Characterization of Immunodominant Linear B-Cell Epitopes on the Carboxy Terminus of the Rinderpest Virus Nucleocapsid Protein

The nucleocapsid (N) protein of rinderpest virus (RPV) is one of the most abundant and immunogenic viral proteins expressed during natural or experimental infection. To identify immunogenic epitopes on the N protein, different forms of RPV N protein, including the full-length protein (N_1-525), an amino-terminal construct (N_1-179), and a carboxy-terminal construct (N_414-496), were expressed in Escherichia coli as glutathione S-transferase (GST) fusion proteins. The antigenicity of each recombinant protein was evaluated by Western immunoblotting. All recombinants were recognized by hyperimmune RPV bovine antisera, indicating that immunoreactive epitopes may be present at both ends of the N protein. However, GST-N_414-496 was much more antigenic than GST-N_1-179 when tested with sera from vaccinated cattle, suggesting that an immunodominant or highly immunogenic epitope(s) may be located at the carboxy terminus of the N protein. Epitope mapping with overlapping peptides representing different regions of the carboxy terminus (amino acids 415 to 524) revealed three nonoverlapping antigenic sites in regions containing the residues ⁴⁴⁰VPQVRKETRASSR⁴⁵² (site 1), ⁴⁷⁹PEADTDPL⁴⁸⁶ (site 2), and ⁵²⁰DKDLL⁵²⁴ (site 3). Among these, antigenic site 2 showed the strongest reactivity with hyperimmune anti-RPV bovine sera in a peptide enzyme-linked immunosorbent assay but did not react with hyperimmune caprine sera raised against peste-des-petits-ruminants virus, which is antigenically closely related to RPV. Identification of an immunodominant linear antigenic site at the carboxy terminus of the N protein may provide an antigen basis for designing diagnostics specific for RPV.     

Mapping of B-cell epitopes of hemagglutinin protein of rinderpest virus

Monoclonal antibodies (mAbs) against secreted hemagglutinin (H) protein of rinderpest virus (RPV) expressed by a recombinant baculovirus were generated to characterize the antigenic sites on H protein and regions of functional significance. Three of the mAbs displayed hemagglutination inhibition activity and these mAbs were unable to neutralize virus infectivity. Western immunoblot analysis of overlapping deletion mutants indicated that three mAbs recognize antigenic regions at the extreme carboxy terminus (between amino acids 569 and 609) and the fourth mAb between amino acids 512 and 568. Using synthetic peptides, aa 569-577 and 575-583 were identified as the epitopes for E2G4 and D2F4, respectively. The epitopic domains of A12A9 and E2B6 mAbs were mapped to regions encompassing aa 527-554 and 588-609. Two epitopes spanning the extreme carboxy terminal region of aa 573 to 587 and 588 to 609 were shown to be immunodominant employing a competitive ELISA with polyclonal sera form vaccinated cattle. The D2F4 mAb which recognizes a unique epitope on RPV-H is not present on the closely related peste des petits ruminant virus HN protein and this mAb could serve as a tool in the seromonitoring program after rinderpest vaccination.     

Mapping of antigenic sites on the nucleocapsid protein of the severe acute respiratory syndrome coronavirus

Antigenic sites on the nucleocapsid (N) protein of severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) were mapped by Pepscan analysis with overlapping peptides that span the N protein sequence. Two major immunodominant epitopes located in the C-terminal region (amino acids [aa] 362 to 412) and middle region (aa 153 to 178) reacted with more than 75% of sera from SARS patients. Several minor immunodominant epitopes were reactive with about 50% of the SARS sera. Antisera from mice immunized with inactivated SARS-CoV recognized the two major immunodominant epitopes and one antigenic site located adjacent to the N-terminal region (aa 76 to 101), which did not react with the sera from SARS patients. Several monoclonal antibodies against SARS-CoV bound to the N- or C-terminal antigenic sites. These results suggest that the above antigenic sites on the N protein are important in eliciting humoral immune response against SARS-CoV in humans and animals and can be used as antigens for developing diagnostic tests.     

Antigenic and Immunogenic Investigation of B-Cell Epitopes in the Nucleocapsid Protein of Peste des Petits Ruminants Virus

Attempts were made to identify and map epitopes on the nucleocapsid (N) protein of peste des petits ruminants virus (PPRV) (Nigeria75/1 strain) using seven monoclonal antibodies (MAbs) and deletion mutants. At least four antigenic domains (A-I, A-II, C-I, and C-II) were identified using the MAbs. Domains A-I (MAb 33-4) and A-II (MAbs 38-4, P-3H12, and P-13A9) were determined to be located on the amino-terminal half (amino acids [aa] 1 to 262), and domains C-I (P-14C6) and C-II (P-9H10 and P-11A6) were within the carboxy-terminal region (aa 448 to 521). Nonreciprocal competition between A-II MAbs and MAbs to C-I and C-II domains was observed, indicating that they may be exposed on the surface of the N protein and spatially overlap each other. Blocking or competitive enzyme-linked immunosorbent assay studies using PPRV serum antibodies revealed that epitopes on the domains A-II and C-II were immunodominant, whereas those on the domains A-I and C-I were not. The competition between MAb and rinderpest virus (RPV) serum antibodies raised against RPV strain LATC was found in two epitopes (P-3H12 and P-13A9) on the domain A-II, indicating that these epitopes may cause cross-reactivity between PPRV and RPV. Identification of immunodominant but PPRV-specific epitopes and domains will provide the foundation in designing an N-protein-based diagnostic immunoassay for PPRV.     

Antigenic and immunogenic investigation of B-cell epitopes in the nucleocapsid protein of peste des petits ruminants virus

Attempts were made to identify and map epitopes on the nucleocapsid (N) protein of peste des petits ruminants virus (PPRV) (Nigeria75/1 strain) using seven monoclonal antibodies (MAbs) and deletion mutants. At least four antigenic domains (A-I, A-II, C-I, and C-II) were identified using the MAbs. Domains A-I (MAb 33-4) and A-II (MAbs 38-4, P-3H12, and P-13A9) were determined to be located on the amino-terminal half (amino acids [aa] 1 to 262), and domains C-I (P-14C6) and C-II (P-9H10 and P-11A6) were within the carboxy-terminal region (aa 448 to 521). Nonreciprocal competition between A-II MAbs and MAbs to C-I and C-II domains was observed, indicating that they may be exposed on the surface of the N protein and spatially overlap each other. Blocking or competitive enzyme-linked immunosorbent assay studies using PPRV serum antibodies revealed that epitopes on the domains A-II and C-II were immunodominant, whereas those on the domains A-I and C-I were not. The competition between MAb and rinderpest virus (RPV) serum antibodies raised against RPV strain LATC was found in two epitopes (P-3H12 and P-13A9) on the domain A-II, indicating that these epitopes may cause cross-reactivity between PPRV and RPV. Identification of immunodominant but PPRV-specific epitopes and domains will provide the foundation in designing an N-protein-based diagnostic immunoassay for PPRV.     

Characterization of monoclonal antibodies raised against recombinant respiratory syncytial virus nucleocapsid (N) protein: identification of a region in the carboxy terminus of N involved in the interaction with P protein.

To investigate structure and biological properties of the nucleocapsid (N) protein of respiratory syncytial virus (RSV), we have generated a panel of 16 monoclonal antibodies, raised against recombinant N protein, and epitope mapped seven of these to three antigenic sites (Site I aa 16-30; Site II aa 341-350; Site III aa 351-365). Characterization by immunofluorescence and by immunoprecipitation assay demonstrated that a monoclonal antibody to antigenic site I can detect N protein complexed with phospho (P) protein. Antibodies to antigenic sites II and III, which are adjacent to each other near the carboxyl terminus of the N protein, have distinct properties. A site III monoclonal antibody detected N protein in cytoplasmic inclusion bodies and in the cytosol, but not when N was complexed to P protein, while the site II antibody reacted with N protein in the nucleocapsid fraction but did not detect cytosolic N protein. Further investigation into the reactivities of the antibodies after binding of P to N in vitro demonstrated that antigenic sites II and III were blocked by the interaction, indicating an involvement for the carboxy domain of N in the N-P interaction. This was confirmed by the ability of peptides from the carboxy terminus of N to inhibit the N-P interaction in vitro.     

Identification of continuous B-cell epitopes on the protein moiety of the 58-kiloDalton cell wall mannoprotein of Candida albicans belonging to a family of immunodominant fungal antigens

The 58-kiloDalton mannoprotein (mp58) on the surface of Candida albicans is highly immunogenic, is expressed by all C. albicans isolates tested, and elicits strong antibody responses during candidiasis. It belongs to a family of immunodominant fungal antigens with representatives also in different species of Aspergillus. The amino acid sequence of the protein portion of mp58 as deduced from the DNA sequence of its encoding gene (FBP1/PRA1) was used to synthesize a complete set of overlapping dodecapeptides (overlap, 7; offset, 5) covalently attached to the surface of derivatized polyethylene pins. The pin-coupled peptides were used in a modified enzyme-linked immunosorbent assay (ELISA) to identify continuous epitopes recognized by a number of antiserum preparations containing anti-mp58 antibodies. This comprehensive epitope-scanning study revealed the presence of multiple immunoreactive continuous B-cell epitopes within the protein sequence. Regions of increased reactivity included both the amino and carboxy termini of the mature protein (encompassing amino acid residues 16 to 50 and 286 to 299, respectively) and four internal regions spanning amino acids at positions 66 to 92, 121 to 142, 148 to 192, and 211 to 232. Further delineation of epitopic regions and identification of the boundaries of the antigenic sites was performed upon ELISA testing with a second Pepset consisting of completely overlapping 8-mer peptides spanning these reactive regions in the protein moiety of mp58. The highly reactive epitopic region at the C terminus of the protein was further evaluated using both window net and replacement net analyses. A synthetic peptide corresponding to the last 10 amino acid residues at the C terminus of the protein was immunogenic when injected into mice after being coupled to a carrier protein. Moreover, antibodies in the resulting sera specifically recognized the homologous mp58 in ELISAs and immunoblot assays. Delineation of the antibody responses to mp58 could provide the basis for the development of novel immunity-based prophylactic, therapeutic, and diagnostic techniques for the management of candidiasis.     

CD4+ T lymphocytes from Anaplasma marginale major surface protein 2 (MSP2) vaccinees recognize naturally processed epitopes conserved in MSP3

Major surface protein 2 (MSP2) and MSP3 of the persistent bovine ehrlichial pathogen Anaplasma marginale are immunodominant proteins that undergo antigenic variation. The recently completed sequence of MSP3 revealed blocks of amino acids in the N and C termini that are conserved with MSP2. This study tested the hypothesis that CD4+ T cells specific for MSP2 recognize naturally processed epitopes conserved in MSP3. At least one epitope in the N terminus and two in the C terminus of MSP2 were also processed from MSP3 and presented to CD4+ T lymphocytes from MSP2-immunized cattle. This T-lymphocyte response to conserved and partially conserved epitopes may contribute to the immunodominance of MSP2 and MSP3.     

Natural antibody responses against the non-repeat-sequence-based B-cell epitopes of the Plasmodium falciparum circumsporozoite protein.

Synthetic peptides and human serum or plasma samples from regions of Brazil, Papua New Guinea, and Kenya in which malaria is endemic were used to identify B-cell epitopes localized outside the repeat region of the circumsporozoite (CS) protein of the human malaria parasite Plasmodium falciparum. In agreement with recent observations, our results confirm the presence of two non-repeat-region-based B-cell epitopes of the CS protein. Of these two epitopes, only the region I epitope (KPKHKKLKQPGDGNP) was previously shown to be recognized by human sera. In this study, we show that human immune sera from malarious regions recognize another B-cell epitope, ENANANNAV, that resides carboxyl to the repeat region. The present study reveals that (i) the repeat-sequence (NANP)-based B-cell epitope of the CS protein is an immunogenic but not immunodominant epitope; (ii) the natural expression of antibody responses to the two non-repeat-region-based B-cell epitopes of the CS protein varies in different populations in which malaria is endemic; (iii) although the host immune responses to the non-repeat-region-based B-cell epitopes increase as a function of host age, this increase is not statistically significant for the region I epitope but is significant for the other epitope; and (iv) the Th1R T-cell site but not the Th2R or Th3R T-cell site induces an antibody response in the human host. This study confirms the immunogenic potential of non-repeat-region-based B-cell epitopes and suggests that antibody pressures may also contribute to the maintenance of the antigenic diversity of the CS protein.     

Characterization of immunodominant and potentially protective epitopes of Mannheimia haemolytica serotype 1 outer membrane lipoprotein PlpE

Mannheimia haemolytica serotype 1 (S1) is the most common bacterial isolate found in shipping fever pneumonia in beef cattle. Currently used vaccines against M. haemolytica do not provide complete protection against the disease. Research with M. haemolytica outer membrane proteins (OMPs) has shown that antibodies to one particular OMP from S1, PlpE, may be important in immunity. In a recently published work, members of our laboratory showed that recombinant PlpE (rPlpE) is highly immunogenic when injected subcutaneously into cattle and that the acquired immunity markedly enhanced resistance to experimental challenge (A. W. Confer, S. Ayalew, R. J. Panciera, M. Montelongo, L. C. Whitworth, and J. D. Hammer, Vaccine 21:2821-2829, 2003). The objective of this work was to identify epitopes of PlpE that are responsible for inducing the immune response. Western blot analysis of a series of rPlpE with nested deletions on both termini with bovine anti-PlpE hyperimmune sera showed that the immunodominant region is located close to the N terminus of PlpE. Fine epitope mapping, in which an array of overlapping 13-mer synthetic peptides attached to a derivatized cellulose membrane was probed with various affinity-purified anti-PlpE antibodies, identified eight highly reactive regions, of which region 2 (R2) was identified as the specific epitope. The R2 region is comprised of eight imperfect repeats of a hexapeptide (QAQNAP) and is located between residues 26 and 76. Complement-mediated bactericidal activity of affinity-purified anti-PlpE bovine antibodies confirmed that antibodies directed against the R2 region are effective in killing M. haemolytica.     

Competitive ELISA for detection of antibodies to porcine reproductive and respiratory syndrome virus using recombinant E. coli-expressed nucleocapsid protein as antigen

The 15 kDa nucleocapsid (N) protein is the most abundant protein of the porcine reproductive and respiratory syndrome virus (PRRSV), and is highly antigenic, which therefore makes it a suitable candidate for the detection of virus-specific antibodies and diagnosis of the disease. In this study, complementary DNA corresponding to the entire N gene of the IAF-Klop strain of PRRSV was cloned into the pGEX-4T-1 vector, and the N protein was expressed in Escherichia coli fused to the glutathione S-transferase (GST) protein. The resulting GST-N recombinant fusion protein was purified by affinity chromatography and used as antigen for serological testing by indirect enzyme-linked immunosorbent assay (ELISA). Two anti-N specific monoclonal antibodies (MAbs) (IAF-K8 and IAF-2B4), obtained following fusion experiments with spleen cells of BAlb/c mice that were immunized with the purified virus, were used in a competitive assay to increase the specificity of the ELISA. Both MAbs were found to be directed against highly conserved conformational epitopes of North American isolates of PRRSV. Optimal concentration of GST-N protein was determined by checkerboard titration, using hyperimmune pig antiserum to the homologous PRRSV strain, and corresponded to a range of 0.1-0.5 microg protein per well. When tested on 95 sera from pigs that were experimentally infected with the IAF-Klop strain, the competitive ELISA (K8-ELISA) was capable of detecting anti-PRRSV antibodies in 86.7% (65/75) and 92.6% (63/68) of pig sera known to be seropositive by indirect immunofluorescence (antibody titers >16) and a currently used commercial ELISA (HerdCheck(R); Idexx), with specificity values of 100 and 96.2%, respectively. When tested on clinical samples (542 sera) from 28 positive and 28 negative pig herds, the K8-ELISA performed in a similar way to HerdCheck(R) and immunofluorescence (IF) tests as shown by kappa values of 0.762 and 0.803. The sensitivity and specificity of K8-ELISA were 100% on a herd basis, whereas sensitivity values of 80 and 82% with a specificity of 98.7% were determined on an individual basis in comparison with HerdCheck(R) and IF tests.     

Identification of a Linear Neutralization Domain in the Protein VP2 of African Horse Sickness Virus

Overlapping fragments of the outermost capsid protein VP2 of African horse sickness virus serotype 4 (AHSV-4) have been expressed in Escherichia coli. Horse sera from infected and vaccinated animals, rabbit sera, and mice monoclonal antibodies specific for AHSV were used to screen these fragments for antigenic regions. The screening revealed that the major antigenic domain of the AHSV-4 VP2 is localized in a central region (amino acids 200 to 413) and that both the N-terminal region (aa 1-159) and the half C-terminal region (aa 414-1060) are not immunogenic. All the fragments containing a region between amino acids 253 and 413 (fragment H) were able to elicit consistently high titers of neutralizing antibodies. The ability of several subfragments of this region to evoke neutralizing antibodies indicates the presence of several sites inside this domain. However, neutralizing antibodies in sera of horse infected or vaccinated with attenuated viruses were not absorbed by fragment H, indicating that this domain is not immunodominant in AHSV. This information might be useful in designing a subunit vaccine against AHSV infection.     

Identification and characterization of Neospora caninum tachyzoite antigens useful for diagnosis of neosporosis.

The purpose of the present study was to identify antigens of the protozoan Neospora caninum that could be useful for the diagnosis of neosporosis in domestic animals. As revealed by immunoblotting, immune sera from a wide range of animal species exhibited a similar recognition pattern of four major and several minor N. caninum antigens. In contrast to preinoculation sera, all tested immune sera recognized nonreduced immunodominant 17-, 29-, 30-, and 27-kDa antigens. A 46-kDa protein which showed faint recognition by preimmune sera also exhibited a strong response by immune sera. Immunolocalization of the four immunodominant N. caninum antigens was investigated by immunogold electron microscopy using monospecific polyclonal antisera. The 17-kDa antigen appears to be associated with the body part of the rhoptries, while the 29- and 30-kDa antigens were associated with the dense granules, network, and limiting membrane of the parasitophorous vacuole. Studies were also conducted to compare antibody responses to N. caninum and the related protozoan Toxoplasma gondii. Although N. caninum and T. gondii (RH strain) tachyzoites shared a few cross-reacting antigens, the immunodominant antigens of both parasites were not recognized by heterologous sera. Also, immunogold staining with rabbit anti-Neospora hyperimmune serum exhibited almost no labeling of external membranes of Neospora tachyzoites compared with the very marked labeling seen when Toxoplasma tachyzoites (RH strain) were incubated with rabbit anti-Toxoplasma hyperimmune serum. These unique antigenic differences should be useful in developing a diagnostic assay for N. caninum.     

Antigenic regions of tumor necrosis factor alpha and their topographic relationships with structural/functional domains.

The immunogenic regions of human Tumor Necrosis Factor alpha (huTNF) have been mapped by studying the interaction between various mouse anti-huTNF sera and synthetic huTNF fragments, spanning the entire sequence of huTNF. Three main immunogenic regions were identified within residues 1-23, 95-116 and 137-157 of huTNF and two other less immunogenic regions within residues 117-136 and 37-55. The same huTNF regions were found to contain antigenic sites by binding studies with cognate anti-peptide sera. Competitive binding experiments with shorter synthetic subfragments provided evidence for the location of strong antigenic sites within residues 1-10, 17-23, 104-112 and 137-143. In particular the immunodominant site was found to be located within residues 104-112. huTNF regions corresponding to residues 24-36, 56-75, 76-94, and 147-157 resulted to be not or poorly antigenic. However, treatment of huTNF with Triton X-100 under conditions that partially dissociate the oligomeric quaternary structure resulted in the exposition of sites recognized by sera against peptides huTNF [56-75] and huTNF [76-94], suggesting that antigenic sites not accessible in the oligomeric huTNF are exposed in the dissociated form. The principal antigenic sites in the oligomeric molecule are localized in the flexible N-terminal part and in hydrophilic segments located in the "middle/top" region of the molecule, opposite to the C-terminus. Protein segments of the "bottom" region, close to the C-terminus, were poorly immunoreactive. Neutralization assays of TNF cytolytic activity on L-M cells showed that binding of antibodies to epitopes located in the "middle/top" regions of huTNF does not affect its cytolytic activity, supporting the hypothesis of a receptor binding site location at the "bottom" of TNF trimer.     

T-cell epitope mapping of the three most abundant extracellular proteins of Mycobacterium tuberculosis in outbred guinea pigs

The three most abundant extracellular proteins of Mycobacterium tuberculosis, the 30-, 32-, and 16-kDa major extracellular proteins, are particularly promising vaccine candidates. We have mapped T-cell epitopes of these three proteins in outbred guinea pigs by immunizing the animals with each protein and assaying splenic lymphocyte proliferation against a series of overlapping synthetic peptides covering the entire length of the mature proteins. The 30-kDa protein contained nine immunodominant epitopes, the 32-kDa protein contained two immunodominant epitopes, and the 16-kDa protein contained a highly immunodominant region at its N terminus. The immunodominant epitopes of the 30- and 32-kDa proteins in outbred guinea pigs were frequently identified in healthy purified-protein-derivative-positive or BCG-vaccinated individuals in previous studies. The immunodominant epitopes of these major extracellular proteins have potential utility in an epitope-based vaccine against tuberculosis.     

Antigenicity of VP60 structural proteinof rabbit haemorrhagic disease virus

Summary.  Five overlapping segments of the VP60 capsid protein gene of rabbit haemorrhagic disease virus have been expressed in E. coli under the control of the T7 RNA polymerase. After purification, the antigenicity of these denatured protein segments has been studied by reactivity with sera from both naturally infected and vaccinated animals in Western blot analysis. The amino terminus segments of the protein (comprising the first 175 amino acids) are highly reactive with the tested sera, between 10 and 100 fold more than any of the segments reproducing the carboxy half of VP60, which is believed to be solvent-exposed in the virus particles. These results strongly suggest that the antigenic structure of the carboxy moiety of VP60 is mainly based on conformation-dependent B-cell epitopes whereas the amino terminal region of VP60 contains continuous antigenic determinants for the immune response elicited during both virus infection and exposure to the inactivated vaccine. Received April 21, 1997 Accepted May 16, 1997     

Epitope Detection in the Envelope of Intracellular Naked Orthopox Viruses and Identification of Encoding Genes

Monoclonal antibodies (MAbs) were generated against vaccinia virus, cowpox virus KR2 Brighton, monkeypox virus Copenhagen, or ectromelia virus. Pairwise epitope specificity studies by competition ELISAs identified 23 distinct antigenic sites in 19 different orthopox virus strains. Six epitopes were completely independent of each other, and 17 closely related antigenic sites formed three separate epitope complexes. As shown by immunogold electron microscopy (ELMI), all MAbs reacted with epitopes in the envelope of intracellular naked virus, 16 MAbs recognized proteins of 32, 30, 16 or 14 kDa in Western blotting (WB), and 9 MAbs neutralized virus infectivity. In rabbitpox virus (RPV) 18 epitopes were detected. A λgt11 expression library of RPV DNA was screened with the corresponding 18 MAbs. Fourteen recombinant bacteriophage clones (ph) were isolated. Cross-hybridizations of phage and RPV DNA demonstrated a reaction with the HindIII A, HindIII D, or HindIII H fragments, respectively. DNA of ph3D was related to the A25L gene, which corresponds to the A-type inclusion body gene of cowpox virus. Two phage clones contained sequences of the 14-kDa fusion protein gene (A27L gene). Ph1A contained nearly the entire 14-kDa gene encoding 4 neutralizing (neutr) and 2 nonneutr epitopes. Ph5, expressing only half of this gene product, encoded 1 nonneutr epitope. The fusion protein of vaccinia virus MVA was isolated by immune-affinity chromatography with a neutr. catching MAb. The protein formed hollow rods (ELMI) and the 6 antigenic sites that were present were identical to those expressed by Escherichia coli infected with ph1A. WB detection with a polyclonal hyperimmune serum detected protein bands of 54, 32, 30, 16, and 14 kDa. The catching MAb bound only to a 16-kDa band. The purified fusion protein induced neutralizing antibodies in mice and rabbits.     

Identification of genus-specific epitopes on the outer membrane complexes of Chlamydia trachomatis and Chlamydia psittaci immunotypes 1 and 2.

Polyclonal and monoclonal antibodies were used to study the immunogenic and antigenic characteristics of chlamydiae. We focused on the most predominant proteins in the outer membrane complex, the major outer membrane protein (MOMP) and the doublet consisting of proteins of 57 and 62 kilodaltons (57-62 kDa doublet). Immunoblot analyses were performed with chlamydial elementary bodies by using (i) immune sera from sheep which had undergone a recent episode of abortion due to the ovine abortion (OA) strain of C. psittaci, (ii) rabbit hyperimmune anti-C. psittaci (OA) and -C. trachomatis sera, and (iii) monoclonal antibodies to the MOMP of C. trachomatis. The typical pattern of response with polyclonal antisera against heterologous elementary bodies was reactivity with the 57-62 kDa doublet and lipopolysaccharide with weak and sometimes no anti-MOMP activity. Three distinct genus-specific anti-C. trachomatis MOMP monoclonal antibodies showed different patterns of reactivity with the MOMPs of the two immunotypes of C. psittaci and C. trachomatis serovars. Our data confirm the predominance of a genus-specific 57-62 kDa doublet response despite the presence of genus-specific epitopes on the MOMP.     

Immunodominant structures of human growth hormone identified by homolog-scanning mutagenesis.

Homolog-scanning mutagenesis has been reported to be useful in elucidating the antigenic epitopes recognized by monoclonal antibodies and hGH binding to its receptor. However, little is known about which structures are recognized as immunodominant by murine serum antibodies. Therefore, the previously published series of hGH homologs and additional mutants of human placental lactogen (hPL), porcine growth hormone (pGH), and human prolactin (hPRL) were examined for their interaction with murine serum derived anti-hGH antibodies. As compared to wild-type hGH, nine of the nineteen segment substituted mutants tested showed a significant reduction in binding to anti-hGH sera. These disruptive substitutions mapped to 5 regions on a structural model of hGH: the length of helix 1 (residues 11-33), the loop between the first disulfide bond and helix 2 (residues 54-74), the beginning of helix 3 (residues 109-112), the carboxyl half of helix 4 (residues 167-182), and the final carboxyl terminus segment of the molecule (residues 184-191). In terms of the current structural model, three of the five immunodominant regions (the loop between residues 54-74, central portion of helix 4 to the carboxyl terminus and part of the amino terminus region of helix 1) closely overlaps the hGH receptor binding epitopes.     

Epitopes of the G1 glycoprotein of La Crosse virus form overlapping clusters within a single antigenic site

Antigenic sites on the G1 glycoprotein of La Crosse bunyavirus were defined by constructing a panel of neutralizing and nonneutralizing monoclonal antibodies (F. Gonzalez-Scarano, R. E. Shope, C. H. Calisher, and N. Nathanson (1982), Virology 120, 42-53). To analyze the relationship between the individual epitopes delineated by monoclonal antibodies, 11 neutralizing antibodies were used to select variant viruses. These variant viruses were tested against the panel of anti-G1 protein monoclonal antibodies by neutralization and by ELISA. The neutralization tests assigned the 11 epitopes to five groups, consisting of 6, 2, 1, 1, and 1 epitopes. ELISA tests gave a similar pattern, but also demonstrated interrelationships between four of the five epitope groups, suggesting that there may be a single immunodominant antigenic site on the G1 protein. When eight nonneutralizing anti-G1 monoclonal antibodies were tested in ELISA, they fell into three of the five epitope groups defined by neutralization; there was no evidence of a separate noneutralizing antigenic site on the G1 protein.