver multicatalytic proteinase showed that the C2 (32-kDa) and C9 (29-kDa) polypeptides are resolved into three and two isoelectric variants, respectively, likely due to post-translational modifications, i.e. phosphorylation, and the presence of two anti-C5 reacting polypeptides (25.5 and 23 kDa). Epitope mapping of the anti-C2-specific antibody with different constructs of the recombinant C2 protein allowed us to determine that one major epitope of this anti-C2 antibody is located within the last 9-11 amino acids of the C2 polypeptide. Affinity purified antibodies directed against the C2 COOH-terminal were able to discriminate the active and latent forms of the multicatalytic proteinase, supporting the conclusion that the C2 protein found in the active form of the enzyme is a polypeptide of 28 kDa, produced by the loss, at least, of the last 9-13 amino acids (DEPAEKADEPMEH) of the intact C2 (32-kDa) component. By in vitro treatment of the latent form of the enzyme with elastase, we show the conversion of the C2 (32-kDa) component to a 28-kDa protein with loss of recognition by the anti-C2 COOH-terminal affinity purified antibodies, but this limited degradation of the C2 component did not have any significant effect on the proteolytic activity (assayed with myelin basic protein and fluorogenic peptides) of the multicatalytic proteinase. It is suggested that the proteolytic cleavage of the C2 COOH-terminal region may be involved in the regulation of the interaction of the multicatalytic proteinase with other cellular proteins and/or in the translocation of the complex to the nucleus.

Animals↗

Use of a designer triple expression hybrid clone for three different lipoyl domain for the detection of antimitochondrial autoantibodies.

The detection of antimitochondrial autoantibodies (AMAs) is critical in the diagnosis of primary biliary cirrhosis (PBC). However, conventional laboratory assays to detect AMA are dependent on the time-consuming method of immunofluorescence microscopy, a method often plagued by problems of nonspecificity. AMAs react against mitochondrial autoantigens including the E2 components of the pyruvate dehydrogenase complex (PDC-E2), the branched-chain 2-oxo-acid dehydrogenase complex (BCOADC-E2), and the 2-oxo-glutarate dehydrogenase complex (OGDC-E2). Interestingly, the immunodominant epitopes of PDC-E2, BCOADC-E2, and OGDC-E2 are all conformational lipoate binding sites, but antibodies against them do not cross-react. Although 80% to 90% of sera from patients with PBC react to PDC-E2, approximately 10% patients with PBC react only to BCOADC-E2 and/or OGDC-E2. We have taken advantage of our epitope-mapping studies of the E2 components of PDC, BCOADC, and OGDC, and constructed a "designer" hybrid clone, designated as pML-MIT3, that coexpresses the immunodominant epitopes within the three distinct lipoyl domains. We examined a total of 321 sera, including 186 sera from patients with PBC, to test the immunoreactivity of pMIT3. Of 186 sera from patients with PBC, 152 sera (81.7%) reacted with recombinant fusion protein of PDC-E2, whereas 171 sera (91.9%) showed positive reactivities when probed by immunoblotting against the recombinant fusion protein expressed from the pML-MIT3 clone. Of 34 PBC sera that did not react with recombinant PDC-E2, 18 sera contained BCOADC-E2-specific AMA and 1 serum possessed only OGDC-E2-specific AMA. We also developed an enzyme-linked immunosorbent assay (ELISA), using affinity-purified recombinant fusion protein of pML-MIT3 clone as the antigen source, to quantify specific AMAs in patients with PBC. None of the 135 control sera from patients with primary sclerosing cholangitis (PSC), chronic autoimmune hepatitis (CAH), systemic lupus erythematosus (SLE), or healthy volunteers showed significant reactivity against pML-MIT3 recombinant fusion protein in the ELISA assay. Our results indicate that an ELISA using recombinant, cloned autoantigen of pML-MIT3 is a powerful and very specific method for the detection of AMA.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗

Immunoreactivity of recombinant human glandular kallikrein using monoclonal antibodies raised against prostate-specific antigen.

The gene encoding human glandular kallikrein (KLK2) was expressed in Escherichia coli, and the corresponding protein (hK2) was produced by fermentation. The hK2 was characterized by Western blotting and epitope map using monoclonal antibodies (MAbs) specific for another protease, prostate-specific antigen (PSA) with high structural identity (80%). MAbs that recognized three different epitopes were bound to hK2, representing 7 out of 23 MAbs tested. One epitope was localized to the sequence region around amino acid position 78, which is believed to be glycosylated in hK2. The affinities of MAbs recognizing hK2 were similar to those for PSA, suggesting that common epitopes seem to contain very conserved structures. The results may help in designing specific diagnostic assays for the assessment of prostate cancer.

Antibodies, Monoclonal↗

Fine-mapping of the B-cell epitope domain at the N-terminus of the preS2 region of the hepatitis B surface antigen.

In this study, we report the exact localization and substitutional characterization of a B-cell epitope domain at the N-terminus of the preS2 region of the hepatitis B surface antigen. A set of deletion variants containing preS2 sequences of different length was generated on the basis of frCP as a carrier. It was found after Western blot analysis that three monoclonal antibodies (MAbs) (2-11B1, 3-11C2, HB.OT10) recognized the linear preS2 sequence within the amino acid (aa) stretch 3-WNSTTFHQTLQDP-13. The importance of each aa residue of the epitope was proved by comparison of antibody binding to alanine-substituted peptides in both free-peptide and Pepscan variants.

Amino Acid Sequence↗

Mapping of human serum-reactive epitopes in virus-like particles of human papillomavirus types 16 and 11.

Most human antibodies against HPV16 can be blocked by the monoclonal antibody H16.V5. To investigate whether H16.V5 and human sera recognize similar epitopes, hybrid capsids containing different parts of HPV16 and HPV11 were evaluated for reactivity with human sera. The antibody responses among HPV 16-/HPV11+sera to HPV11 and to hybrid capsids containing the HPV11 C-terminus were strongly correlated. The antibody responses among HPV 16+/HPV11-sera to HPV16 and to a hybrid containing the HPV16 C-terminus were correlated and there was also reactivity with a hybrid containing the H16.V5 epitope in the HPV11 backbone. Several HPV16-/11- children's sera were reactive with hybrid capsids, implying that a native capsid structure is essential for serological specificity. For both HPV16 and HPV11, the major serologic reactivity was directed toward the C-terminal part of the protein and the H16.V5 binding site appeared to be a major serologically reactive epitope of HPV16.

Antibodies, Monoclonal↗

Antigenic properties of the Leishmania infantum GRP94 and mapping of linear B-cell epitopes.

In this study, we show that the glucose-regulated protein 94 (GRP94) from Leishmania infantum is a major target for humoral immune response during both visceral (VL) and mucocutaneous leishmaniasis (MCL). Also, the time-course of appearance of anti-GRP94 antibodies along the infection was analysed in hamsters (Mesocricetus auratus) experimentally infected with L. infantum. Remarkably, the reactivity against the Leishmania GRP94 was observed very soon after challenge, at the time of appearance of a humoral response against Leishmania total proteins, and long before that the animals develop clinical symptoms of disease. Therefore, at least for golden hamsters, the reactivity against Leishmania GRP94 is an early marker of infection. Using a collection of synthetic peptides covering the complete sequence of the L. infantum GRP94, we have determined the main linear antigenic determinants recognised by sera from humans, dogs, and hamsters suffering from VL. Four synthetic peptides, located in highly divergent regions of the protein, were found to be immunodominants and recognised by VL sera of these three different origins. We discuss that the prominent antigenicity of Leishmania GRP94 may be related to recent findings involving GRP94, and other heat shock proteins, in relevant immune functions such as tumour immunogenicity and antigen presentation.

Adolescent↗

Structural and functional domains in human tumour necrosis factors.

Human tumour necrosis factors (hTNFs) alpha and beta are related pleiotropic cytokines which share many activities and compete with each other for binding to two receptor components on many cell types. Although structural and biological data indicate that the active form of hTNF-alpha may be a symmetrical trimer, the manner in which hTNFs interact with their receptors to trigger a myriad of cell type-dependent responses is not clear. A combination of chemical modification, epitope mapping and site-directed mutagenesis approaches suggest that at least four distinct peptide sequences are important for the biological activity of hTNF-alpha. In particular, certain peptide sequences between amino acid positions 11 and 35 in hTNF-alpha appear to be critical for receptor binding and triggering biological responses. The recent cloning of the two hTNF-alpha/beta receptors opens the way for precise mapping of the functional domains in hTNFs.

Amino Acid Sequence↗

Monoclonal antibodies against boar sperm zona pellucida-binding protein AWN-1. Characterization of a continuous antigenic determinant and immunolocalization of AWN epitopes in inseminated sows.

Boar spermadhesin AWN-1 is a sperm surface-associated 14.7-kDa lectin and a major protein of porcine seminal plasma. AWN-1 binds to beta-galactosides and to porcine zona pellucida glycoproteins, suggesting that this protein might play a role in the primary binding of spermatozoa to the egg's external glycoprotein matrix. We have produced a collection of murine monoclonal antibodies against purified AWN-1. Five monoclonal antibodies recognized sequential antigenic determinants. All these epitopes were located at the C-terminal region of AWN-1 (residues 109-123) by competitive ELISA using overlapping synthetic peptides that cover the complete 133 amino acid sequence of the lectin. In a structural model of spermadhesin AWN-1, the polypeptide stretch 109-123 is fully solvent-exposed, providing a reasonable explanation for its high immunogenicity. In addition to epitope mapping, we have employed anti-AWN monoclonal antibodies for immunolocalization of the protein in the genital tract of inseminated sows. Clusters of AWN epitopes were occasionally found attached to the epithelium of the uterotubal junction and the adjacent lower isthmus. However, neither AWN-1 nor other seminal plasma proteins were found in the isthmic fluid collected 10-26 h after insemination. These results suggest that the whole amount of seminal plasma proteins are absorbed by the epithelium of the female genital tract, supporting the claim that removal of seminal plasma components from spermatozoa might be a major event in both in vitro and in vivo sperm capacitation.

Animals↗

Mapping of a dengue virus neutralizing epitope critical for the infectivity of all serotypes: insight into the neutralization mechanism.

Dengue virus infections are a growing public health concern and strategies to control the spread of the virus are urgently needed. The murine monoclonal antibody 4E11 might be of interest, since it neutralizes dengue viruses of all serotypes by binding to the 296-400 segment of the major dengue virus envelope glycoprotein (DE). When phage-displayed peptide libraries were screened by affinity for 4E11, phage clone C1 was selected with a 50% frequency. C1 shared three of nine residues with DE(306-314) and showed significant reactivity to 4E11 in ELISA. C1-induced antibodies cross-reacted with DE(296-400) in mice, suggesting that it was a structural equivalent of the native epitope of 4E11 on DE. Accordingly, 4E11 bound to the DE(306-314) synthetic peptide and this reaction was inhibited by DE(296-400). Moreover, DE(306-314) could block dengue virus infection of target cells in an in vitro assay. A three-dimensional model of DE revealed that the three amino acids shared by DE(296-400) and C1 were exposed to the solvent and suggested that most of the amino acids comprising the 4E11 epitope were located in the DE(306-314) region. Since 4E11 blocked the binding of DE(296-400) to heparin, which is a highly sulfated heparan sulfate (HSHS) molecule, 4E11 may act by neutralizing the interaction of DE(306-314) with target cell-displayed HSHS. Our data suggest that the DE(306-314) segment is critical for the infectivity of all dengue virus serotypes and that molecules that block the binding of DE(306-314) to HSHS may be antiviral reagents of therapeutic interest.

Amino Acid Sequence↗

Mapping and characterization of the functional epitopes of tissue inhibitor of metalloproteinases (TIMP)-3 using TIMP-1 as the scaffold: a new frontier in TIMP engineering.

Tumor necrosis factor-alpha (TNF-alpha) converting enzyme (TACE/ADAM-17) is responsible for the release of TNF-alpha, a potent proinflammatory cytokine associated with many chronic debilitating diseases such as rheumatoid arthritis. Among the four variants of mammalian tissue inhibitor of metalloproteinases (TIMP-1 to -4), TACE is specifically inhibited by TIMP-3. We set out to delineate the basis for this specificity by examining the solvent accessibility of every epitope on the surface of a model of the truncated N-terminal domain form of TIMP-3 (N-TIMP-3) in a hypothetical complex with the crystal structure of TACE. The epitopes suspected of interacting with TACE were systematically transplanted onto N-TIMP-1. We succeeded in transforming N-TIMP-1 into an active inhibitor for TACE (K(i)(app) 15 nM) with the incorporation of Ser4, Leu67, Arg84, and the TIMP-3 AB-loop. The combined effects of these epitopes are additive. Unexpectedly, introduction of "super-N-TIMP-3" epitopes, defined in our previous work, only impaired the affinity of N-TIMP-1 for TACE. Our mutagenesis results indicate that TIMP-3-TACE interaction is a delicate process that requires highly refined surface topography and flexibility from both parties. Most importantly, our findings confirm that the individual characteristics of TIMP could be transplanted from one variant to another.

ADAM Proteins↗

Mapping and characterization of a sequential epitope on the rabies virus glycoprotein which is recognized by a neutralizing monoclonal antibody, RG719.

We have established a murine hybridoma cell line RG719 which produces a rabies virus-neutralizing IgM-type monoclonal antibody (referred to as MAb RG719). Immunoblot analysis indicated that the antibody recognized a sequential epitope of G protein. Among four rabies virus strains tested, the antigenicity to MAb RG719 was absent from the Nishigahara strain, while the other three strains (HEP, ERA and CVS) reacted to the MAb. Studies with deletion mutants of the G protein indicated that the epitope was located in a middle region of the primary structure of G protein, ranging from position 242 to 300. By comparing the estimated amino acid sequence of the four strains, we found in this region two amino acids (at positions 263 and 291) which are common to three of those strains but are not shared by the Nishigahara strain. The site-directed point mutagenesis revealed that replacement of phenylalanine-263 by leucine destroyed the epitope of the HEP G protein, while the epitope was generated on the Nishigahara G protein whose leucine-263 was replaced by phenylalanine. These observations suggest that phenylalanine-263 is essential for constructing the epitope for MAb RG719. The synthetic 20-mer peptide produced by mimicking the amino acid sequence (ranging from amino acid positions 249 to 268) of the presumed epitope region was shown to bind specifically to MAb RG719 and also to raise the virus-neutralizing antibodies in rabbits. Vaccination with the HEP vaccine produced in Japan induced in humans and rabbits production of significant amounts of the antibodies which reacted with the 20-mer peptide.

Amino Acid Sequence↗