Long-term outcome of congenital cystic adenomatoid malformation

To determine the long-term outcome of congenital cystic adenomatoid malformation (CCAM), the records of all patients with CCAM treated in three Hungarian paediatric surgical centers between 1977 and 1996 were reviewed. Patients were followed for up to 20 years following diagnosis and treatment. In 20 patients CCAM was diagnosed postnatally and in 3 prenatally. Biodata including the operative procedures are presented. Follow-up findings between 18 months and 20 years after diagnosis showed better height and weight growth in patients operated upon in later childhood compared with those operated upon in infancy. The older the patient at the time of diagnosis, the better was the long-term outcome.

The hypervariable domain of the murine leukemia virus surface protein tolerates large insertions and deletions, enabling development of a retroviral particle display system

The surface proteins (SU) of murine type-C retroviruses have a central hypervariable domain devoid of cysteine and rich in proline. This 41-amino-acid region of Friend ecotropic murine leukemia virus SU was shown to be highly tolerant of insertions and deletions. Viruses in which either the N-terminal 30 amino acids or the C-terminal 22 amino acids of this region were replaced by the 7-amino-acid sequence ASAVAGA were fully infectious. Insertions of this 7-amino-acid sequence at the N terminus, center, and the C terminus of the hypervariable domain had little effect on envelope protein (Env) function, while this insertion at a position 10 amino acids following the N terminus partially destabilized the association between the SU and transmembrane subunits of Env. Large, complex domains (either a 252-amino-acid single-chain antibody binding domain [scFv] or a 96-amino-acid V1/V2 domain of HIV-1 SU containing eight N-linked glycosylation sites and two disulfides) did not interfere with Env function when inserted in the center or C-terminal portions of the hypervariable domain. The scFv domain inserted into the C-terminal region of the hypervariable domain was shown to mediate binding of antigen to viral particles, demonstrating that it folded into the active conformation and was displayed on the surface of the virion. Both positive and negative enrichment of virions expressing the V1/V2 sequence were achieved by using a monoclonal antibody specific for a conformational epitope presented by the inserted sequence. These results indicated that the hypervariable domain of Friend ecotropic SU does not contain any specific sequence or structure that is essential for Env function and demonstrated that insertions into this domain can be used to extend particle display methodologies to complex protein domains that require expression in eukaryotic cells for glycosylation and proper folding.

Potent neutralization of primary HIV-1 isolates by antibodies directed against epitopes present in the V1/V2 domain of HIV-1 gp120

Although it is known that some human immune sera possess potent neutralizing activities for primary viruses, the identity of the target epitopes mediating this neutralization is unknown, and currently available immunogens have not been able to induce such activities. Using recombinant fusion glycoproteins expressing native V1/V2 domains of gp120 we have found that sera from a subset of HIV-1-infected humans contain antibodies that recognize broadly conserved V1/V2 epitopes. Such antibodies were isolated from one human serum by affinity chromatography on a column containing a V1/V2 fusion protein, and shown to efficiently neutralize several macrophage-tropic HIV-1 isolates. Rodents immunized with the purified V1/V2 fusion protein produced antibodies reactive with unrelated V1/V2 fusion proteins and with heterologous gp120s. V1/V2-specific immunoglobulins isolated from sera of these animals by affinity chromatography also possessed potent neutralization activity for several primary HIV-1 isolates. These results indicate that the V1/V2 domain of HIV-1 gp120 contains conserved epitopes that mediate potent neutralization of primary viruses, and suggest that subunit vaccines that efficiently induce such antibodies may provide protective humoral immunity against clinically relevant HIV-1 isolates.

Allopregnanolone-induced modification of presynaptic basal and K+-induced [3H]-norepinephrine efflux from rat cortical slices during the estrous cycle

Superfused frontal slices of cerebral cortex were preloaded with [3H]-norepinephrine ([3H]NE). Basal [3H]NE efflux and K+-induced [3H]NE release were studied during the estrous cycle and in the presence of neurosteroids. Basal [3H]NE efflux showed estrous cycle-related variations, with lowest values found during estrus and diestrus II. Allopregnanolone (10(-9) M) potentiated basal [3H]NE efflux from the 1st minute of its application; the effect of the steroid was still present after 20 min. This effect was also dependent upon the estrous cycle, since basal [3H]NE efflux was mainly increased during estrus diestrus I, and to a lesser degree only during proestrus. During diestrus II and after ovariectomy, basal [3H]NE efflux was no longer affected by the neurosteroid. In the presence of yohimbine (10(-6) M), the effect of allopregnanolone on basal efflux was potentiated only during the first 3 min but vanished thereafter. Allopregnanolone (10(-9) M) potentiated the K+-induced [3H]NE release during estrus, but pregnenolone (10(-9) M) was ineffective, suggesting specificity of the neurosteroid. Yohimbine (10(-6) M) also potentiated K+-induced [3H]NE release. When applied simultaneously with allopregnanolone (10(-9) M), a potentiating effect on [3H]NE release was observed. The present results suggest that allopregnanolone is a neurosteroid able to modulate norepinephrine release in the cerebral cortex in an estrous cycle-dependent manner, and that the effect could involve noradrenergic alpha-2 receptors.

Immunologic cross-reaction between HIV type 1 p17 and Mycoplasma hyorhinis variable lipoprotein

Monoclonal antibodies directed against the HIV-1 matrix protein p17 that react with a component present on the surface of HIV-1-infected cells have previously been described. In this study we show that one of these monoclonal antibodies binds to persistently HIV-1-infected cell lines that are coinfected with Mycoplasma hyorhinis, but not to cell lines that are uninfected with mycoplasma. Mycoplasma-infected cells secrete HIV-1 at a higher rate, have a slight increase in cell surface expression of gp120 and gp41, and are less sensitive to immunotoxins than uninfected cells. The anti-p17 antibody binds to a protein of M. hyorhinis grown in cell-free culture. The variable expression and size of the protein among strains is typical of the variable lipoprotein (Vlp) system of M. hyorhinis. Confirmation of the reactivity of the antibody with a Vlp was provided by demonstrating its specific binding to recombinant VlpF expressed in E. coli, and to a synthetic peptide representing the carboxy-terminal region of VlpF, but not to other recombinant Vlp products or peptides. This is a true cross-reaction because the antibody also binds to recombinant p17 expressed in E. coli and the binding is inhibited by the VlpF peptide. These analyses highlight the potential of mycoplasma contamination of tissue culture cell lines to cause anomalous results. With regard to HIV-1, mycoplasma infection of cells results in increased rates of virus secretion, and introduces a potential confounding immunologic cross-reaction as well. The existence of a cell surface form of p17 is unlikely.

Localization of the labile disulfide bond between SU and TM of the murine leukemia virus envelope protein complex to a highly conserved CWLC motif in SU that resembles the active-site sequence of thiol-disulfide exchange enzymes

Previous studies have indicated that the surface (SU) and transmembrane (TM) subunits of the envelope protein (Env) of murine leukemia viruses (MuLVs) are joined by a labile disulfide bond that can be stabilized by treatment of virions with thiol-specific reagents. In the present study this observation was extended to the Envs of additional classes of MuLV, and the cysteines of SU involved in this linkage were mapped by proteolytic fragmentation analyses to the CWLC sequence present at the beginning of the C-terminal domain of SU. This sequence is highly conserved across a broad range of distantly related retroviruses and resembles the CXXC motif present at the active site of thiol-disulfide exchange enzymes. A model is proposed in which rearrangements of the SU-TM intersubunit disulfide linkage, mediated by the CWLC sequence, play roles in the assembly and function of the Env complex.

The critical N-linked glycan of murine leukemia virus envelope protein promotes both folding of the C-terminal domains of the precursor polyprotein and stability of the postcleavage envelope complex

The infectivity of Friend ecotropic murine leukemia virus was previously shown to be highly sensitive to modification in its envelope protein (Env) at only one of the eight signals for N-linked glycan attachment, the fourth from the N terminus (gs4). In the present study, a set of six single-amino-acid substitutions in or near gs4 was used to determine the function of this region of Env and the role played by the glycan itself. One mutant that lacked the gs4 glycan was fully infectious, while one that retained this glycan was completely noninfectious, indicating that the gs4 glycan per se is not required for Env function. Infectivity correlated with the level of mature Env complex incorporated into virus particles, which was determined by the severity of defects in transport of the envelope precursor protein (gPrEnv) from the endoplasmic reticulum into the Golgi apparatus, in cleavage of gPrEnv into the two envelope subunits (the surface protein [SU] and the transmembrane protein [TM]), and in the association of SU with cellular membranes. All of the mutants induced the wild-type level of superinfection interference, indicating that the gs4 region mutations did not interfere with proper folding of the N-terminal domain of SU. These results suggest that the gs4 region mediates folding of the C-terminal domains of gPrEnv and stability of the interaction between SU and TM. Although the gs4 glycan was not essential for infectivity, processing of all mutant Envs lacking this glycan was significantly impaired, suggesting that efficient folding of gPrEnv requires a glycan at this position. The conservation of a glycosylation site homologous to gs4 across a broad range of retroviruses suggests that this sequence may play a similar role in many retroviral Envs.

Vaccine-specific antibody responses induced by HIV-1 envelope subunit vaccines

The first generation of candidate vaccines to prevent HIV infection consisted of recombinant envelope proteins (Env, gp120, and gp160) derived from a single laboratory strain of HIV, designated IIIB/LAV, but produced with different expression systems. In this study we examined the fine specificity of the human Ab response to each vaccine and compared them to the responses of laboratory workers infected with the same strain of HIV. The best responders from each vaccine protocol were studied and compared. Detailed comparisons of the fine specificity of the Ab response were possible because all immunologic assays were performed using homologous recombinant proteins, peptides, and virus stocks. Although the total amounts of anti-Env Ab were comparable, the groups exhibited significant differences in epitope specificity, avidity, and functional capacity of the Ab response. The data demonstrate that the form of the immunogen (e.g., live virus or recombinant protein) is important in determining the quality of the Ab response. Conclusions are also drawn regarding characteristics of the anti-HIV-neutralizing Ab response. These studies represent one of the most detailed analyses of the human Ab response to any Ag and have implications for the development of vaccines for HIV as well as for other microbial pathogens.

Vaccine-specific antibody responses induced by HIV-1 envelope subunit vaccines

The first generation of candidate vaccines to prevent HIV infection consisted of recombinant envelope proteins (Env, gp120, and gp160) derived from a single laboratory strain of HIV, designated IIIB/LAV, but produced with different expression systems. In this study we examined the fine specificity of the human Ab response to each vaccine and compared them to the responses of laboratory workers infected with the same strain of HIV. The best responders from each vaccine protocol were studied and compared. Detailed comparisons of the fine specificity of the Ab response were possible because all immunologic assays were performed using homologous recombinant proteins, peptides, and virus stocks. Although the total amounts of anti-Env Ab were comparable, the groups exhibited significant differences in epitope specificity, avidity, and functional capacity of the Ab response. The data demonstrate that the form of the immunogen (e.g., live virus or recombinant protein) is important in determining the quality of the Ab response. Conclusions are also drawn regarding characteristics of the anti-HIV-neutralizing Ab response. These studies represent one of the most detailed analyses of the human Ab response to any Ag and have implications for the development of vaccines for HIV as well as for other microbial pathogens.

A novel antibody-dependent cellular cytotoxicity epitope in gp120 is identified by two monoclonal antibodies isolated from a long-term survivor of human immunodeficiency virus type 1 infection

Two monoclonal antibodies (MAbs), 42F and 43F, were isolated some 14 months apart from a single long-term survivor of human immunodeficiency virus type 1 (HIV-1) infection. These MAbs were found to be indistinguishable in terms of their isotypes, specificities, affinities, and biological activities. Both 42F and 43F directed substantial antibody-dependent cellular cytotoxicity (ADCC) against cells infected with four divergent lab-adapted strains of HIV-1, but no neutralizing activity against these strains was detectable. The ability of MAbs 42F and 43F, as well as that of MAbs against two other gp120 epitopes, to direct ADCC against uninfected CD4+ cells to which recombinant gp120SF2 had been adsorbed (i.e., "innocent bystanders") was demonstrated to be less efficient by at least an order of magnitude than their ability to direct ADCC against HIV-1-infected cells. Flow cytometry analyses showed that 42F and 43F also bind to native primary isolate Envs from clades B and E expressed on cell surfaces. By direct binding and competition assays, it was demonstrated that the 42F/43F epitope lies in a domain of gp120 outside the previously described CD4-binding site and V3 loop ADCC epitope clusters. Immunoblot analysis revealed that the 42F/43F epitope is not dependent on disulfide bonds or N-linked glycans in gp120. Epitope mapping of 42F and 43F by binding to linear peptides demonstrated specificity of these MAbs for a sequence of 10 amino acids in the C5 domain comprising residues 491 to 500 (Los Alamos National Laboratory numbering for the HXB2 strain). Thus, 42F and 43F define a new ADCC epitope in gp120. Because of the relative conservation of this epitope and the fact that it appears to have been significantly immunogenic in the individual from which these MAbs were derived, it may prove to be a useful component of HIV vaccines. Furthermore, these MAbs may be used as tools to probe the potential importance of ADCC as an antiviral activity in HIV-1 infection.

In vitro effects of anti-HIV immunotoxins directed against multiple epitopes on HIV type 1 envelope glycoprotein 160

We have used a panel of anti-gp160 MAbs to construct anti-HIV immunotoxins by coupling antibodies to ricin A chain (RAC). The ability of the immunotoxins to kill HIV-1-infected cells and halt the spread of infection was tested in tissue culture on persistently and acutely infected cell lines and primary lymphocyte cultures stimulated with phytohemagglutinin (PHA blasts). Laboratory strains and clinical isolates of HIV both were tested. The constitution and antigen-binding capacity of the immunotoxins were confirmed by ELISA and indirect immunofluorescence. Immunotoxins that bind epitopes exposed on the cell surface effectively killed persistently infected cells, although killing was not directly proportional to binding of immunotoxin to cell. The activity of anti-gp41, but not anti-gp120, immunotoxins was markedly enhanced in the presence of soluble CD4 or peptides corresponding to the CDR3 region of CD4. CD4-mediated enhancement of anti-gp41 immunotoxin activity was observed for laboratory strains neutralized by sCD4 and for clinical isolates that were resistant to neutralization by sCD4. Immunotoxin action was potentiated by brefeldin A, bafilomycin A1, cortisone, and an amphipathic fusion peptide, but not by cytochalasin D, nocodazol, monodansyl cadaverine, or trans-retinoic acid. Anti-HIV immunotoxins are useful tool with which to study the functional expression of gp120/gp41 antigens on the surface of HIV-infected cells, as well as potential AIDS therapeutics. Because these studies relate to the accessibility of viral antigens to antibody-mediated attack, these studies also have relevance for vaccine development.

Synergistic neutralization of human immunodeficiency virus type 1 by a chimpanzee monoclonal antibody against the V2 domain of gp120 in combination with monoclonal antibodies against the V3 loop and the CD4-binding site

Synergistic neutralization of human immunodeficiency virus type 1 (HIV-1) was observed in studies using a chimpanzee anti-V2 monoclonal antibody (MAb), C108G, in combination with anti-V3 loop and anti-CD4 binding-site (bs) MAbs of different epitope specificities. C108G paired with either of two anti-V3 loop MAbs or either of two anti-CD4 bs MAbs synergistically neutralized both the uncloned IIIB and clonal HXB2 strains of virus in H9 target cells. Synergism was quantitated by calculation of combination indices. Significant synergy with a given MAb pair was seen over a range of MAb ratios, with the optimal effect centering around the ratio at which the MAbs were equipotent for a given HIV-1 strain (on the basis of the 50% neutralization titer). In preliminary experiments with monocytotropic strains of HIV-1 in peripheral blood mononuclear cell targets, significant synergism was also observed between anti-V2-anti-V3 and anti-V2-anti-CD4 bs MAb pairs. Synergism by all MAb pairs tested was greater against heterogeneous isolates of HIV-1 (IIIB and Ba-L) than against clonal isolates (HXB2 and NLHXADA), suggesting that strain broadening may be a component of the synergism observed against the heterogeneous isolates. In addition, conformational changes in gp120 upon binding of one or both MAbs may result in increased affinity or exposure of the epitope of one or both MAbs. Finally, a three-MAb combination of C108G, an anti-V3 MAb, and an anti-CD4 bs MAb was more effective in neutralizing the HXB2 strain of HIV-1 than any of the three two-MAb combinations within this trio, as determined by the dose reduction indices of each MAb required to achieve a given level of neutralization. This is the first report of synergistic neutralization of HIV-1 by a three-MAb combination composed of MAbs directed against the three major neutralization epitope clusters in gp120. Implications for vaccine design and for immunoprophylaxis and immunotherapy with a combination of MAbs are discussed.

Tumors of the bladder, kidney, and intestine of F344 rats and liver of B6C3F1 mice administered o-nitroanisole in feed

o-Nitroanisole, a mutagenic intermediate used in the manufacture of azo dyes, was administered in feed for 2 years at concentrations of 0, 222, 666, or 2000 ppm to groups of 60 male and 60 female F344 rats. No significant increase in neoplasms occurred in these groups of rats. Additional (stop exposure) groups of 60 male and 60 female F344 rats received diets containing 0, 6000, or 18,000 ppm for 27 weeks followed by maintenance on control diets for up to an additional 77 weeks. Survival of the stop exposure groups was reduced because of the development of chemical related neoplasms of the urinary bladder. After 13, 28, 40, and 65 weeks on study, 10 rats per group were necropsied and evaluated for the presence of chemical associated lesions. Hyperplasia of the epithelium of the urinary bladder was significantly increased at all interim evaluations. A transitional cell carcinoma was observed at the 13-week evaluation in one male rat that received 18,000 ppm and thereafter transitional cell neoplasms of the bladder were present in male and female rats at each interim evaluation. Adenomatous polyps of the large intestine were significantly increased in groups that received 6000 or 18,000 ppm. In addition carcinomas of the large intestine were present in four males and two females that received 18,000 ppm. Hyperplasia of the transitional epithelium of the renal pelvis was significantly increased in groups of rats that received 6000 or 18,000 ppm and transitional cell papillomas were observed in three males and one female that received 18,000 ppm. Transitional cell carcinomas of the kidney occurred in one male that received 6000 ppm and six males and one female that received 18,000. Groups of 60 male and 60 female B6C3F1 mice received dietary concentrations of 0, 666, 2000, or 6000 ppm o-nitroanisole for 2 years. No stop exposure study was conducted with mice. The only neoplastic response observed in mice was in the liver of males; hepatocellular adenomas or carcinomas were increased in groups of male mice that received 2000 or 6000 ppm. No increase in neoplasms associated with chemical exposure occurred in female mice.

Variations in hypothalamic somatostatin release and content during the estrous cycle in the rat. Effects of ovariectomy and estrogen supplementation

To investigate the secretory pattern of somatostatin (SS) from the median eminence (ME) in the female rat, as well as estrogenic influence on this secretion, we measured both SS release and hypothalamic content in cycling, 10-day ovariectomized, and ovariectomized rats treated with estradiol for 3 days before. Animals were stereotaxically implanted with a push-pull cannula into the ME, and 10 days later the hypothalamic structure was perfused with artificial cerebrospinal fluid for 120-150 min at a regular flow rate of 17 mu l/min. Secretion peaks were observed in the pattern of SS release, whatever the stage of the estrous cycle. The mean amplitude of SS peaks was similar throughout the cycle: 11.7 +/- 4.0, 8.6 +/- 1.5 and 10.5 +/- 1.3 pg at proestrus, estrus and diestrus, respectively, and it was affected neither by ovariectomy (7.4 +/- 1.3 pg) nor by estrogen replacement (5.5 +/- 1.0 pg). By contrast, mean SS release levels in the proestrus phase were significantly higher than those measured in the other phases: 21.6 +/- 2.1 vs. 17.7 +/- 1.2 pg/15 min in diestrus (p < 0.05) and vs. 12.0 +/- 0.7 pg/15 min in estrus (p < 0.001). Hypothalamic SS content showed variations quite similar to those observed during its release, i.e. with the highest values corresponding to the proestrus phase (1,170.5 +/- 224.9 pg/mg of tissue) and to the diestrus (1,156.5 +/- 332.1 pg/mg of tissue) and the lowest values in the estrus (511.5 +/- 52.9 pg/mg of tissue; p < 0.05 vs. proestrus and diestrus). In addition, the lowest SS content and secretion values were found in ovariectomized animals: 95.5 +/- 5.1 pg/mg of tissue (p < 0.001 compared to the values obtained for each stage of the estrous cycle) and 10.0 +/- 0.9 pg/15 min (p < 0.001 vs. proestrus and diestrus), respectively. Patterns of SS release and SS hypothalamic content were not modified by estradiol treatment in ovariectomized animals. Our results suggest that (1) whatever the stage of the estrous cycle, SS release from the ME is not uniform and exhibits irregular peaks; (2) mean SS release levels were subjected to gonadal influence; (3) the occurrence of SS peaks seems to be estrogen-independent, and (4) variations in hypothalamic SS content were generally in good agreement with those of neurohormone release.

Characterization of neutralization epitopes in the V2 region of human immunodeficiency virus type 1 gp120: role of glycosylation in the correct folding of the V1/V2 domain

A number of monoclonal antibodies (MAbs) with various levels of neutralizing activity that recognize epitopes in the V1/V2 domain of LAI-related gp120s have been described. These include rodent antibodies directed against linear and conformational epitopes and a chimpanzee MAb, C108G, with extremely potent neutralizing activity directed against a glycan-dependent epitope. A fusion glycoprotein expression system that expressed the isolated V1/V2 domain of gp120 in native form was used to analyze the structural characteristics of these epitopes. A number of MAbs (C108G, G3-4, 684-238, SC258, 11/68b, 38/66a, 38/66c, 38/62c, and CRA3) that did not bind with high affinity to peptides immunoprecipitated a fusion glycoprotein expressing the V1/V2 domain of HXB2 gp120 in the absence of other human immunodeficiency virus sequences, establishing that their epitopes were fully specified within this region. Biochemical analyses indicated that in the majority of V1/V2 fusion molecules only five of the six glycosylation signals in the V1/V2 domain were utilized, and the glycoforms were found to be differentially recognized by particular MAbs. Both C108G and MAbs directed against conformational epitopes reacted with large fractions of the fully glycosylated molecules but with only small fractions of the incompletely glycosylated molecules. Mutational analysis of the V1 and V2 glycosylation signals indicated that in most cases the unutilized site was located either at position 156 or at position 160, suggesting the occurrence of competition for glycan addition at these neighboring positions. Mutation of glycosylation site 160 destroyed the C108G epitope but increased the fraction of the molecules that presented the conformational epitopes, while mutation of the highly conserved glycosylation site at position 156 greatly diminished the expression of the conformational epitopes and increased expression of the C108G epitope. Similar heterogeneity in glycosylation was also observed when the HXB2 V1/V2 fusion glycoprotein was expressed without most of the gp70 carrier protein, and thus, this appeared to be an intrinsic property of the V1/V2 domain. Heterogeneity in expression of conformational and glycan-dependent epitopes was also observed for the natural viral env precursor, gPr160, but not for gp120. These results suggested that the closely spaced glycosylation sites 156 and 160 are often alternatively utilized and that the pattern of glycosylation at these positions affects the formation of the conformational structures needed for both expression of native epitopes in this region and processing of gPr160 to mature env products.

Bathophenanthroline disulfonate and soluble CD4 as probes for early events of HIV type 1 entry

We report here that a metalloprotease inhibitor, bathophenanthroline disulfonate (Bphe-ds), neutralizes both laboratory-adapted and primary strains of HIV-1. Presaturation of Bphe-ds with zinc does not alter its neutralizing activity, suggesting that the metal-chelating ability of Bphe-ds is not required for neutralization. Bphe-ds blocks infection of CD4+ cells at the stage of viral entry, not through a direct viricidal effect, but by interfering with both binding and postbinding events. This drug interacts with HIV-1 envelope, blocking almost completely the binding of three MAbs that recognize epitopes overlapping the CD4-binding site on gp120, but has no effect on the binding of MAbs directed to the cellular receptor CD4. The exposure of epitopes in the V2 and V3 but not C5 domains of gp120 is partially decreased in the presence of Bphe-ds, suggesting that the drug induces conformational changes in the envelope glycoprotein(s). Binding of both virions and soluble gp120 to CD4+ cells is inhibited by this drug in a dose-dependent manner. This contrasted with the effects of soluble CD4, which actually increased binding of virions to cells at 4 degrees C, while inhibiting the binding of soluble gp120. Bphe-ds also increases shedding of gp120 from cells infected with HIV-1IIIB. Thus, Bphe-ds appears to be an envelope-directed inhibitor of HIV-1 that neutralizes HIV-1 infectivity via multiple mechanisms.

Role of N-linked glycosylation in the activity of the Friend murine leukemia virus SU protein receptor-binding domain

The 243 N-terminal residues of Friend Murine Leukemia Virus envelope glycoprotein (SU) fold into a structurally and functionally autonomous domain which contains the determinants for binding to the ecotropic virus receptor. The two N-linked glycosylation sites present in this N-terminal portion of the viral SU were removed by site-directed mutagenesis without disturbing its biosynthesis and incorporation into infectious virions. A truncated version of the mutant protein which included only the N-terminal domain was poorly transported but still able to interact with the receptor. Interference assays indicated that the interaction between the mutated protein and the virus receptor was weaker. We conclude that the elimination of N-linked oligosaccharide chains in the envelope N-terminal domain do not prevent receptor interaction but results in subtle conformational changes that may alter recognition and binding.

A novel, glycan-dependent epitope in the V2 domain of human immunodeficiency virus type 1 gp120 is recognized by a highly potent, neutralizing chimpanzee monoclonal antibody

An anti-gp120 monoclonal antibody (MAb), C108G (gamma 1, kappa), was isolated from a chimpanzee that had been infected with strain IIIB of human immunodeficiency virus type 1 (HIV-1IIIB) and subsequently immunized with the recombinant glycoprotein rgp160MN. This MAb is specific for the IIIB strain of HIV-1 and related clones and exhibits very potent neutralization of these viruses; e.g., 100% neutralization of approximately 8 x 10(3) infectious units of HXB2 was achieved with 125 ng of C108G per ml. Commensurate with this potent neutralizing activity, the apparent affinity of C108G for rgp160LAI was very high, i.e., approximately 3 x 10(10) liters/mol. The C108G epitope was not destroyed by reduction of gp120 disulfide bonds but was profoundly disrupted by removal of N-linked sugars from gp120. Despite the importance of a glycan(s) in forming the C108G epitope, specific binding of C108G to synthetic peptides overlapping in amino acids 162 to 169 of the V2 region was detected, albeit with an affinity approximately 2,000-fold lower than that of C108G's binding to glycosylated envelope protein. This epitope mapping correlated with results of competition assays using MAbs of known epitope specificities. To our knowledge, this is the first description of an anti-V2 MAb raised in response to HIV-1 infection. Its potent neutralizing activity and epitope specificity indicate that the V2 domain of gp120 may be an effective target of the protective immune response and, therefore, potentially an important component of HIV vaccines.

Presentation of native epitopes in the V1/V2 and V3 regions of human immunodeficiency virus type 1 gp120 by fusion glycoproteins containing isolated gp120 domains

The immune response to viral glycoproteins is often directed against conformation- and/or glycosylation-dependent structures; synthetic peptides and bacterially expressed proteins are inadequate probes for the mapping of such epitopes. This report describes a retroviral vector system that presents such native epitopes on chimeric glycoproteins in which protein fragments of interest are fused to the C terminus of the N-terminal domain of the murine leukemia virus surface protein, gp70. The system was used to express two disulfide-bonded domains from gp120, the surface protein of human immunodeficiency virus type 1 (HIV-1), that include potent neutralization epitopes. The resulting fusion glycoproteins were synthesized at high levels and were efficiently transported and secreted. A fusion protein containing the HXB2 V1/V2 domain was recognized by an HIVIIIB-infected patient serum as well as by 17 of 36 HIV-1 seropositive hemophiliac, homosexual male and intravenous drug user patient sera. Many of these HIV+ human sera reacted with V1/V2 domains from several HIV-1 clones expressed in fusion glycoproteins, indicating the presence of cross-reactive antibodies against epitopes in the V1/V2 domain. Recognition of gp(1-263):V1/V2HXB2 by the HIVIIIB-infected human patient serum was largely blocked by synthetic peptides matching V1 but not V2 sequences, while recognition of this construct by a broadly cross-reactive hemophiliac patient serum was not blocked by individual V1 or V2 peptides or by mixtures of these peptides. A construct containing the V3 domain of the IIIB strain of HIV-1, gp(1-263):V3HXB2, was recognized by sera from a human and a chimpanzee that had been infected by HIVIIIB but not by sera from hemophiliac patients who had been infected with HIV-1 of MN-like V3 serotype. The reactive sera had significantly higher titers when assayed against gp(1-263):V3HXB2 than when assayed against matching V3 peptides. Immunoprecipitation of this fusion glycoprotein by the human serum was only partially blocked by V3 peptide, indicating that this infected individual produced antibodies against epitopes in V3 that were expressed on the fusion glycoprotein but not by synthetic peptides. These data demonstrated that the chimeric glycoproteins described here effectively present native epitopes present in the V1/V2 and V3 domains of gp120 and provide efficient methods for detection of antibodies directed against native epitopes in these regions and for characterization of such epitopes.

Diversity of V3 region sequences of human immunodeficiency viruses type 1 from the central African Republic

Nucleotide sequences of the central portion of gp120, including the third hypervariable (V3) loop, were obtained from lymphocytes cocultivated with SupT1 cells from 29 AIDS patients in Bangui, Central African Republic. These sequences displayed significantly greater diversity (average distance, 23%) than has been previously observed in isolates from comparably restricted geographical areas. Isolates belonging to four major subtypes of HIV-1 were found; the only subtype not represented was the North American/European subtype B. Unlike the situation in Zaire and Uganda, where subtypes A and D account equally for virtually all isolates of HIV-1, the predominant subtypes in the Central African Republic, accounting for two-thirds of the isolates, were subtypes A (10 isolates) and E (9 isolates). Subtype E represents a group of variants that have previously been found only in Thailand. Only one isolate belonging to subtype D was found. Also recovered were two isolates of subtype C, a subtype associated with southern African and Indian isolates but not previously detected in central Africa. These isolates, although clearly clustering with subtype C, formed a distinct subset, differing from one another by 8.8% and from the Indian and South African subtype C isolates by an average of 22.5%. High interpatient, intrasubtype variation was also seen among the CAR subtype A (average pairwise difference, 19.3%) and subtype E (10.9%) isolates. The diversity of V3 sequences in this set has implications for immunization protocols that rely on the recognition of V3. This study underscores the necessity of basing intervention strategies on knowledge of the particular sequences present in the target population or geographical area.

A potent, neutralizing human monoclonal antibody against a unique epitope overlapping the CD4-binding site of HIV-1 gp120 that is broadly conserved across North American and African virus isolates

A human monoclonal antibody (HuMAb), 5145A, against HIV-1 gp120 was isolated from an asymptomatic, seropositive hemophiliac. The epitope of this HuMAb was destroyed by reduction of gp120 disulfide bonds, but not by removal of N-linked carbohydrates. This epitope overlaps the CD4-binding site of gp120, because binding of 5145A to gp120 is inhibited by soluble CD4 and by 1125H, a previously described HuMAb directed toward the CD4-binding site. However, the 5145A epitope differs from those of 1125H and other anti-CD4-binding site HuMAbs previously described, as documented by the viral strain specificity of 5145A and its reactivity with a panel of gp120 mutants. Specifically, 5145A reacted with 14 of 15 HIV-1 isolates tested, including 9 isolates from the Central African Republic, 6 of which were not recognized by 1125H. Partial epitope mapping of 5145A, using a series of gp120 mutants, demonstrated its lack of sensitivity to mutations in residues 257 and 427, contrasting with a marked sensitivity to mutations in residues 368 and 370. This pattern of reactivity distinguishes its epitope from that of any HuMAb against the CD4-binding site region described to date. In addition, 5145A exhibited potent and essentially equivalent neutralization of the MN, SF-2, IIIB, and RF strains and possessed significant neutralizing activity against three of three African strains tested. Finally, 5145A synergistically neutralized the MN and SF-2 strains of HIV-1 when combined with 4117C, a HuMAb against the V3 loop. The broad strain specificity and potent neutralizing activity of 5145A, together with its ability to synergize with an anti-V3 loop HuMAb in neutralizing HIV-1, indicate that 5145A has excellent potential as a passive immunotherapeutic agent against HIV-1.

In vitro progesterone effects on 3H-norepinephrine release from rat cerebral cortex slices

The effect of progesterone in vitro (0.05-5 microM) on K(+)-induced, Ca(2+)-dependent release of 3H-NE from brain slices obtained from the occipital region of rats, during the oestrous cycle or 7 days after ovariectomy or on the fifth day of pregnancy was studied. The hormone reduced the K+ (20 mM) effect in all the stages of the cycle, but did not modify the reduced release found after ovariectomy or pregnancy or the release induced from male slices. Yohimbine blocked the effect of progesterone. The results suggest the releasing process of norepinephrine in the cerebral cortex as a target for progesterone modulatory influences on brain function.

Conformational changes affecting the V3 and CD4-binding domains of human immunodeficiency virus type 1 gp120 associated with env processing and with binding of ligands to these sites

Two neutralizing human monoclonal antibodies (HuMAbs) directed against epitopes located near the tip of the V3 loop of human immunodeficiency virus type 1 env protein recognized solubilized gPr160, but not gp120, in radioimmunoprecipitation assays. Efficient immunoprecipitation of solubilized gp120 by these antibodies did occur in the presence of HuMAb 1125H, directed against a conformational epitope overlapping the CD4-binding site, or its F(ab')2 fragment. In contrast to the inability of the anti-V3 antibodies to immunoprecipitate solubilized gp120, these HuMAbs did bind to gp120 in intact virions; this level of binding increased severalfold in the presence of the F(ab')2 fragment of 1125H. These results demonstrate that neutralization epitopes in the V3 loop are sequestered in soluble gp120 but partly exposed in gPr160 and in virion-associated gp120 and that binding of antibodies to the discontinuous CD4-binding site leads to conformational changes that result in the exposure of V3 epitopes in soluble gp120 and their enhanced accessibility in gPr160 and in virion-associated gp120. Enhanced binding of suboptimal concentrations of 1125H to soluble gp120 was also induced by the presence of an anti-V3 HuMAb, indicating the occurrence of reciprocal allosteric interactions between the V3 loop and the CD4-binding site. It is likely that these effects contribute to the synergistic neutralization of human immunodeficiency virus type 1 previously reported for antibodies directed against these two regions.

Erythropoietin receptor (EpoR)-dependent mitogenicity of spleen focus-forming virus correlates with viral pathogenicity and processing of env protein but not with formation of gp52-EpoR complexes in the endoplasmic reticulum

Recent evidence suggests that interactions between spleen focus-forming virus (SFFV) env products and the erythropoietin receptor (EpoR) are responsible for viral pathogenicity. Infection of factor-dependent cell lines expressing epoR (the cloned gene for EpoR) with SFFVP is mitogenic, generating cell lines that are no longer dependent on added growth factor, and an immunoprecipitable complex between EpoR and immature env protein in the endoplasmic reticulum has been identified. The dependence of these in vitro activities on env protein processing and their relationship to pathogenicity of SFFV were explored by using glycosylation site mutants of SFFV env. Mutants carrying Asn-->Asp mutations at each of the two consensus signals for N-linked glycosylation in the N-terminal domain of SFFVAP-L env (gs1 and gs2), the gs1-2- double mutant, and the gs0 quadruple mutant (mutated at all four signals utilized for N-linked glycosylation in SFFVAP-L env) were made. The primary translation products (gp52) of single-site mutant envs were processed into more highly glycosylated forms, and the corresponding viruses induced splenomegaly in susceptible mice, whereas the gs1-2- and gs0 proteins were not processed, and these viruses were not pathogenic. Unprocessed env proteins of both pathogenic and nonpathogenic mutants coprecipitated with EpoR. In the BaF3 cell assay for epoR-dependent mitogenicity, the pathogenic single mutants induced factor-independent growth efficiently whereas the nonpathogenic gs1-2- and gs0 mutants did not. These data demonstrate that the ability of gp52 to form complexes with EpoR in the endoplasmic reticulum is not sufficient for either mitogenicity in cell culture or induction of splenomegaly in mice while supporting the hypothesis that pathogenicity and mitogenicity of SFFV both result from an interaction between EpoR and SFFV env protein.

In vitro progesterone effects on 3H-dopamine release from rat corpus striatum slices obtained under different endocrine conditions

The release of dopamine (DA) from corpus striatum is affected by the endocrine state of the animal being progesterone suggested as a potential hormonal modulatory signal. Most of its actions have been described on endogenous DA release induced by amphetamine. However, the release of DA and the mechanism of the drug effect have been shown to be highly complexes. Considering that DA recently incorporated and/or synthetized is preferentially used we have characterized the effect of progesterone in vitro on the K(+)-induced release of 3H-dopamine (3H-DA) from rat corpus striatum slices. These were obtained during the estrous cycle or under conditions of high or low levels of endogenous progesterone (pregnant and ovariectomized rats). The release of 3H-DA was independent of the cycle. However, progesterone in vitro modified the induced release in a cycle-dependent way. Low concentrations of the hormone (100-200 mM) reduced the K+ (30 mM) effect while higher doses (300-500 mM) were facilitatories. After 7 days of ovariectomy, the induced release of 3H-DA was unchanged while in pregnant rats it was found decreased. In both cases the inhibitory effect of the hormone disappeared. Both progesterone (200 nM) and omission of Ca++ from the superfusion medium did not modified tyramine (20 microM) or K+ induced release, respectively. Data suggest that the pool of DA, related to exocytotic mechanism of release, could be specifically affected by progesterone, in a bimodal way, probably through independent genomic and non-genomic influences.