MAb B6 Research Articles

Dissection of the anti-Candida albicans mannan immune response using synthetic oligomannosides reveals unique properties of \u03b2-1,2 mannotriose protective epitopes

Candida albicans mannan consists of a large repertoire of oligomannosides with different types of mannose linkages and chain lengths, which act as individual epitopes with more or less overlapping antibody specificities. Although anti-C. albicans mannan antibody levels are monitored for diagnostic purposes nothing is known about the qualitative distribution of these antibodies in terms of epitope specificity. We addressed this question using a bank of previously synthesized biotin sulfone tagged oligomannosides (BSTOs) of α and β anomery complemented with a synthetic β-mannotriose described as a protective epitope. The reactivity of these BSTOs was analyzed with IgM isotype monoclonal antibodies (MAbs) of known specificity, polyclonal sera from patients colonized or infected with C. albicans, and mannose binding lectin (MBL). Surface plasmon resonance (SPR) and multiple analyte profiling (MAP) were used. Both methods confirmed the usual reactivity of MAbs against either α or β linkages, excepted for MAb B6.1 (protective epitope) reacting with β-Man whereas the corresponding BSTO reacted with anti-α-Man. These results were confirmed in western blots with native C. albicans antigens. Using patients’ sera in MAP, a significant correlation was observed between the detection of anti-mannan antibodies recognizing β- and α-Man epitopes and detection of antibodies against β-linked mannotriose suggesting that this epitope also reacts with human polyclonal antibodies of both specificities. By contrast, the reactivity of human sera with other α- and β-linked BSTOs clearly differed according to their colonized or infected status. In these cases, the establishment of an α/β ratio was extremely discriminant. Finally SPR with MBL, an important lectin of innate immunity to C. albicans, classically known to interact with α-mannose, also interacted in an unexpected way with the protective epitope. These cumulative data suggest that structure/activity investigations of the finely tuned C. albicans anti-mannose immune response are worthwhile to increase our basic knowledge and for translation in medicine.

Immunoadjuvant Effect of Ginsenoside F4

There have been many attempts to treat candidal infections by immunological approaches. One attempt is to find a certain adjuvant that induces a protective antibody in host. Previously, we have reported that MAb B6.1, specific for β-1,2 mannotriose located on the Candida albicans cell wall (CACW), protects mice against disseminated candidiasis and vaginal infection. However, the isolation of such an epitope is very costly and requires tremendous amount of time. Thus, this led us to find a simple way to obtain a compound that induces protective antibody. For this purpose, we focused on the discovery of immuoadjuvants capable of inducing protective antibodies. In the present study, we tested whether ginsenoside F4 from Red Ginseng has immunoadjuvant activity against fungal infection. Data displayed that a formulae of CACW combined with F4 (CACW/F4) enhanced production of anti-C. albicans antibody in mice. Analyses by IgG isotyping showed that the formulae suppressed IgG1 (Th2-immunity polarized) but enhanced IgG2b (Th1-immunity polarized), thus resulting in a Th1 immune response. This effect was assessed in a murine model of disseminated candidiasis due to C. albicans. The assesment displayed that the formulae enhanced resistance of mice against the candidiasis, whereas CACW alone was not protective. Overall, F4 has immunoadjuvant activity that provokes the induction of protective antibody in mice through a possible mechanism that enhances Th1 immunity in mice.

Limited or no protection by weakly or nonneutralizing antibodies against vaginal SHIV challenge of macaques compared with a strongly neutralizing antibody

To guide vaccine design, we assessed whether human monoclonal antibodies (MAbs) b12 and b6 against the CD4 binding site (CD4bs) on HIV-1 gp120 and F240 against an immundominant epitope on gp41 could prevent vaginal transmission of simian HIV (SHIV)-162P4 to macaques. The two anti-gp120 MAbs have similar monomeric gp120-binding properties, measured in vitro, but b12 is strongly neutralizing and b6 is not. F240 is nonneutralizing. Applied vaginally at a high dose, the strongly neutralizing MAb b12 provided sterilizing immunity in seven of seven animals, b6 in zero of five animals, and F240 in two of five animals. Compared with control animals, the protection by b12 achieved statistical significance, whereas that caused by F240 did not. For two of three unprotected F240-treated animals there was a trend toward lowered viremia. The potential protective effect of F240 may relate to the relatively strong ability of this antibody to capture infectious virions. Additional passive transfer experiments also indicated that the ability of the administered anti-gp120 MAbs to neutralize the challenge virus was a critical influence on protection. Furthermore, when data from all of the experiments were combined, there was a significant increase in the number of founder viruses establishing infection in animals receiving MAb b6, compared with other nonprotected macaques. Thus, a gp120-binding, weakly neutralizing MAb to the CD4bs was, at best, completely ineffective at protection. A nonneutralizing antibody to gp41 may have a limited capacity to protect, but the results suggest that the central focus of HIV-1 vaccine research should be on the induction of potently neutralizing antibodies.

Combination immunotherapy of MAb B6.1 with fluconazole augments therapeutic effect to disseminated candidiasis

We recently reported that IgM MAb B6.1, specific for β-1, 2-mannotriose on the cell wall of Candida albicans, is therapeutic to disseminated candidiasis due to C. albicans. In the current study, we examined if MAbB6.1 enhances therapeutic effect of fluconazole (FLC) to the disseminated disease. To assess the combination effect, determination by the kidneys-colony forming unit and survival times were used. Results showed that the therapeutic effect of FLC on mice with disseminated candidiasis was dose-dependent, but a FLC dose at 0.8 mg/kg body weight of mice was ineffective. To determine combination effect, mice treated intraperitoneally with a combination of FLC plus MAb B6.1 at 1 h post-infection - a condition of developing partial therapeutic activity - enhanced survival times beyond the effect by only antibody (p < 0.05). The resulting MST (mean survival times) value from the combination-received mice was almost the same as MST value from 3.2 mg FLC dose-given animals (p < 0.05). Another combination of 1.6 mg FLC dose and B6.1 reduced severity of the disseminated disease at almost the same rate as combination efficacy of 0.8 mg FLC dose plus B6.1. This data indicates that B6.1 acts in concert with FLC and that this combination therapy augments protection, which suggests a possibility of reducing FLC dose. The augmentation response was specific because an irrelevant IgM MAb S9 was not effective to the disseminated disease. Thus, our present studies demonstrate that this combination immunotherapy may be a way of solving the problem of limited antifungal drug choices caused by drug-resistant C. albicans.

Efficacy of combination immunotherapy of IgM MAb B6.1 and amphotericin B against disseminated candidiasis

We previously reported that the IgM MAb B6.1, specific for β-1,2-mannotriose on the surface of the cell wall of Candida albicans, prevents mice from disseminated candidiasis. The preventive activity of the antibody is mediated by enhanced phagocytosis that caused killing of the fungus and involvement of the complement system. In the present study, MAb B6.1 was tested if the antibody enhances therapeutic efficacy of amphotericin B (Amp B) in a murine model of disseminated candidiasis due to C. albicans. Determination by the kidneys-cfu (colony forming unit) and survival times was used to assess treatment. Mice treated intraperitoneally with MAb B6.1 at 1 h post-infection with C. albicans (5 × 10 5 yeast cells/mouse) developed fewer 28% cfu and prolonged survival rates than negative controls, whereas administration of B6.1 to mice at 2 h post-infection was ineffective. Therapeutic effect of Amp B on mice with the disseminated disease was dose-dependent, but dosage of Amp B (0.5 mg/kg body weight of mice) was not effective. A combination of MAb B6.1given at 1 h post-infection plus Amp B (0.5 mg dose) enhanced survival times beyond the effect due to only antibody ( P < 0.05). The MST (mean survival times) value resulted from the combination therapy-received mice was as almost the same as MST value from 2 mg dose of Amp B-given animals ( P < 0.05). In case mice given a combination of Amp B (0.5 mg dose) plus MAb B6.1 at 2 h post-infection — a condition of developing no therapeutic efficacy, the combination also reduced disease severity. All these data indicate that MAb B6.1 acts in concert with Amp B, the antibody enhances therapeutic efficacy of Amp B, and this combination therapy augments protection which implies a possibility of reducing Amp B dose. The augmentation of the response appeared to be specific because an irrelevant IgM carbohydrate-specific MAb was not protective. In conclusion, these studies show that Amp B combined with MAb B6.1 may be an option of solving the problem of limited antifungal drug choices due to drug-resistant C. albicans

Directed evolution of an anti-human red blood cell antibody

We have earlier described a haemagglutination-based assay for on-site detection of antibodies to HIV using whole blood. The reagent in this assay comprises of monovalent Fab fragment of an anti-human RBC antibody fused to immunodominant antigens of HIV-1 and HIV-2. In the present work, we describe a rational and systematic method for directed evolution of scFv and Fab anti-human RBC antibody fragments. Based on homology modeling and germline sequence alignments of antibodies, target residues in the anti-RBC MAb B6 sequence were identified for mutagenesis. A combinatorial library of 107 clones was constructed and subjected to selection on whole RBC under competitive binding conditions to identify several phage-displayed B6 scFv clones with improved binding as determined in an agglutination assay. Selected VL and VH sequences were shuffled to generate a second generation phage-displayed Fab library which on panning yielded Fab clones with several fold better binding than wild type. The mutants with better binding also displayed more Fab molecules per phage particle indicating improved in vivo folding which was also confirmed by their increased periplasmic secretion compared to the wild type. The mutant Fab molecules also showed superior characteristics in large scale production by in vitro folding of LC and Fd. The biophysical measurements involving thermal and chemical denaturation and renaturation kinetics clearly showed that two of the mutant Fab molecules possessed significantly improved characteristics as compared to the wild type B6 Fab. Structural modelling revealed that B6 Fab mutants had increased hydrogen bonding resulting in increased stability. Our approach provides a novel and useful strategy to obtain recombinant antibodies with improved characteristics.

Re-evaluation of the prolactin receptor expression in human breast cancer

The pituitary hormone PRL is involved in tumorigenesis in rodents and humans. PRL promotes proliferation, survival and migration of cancer cells acting via the PRL receptor (PRLR). Aiming to perform a large-scale immunohistochemical (IHC) screening of human mammary carcinomas for PRLR expression, we evaluated the specificity of commercially available anti-human PRLR antibodies (B6.2, U5, PRLRi pAb, 1A2B1, 250448 and H-300). The latter three antibodies were found to specifically recognise PRLR. The relative PRLR expression level detected with these antibodies closely reflected the level of (125)I-PRL binding to the cell surface. The monoclonal antibody (mAb) 250448 was specific for the N-()glycosylated form of PRLR and blocked PRL binding and signalling. The PRLRi polyclonal antibody recognised cytokeratin-18. The mAb B6.2, previously used in a number of studies, was found to lack specificity for PRLR and to rather recognise a PRLR-associated protein. The mAb U5 raised against the rat PRLR did not cross-react with the human receptor. Only one mAb, 1A2B1, was found useful for detection of PRLR in IHC applications. This antibody recognised PRLR expressed in human breast cancer cell lines and decidual cells in tissue sections of human placenta. Screening of 160 mammary adenocarcinomas demonstrated significant immunoreactivity in only four tumours, indicating that PRLR is generally not strongly upregulated in human breast cancer. However, even a very low level of PRLR expression was found to be sufficient to mediate PRL responsiveness in breast cancer cell lines.

The histidine kinases of Candida albicans: regulation of cell wall mannan biosynthesis.

Previously, we have used both biochemical and immunological approaches to determine that the two-component, histidine kinase Chk1p regulates cell wall biosynthesis in Candida albicans. These data were obtained by comparing wild-type cells to a strain of C. albicans deleted in CHK1. The dysregulation of cell wall biosynthesis in the mutant reduces its adherence to human esophageal tissue and results in avirulence. In the current study, we used transmission immune electron microscopy (IEM) to visualize the cell surface of both wild-type (CAF2) and the chk1 mutant (CHK21). IEM was performed using two IgM monoclonal antibodies to either an acid-stable mannan epitope (Mab B6) or to an acid-labile mannan epitope (Mab B6.1). We observed that the cell surface of the CHK21 mutant was more reactive than wild-type cells with Mab B6, while the reactivity of Mab B6.1 was similar for both CAF2 and CHK21. These observations correlate with previous data on the Western blotting of mutant and wild-type cells using the same monoclonal antibodies, i.e., greater activity with Mab B6 than with Mab B6.1. In addition to CHK1, two other histidine kinases (SLN1 and NIK1) have been described in C. albicans. Mutants in both sln1Delta and nik1Delta were compared by Western blotting using Mab B6 and Mab B6.1. Reactivity of each mutant to Mab B6 was similar to that observed with the chk1 mutant; on the other hand, the mannoprotein profiles obtained with Mab B6.1 in all mutants were similar to wild-type cells. We also compared the expression of 29 genes involved in mannan synthesis by reverse transcription-polymerase chain reaction (RT-PCR) and found that expression of a subset of six genes (ALG2, ALG6, ALG8, MNT3, PMT6, KRT2) was upregulated in all histidine kinase mutants, while increased expression of ALG7 was only observed in the sln1 and nik1 mutants, MNN1 was upregulated in the chk1 and nik1 mutants, and MNN4 was upregulated in the nik1Delta. Our data indicate that each of the C. albicans HK proteins may regulate similar functions in cell wall biosynthesis. This activity could be achieved in either a common or parallel, redundant signal transduction pathway(s).

Spontaneous apoptosis of circulating T-lymphocytes and its correlation to their prolactin receptor expression and prolactin plasma levels in patients with breast cancer

We have previously shown that a higher percentage of circulating CD3+ T lymphocytes undergo spontaneous apoptosis in cancer patients as compared with normal controls. Prolactin (PRL) has been reported to inhibit apoptosis in various cell types, including a Nb2 rat lymphoma cell line. In addition, there is evidence that the human PRL-antagonist hPRL-G129R induces apoptosis in breast cancer cell lines. We investigated a possible relationship between prolactin receptor (PRL-R) expression and apoptosis of CD3+ T lymphocytes, as well as PRL plasma levels, in patients with breast cancer. Peripheral blood mononuclear cells of patients (n = 11) and sex-matched normal controls (n = 12) were stained with AnnexinV, anti-Fas mAb (CD95), mouse antihuman PRL-R mAb B6.2, anti-CD3 mAb and respective isotype control mAbs. Multicolor flow cytometry was used to compare expression of these markers on T cell. In patients, 37 ± 19% (median ± SD) of CD3+ cells bound AnnexinV, marking early apoptosis of T lymphocytes compared with 17 ± 10% in controls (P <0.004). Furthermore, 82 ± 15% of the CD3+ T cells were Fas+ in patients, compared with 51 ± 9% in controls (P <0.0001). All CD3+ T lymphocytes were positive for PRL-R expression in breast cancer patients, as well as in normal control individuals. The mean fluorescence intensity of PRL-R on T lymphocytes of breast cancer patients was 106-172 (median 119) compared with 87-176 (median 123), suggesting no difference in PRL-R expression on T lymphocytes in patients versus controls. PRL plasma levels were comparable in patients and normal controls (4.8 ± 3.4 ng/ml versus 9.8 ± 4.6 ng/ml). In concordance with these findings, PRL was not able to inhibit the onset of apoptosis of Jurkat cells, a thymic lymphoma cell line, incubated with Fas cross-linking CH-11 mAb. These results indicate that PRL/PRL-R might not be involved in modulating Fas/Fas ligand interactions, which are, in part, responsible for apoptosis of T lymphocytes, leading to excessive turnover of T cells in the circulation of patients with breast cancer.

Antibody response that protects against disseminated candidiasis

We previously showed that surface mannans of Candida albicans function as adhesins during yeast cell attachment to mouse splenic marginal zone macrophages. The mannan adhesin fraction was encapsulated into liposomes and used to vaccinate mice over a 5- to 6-week period. Circulating agglutinins specific for the fraction correlated with increased resistance to disseminated candidiasis. Antiserum from vaccinated animals protected naive BALB/cByJ mice against C. albicans serotype A and B strains and Candida tropicalis. Antiserum also protected SCID mice against disseminated disease. The serum protective ability was stable at 56 degrees C, but this ability was adsorbed by C. albicans cells. The antiserum was divided into three fractions after separation by high-performance liquid chromatography. One fraction contained all of the agglutinin activity and transferred resistance to naive mice. A second fraction also transferred resistance. Two monoclonal antibodies (MAbs) specific for candidal surface determinants were obtained. MAb B6.1 is specific for a mannan epitope in the adhesin fraction, and MAb B6 is specific for a different epitope in the fraction. Both MAbs are immunoglobulin M, and both strongly agglutinate candidal cells, but only MAb B6.1 protected both normal and SCID mice against disseminated candidiasis. In one experiment, 10 normal mice were given MAb B6.1 and challenged with yeast cells. Six mice survived the 67-day observation period; 4 of the survivors were cured as evidenced by the lack of CFU in the kidney and spleen. Our studies show that antibodies against certain cell surface antigens of C. albicans help the host resist disseminated candidiasis.

Monoclonal antibodies that react with human band 3 residues 542-555 recognize different conformations of this protein in uninfected and Plasmodium falciparum infected erythrocytes.

A monoclonal antibody generated against synthetic peptides patterned on amino acids 542-555 of human band 3, designated 1F4, specifically immunostained Plasmodium falciparum-infected erythrocytes and inhibited the cytoadherence of P. falciparum-infected erythrocytes to C32 amelanotic melanoma cells. 1F4 did not recognize intact band 3 protein on immunoblots, however it was reactive towards proteolytic fragments of band 3. The binding region of another murine monoclonal antibody previously reported to recognize the membrane spanning domain of human band 3, designated B6, was found to also recognize residues 542-555, however its properties differed from 1F4. Mab B6 recognized both infected and uninfected red cells, and reacted only with intact band 3 on immunoblots. Mab B6 was without effect on cytoadherence. These results demonstrate that monoclonal antibodies reactive against a common peptide sequence may bind to different conformations of the peptide sequence and suggest that the adherent competency of P. falciparum-infected erythrocytes may result from a change in the surface topography of human band 3 protein.

A 43 kDa protein inserted at the plasma membrane-cytoskeleton interface in rumen entodiniomorphid ciliates

The P-43 ofEudiplodinium and homologous proteins in three other entodiniomorphid species, free-living ciliates, flagellates, and HeLa cells, were identified at the plasma membrane-cytoskeleton interface. Proteins cross-reacting with MAb B6 were also located at the ciliary inner surface of the plasma membrane. Due to the strong adhesion of the plasma membrane to the underlying cytoskeleton, classical extraction with detergents, urea, NaOH, and PTA, failed to separate the two components completely. However, the extraction properties of P-43, associated with its membrane-cytoskeleton interactive functions, suggest that this unglycosylated protein may present some analogies with proteins of the intermediate filaments. Their ubiquity and localization suggest that P-43 and MAb B6 crossreacting proteins may not be strictly epiplasmic but could be amphitropic proteins, strongly anchored to both the plasma membrane and the underlying microfilament framework, via protein-protein binding or by direct insertion in the lipid bilayer.

Definition of the expression of the human carcinoembryonic antigen and non‐specific cross‐reacting antigen in human breast and lung carcinomas

Mouse cell lines transfected with carcinoembryonic antigen (CEA) and with 2 other members of the human CEA gene family, non-specific cross-reacting antigen (NCA) and biliary glycoprotein (BGP), were used to analyze the specificity of several monoclonal antibodies (MAbs). MAbs COL-1 and COL-6 were shown to react with the transfected CEA gene product but not with NCA, confirming previous results. Cells expressing the transfected BGP gene product also failed to react with COL-1 and COL-6. The MAb B6.2 reacted with cells expressing the NCA gene product but not with those expressing CEA or BGP. The MAb B1.1 reacted strongly with the transfected CEA and BGP gene products but only weakly with the NCA gene product. These antibodies were then utilized in the histochemical analysis of a number of primary and secondary breast and lung tumors. The results indicate that a majority of breast and lung tumors express CEA, and nearly all breast and lung tumors express NCA. Fairly homogeneous expression of CEA and NCA was seen in the majority of both breast and lung tumors. Our results indicate that CEA may be an important target for immunotherapy in a large number of patients with breast and lung tumors.

Herpes simplex virus type 1-specific immunity induced by peptides corresponding to an antigenic site of glycoprotein B

Herpes simplex virus (HSV) envelope glycoproteins are the prime targets of adaptive antiviral immunity. Previous investigation identified a protective, neutralizing, glycoprotein B1 (gB-1)-reactive monoclonal antibody (MAb B6) and localized the linear epitope recognized by the MAb to residue 84 of gB-1. Three overlapping peptides (two 20-mers and one 18-mer), together spanning amino acids 63 to 110 of the wild-type sequence of gB-1, were synthesized and analyzed for their ability to stimulate immunity which cross-reacts with HSV-1. All stimulated some level of response. Two peptides, the gB 18-mer and 20.1-mer, were recognized by MAb B6 and HSV-immune antibody but were unable to stimulate virus-neutralizing antibody or serum able to protect against zosteriform spread in vivo. The 20.2-mer peptide, however, which was not recognized by MAb B6 or HSV-generated immune antibody, stimulated the production of neutralizing antibody and serum able to protect against zosteriform spread. Immunization with all of the peptides was able to enhance viral clearance of a low dose of HSV-1 in an ear challenge model and induce antibody reactive in antibody-dependent complement-mediated lysis of HSV-1-infected cells in vitro. These results are the first report of HSV immunity induced by peptides corresponding to gB and indicate that the best immunogen, in terms of stimulating neutralizing antiserum able to protect in vivo against HSV-1, was a peptide not recognized by HSV-immune mechanisms or by the MAb used to localize it.

The incidence of a new human cross-reactive idiotype linked to subgroup V HIII heavy chains

Cross-reactive idiotypes (CRI) on human rheumatoid factors (RF), which are identified by murine monoclonal antibodies (mAb), have proved useful in defining both the incidence and the structural characteristics of these autoantibodies. In this study, a new murine anti-idiotypic reagent, mAb B6, has been used to identify and define the expression of a distinct heavy chain CRI. The B6 CRI was found on 20% of monoclonal IgM (16 of 81), but on only 5% of monoclonal IgA (1 of 20) and on no monoclonal IgG. In addition, this CRI was expressed exclusively on a subset of Ig derived from the V HIII protein variable region subgroup. In immunoblotting experiments, the mAb B6 bound directly to the heavy (H) chains of CRI positive proteins. The B6 CRI was found frequently on monoclonal IgM-RF molecules, and the mAb B6 could inhibit the binding of the RF to its IgG antigen. It was also demonstrated that Staphylococcus aureus protein A (SpA), which has recently been shown to bind to the F(ab) region of V HIII molecules, could block the interaction of some B6 CRI positive IgM to the anti-CRI. These experiments suggest that the B6 CRI is a marker for one or a few V HIII genes and that it is expressed commonly on IgM paraproteins, many of which have RF activity.

Monoclonal antibodies define a domain on herpes simplex virus glycoprotein B involved in virus penetration

In an earlier report (S.D. Marlin, S.L. Highlander, T.C. Holland, M. Levine, and J.C. Glorioso, J. Virol. 59: 142-153), we described the production and use of complement-dependent virus-neutralizing monoclonal antibodies (MAbs) and MAb-resistant (mar) mutants to identify five antigenic sites (I to V) on herpes simplex virus type 1 glycoprotein B (gB). In the present study, the mechanism of virus neutralization was determined for a MAb specific for site III (B4), the only site recognized by MAbs which exhibited complement-independent virus-neutralizing ability. This antibody had no detectable effect on virus attachment but neutralized viruses after adsorption to cell monolayers. These findings implied that the mechanism of B4 neutralization involved blocking of virus penetration. The remaining antibodies, which recognized sites I, II, and IV, required active complement for effective neutralization. These were further studied for their ability to impede virus infectivity in the absence of complement. Antibodies to sites I (B1 and B3) and IV (B6) slowed the rate at which viruses penetrated cell surfaces, supporting the conclusion that antibody binding to gB can inhibit penetration by a virus. The data suggest that MAbs can interfere with penetration by a virus by binding to a domain within gB which is involved in this process. In another assay of virus infection, MAb B6 significantly reduced plaque development, indicating that antibody binding to gB expressed on infected-cell surfaces can also interfere with the ability of a virus to spread from cell to cell. In contrast to these results, antibodies to site II (B2 and B5) had no effect on virus infectivity; this suggests that they recognized structures which do not play a direct role in the infectious process. To localize regions of gB involved in these phenomena, antibody-binding sites were operationally mapped by radioimmunoprecipitation of a panel of truncated gB molecules produced in transient-expression assays. Residues critical to recognition by antibodies which affect penetration by a virus (sites I, III, and IV) mapped to a region of the molecule (amino acid residues 241 to 441) which is centrally located within the external domain. Antibodies which had no effect on penetration (site II) recognized sequences distal to this region (residues 596 to 737) near the transmembrane domain. The data suggest that these gB-specific MAbs recognize two major antigenic sites which reside in physically distinct components of the external domain of gB.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural and functional studies of a 39,000-Mr immunodominant protein of vaccinia virus.

Little is known about the nature of poxvirus proteins involved in the host immune response. Screening a lambda gt11 expression library of genomic rabbit poxvirus DNA with hyperimmune rabbit anti-vaccinia virus serum and selection of monospecific antibodies identified a highly antigenic viral protein of about 39,000 molecular weight (39K protein). The same-size protein of vaccinia virus was also identified with a monoclonal antibody (MAb B6) obtained from hybridomas generated after fusion of hyperimmunized mouse spleen cells with mouse myeloma cells. Structural analysis revealed that the 39K protein is an acidic polypeptide, that it can exist in two molecular forms because of intramolecular disulfide linkages, and that it is part of the virus core. This protein shares antigenic determinants with a cytoplasmic component(s) from uninfected cells. Functional studies revealed that the 39K protein is synthesized at late times postinfection and appears to be required for virus assembly. This protein is highly conserved in members of the Orthopoxvirus group, but in cowpox virus, a 41K virion protein was specifically recognized by antibodies that reacted against the vaccinia virus 39K protein. Significantly, during long-term passages of Friend erythroleukemia cells persistently infected with vaccinia virus, some virus mutants were found to increase or decrease by about 2 kilodaltons the size of the 39K protein. Mapping analysis localized sequences encoding the 39K protein in a rifampin-sensitive gene cluster between the two major core-associated viral polypeptides, 4a and 4b. The fact that the 39K core protein of vaccinia virus elicits strong humoral immune response, induces antibodies that react against a host component(s), and is subjected to genetic variability suggests that this protein has important biological functions.