Hybrid papillomavirus L1 molecules assemble into virus-like particles that reconstitute conformational epitopes and induce neutralizing antibodies to distinct HPV types

Human papillomavirus (HPV) hybrid virus-like particles (VLPs) were prepared using complementary regions of the major capsid L1 proteins of HPV-11 and -16. These hybrid L1 proteins were tested for assembly into VLPs, for presentation and mapping of conformational neutralizing epitopes, and as immunogens in rabbits and mice. Two small noncontiguous hypervariable regions of HPV-16 L1, when replaced into the HPV-11 L1 backbone, produced an assembly-positive hybrid L1 which was recognized by the type-specific, conformationally dependent HPV-16 neutralizing monoclonal antibody (N-MAb) H16.V5. Several new N-MAbs that were generated following immunization of mice with wild-type HPV-16 L1 VLPs also recognized this reconstructed VLP, demonstrating that these two hypervariable regions collectively constituted an immunodominant epitope. When a set of hybrid VLPs was tested as immunogens in rabbits, antibodies to both HPV-11 and -16 wild-type L1 VLPs were obtained. One of the hybrid VLPs containing hypervariable FG and HI loops of HPV-16 L1 replaced into an HPV-11 L1 background provoked neutralizing activity against both HPV-11 and HPV-16. In addition, conformationally dependent and type-specific MAbs to both HPV-11 and HPV-16 L1 VLP were obtained from mice immunized with hybrid L1 VLPs. These data indicated that hybrid L1 proteins can be constructed that retain VLP-assembly properties, retain type-specific conformational neutralizing epitopes, can map noncontiguous regions of L1 which constitute type-specific conformational neutralizing epitopes recognized by N-MAbs, and trigger polyclonal antibodies which can neutralize antigenically unrelated HPV types.

Human brain carboxypeptidase B, which cleaves β-amyloid peptidesin vitro, is expressed in the endoplasmic reticulum of neurons

Intracellular localization of novel human brain carboxypeptidase B (HBCPB) was investigated in human hippocampus, using immunohistochemistry by confocal laser microscopy and biochemical purification of the homogenate by density gradient ultracentrifugation. The former revealed that the majority of HBCPB was expressed in the endoplasmic reticulum, in which the HBCPB-specific C14-module immunoreactivity was colocalized with GRP78 immunoreactivity, a stress 70 heat shock protein specifically expressed in the endoplasmic reticulum. The latter showed that anti-C14-module immunoreactivity and prepro-HBCPB immunoreactivity were both enriched in the microsome fraction, especially in that of the endoplasmic reticulum-density fraction of normal human hippocampal homogenates from various sources. However, HBCPB prepared from human hippocampus showed exopeptidase activity for synthetic beta-amyloid 1-42 peptide, in which Abeta X-42 C-terminus immunoreactivity was decreased in a fashion dose-dependent of the amount of the protease added. These findings indicate that HBCPB, which is expressed in the endoplasmic reticulum of a group of neuronal perikarya, may play an important physiological role in degradation of beta-amyloid 1-42, which is specifically generated in the endoplasmic reticulum of human and rodent neurons and is also regarded as the most pathogenic and aggregatable species among all beta-amyloid peptides.

Epitope tagging of chromosomal genes in Salmonella

We have developed a simple and efficient procedure for adding an epitope-encoding tail to one or more genes of interest in the bacterial chromosome. The procedure is a modification of the gene replacement method of Datsenko and Wanner [Datsenko, K. A. & Wanner, B. L. (2000) Proc. Natl. Acad. Sci. USA 97, 6640-6645]. A DNA module that begins with the epitope-encoding sequence and includes a selectable marker is amplified by PCR with primers that carry extensions (as short as 36 nt) homologous to the last portion of the targeted gene and to a region downstream from it. Transformation of a strain expressing bacteriophage lambda red functions yields recombinants carrying the targeted gene fused to the epitope-encoding sequence. The resulting C-terminal-tagged protein can be identified by standard immuno-detection techniques. In an initial application of the method, we have added the sequences encoding the FLAG and 3xFLAG and influenza virus hemagglutinin epitopes to various genes of Salmonella enterica serovar Typhimurium, including putative and established pathogenic determinants present in prophage genomes. Epitope fusion proteins were detected in bacteria growing in vitro, tissue culture cells, and infected mouse tissues. This work identified a prophage locus specifically expressed in bacteria growing intracellularly. The procedure described here should be applicable to a wide variety of Gram-negative bacteria and is particularly suited for the study of intracellular pathogens.

T cell epitopes of human myelin oligodendrocyte glycoprotein identified in HLA-DR4 (DRB1*0401) transgenic mice are encephalitogenic and are presented by human B cells

Myelin oligodendrocyte glycoprotein (MOG) is an Ag present in the myelin sheath of the CNS thought to be targeted by the autoimmune T cell response in multiple sclerosis (MS). In this study, we have for the first time characterized the T cell epitopes of human MOG restricted by HLA-DR4 (DRB1*0401), an MHC class II allele associated with MS in a subpopulation of patients. Using MHC binding algorithms, we have predicted MOG peptide binding to HLA-DR4 (DRB1*0401) and subsequently defined the in vivo T cell reactivity to overlapping MOG peptides by testing HLA-DR4 (DRB1*0401) transgenic mice immunized with recombinant human (rh)MOG. The data indicated that MOG peptide 97-108 (core 99-107, FFRDHSYQE) was the immunodominant HLA-DR4-restricted T cell epitope in vivo. This peptide has a high in vitro binding affinity for HLA-DR4 (DRB1*0401) and upon immunization induced severe experimental autoimmune encephalomyelitis in the HLA-DR4 transgenic mice. Interestingly, the same peptide was presented by human B cells expressing HLA-DR4 (DRB1*0401), suggesting a role for the identified MOG epitopes in the pathogenesis of human MS.

Structural and functional characterization of a monoclonal antibody specific for the preS1 region of hepatitis B virus

The monoclonal antibody 5a19, raised against the ay serotype of hepatitis B virus, binds to the segment of the preS1 region comprising residues 37-43, which is implicated in attachment of the virus to hepatocytes. The dissociation constant, derived from kinetic studies using surface plasmon resonance techniques, is in the low nanomolar range. The nucleotide sequence of the variable domains has been determined and the corresponding germ-line genes have been identified. The three-dimensional structure of the Fab fragment has been determined by X-ray crystallography to 2.6 A resolution.

Mapping of epitopes in discoidin domain receptor 1 critical for collagen binding

The binding and activation of the discoidin domain receptor 1 by collagen has led to the conclusion that proteins from the extracellular matrix can directly induce receptor tyrosine kinase-mediated signaling cascades. A region in the extracellular domain of DDR1 homologous to the Dictyostelium discoideum protein discoidin-I is also present in the secreted human protein RS1. Mutations in RS1 cause retinoschisis, a genetic disorder characterized by ablation of the retina. By introducing point mutations into the discoidin domain of DDR1 at positions homologous to the retinoschisis mutations, ligand binding epitopes in the discoidin domain of DDR1 were mapped. Surprisingly, some residues only affected receptor phosphorylation, whereas others influenced both collagen-binding and receptor activation. Furthermore, two truncated DDR1 variants, lacking either the discoidin domain or the stalk region between the discoidin and transmembrane domain, were generated. We showed that (i) the discoidin domain was necessary and sufficient for collagen binding, (ii) only the region between discoidin and transmembrane domain was glycosylated, and (iii) the entire extracellular domain was essential for transmembrane signaling. Using these results, we were able to predict key sites in the collagen-binding epitope of DDR1 and to suggest a potential mechanism of signaling.

Regression of human T-cell leukemia virus type I (HTLV-I)-associated lymphomas in a rat model: peptide-induced T-cell immunity

BACKGROUND

Human T-cell leukemia virus type I (HTLV-I) is etiologically linked to adult T-cell leukemia (ATL). The disease has a high mortality rate and is resistant to chemotherapy; therefore, immunologic approaches to treatment could be of interest. We have previously shown that athymic rats inoculated with a syngeneic (i.e., with the same genetic background) HTLV-I-infected T-cell line (FPM1-V1AX) develop ATL-like disease and that the transfer of T cells from normal syngeneic rats immunized with FPM1-V1AX cells prevents disease development. In this study, we further characterized the host antitumor immunity to explore the possibility of peptide-based vaccination against the ATL-like disease.

METHODS

Immune T cells from rats immunized with FPM1-V1AX cells were analyzed for their phenotypes and cytotoxic properties. The epitope recognized by the T cells was analyzed by fine mapping. To evaluate the antitumor effects of a peptide-based vaccine, normal rats were immunized with synthetic oligopeptides corresponding to the epitope, the T cells were transferred to athymic rats inoculated with HTLV-I infected cells, and tumor size was monitored.

RESULTS

Both CD4+ and CD8+ T-cell populations from rats immunized with FPM1-V1AX cells inhibited the growth of FPM1-V1AX cell-induced lymphomas in vivo. Long-term culture of splenic T cells from the immunized rats repeatedly resulted in establishment of CD8+ HTLV-I-specific cytotoxic T lymphocyte (CTL) lines restricted to the rat major histocompatibility complex class I molecule, RT1.A(l). The cytotoxicity of these lines was directed against the HTLV-I regulatory protein Tax and, specifically, against the epitope, amino acids 180-188 (GAFLTNVPY). Adoptive transfer of the Tax 180-188-specific CTL line or freshly prepared T cells from rats vaccinated with the Tax 180-188 oligopeptide prevented the development of FPM1-V1AX-cell induced lymphomas in athymic rats in comparison with control groups (two rats in each group).

CONCLUSIONS

This study indicated a potential therapeutic effect of peptide-based vaccination against HTLV-I-induced lymphoproliferative disease.

Comparison of phage pIII, pVIII and GST as carrier proteins for peptide immunisation in Balb/c mice

Carrier proteins are important for improving the efficiency of synthetic peptide vaccines. Recently, genetically-based systems such as filamentous phage display or glutathione S-transferase (GST)-fusion proteins have been employed for immunisation. Whilst these carrier systems can facilitate the evaluation of a potential vaccine by reducing the time and cost of production, their relative efficacy and the kinetics of the immune response to each carrier has not been directly compared. In this study, we have displayed the epitopes of the anti-ErbB-2 Mabs N12 (C531-A586, EP531) and N28 (T216-C235, EP216) on phage minor coat protein pIII, major coat protein pVIII and GST. Balb/c H-2(d) mice were immunised with the constructs and the sera were tested after the initial, the 3rd, 5th and 6th immunisations for an anti-peptide, an anti-ErbB-2 and an anti-carrier response. The specificity of the antibody response was also mapped using synthetic peptides. It was found that GST was the best of the three carriers, both in terms of the magnitude and the kinetics of the induced anti-peptide and anti-ErbB-2 response. Multiple (five) administrations of the immunogens were necessary to obtain a high titre of antibodies specific for ErbB-2. It was further noted that whilst an anti-EP531 response was induced using all three carriers, EP216 was not immunogenic irrespective of the carrier used. The lack of immunogenicity of EP216 implies it does not contain a H-2(d) T cell recognition site. All three carriers provide a useful system for vaccination and consequently facilitate the identification of T-cell epitopes in Balb/c inbred mice.

Multiple overlapping epitopes in the repetitive unit of the shed acute-phase antigen from Trypanosoma cruzi enhance its immunogenic properties

The repetitive shed acute-phase antigen (SAPA) from Trypanosoma cruzi was thoroughly mapped by SPOT peptides and phage display strategies, showing that a single SAPA repeat is composed of multiple overlapping B-cell epitopes. We propose that this intricate antigenic structure constitutes an alternative device to repetitiveness in order to improve its immunogenicity.

Quantity and quality of virus-specific CD8 cell response: relevance to the design of a therapeutic vaccine for chronic HBV infection

Chronic hepatitis B virus (HBV) infection is a major cause of morbidity and mortality worldwide, yet currently available therapies fail to provide long-term control of viral replication in most patients. Strategies to boost the weak virus-specific T-cell response typically found in patients with chronic hepatitis B have been proposed as a means of terminating persistent HBV infection. The potential problems arising from the stimulation of virus-specific immunity in a disease caused by a non-cytopathic virus, where viral control and liver injury are mediated by the immune system, are discussed. Furthermore, the concept of augmenting the HBV-specific T-cell response, which has previously been focused solely on quantitative issues, is expanded in the light of new findings of qualitative differences in the HBV-specific CD8 cell response.

Antibodies against the carboxyl-terminal end of the Trypanosoma cruzi ribosomal P proteins are pathogenic

Sera from patients with chronic Chagas heart disease recognize the carboxyl-terminal regions of the Trypanosoma cruzi ribosomal P proteins defined by B cell epitopes P013 (EDDDDDFGMGALF) and R13 (EEEDDDMGFGLFD) corresponding to the T. cruzi ribosomal P0 (TcP0) and P2beta (TcP2beta) proteins, respectively. It has been hypothesized that both epitopes may induce antibodies that cross-react and stimulate the beta1-adrenoreceptor. However, no proof as to their pathogenicity has been obtained. We investigated the consequences of immunizing mice with either TcP0 or TcP2beta proteins. Of 24 immunized animals, 16 generated antibodies against the carboxyl-terminal end of the corresponding protein, 13 of which showed an altered ECG (P<0.001, 81%). Immunization with TcP0 induced anti-P013 antibodies that bind to and stimulate cardiac G-protein-coupled receptors and are linked to the induction of supraventricular arrhythmia, repolarization, and conduction abnormalities as monitored by serial electrocardiographic analysis. In contrast, immunization with TcP2beta generated anti-R13 antibodies with an exclusive beta1-adrenergic-stimulating activity whose appearance strictly correlated with the recording of supraventricular tachycardia and death. These findings demonstrate that anti-P antibodies are arrhythmogenic in the setting of a normal heart, since no inflammatory lesions or fibrosis were evident to light microscopic examination.

Identification of epitopes on the envelope (E) protein of dengue 2 and dengue 3 viruses using monoclonal antibodies

Of a panel of forty-six anti-dengue 3 monoclonal antibodies (MAbs) only three neutralised infection of BHK cells by dengue 3 virus. Attempts to select neutralisation escape mutants (n.e.m.) with two of these antibodies failed. The n.e.m. population selected in the presence of the third neutralising antibody, 1H9, had a nucleotide change at position 1157 of the E protein gene resulting in a non-conservative amino acid change at E386 for a Lys to an Asn. A dengue 2 n.e.m. was selected with the flavivirus crossreactive IgG monoclonal antibody 4G2, had deduced amino acid changes at E169 (Ser to Pro) and E275 (Gly to Arg). This dengue 2 n.e.m. population produced smaller plaques in BHK cells than the parental virus, decreased fusion activity (FFWI) and had lost the ability to agglutinate gander erythrocyes at pH 6.0 to 6.7.

Unique monoclonal antibody recognizing the third extracellular loop of CXCR4 induces lymphocyte agglutination and enhances human immunodeficiency virus type 1-mediated syncytium formation and productive infection

To increase insight into the structural basis of CXCR4 utilization in human immunodeficiency virus type 1 (HIV-1) infection, a new generation of three monoclonal antibodies (MAbs) was developed in WKA rats. The A80 MAb, which binds an epitope in the third extracellular loop (ECL3) of CXCR4, has unique biologic properties that provide novel insights into CXCR4 function. This agent enhanced syncytium formation in activated human peripheral blood mononuclear cells (PBMC) infected with X4 or R5 and CEM cells infected with X4 HIV-1 strains. Exposure to A80 increased the productive infection of activated CD4(+) T cells and CEM cells with R5 and X4 viruses, respectively. This antibody uniquely induced agglutination of PBMC and CEM cells but did not activate calcium mobilization. Agglutination induced by A80 was inhibited by stromal cell-derived factor 1, T22, and phorbol 12-myristate 13-acetate but was not significantly altered by pretreatment of cells with pertussis toxin, wortmannin, or MAbs to LFA-1, ICAM-1, ICAM-2, and ICAM-3. The binding of the A145 and A120 MAbs was mapped to the N-terminal extracellular domain and a conformational epitope involving ECL1 and ECL2, respectively. Both of these MAbs inhibited HIV-1 infection and lacked the novel properties of A80. These results suggest a new role for CXCR4 in homologous lymphocyte adhesion that is ligand independent and in HIV-1 infection.

Implication of protein S thrombin-sensitive region with membrane binding via conformational changes in the gamma-carboxyglutamic acid-rich domain

In the vitamin K-dependent protein family, only protein S (PS) contains a thrombin-sensitive region (TSR), located between the domain containing the gamma-carboxyglutamic acid and the first epidermal growth factor-like domain. To better define the role of TSR in the PS molecule, we expressed a recombinant human PS (rHPS) and its analogue lacking TSR (rTSR-less), and prepared factor Xa- and thrombin-cleaved rHPS. A peptide reproducing TSR (TSR-peptide) was also synthesized in an attempt to obtain direct evidence of the domain involvement in PS anticoagulant activity. In a coagulation assay, both rTSR-less and factor Xa-cleaved PS were devoid of activated protein C cofactor activity. The TSR-peptide did not inhibit rHPS activity, showing that TSR must be embedded in the native protein to promote interaction with activated protein C. The binding of rHPS to activated platelets and to phospholipid vesicles was not modified after factor Xa- or thrombin-mediated TSR cleavage, whereas the binding of rTSR-less was markedly reduced. This suggested a role for TSR in conferring to PS a strong affinity for phospholipid membranes. TSR-peptide did not directly bind to activated platelets or compete with rHPS for phospholipid binding. The results of the present study show that TSR may not interact directly with membranes, but probably constrains the gamma-carboxyglutamic acid-rich domain in a conformation allowing optimal interaction with phospholipids.

Antiaggregating antibody raised against human PrP 106-126 recognizes pathological and normal isoforms of the whole prion protein

Antibodies to the prion protein (PrP) have been critical to the neuropathological and biochemical characterization of PrP-related degenerative diseases in humans and animals. Although PrP is highly conserved evolutionarily, there is some sequence divergence among species; as a consequence, anti-PrP antibodies have a wide spectrum of reactivity when challenged with PrP from diverse species. We have produced an antibody [monoclonal antibody (mAb) 2-40] raised against a synthetic peptide corresponding to residues (106-126 of human PrP and have characterized it by epitope mapping, Western immunoblot analysis, and immunohistochemistry. The antibody recognizes not only human PrP isoforms but also pathological PrP from all species tested (i.e., sheep, hamsters, and mice). Together with the fact that it recognizes the whole PrP in both cellular and scrapie isoforms, mAb 2-40 may be helpful in studying conformational changes of the PrP, as well as establishing a possible connection between human and animal diseases.

Sandwich enzyme-linked immunosorbent assay system for micro-detection of the wheat allergen, Tri a Bd 17 K

Seven monoclonal antibodies (mAbs) against the wheat allergen, Tri a Bd 17 K, were prepared to obtain mAbs suitable for a sandwich enzyme-linked immunosorbent assay (sandwich ELISA) for determination of the allergen. Two of the mAbs strongly immunoblotted the allergen purified from wheat flour. However, only one (1G11) of them was found to be suitable for sandwich ELISA. Epitope mapping against mAb-1G11 on the allergen showed that the mAb recognized the peptide containing Lys-38 and Gln-39 of the allergen. We developed a sandwich ELISA method consisting of Aleuria aurantia lectin for fixing the allergen and 1G11 as the first antibody that enabled 4-4,000 ng/well of the allergen to be determined.

Somatic lamins in germinal vesicles of goldfish (Carassius auratus) vitellogenic oocytes

In fish and amphibians, B-type lamins are divided into somatic (B1, B2) and oocyte-type (B3) lamins. In this study, we purified nuclear lamins from rainbow trout erythrocytes, raised an anti-lamin monoclonal antibody (L-200) that recognizes goldfish somatic-lamins, and isolated cDNAs encoding goldfish B-type lamins (B1 and B2) from a goldfish cell culture cDNA library. Goldfish B-type lamins are structurally similar to lamins found in other vertebrates with minor amino acid substitutions in the conserved region. Western blot analysis showed that goldfish oocytes contained mainly GV-lamin B3 as well as some somatic lamins. Laser-confocal microscope observations revealed that lamin B3 was present only in GV nuclear lamina, whereas somatic lamins were present in dense fibrillar structures throughout nuclear gels of isolated GVs. Similar nuclear filamentous structures were also observed in GVs of paraffin embedded oocytes. Epitope mapping indicated that L-200 recognized a conserved region containing a short stretch of the alpha-helix coiled-coil rod domain (Y(E/Q)(Q/E)LL). A similar motif is also present in other cytoplasmic intermediate filaments (i.e., vimentin, desmin, peripherin and GFAP). Taken together, these findings suggest that lamins or lamin-related intermediate filaments are an important component of the interior architecture of goldfish vitellogenic oocyte nuclei (GVs).

Individuation of monoclonal anti-HPV16 E7 antibody linear peptide epitope by computational biology

We applied computational biology to identify the linear amino acid sequence recognized by a mouse monoclonal antibody raised against the full length HPV16 E7 oncoprotein. Computer-assisted search for the epitopic peptide used two parameters: the capability of E7 peptides to bind to MHC class II molecules, and the similarity level of the oncoprotein sequence to the mouse proteome. We report that anti-E7 mAb recognized the peptide having both high binding potential to MHC II molecules and low level of molecular mimicry to mouse proteome. Peptide ability to bind to MHC II molecules appears a necessary but not sufficient condition to determine peptide immunodominance, by needing to be supported by a low degree of peptide similarity to the host's proteome.

Cervicovaginal secretory antibodies to human immunodeficiency virus type 1 (HIV-1) that block viral transcytosis through tight epithelial barriers in highly exposed HIV-1-seronegative African women

Antibodies to human immunodeficiency virus (HIV) of the IgA, IgG, and IgM isotypes and high levels of the HIV suppressive beta-chemokine RANTES (regulated on activation, normally T cell expressed and secreted) were found in the cervicovaginal secretions (CVSs) of 7.5% of 342 multiply and repeatedly exposed African HIV-seronegative female sex workers. The antibodies are part of a local compartmentalized secretory immune response to HIV, since they are present in vaginal fluids that are free of contaminating semen. Cervicovaginal antibodies showed a reproducible pattern of reactivity restricted to gp160 and p24. Locally produced anti-env antibodies exhibit reactivity toward the neutralizing ELDKWA epitope of gp41. Study results show that antibodies purified from CVSs block the transcytosis of cell-associated HIV through a tight epithelial monolayer in vitro. These findings suggest that genital resistance to HIV may involve HIV-specific cervicovaginal antibody responses in a minority of highly exposed HIV-seronegative women in association with other protecting factors, such as local production of HIV-suppressive chemokines.

Epitope mapping using the X-ray crystallographic structure of complement receptor type 2 (CR2)/CD21: identification of a highly inhibitory monoclonal antibody that directly recognizes the CR2-C3d interface

Complement receptor type 2 (CR2)/CD21 is a B lymphocyte cell membrane C3d/iC3b receptor that plays a central role in the immune response. Human CR2 is also the receptor for the EBV viral membrane glycoprotein gp350/220. Both C3d and gp350/220 bind CR2 within the first two of 15-16 repetitive domains that have been designated short consensus/complement repeats. Many mAbs react with human CR2; however, only one currently available mAb is known to block both C3d/iC3b and gp350/220 binding. We have used a recombinant form of human CR2 containing the short consensus/complement repeat 1-2 ligand-binding fragment to immunize Cr2(-/-) mice. Following fusion, we identified and further characterized four new anti-CR2 mAbs that recognize this fragment. Three of these inhibited binding of CR2 to C3d and gp350/220 in different forms. We have determined the relative inhibitory ability of the four mAbs to block ligand binding, and we have used overlapping peptide-based approaches to identify linear epitopes recognized by the inhibitory mAbs. Placement of these epitopes on the recently solved crystal structure of the CR2-C3d complex reveals that each inhibitory mAb recognizes a site either within or adjacent to the CR2-C3d contact site. One new mAb, designated 171, blocks CR2 receptor-ligand interactions with the greatest efficiency and recognizes a portion of the C3d contact site on CR2. Thus, we have created an anti-human CR2 mAb that blocks the C3d ligand by direct contact with its interaction site, and we have provided confirmatory evidence that the C3d binding site seen in its crystal structure exists in solution.

Complexity of the single linear neutralization epitope of the mouse arterivirus lactate dehydrogenase-elevating virus

Results from indirect ELISAs using synthetic peptides of various length that represent segments of the ectodomain of the envelope glycoprotein, VP-3P, of lactate dehydrogenase-elevating virus (LDV) showed that the primary neutralization epitope of LDV is located in a short linear hydrophilic segment in the center of the ectodomain. The epitope becomes slightly altered by amino acid substitutions in the ectodomain and inactivation of virions by various treatments. Neutralizing anti-VP-3P antibodies (Abs) to the epitope interact with the synthetic peptides only if they possess a certain conformation. When the peptides were immobilized on ELISA plates, neutralizing mAbs elicited to inactivated LDV and neutralizing Abs from infected mice bound best to the peptides that consisted of the full-length, 30-amino-acid-long ectodomain. The Abs bound poorly, if at all, to most of the shorter peptides when immobilized, whether truncated at the N- or C-end, but when in solution the same peptides strongly inhibited the binding of the Abs to immobilized full-length peptides. Thus, a conformation of the epitope required for Ab binding and (or) its steric accessibility were lost upon immobilization of the shorter peptides on ELISA plates. Abs raised in mice to peptide-bovine serum albumin conjugates reacted only with immobilized peptides in the indirect ELISA and failed to neutralize LDV. The neutralization epitope of the common LDV quasispecies, LDV-P and LDV-vx, is flanked by N-glycans that block the immunogenicity of the epitope and the neutralization of these LDVs. Abs to a second weakly immunogenic and probably discontinuous epitope appear in LDV infected mice about 1 month postinfection.

Analysis of the proliferative responses to peptides in individuals with vigorous Gag protein-specific proliferation

Proliferative responses to recombinant HIV proteins in infected individuals may represent a correlate of protection from disease progression. In this study, the proliferative responses to HIV p24, p55 and gp120 were evaluated in infected subjects. Whereas, vigorous proliferative responses directed at the Gag proteins were detected in several individuals, Env-specific proliferation was observed in only one subject. Epitope mapping using overlapping peptides demonstrated proliferative responses of PBMC to Gag peptides. Responses were broadly directed at multiple peptides in some subjects. Although several of the peptides that induced proliferative responses also contain CTL epitopes potentially relevant in the particular individuals, many additional Gag T cell epitopes were present in each subject. This finding may be relevant for the design and testing of HIV candidate vaccines.

Frequency and function of HIV-specific CD8(+) T cells

The virus-specific CD8(+) T cell responses of 27 HIV-infected patients were studied, including a unique cohort of long term nonprogressors (LTNP) with normal CD4(+) T cell counts, low levels of plasma viral RNA, strong proliferative responses to HIV antigens and an over-representation of the HLA B*5701 class I allele. The frequencies of CD8(+) T cells specific to the majority of HIV gene products were measured by flow cytometric detection of intracellular interferon-gamma (IFN-gamma) in response to HIV-vaccinia recombinant infected autologous B cells. Very high frequencies (1.4-22%) of circulating CD8(+) T cells were found to be HIV-specific and were not only found in LTNP with reduced plasma virus. No correlation was evident between the frequency of HIV-specific CD8(+) T cells and levels of plasma viremia. In each case, the vast majority of cells (up to 17.2%) responded to Gag-Pol gene products. Although similar frequencies of Gag peptide-specific CD8(+) T cells were found in LTNP and progressors by either intracellular IFN-gamma or MHC class I tetramer staining, the breadth of these responses was greater in patients with progressive HIV infection compared with the LTNP group. The frequency of CD8(+) T cells specific for a single peptide was not representative of an individual patient's total HIV-specific CD8(+) T cell response. These data demonstrate that high numbers of HIV-specific CD8(+) T cells exist even in patients with high level viremia and progressive disease. Further, they suggest that other qualitative parameters of the CD8(+) T cell response may differentiate some patients with very low levels of plasma virus and nonprogressive infection.

Identification of an antigenic epitope in Helicobacter pylori urease that induces neutralizing antibody production

We previously reported a mouse monoclonal antibody (MAb), termed L2, specific for Helicobacter pylori urease strongly inhibited its enzymatic activity. Here, to gain insight into how this antibody affects urease activity, the epitope that was recognized by the antibody was determined. By screening a panel of overlapping synthetic peptides covering the entire sequence of the two subunits (UreA and UreB), we identified a stretch of UreB-derived 19 amino acid (aa) residues (UB-33; aa 321 to 339, CHHLDKSIKEDVQFADSRI) that was specifically recognized by the L2 antibody. Further sequential amino acid deletion of the 19-mer peptide from either end allowed us to determine the minimal epitope as 8 amino acid residues (F8; SIKEDVQF) for L2 reactivity. This epitope appears to lie exactly on a short sequence which formed a flap over the active site of urease, suggesting that binding of the L2 antibody sterically inhibits access of urea, the substrate of urease. Finally, immunization of rabbits with either the 19-mer peptide or the 8-mer minimal epitope resulted in generation of antiurease antibodies that were capable of inhibiting the enzymatic activity. Since urease is critical for virulence of H. pylori, antigenic peptides that induce production of antibodies to inhibit its enzymatic activity may potentially be a useful tool as a vaccine for prevention and treatment of H. pylori infection.