Human leukocytes kill varicella-zoster virus-infected fibroblasts in the presence of murine monoclonal antibodies to virus-specific glycoproteins.

Seven murine monoclonal antibodies reacting with major glycoproteins of varicella-zoster virus were tested for functional activity in assays for antibody-dependent cellular cytotoxicity (ADCC) and antibody-plus-complement-mediated lysis. Human peripheral blood mononuclear cells killed varicella-zoster virus-infected fibroblasts in the presence of three of four monoclonal antibodies directed against gp98/62 and a single monoclonal antibody directed against gp118. Neither of two monoclonal antibodies directed against gp66 was able to mediate ADCC. In 18-h assays, adherent effector cells were more active than nonadherent effector cells in mediating ADCC. Adherent cells treated with anti-Leu-11b and complement retained their cytotoxic activity, suggesting that monocytes are responsible for most of the adherent-cell-mediated cytotoxicity. Both immunoglobulin G1 and G2a murine monoclonal antibodies were able to participate in ADCC. Of the two immunoglobulin G2a monoclonal antibodies tested, both of which reacted with gp98/62, only one mediated lysis in the presence of complement. These results indicate that some murine monoclonal antibodies against major glycoproteins of varicella-zoster virus have functional activity in cytotoxicity assays.     

Morphological and biochemical changes of isolated chicken egg-envelope during sperm penetration: degradation of the 97-kilodalton glycoprotein is involved in sperm-driven hole formation on the egg-envelope

The chicken egg-envelope is made of two major glycoprotein components, which are designated as gp97 and gp42 (after their molecular masses). To elucidate how these two components are involved in macromolecular organization of the chicken egg-envelope, the isolated egg-envelope was characterized by immunochemical and biochemical methods. The gp97 was suggested to be a homologue of mouse ZPB based on the similarities of N-terminal and internal sequences. Immunoblotting using anti-gp97 monoclonal antibodies and two-dimensional gel electrophoresis with or without mercaptoethanol treatment revealed that gp97 formed a homodimer through disulfide bonds, whereas gp42 did not. Under indirect immunofluorescence microscopy, the anti-gp97 antibody visualized indistinct, small spots on the egg-envelope, whereas the anti-gp42 antibody showed a meshwork of blurry, fibrous structures. The hole formation on the egg-envelope by in vitro sperm penetration was completely inhibited by two anti-gp97 monoclonal antibodies. Interestingly, the anti-gp97 monoclonal antibodies blocked the proteolysis not only of gp97 but also of gp42 during incubation of the egg-envelope with either sperm or the crude chicken acrosin. Taken together, these results indicate that gp97 may play pivotal roles not only in constitution of the macromolecular organization of the egg-envelope but also in triggering hydrolysis of the egg-envelope during sperm penetration.     

Identification of a putative receptor for subgroup A feline leukemia virus on feline T cells.

Retrovirus infection is initiated by the binding of virus envelope glycoprotein to a receptor molecule present on cell membranes. To characterize a receptor for feline leukemia virus (FeLV), we extensively purified the viral envelope glycoprotein, gp70, from culture supernatants of FeLV-61E (subgroup A)-infected cells by immunoaffinity chromatography. Binding of purified 125I-labeled gp70 to the feline T-cell line 3201 was specific and saturable, and Scatchard analysis revealed a single class of receptor binding sites with an average number of 1.6 x 10(5) receptors per cell and an apparent affinity constant (Ka) of 1.15 x 10(9) M-1. Cross-linking experiments identified a putative gp70-receptor complex of 135 to 140 kDa. Similarly, coprecipitation of 125I-labeled cell surface proteins with purified gp70 and a neutralizing but noninterfering anti-gp70 monoclonal antibody revealed a single cell surface protein of approximately 70 kDa. These results indicate that FeLV-A binds to feline T cells via a 70-kDa cell surface protein, its presumptive receptor.     

Determination of the protective epitopes on the glycoproteins of Venezuelan equine encephalomyelitis virus by passive transfer of monoclonal antibodies

We have previously characterized seven unique antigenic epitopes on the two envelope glycoproteins of the Venezuelan equine encephalomyelitis (VEE) virus vaccine strain, TC-83, by using monoclonal antibodies. The in vitro function of virus neutralization was primarily associated with one epitope on the gp56 (gp56c). To determine which epitopes were important in protecting animals from VEE infection, purified monoclonal antibodies were inoculated i.v. into 3-wk-old Swiss mice. Twenty-four hours later these animals were challenged i.p. with 100 IPLD50 of virulent VEE virus (Trinidad donkey). High-avidity anti-gp56c, anti-gp50b, anti-gp50c, and anti-gp50d monoclonal antibodies protected animals from virus challenge. Rabbit antisera to the gp56 and the gp50 glycoproteins were also effective in protecting mice from challenge with virulent VEE virus. Less antibody was needed to protect animals if the antibody was directed against the critical neutralization site. Less avid antibodies to the gp56c and gp50b epitopes demonstrated little or no protection in vivo. Protection, therefore, appeared to be a function of the passive antibody's specificity, avidity, and ability to bind to virion antigenic determinants topologically proximal to the critical neutralization site.     

Interleukin-6 signal transducer gp130 mediates oncostatin M signaling.

Oncostatin M (OM) is a multifunctional cytokine that is structurally and functionally related to interleukin 6 (IL-6) and leukemia inhibitory factor (LIF). The specific receptor for OM has been demonstrated (by chemical cross-linking) to be a 150-kDa protein in a number of cell lines. The IL-6 signal transducer, gp130, is also an affinity converter for the LIF receptor. It does not bind to either IL-6 or LIF, but associates with the alpha subunits of the receptors and transduces the signals. We examined the possible involvement of gp130 in OM binding and signaling. We demonstrate that: (a) anti-gp130 monoclonal antibodies (mAbs) block the inhibitory effect of OM on A375 cell growth, (b) the binding and cross-linking of 125I-OM to H2981 cells are completely abolished by anti-gp130 mAbs, (c) the cross-linked OM-receptor complex is immunoprecipitated by anti-gp130 mAbs, and (d) COS-7 cells transfected with the full-length cDNA encoding gp130 exhibit increased OM binding and cross-linking, which are also blocked by anti-gp130 mAbs. Therefore, we conclude that the 150-kDa OM binding protein previously characterized in a variety of cell lines is gp130. OM is the natural ligand for gp130 and gp130 mediates the biological responses of OM.     

The contact site A glycoprotein mediates cell-cell adhesion by homophilic binding in Dictyostelium discoideum

Dictyostelium discoideum expresses a developmentally regulated cell surface glycoprotein of Mr 80,000 (gp80), which has been implicated in the formation of the EDTA-resistant contact sites A at the cell aggregation stage. To determine whether gp80 participates directly in cell binding and, if so, its mode of action, we conjugated purified gp80 to Covaspheres (Covalent Technology Corp., Ann Arbor, MI) and investigated their ability to bind to cells. The binding of gp80- Covaspheres was dependent on the developmental stage of the cells, with maximal interaction at the late aggregation stage. Scanning electron microscopic studies revealed the clustering of gp80-Covaspheres at the polar ends of these cells, similar to the pattern of gp80 distribution on the cell surface as reported earlier (Choi, A. H. C., and Siu, C.- H., 1987, J. Cell Biol., 104:1375-1387). Precoating cells with an adhesion-blocking anti-gp80 monoclonal antibody inhibited the binding of gp80-Covaspheres, suggesting that Covasphere-associated gp80 might undergo homophilic interaction with gp80 on the cell surface. Quantitative binding of 125I-labeled gp80 to intact cells gave an estimate of 1.5 X 10(5) binding sites per cell at the aggregation stage. Binding of soluble gp80 to cells was blocked by precoating cells with the anti-gp80 monoclonal antibody. The ability of gp80 to undergo homophilic interaction was further tested in a filter-binding assay, which showed that 125I-labeled gp80 was able to interact with gp80 bound on nitrocellulose in a dosage-dependent manner. In addition, reassociation of cells was significantly inhibited in the presence of soluble gp80, suggesting that gp80 has a single cell-binding site. These results are consistent with the notion that gp80 mediates cell- cell binding at the aggregation stage of development via homophilic interaction.     

Fine definition of the epitope on the gp41 glycoprotein of human immunodeficiency virus type 1 for the neutralizing monoclonal antibody 2F5

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), in combination with proteolytic protection assays, has been used to identify the functional epitope on human immunodeficiency virus envelope glycoprotein gp41 for the broadly neutralizing anti-gp41 human monoclonal antibody 2F5. In this protection assay-based procedure, a soluble gp140 protein with a stabilizing intermolecular disulfide bond between the gp120 and gp41 subunits (SOS gp140) was affinity bound to immobilized 2F5 under physiological conditions. A combination of proteolytic enzymatic cleavages was then performed to remove unprotected residues. Residues of SOS gp140 protected by their binding to 2F5 were then identified based on their molecular weights as determined by direct MALDI-MS of the immobilized antibody beads. The epitope, NEQELLELDKWASLWN, determined by this MALDI-MS protection assay approach consists of 16 amino acid residues near the C terminus of gp41. It is significantly longer than the ELDKWA core epitope previously determined for 2F5 by peptide enzyme-linked immunosorbent assay. This new knowledge of the structure of the 2F5 epitope may facilitate the design of vaccine antigens intended to induce antibodies with the breadth and potency of action of the 2F5 monoclonal antibody.     

Binding of leukemia inhibitory factor (LIF) to mutants of its low affinity receptor, gp190, reveals a LIF binding site outside and interactions between the two cytokine binding domains.

The gp190 transmembrane protein, the low affinity receptor for the leukemia inhibitory factor (LIF), belongs to the hematopoietin family of receptors characterized by the cytokine binding domain (CBD). gp190 is one of the very few members of this family to contain two such domains. The membrane-proximal CBD (herein called D2) is separated from the membrane-distal one (called D1) by an immunoglobulin-like (Ig) domain and is followed by three fibronectin type III repeats. We used truncated gp190 mutants and a blocking anti-gp190 monoclonal antibody to study the role of these repeats in low affinity receptor function. Our results showed that the D1Ig region was involved in LIF binding, while D2 appeared to be crucial for the proper folding of D1, suggesting functionally important interactions between the two CBDs in the wild-type protein. In addition, a point mutation in the carboxyl terminus of the Ig region strongly impaired ligand binding. These findings suggest that at least two distinct sites, both located within the D1Ig region, are involved in LIF binding to gp190, and more generally, that ligand binding sites on these receptors may well be located outside the canonical CBDs.     

Distribution of linear antigenic sites on glycoprotein gp55 of human cytomegalovirus.

Human convalescent serum and bacterial fusion proteins constructed from overlapping open reading frames of the nucleotide sequence encoding the human cytomegalovirus gp55 component of the major envelope glycoprotein complex, gp55-116 (gB), were used to localize antigenic regions recognized by human antibodies. All donor serum analyzed contained antibody reactivity for an antigenic site(s) located between amino acids (AA) 589 and 645, a region containing a previously defined linear site recognized by neutralizing monoclonal antibodies (U. Utz, B. Britt, L. Vugler, and M. Mach, J. Virol. 63:1995-2001, 1989). Furthermore, in-frame insertion of two different synthetic oligonucleotides encoding four amino acids into the sequence at nucleotide 1847 (AA 616) eliminated antibody recognition of the fusion protein. A second antibody binding site was located within the carboxyl terminus of the protein (AA 703 through 906). A competitive binding inhibition assay in which monoclonal antibodies were used to inhibit human antibody reactivity with recombinant gp55-116 (gB) suggested that the majority of human anti-gp55-116 (gB) antibodies were directed against a single antigenic region located between AA 589 and 645. Furthermore, inoculation of mice with fusion proteins containing this antigenic site led to a boostable antibody response. These results indicated that the antigenic site(s) located between AA 589 and 645 was an immunodominant antibody recognition site on gp55 and likely the whole gp55-116 (gB) molecule. The enhanced immunogenicity of this region in vivo may account for its immunodominance.     

Soluble glycoprotein 130 (gp130) attenuates OSM- and LIF-induced cartilage proteoglycan catabolism

Oncostatin M (OSM) and leukaemia inhibitory factor (LIF) exhibit pleiotropic biological activities and share many structural and genetic features. The two cytokines bind with high affinity to the same receptor (LIF/OSM receptor), which consists of the LIF receptor alpha chain (LIFRalpha) and the signal transduction unit gp130. A soluble form of the beta chain of the receptor complex called soluble gp130 (sgp130) has been cloned. In this study, we sought to determine whether recombinant sgp130 or anti-gp130 Ab could attenuate the resorption of proteoglycans induced by OSM and LIF in articular cartilage explants. The results show that at high concentrations sgp130 is capable of attenuating both LIF and OSM mediated resorption. In contrast, anti-gp130 Ab selectively inhibited the stimulation of proteoglycan (PG) release by OSM, albeit minimally. The failure of anti-gp130 to attenuate LIF stimulated PG resorption may be due to the normal interaction of LIF with LIFRalpha and unfettered heterodimerization of LIFRalpha with gp130 in the presence of the antibody. The results indicate that sgp130 and anti-gp130 can modulate cartilage PG metabolism in vitro. Whether sgp130 may have therapeutic activity in models of arthritis or indeed in arthritic diseases remains to be determined.     

Schistosome antigen gp50 is responsible for serological cross-reactivity with Trichinella spiralis.

The 50-kDa component (gp50) present in Schistosoma mansoni eggs and secretions of the various life stages of the parasite was recognized by experimentally infected mice and by humans with S. mansoni, Schistosoma haematobium, and Schistosoma japonicum infection. All sera reacting with crude S. mansoni-soluble egg antigens (SEA) also reacted strongly with gp50 in enzyme-linked immunosorbent assay. No reactivity against gp50 was seen with sera from individuals without schistosomiasis, with the exception of sera from patients with Trichinella spiralis infection. All of 10 sera from patients with trichinellosis also reacted with schistosomes by immunofluorescence essentially recognizing testes, ovaries, ootype epithelium and ducts of the reproductive system. Cross-reacting antigens were seen in T. spiralis hypodermis, stichocytes and possibly germinal primordia using anti-gp50 monoclonal antibodies and anti-gp50-positive schistosomiasis patient sera. The results suggest that the anti-gp50 antibody response constitutes a significant part of the anti-SEA antibody response in infected individuals and is a major reason for the previously recognized serological cross-reactivity between T. spiralis and schistosome species.     

Analysis of three late varicella-zoster virus proteins, a 125,000-molecular-weight protein and gp1 and gp3

Two monoclonal antibodies were prepared against varicella-zoster virus proteins. One of the monoclonal antibodies (10.2) reacted only with the nuclei of infected cells and immunoprecipitated one nonglycosylated late viral protein (125,000 molecular weight). The other monoclonal antibody (19.1) with neutralizing activity, reacted with membrane antigens of infected cells and with the varicella-zoster virus envelope and immunoprecipitated two late major viral glycoproteins (gp1 and gp3). Synthesis of the 125,000-molecular-weight protein, gp1, and gp3 began at 20 to 22 h postinfection, 2 h after the peak of viral DNA synthesis, and continued until 29 h postinfection, when the first progeny virus appeared in infected cells. Pulse-chase experiments showed that during pulse-labeling, only gp1 was detected, whereas during the chase period, gp1 as well as gp3 was detected in infected cells. Under nonreducing conditions, gp3 migrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a 130,000-molecular-weight protein as compared with the 62,000-molecular-weight species obtained when gels were resolved under reducing conditions. This finding indicates that gp3 is a dimer that is disulfide linked.     

Immunoglobulins against gp273, the ligand for sperm-egg interaction in the mollusc bivalve Unio elongatulus,are directed against charged O-linked oligosaccharide chains bearing a Lewis-like structure and interact with epitopes of the human zona pellucida

In oocytes of the mollusc bivalve Unio elongatulus, gp273 is the ligand molecule for sperm-egg interaction and binding is mediated by its O-glycans. A serum raised against this protein enabled its localization in the crater region, the area of the vitelline coat where sperm recognition occurs, and showed that after cyanogen bromide fragmentation, the anti-gp273 epitope(s) was retained by a peptide where the O-glycans are localized. In this article, we utilized purified anti-gp273 immunoglobulins to characterize the corresponding epitope by: (i) immunoblotting analysis of the protein after removal of O- and N-glycans; (ii) solid phase binding analysis of anti-gp273 IgG to gp273 N- and O-glycans; and (iii) binding analysis of the same antibody to commercially available oligosaccharides. The results showed that the epitope consists of O-glycans and contains a Lewis-like structure with fucose as determinant. Anti-gp273 IgG were then used to investigate human zona pellucida by immunoelectronmicroscopy and immunoblotting. Epitopes recognized by the antibody were demonstrated on the outer surface of the zona pellucida and shown to belong to a zona pellucida protein having electrophoretic mobility similar to human ZP3. Since human sperm specifically bind to gp273, and anti-gp273 interferes with this binding a functional role for these epitopes is suggested.     

Molecular cloning of gp49, a cell-surface antigen that is preferentially expressed by mouse mast cell progenitors and is a new member of the immunoglobulin superfamily.

gp49 is a Mr 49,000 glycoprotein expressed on the surface of mouse bone marrow-derived mast cells, which are progenitors for the major in vivo mast cell subclasses, typified by intestinal mucosal mast cells and serosal mast cells. The amino-terminal amino acid sequence of gp49 was determined after isolation of the solubilized membrane protein by affinity chromatography with the B23.1 anti-gp49 monoclonal antibody. Redundant oligonucleotides were used to isolate a full-length 1.3-kilobase cDNA from a mouse mast cell library. The predicted amino acid sequence contains a signal peptide of 23 residues, an extracellular domain of 215 residues with three potential sites of N-linked glycosylation, a transmembrane domain of 23 residues, and a cytoplasmic tail of 42 residues. Hybridization of the gp49 cDNA was limited to mRNA extracted from those cell types that also bound the B23.1 monoclonal antibody as assessed by cytofluorographic analyses. The predicted extracellular domain of gp49 contains two regions of 48 and 51 amino acids, each flanked by cysteine residues. Both regions meet criteria for being C2-type domains of the immunoglobulin superfamily based upon the alignment of consensus amino acids and their predicted secondary structure organization. Thus, gp49, a membrane glycoprotein preferentially expressed by the progenitor mast cell population, is a new member of the immunoglobulin superfamily.     

Enhanced in vitro human immunodeficiency virus type 1 replication in B cells expressing surface antibody to the TM Env protein.

The human immunodeficiency virus type 1 (HIV-1) external envelope glycoprotein gp120 tightly binds CD4 as its principal cellular receptor, explaining the tropism of HIV-1 for CD4+ cells. Nevertheless, reports documenting HIV infection or HIV binding in cells lacking CD4 surface expression have raised the possibility that cellular receptors in addition to CD4 may interact with HIV envelope. Moreover, the lymphocyte adhesion molecule LFA-1 appears to play an important role in augmenting HIV-1 viral spread and cytopathicity in vitro, although the mechanism of this function is still not completely defined. In the course of characterizing a human anti-HIV gp41 monoclonal antibody, we transfected a CD4-negative, LFA-1-negative B-cell line to express an anti-gp41 immunoglobulin receptor (surface immunoglobulin [sIg]/gp41). Despite acquiring the ability to bind HIV envelope, such transfected B cells could not be infected by HIV-1. These cells were not intrinsically defective for supporting HIV-1 infection, because when directed to produce surface CD4 by using retroviral constructs, they acquired the ability to replicate HIV-1. Interestingly, transfected cells expressing both surface CD4 and sIg/gp41 receptors replicated HIV much better than cells expressing only CD4. The enhancement resided specifically in sIg/gp41, because isotype-specific, anti-IgG1 antibodies directed against sIg/gp41 blocked the enhancement. These data directly establish the ability of a cell surface anti-gp41 receptor to enhance HIV-1 replication.     

Analysis of the cross-reactive anti-gp120 antibody population in human immunodeficiency virus-infected asymptomatic individuals.

This study was undertaken to analyze the specificity and neutralizing properties of cross-reactive anti-gp120 antibodies (Abs) in the sera of two human immunodeficiency virus (HIV)-infected asymptomatic individuals. Two panels of murine monoclonal anti-idiotype Abs (anti-id MAbs) were established against cross-reactive polyclonal anti-gp120 Abs purified from HIV+ sera by sequential affinity chromatography using gp120SF2- and gp120IIIB-Sepharose columns. These panels of anti-id MAbs were then used to affinity purify idiotype-positive (Id+) anti-gp120 Abs from HIV+ sera. The recovery of each of these Id+ Abs by purification indicated that several idiotypically distinct cross-reactive anti-gp120 Abs are present in sera over a wide range of concentrations. Immunological and biological studies showed that although all of the Id+ Abs were reactive against gp120SF2 and gp120IIIB, they exhibited unique epitope specificities and distinct neutralizing activities. Most of the Id+ Abs were directed against epitopes in the CD4 attachment site (CD4 site epitopes) of gp120 and exhibited a spectrum of broadly neutralizing activities. On the other hand, a minor population of Id+ Abs showed specificity for the V3 region of gp120 and exhibited limited cross-neutralizing activities. Together, these studies indicate that the CD4 site epitope-specific Abs are heterogeneous with respect to their clonality, neutralizing activity, and concentration in sera. This heterogeneity suggests that anti-gp120 Abs to the CD4 attachment site are developed in response to multiple overlapping epitopes present on the original virus isolate and/or epitopes on mutated variants which emerged over time.     

Surface glycoprotein, gp24, involved in early adhesion of Dictyostelium discoideum

A membrane glycoprotein of 24,000 Da (gp24) was purified from developed cells of Dictyostelium discoideum and shown to neutralize a crude antiserum (R695) that blocks EDTA-sensitive cell-cell adhesion during the early developmental stages of this organism. Purified gp24 was used to raise rabbit polyclonal antibodies and mouse monoclonal antibodies. Rabbit antiserum R851 was shown to be highly specific to gp24 by both Western analysis and immunoprecipitation. IgG of R851 is able to block adhesion of dissociated cells swirled in suspension. Adhesion of wild-type cells is blocked by R851 antibodies during the first 8 hr of development but not thereafter when other adhesion mechanisms come into play. The glycoprotein gp80 plays an essential role in the second adhesion system that appears during the aggregation stage of D. discoideum. By adding both anti-gp24 and anti-gp80 antibodies, adhesion of aggregation stage cells could be blocked. Late in development a third adhesion mechanism appears that is not blocked by either antibodies to gp24 or gp80 or both antibodies together. Western analysis and immunoprecipitation with monoclonal antibody mLJ11, specific for gp24, indicated that gp24 is absent in cells growing exponentially on bacteria but is rapidly synthesized and accumulated following the initiation of development. Synthesis of gp24 is maximal during the first 4 hr of development and then continues at a reduced rate throughout the remainder of development. The coordinate appearance of gp24 and EDTA-sensitive cell-cell adhesion as well as the ability of this glycoprotein to neutralize the adhesion blocking activity of R695 and R851 antibodies indicates that it plays a role in early cell-cell adhesion.     

Synergistic inhibition of human immunodeficiency virus type 1 envelope glycoprotein-mediated cell fusion and infection by an antibody to CD4 domain 2 in combination with anti-gp120 antibodies.

Antibodies to several epitopes of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (gp120-gp41) can synergize in inhibiting HIV-1 infection. In the present study we tested the ability of a monoclonal antibody (MAb), 5A8, which interacts with CD4 domain 2, and other CD4-specific MAbs to synergize with antibodies against gp120. We have previously found that 5A8 inhibits HIV-1 entry without interfering with gp120 binding to CD4, presumably by affecting a postbinding membrane fusion event. Because antibodies to the gp120 V3 loop also affect post-CD4-gp120-binding events, 5A8 was first tested in combination with anti-V3 loop antibodies for possible synergy. The anti-V3 loop antibodies 0.5 beta, NEA-9205, and 110.5 acted synergistically with 5A8 in inhibiting syncytium formation between gp120-gp41- and CD4-expressing cells. A human MAb to an epitope of gp120 involved in CD4 binding, IAM 120-1B1, and another anti-CD4 binding site antibody, PC39.13, also exerted synergistic effects in combination with 5A8. Similarly, an antibody against the gp120 binding site on CD4, 6H10, acted synergistically with an anti-V3 loop antibody, NEA-9205. However, a control anti-CD4 antibody, OKT4, which does not significantly inhibit syncytium formation alone, produced only an additive effect when combined with NEA-9205. Serum from HIV-1-infected individuals, which presumably contains antibodies to the V3 loop and the CD4 binding site, exhibited a strong synergistic effect with 5A8 in inhibiting infection by a patient HIV-1 isolate (0104B) and in blocking syncytium formation. These results indicate that therapeutics based on antibodies affecting both non-gp120 binding and gp120 binding epitopes of the target receptor molecule, CD4, could be efficient in patients who already contain anti-gp120 antibodies and could also be used to enhance passive immunization against HIV-1 in combination with anti-gp120 antibodies.     

Analysis of the interaction of the human immunodeficiency virus type 1 gp120 envelope glycoprotein with the gp41 transmembrane glycoprotein.

The human immunodeficiency virus type 1 (HIV-1) gp120 exterior envelope glycoprotein interacts with the viral receptor (CD4) and with the gp41 transmembrane envelope glycoprotein. To study the interaction of the gp120 and gp41 envelope glycoproteins, we compared the abilities of anti-gp120 monoclonal antibodies to bind soluble gp120 and a soluble glycoprotein, sgp140, that contains gp120 and gp41 exterior domains. The occlusion or alteration of a subset of gp120 epitopes on the latter molecule allowed the definition of a gp41 "footprint" on the gp120 antibody competition map. The occlusion of these epitopes on the sgp140 glycoprotein was decreased by the binding of soluble CD4. The gp120 epitopes implicated in the interaction with the gp41 ectodomain were disrupted by deletions of the first (C1) and fifth (C5) conserved gp120 regions. These deletions did not affect the integrity of the discontinuous binding sites for CD4 and neutralizing monoclonal antibodies. Thus, the gp41 interface on the HIV-1 gp120 glycoprotein, which elicits nonneutralizing antibodies, can be removed while retaining immunologically desirable gp120 structures.