A simple, secure and universal pancreaticojejunostomy following pancreaticoduodenectomy

Although the operative mortality of pancreaticoduodenal resection has decreased recently, the operative morbidity resulting from a leaking pancreatic anastomosis remains high. We described our experience in 50 consecutive cases with a simple, secure end to side pancreaticojejunostomy. We used a paediatric nasogastric tube in the pancreatic remnant duct as a temporary external pancreatic drain. There were 29 men and 21 women ranging from 12 to 84 years with a median age of 61 years. Forty-two patients underwent a standard Whipple procedure and eight a pylorus preserving pancreaticoduodenectomy. Average operating time was 270 minutes with a range of 170 to 480 minutes. The pancreaticojejunostomy could be constructed in a mean of 8 minutes. Intraoperative blood loss ranged from 150 to 3500 mL with a mean of 910 mL. Twenty-five patients (50%) received no blood transfusion. The consistency of the pancreatic remnant was hard in 12 patients (24%) and normal in 38 patients (76%). The pancreatic duct was dilated (> 4 mm) in 15 patients (30%). There was no operative mortality and only three (6.0%) minor leaks from the pancreatic anastomosis which healed spontaneously. It was difficult to determine if the leaks were related to the consistency of the pancreatic remnant, the size of the pancreatic duct, the amount of intraoperative blood loss, operating time, sex of the patient or experience of the surgeon, as there were only three leaks. We concluded that our technique for pancreaticojejunal anastomosis following pancreaticoduodenectomy was safe and applicable to, standard Whipple or pylorus preserving pancreaticoduodenectomy, small or dilated pancreatic ducts, normal or fibrotic pancreas.

Inhibition of antigen-specific IgE production by antigen coupled to membrane IgE peptide

The membrane IgE peptide (MEP) encompassing 20 amino acids proximal to the C terminus of membrane IgE molecules, and secretory IgE peptides (SEP), spanning CH epsilon 1 to 4 domain were synthesized according to IgE genomic and cDNA sequences. Inhibition of anti-KLH and anti-BGG IgE, but not IgG responses was observed in mice treated with MEP-protein but not SEP-protein conjugates in complete/incomplete Freund's adjuvant. Only IgE responses directed toward proteins to which MEP was conjugated, were inhibited, while IgE responses to a concomitantly injected, unrelated antigen were not. Inhibition of antigen-specific IgE was also not correlated with levels of anti-MEP or anti-IgE antibodies, moreover, levels of total IgE remained comparable among mice treated with MEP-protein conjugates, native or glutaraldehyde-modified protein carriers. This observation may have significant import on future design of IgE immunotherapy. Treatment of MEP conjugated allergens prevents formation of IgE-anti-IgE complexes because the MEP sequence is absent from the secretory IgE.

Transverse abdominis musculo-peritoneal (TRAMP) flap for the repair of large duodenal defects

Definitive surgical management of major acute injuries to the second and third portions of the duodenum has been enigmatic. Sometimes, the defect is so large that it is unwise to do primary repair, and resection at this critical portion of the intestinal tract is technically hazardous or impossible. A serosal or mucosal patch technique has been used to repair this kind of duodenal defect with encouraging results. Since the use of this technique has proved effective, such a defect was not necessarily treated with the more complicated pancreaticoduodenectomy and was managed with less morbidity and mortality. But these techniques are still controversial. So, we tried a pedicle flap, called the transverse abdominis musculo-peritoneal (TRAMP) flap, for repair of large duodenal defect. We have used this flap in 25 rabbits, and the specimens were followed up to a period of 3 months. The flap showed satisfactory results and is presented as another option for repair of large duodenal defects.

Structural features of the extracellular portion of membrane-anchoring peptides on membrane-bound immunoglobulins

Membrane-bound immunoglobulins, mIgs, are displayed as transmembrane proteins on the surface of B cells, where they serve as antigen receptors. The mIgs are anchored to the membrane through a carboxy-terminal extension of the immunoglobulin heavy chain. Three distinct structural regions of these membrane-anchor peptides, of mouse and human mIgs, have been delineated: (1) a central conserved stretch of 25 hydrophobic, unchanged amino acid residues, which spans the membrane lipid bilayer; (2) a C-terminal hydrophilic region of 3-28 amino acids, which is intracytoplasmic; and (3) an N-terminal extracellular hydrophilic region of 13-67 amino acids, which is isotype-specific. Here we report predicted secondary and tertiary structures of the third structural region of the membrane anchoring peptide along with corroborating experimental evidence. The predictions of secondary and tertiary structure indicate that most of these regions can assume an chi-helical conformation. Circular dichroism spectroscopy of corresponding synthetic peptide confirms this essential feature. The choice of solvent and pH have dramatic effects on peptide helicity; solvent conditions consistent with a membrane-proximal environment promote helicity. Additional studies suggest that the two adjacent extracellular peptides may be stabilized through coiled-coil interactions similar to those described for some other transmembrane proteins.

Human IgA monoclonal antibodies specific for a major ragweed pollen antigen

Human hybridoma cell lines secreting IgG specific for the major allergen in the pollen of short ragweed, Amb a I, were established from patients who had been receiving antigen injections for immunotherapy. Recombinant Ig genes were then constructed by cloning the heavy and light chain variable region genes of the human hybridoma cell line and joining them to the human alpha or kappa constant region genes in mammalian expression vectors. Amb a I-specific IgA was expressed in two mouse myeloma cell lines, NS0 and Sp2/0. In both systems, transfected alpha and kappa chains were assembled into IgA monomers or into dimers covalently linked by the endogenous murine J chains. We propose that recombinant IgA monoclonal antibodies specific for airborne allergens may be applied to the mucosal surface of the nasal linings or of the lower airway of sensitized individuals to inhibit the entry of allergenic molecules across the mucosal epithelium and, therefore, to prevent the development of allergic responses.

Resting tremor only: a variant of Parkinson's disease or of essential tremor

Resting tremor is one of the characteristic features of Parkinson's disease. However, there are a number of patients who typically have resting tremor alone for at least 5 years without development of other parkinsonian signs or symptoms. The etiology of an isolated resting tremor is still obscure. Recently, positron emission tomography was used to study these patients with isolated resting tremor, and demonstrated a markedly decreased striatal uptake of fluoro-dopa to the range of Parkinson's disease. These findings suggested the existence of a separate subtype, namely, tremulous Parkinson's disease with a manifestation of resting tremor alone. In order to confirm the existence of this subgroup of tremulous Parkinson's disease and further investigate its morphological changes and the usefulness of magnetic resonance imaging, we collected 5 patients who typically have resting tremor for at least 8 years in the absence of other features of Parkinson's disease. MRI was performed and the results of the images showed typical findings of Parkinson's disease with smudging or decreased distance between substantia nigra and red nucleus. Quantitative analysis also demonstrated a significant decrease of the above-noted distance when the resting tremor group was compared to the essential tremor group. Therefore, patients with an isolated resting tremor can have morphological abnormalities in addition to functional disturbances shown by positron emission tomography. To our knowledge, this is the first paper to report that resting tremor is a variant of Parkinson's disease rather than essential tremor, by using a double-blind method, with magnetic resonance imaging to support.

Pulsatile flow through a bifurcation with a cerebrovascular aneurysm

Laser-Doppler velocimetry measurements and flow visualization were complementarily made in pulsatile and steady flow in a cerebrovascular aneurysm model with bifurcation angles of 60, 90, and 140 deg, and volume-flow rate ratios between the branches of 1 to 1 and 3 to 1. The mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 800, and 280, respectively. For uneven branch flow, it is found that the flow activity inside the aneurysm and the stresses acting on the aneurysmal wall increase with increasing bifurcation angle. More importantly, the present angle suggests the presence of a critical bifurcation angle below which the aneurysm is prone to thrombosis, whereas above which the aneurysm is susceptible to progression or rupture. For evenly distributed branch flow, the intra-aneurysmal flow is sluggish and therefore prone to thrombosis for all studied bifurcation angles.

Pharmacokinetics of an HIV-1 gp120-specific chimeric antibody in patients with HIV-1 disease

The pharmacokinetics of mouse V/human C (gamma 1, kappa) chimeric monoclonal antibody CGP 47 439 specific for the principal neutralizing determinant of human immunodeficiency virus type 1 (HIV-1) was studied in patients with stage IV HIV-1 disease in an open-labeled phase I/IIA trial. Twelve male patients were enrolled and nine completed the study. Patients were divided into three groups according to the extent of CGP 47 439 to bind to gp120 from their viral isolates: undetectable for group 1, modestly reactive for group 2, and strongly reactive for group 3. A first dose of 1, 10, or 25 mg was administered by intravenous infusion to group 1, group 2 and group 3 patients, respectively. The patients then received seven doses of 50, 100, or 200 mg, respectively, every three weeks. CGP 47 439 serum concentrations were determined by an ELISA using monoclonal antibody AB19-4 specific for the idiotope of CGP 47 439. Half an hour after infusion only 25.5-36.1% of the administered antibody was found in the serum, reflecting its rapid distribution in the extravascular space and possibly binding to gp120 antigen in some of the patients. The terminal elimination half-life (T1/2) was 16.2 days in group 1 patients, 9.7 days in group 2 and in group 3 patients 7.5 days and 9.1 days. An antibody response to CGP 47 439 was not a factor in determining elimination rates, because only very low and transient responses were found in three patients. These results suggest that the reactivity of CGP 47 439 with HIV-1 gp120 contributed to its elimination in HIV-1 infected patients.

Analysis of the Drosophila gene for the laminin B1 chain

We have isolated and sequenced a Drosophila genomic DNA that encodes the entire coding region of the laminin B1 chain. The genomic DNA sequenced spans 11,787 bp, including a 1.1-kb 5'-flanking region, 5 exons, 4 introns, and a 1.4-kb 3'-flanking region. The open reading frame is within the two largest exons, the exons 3 and 4, while the first two and the last exons are much smaller and are untranslated. The structure of the Drosophila laminin B1 gene is similar to the Drosophila laminin B2 gene. Their exon-intron lengths and Eco RI, Pst I restriction maps are quite conserved. Both of their open reading frames are very compact, and their first introns are much larger than all of the rest of the introns. These results are consistent with the suggestion that the B1 and B2 genes could be derived from an ancestral gene. The similarity of the proximal 5'-flanking regions of the Drosophila B1 and B2 genes is 46.6%. Also, similar sequences of transcriptional regulatory elements, even though not site conserved, are found in both proximal 5'-flanking regions of the B1 and B2 genes. When transfected into Drosophila SL-2 cells, pCAT plasmid containing 1,048 bp of 5'-flanking region shows a strong expression of chloramphenicol acetyltransferase (CAT) activity. The deletion clones that contain sequences between nucleotides -462 to +150, and -282 to +150 all show strong CAT activity. These results suggest that this 5'-flanking promoter region may contain DNA sequences that can promote the expression of the laminin B1 gene.

Can anti-IgE be used to treat allergy?

A summary of the properties of CGP 51901 is shown in Table 3. On the basis of its binding to IgE and IgE-secreting cells and its activity in vitro and in vivo, CGP 51901 is expected to be able to decrease serum IgE by direct clearance of IgE and by reduction of the numbers and productivity of IgE-secreting cells. The end result of reduction of IgE in the circulation and on mast cells is expected to be the attenuation of IgE-mediated reactions and the improvement in allergy symptoms. The effective serum concentration of CGP 51901 is expected to be in the range 1-10 micrograms/ml. Because CGP 51901 is an antibody specific for IgE, it is expected to be highly selective in its activity. Because IgE does not appear to be essential and because CGP 51901 has been rigorously tested to confirm its non-anaphylactic nature, this treatment is not expected to have any adverse effects. Therefore, CGP 51901 is expected to be safe and to have a good probability of being effective when it is tested in human clinical trials.

Comparison of two different trauma assessment scores in predicting trauma outcome

We reviewed 1,455 trauma cases admitted through the Emergency Department of National Cheng Kung University Hospital from June 1988 to December 1991. Of these, 1,251 patients had Revised Trauma Scores (RTS) and 1,452 cases had Injury Severity Scores (ISS) available for analysis of final trauma outcome. Several statistical methods such as simple logistic regression, the contingency table approach, and stepwise logistic regression were adopted to obtain the critical regions of major trauma which satisfied the requirements for sensitivity and specificity with the largest probability of a correct classification. We found that RTS < or = 5.7 and ISS > or = 17 were the best critical regions for defining major trauma. These patients deserve more attention during prehospital and interhospital disposition. Moreover, RTS contributes more to the prediction of patient outcome than ISS, indicating the power of RTS at the time of field evaluation in predicting patients' survival probability. The ISS is calculated retrospectively and is of limited value in acute settings. Therefore, based on our trauma database, we recommended that the RTS be used as a triage tool to select severely ill patients. We also urge that a generalized trauma registry be established in order to validate its usefulness.

Immune enhancers composed of polyvalent binding sites of anti-CD3 antibodies

Anti-CD3 antibodies of some IgG subclasses are very potent T lymphocyte mitogens in vitro and, seemingly contradictorily, very effective immunosuppressive agents in vivo. Using hamster anti-murine CD3 monoclonal antibody, 2C11, as a model, we have found that 2C11.IgG, or its F(ab')2 fragment, coupled to microbeads can provide short-term and vigorous activation of T cells and expansion of the lymphoid system in vivo. In contrast to free 2C11.IgG, these conjugates do not kill mice and cause T cell depletion, and can enhance immune responses. This study suggests that properly modified anti-CD3 antibodies can serve as in vivo immune system enhancers potentially useful in the treatment of cancer and chronic infectious diseases.

hu-PBL-SCID mice can be protected from HIV-1 infection by passive transfer of monoclonal antibody to the principal neutralizing determinant of envelope gp120

OBJECTIVE

To determine whether passive transfer of a monoclonal antibody specific for the principal neutralizing determinant in the V3 region of HIV-1IIIB gp120 can protect mice with severe combined immunodeficiency (SCID) transplanted with normal human peripheral blood leukocytes (hu-PBL), designated hu-PBL-SCID mice, from subsequent challenge with the homologous viral strain.

DESIGN AND METHODS

hu-PBL-SCID mice were given intraperitoneal injections of an anti-HIV-1 neutralizing murine monoclonal antibody (BAT123), its mouse-human chimeric form (CGP 47 439), or a control murine antibody (PNTU), at a dose of 40 mg/kg. The mice were then challenged intraperitoneally with 10 mouse infectious doses of HIV-1IIIB. Three weeks later the mice were killed, and spleen cells and peritoneal lavage collected for determination of infection by coculture for viral isolation and by detection of HIV-1 DNA using polymerase chain reaction (PCR).

RESULTS

All three antibodies had similar serum half-lives of 9-12 days. No toxicity was observed in the animals. HIV-1 was recovered by coculture from five out of the six mice given PNTU, and by PCR from two out of the six mice given PNTU, but was not recovered by either technique from any of the 12 mice given BAT123 or CGP 47 439.

CONCLUSION

BAT123 and CGP 47 439, which are specific for the principal neutralizing determinant of HIV-1IIIB, protect hu-PBL-SCID mice from infection by this viral strain. Our findings support the use of the hu-PBL-SCID mouse as an in vivo model for studying protection against HIV-1 infection by passive immunization with anti-HIV-1 neutralizing antibodies.

Blood levels of platelet-activating factor in endotoxin-sensitive and endotoxin-resistant mice during endotoxemia

Platelet-activating factor (PAF) is a phosphoglyceride secreted by a variety of cells and has been implicated in endotoxin toxicities. To further confirm its role in endotoxin-induced tissue injuries and death, we conducted an experiment on endotoxin-resistant (C3H/HeJ strain) and endotoxin-sensitive (C3H/HeN strain) mice. The experiment consisted of three parts: 1) the LD50 of endotoxin from E. coli 0127:B8 cells was quantitated in C3H/HeN mice; 2) the lethality of PAF in C3H/HeJ mice at a dose lethal to C3H/HeN mice was determined; and 3) the blood levels of PAF in C3H/HeJ and C3H/HeN mice were measured after a dose of endotoxin lethal to the C3H/HeN strain was injected. PAF contained in the blood samples was extracted by a solid phase procedure and assayed by a radioimmunoassay method. The results showed that endotoxin-resistant and endotoxin-sensitive mice were equally susceptible to death induced by the same lethal dose of PAF. After injection with endotoxin, the blood PAF levels in C3H/HeN mice increased significantly (p < 0.01) at 60 minutes and 90 minutes, with a peak level three times that of the control group. The blood PAF levels in C3H/HeJ mice, however, remained unelevated throughout the experiment. The timing of the occurrence of the peak blood PAF level in the C3H/HeN mice corresponded with the emergence of their illness from the endotoxin injection. These findings shed new light on our understanding of the resistant mechanisms of C3H/HeJ mice to bacterial endotoxin and affirm the possible role of PAF in mediating endotoxin toxicities.

Mouse/human chimeric anti-HIV-1 gp120 antibody to the principal neutralizing determinant: tolerability and pharmacokinetics in cynomolgus monkeys, Macaca fascicularis

In preparing for testing a pharmaceutical grade preparation of chimeric (mouse/human) antibody CGP 47,439 in HIV-1 infected individuals, it was administered to Macaca fascicularis (cynomolgus) monkeys to study tolerability, immunogenicity and pharmacokinetics. Four groups of monkeys, three males and three females per group, received respectively four infusions of 0, 1.43, 4.3, and 14.3 mg of CGP 47,439/kg body weight at one-week intervals. The chimeric antibody induced no fever, was tolerated well throughout the 50-day observation period, elicited no tissue damage and no anti-antibody response. The pharmacokinetic profile was similar at all dose levels with a mean T1/2 alpha of 14.2 h (range 11.8-19.3 h) and a mean T1/2 beta of 172.6 h (range 137.2-220.5h). Following four successive antibody infusions serum concentrations of CGP 47,439 increased without reaching a steady state, and its measured concentrations were comparable to the simulated values. Collectively the study has provided safety and pharmacokinetic data that would allow human studies with this antibody in AIDS patients.

Potential use of immunoconjugates for AIDS therapy

More than a dozen of hybrid proteins possessing reactivity with human immunodeficiency virus-type 1-(HIV-1) infected cells and cytotoxicity have been produced and studied by several groups. These proteins are prepared either by chemical cross-linking of a toxin and a carrier molecule or by expressing fused genes of the two moieties. These cytotoxic agents have been investigated to eliminate HIV-1-infected cells in vitro. The ID50 of these agents range from pM to nM. This article compares the results of the various approaches and discusses the limits and potential of immunoconjugates for AIDS therapy.

Identification and characterization of a neutralization site within the second variable region of human immunodeficiency virus type 1 gp120

Two monoclonal antibodies designated BAT085 and G3-136 were raised by immunizing BALB/c mice with gp120 purified from human immunodeficiency virus type 1 (HIV-1) IIIB-infected H9 cell extracts. Among three HIV-1 laboratory isolates (IIIB, MN, and RF), BAT085 neutralized only IIIB infection of CEM-SS cells, whereas G3-136 neutralized both IIIB and RF. These antibodies also neutralized a few primary HIV-1 isolates in the infection of activated human peripheral blood mononuclear cells. In indirect immunofluorescence assays, BAT085 bound to H9 cells infected with IIIB or MN, while G3-136 bound to H9 cells infected with IIIB or RF, but not MN. Using sequence-overlapping synthetic peptides of HIV-1 IIIB gp120, the binding site of BAT085 and G3-136 was mapped to a peptidic segment in the V2 region (amino acid residues 169 to 183). The binding of these antibodies to immobilized gp120 was not inhibited by the antibodies directed to the principal neutralization determinant in the V3 region or to the CD4-binding domain of gp120. In a competition enzyme-linked immunosorbent assay, soluble CD4 inhibited G3-136 but not BAT085 from binding to gp120. Deglycosylation of gp120 by endo-beta-N-acetylglucosaminidase H or reduction of gp120 by dithiothreitol diminished its reactivity with G3-136 but not with BAT085. These results indicate that the V2 region of gp120 contains multiple neutralization determinants recognized by antibodies in both a conformation-dependent and -independent manner.

Human mb-1 gene: complete cDNA sequence and its expression in B cells bearing membrane Ig of various isotypes

The transmembrane protein, IgM-alpha, a product of mb-1 gene, has been shown to be specifically associated with membrane-bound IgM on the plasma membrane of B lymphocytes. Recent studies have suggested that IgM-alpha may play a role in transducing signals from the Ag receptors during the activation of B cells. A large amount of information has been obtained in the mouse system regarding IgM-alpha and other components of the newly conceived B cell Ag receptor complex. Here we report the cloning and the nucleotide sequencing of cDNA clones of human mb-1, covering the entire length of the mRNA. At the amino acid sequence level, human and murine mb-1 share a high homology in their transmembrane and intracytoplasmic segments, suggesting an important biologic function for these regions of mb-1. A major difference, mainly in the 3' untranslated part, exists between our cDNA sequence and the published partial human mb-1 cDNA sequence. It has also been observed that human mb-1 is expressed not only by B cell lines expressing membrane-bound Ig of mu and delta isotypes but also those expressing membrane-bound Ig of alpha and gamma isotypes.

Human mb-1 gene: complete cDNA sequence and its expression in B cells bearing membrane Ig of various isotypes

The transmembrane protein, IgM-alpha, a product of mb-1 gene, has been shown to be specifically associated with membrane-bound IgM on the plasma membrane of B lymphocytes. Recent studies have suggested that IgM-alpha may play a role in transducing signals from the Ag receptors during the activation of B cells. A large amount of information has been obtained in the mouse system regarding IgM-alpha and other components of the newly conceived B cell Ag receptor complex. Here we report the cloning and the nucleotide sequencing of cDNA clones of human mb-1, covering the entire length of the mRNA. At the amino acid sequence level, human and murine mb-1 share a high homology in their transmembrane and intracytoplasmic segments, suggesting an important biologic function for these regions of mb-1. A major difference, mainly in the 3' untranslated part, exists between our cDNA sequence and the published partial human mb-1 cDNA sequence. It has also been observed that human mb-1 is expressed not only by B cell lines expressing membrane-bound Ig of mu and delta isotypes but also those expressing membrane-bound Ig of alpha and gamma isotypes.

A new isoform of human membrane-bound IgE

The epsilon-chain of membrane-bound IgE on the surface of B lymphocytes is known to contain a membrane-anchoring peptide segment that is encoded by two membrane exons, me.1 and me.2. In analyzing pertinent segments in mRNA from human IgE-expressing B cells by using PCR methods and Northern blotting analyses, we have identified three species of mRNA of epsilon-chain with variations in the splicing of the membrane exons. The conventional species (m/s) contains the predicted me.1 and me.2; species m/1 harbors 156 extra nucleotides 5' of me.1 with unaltered reading frame; species s/t lacks me.1 and hence the segment encoding the hydrophobic transmembrane stretch and contains a shifted me.2 reading frame. Rabbit antibodies, which were prepared by immunization using a peptide of 36 amino acid residues representing an encoded segment unique to mRNA species m/l, could specifically bind to human IgE-expressing B cell lines and react with an epsilon-chain on Western immunoblots. These results indicate that there exists a previously unidentified isoform of human membrane-bound IgE.

A new isoform of human membrane-bound IgE

The epsilon-chain of membrane-bound IgE on the surface of B lymphocytes is known to contain a membrane-anchoring peptide segment that is encoded by two membrane exons, me.1 and me.2. In analyzing pertinent segments in mRNA from human IgE-expressing B cells by using PCR methods and Northern blotting analyses, we have identified three species of mRNA of epsilon-chain with variations in the splicing of the membrane exons. The conventional species (m/s) contains the predicted me.1 and me.2; species m/1 harbors 156 extra nucleotides 5' of me.1 with unaltered reading frame; species s/t lacks me.1 and hence the segment encoding the hydrophobic transmembrane stretch and contains a shifted me.2 reading frame. Rabbit antibodies, which were prepared by immunization using a peptide of 36 amino acid residues representing an encoded segment unique to mRNA species m/l, could specifically bind to human IgE-expressing B cell lines and react with an epsilon-chain on Western immunoblots. These results indicate that there exists a previously unidentified isoform of human membrane-bound IgE.

Another discontinuous epitope on glycoprotein gp120 that is important in human immunodeficiency virus type 1 neutralization is identified by a monoclonal antibody

To define the domains in the envelope glycoprotein important for antibody neutralization of the human immunodeficiency virus type 1 (HIV-1), monoclonal antibodies (mAbs) were generated by immunizing mice with purified glycoprotein gp120 of the IIIB isolate. One mAb, G3-4, reacted with the gp120 of homologous (IIIB) and heterologous (RF) isolates. In addition, mAb G3-4 efficiently neutralized both IIIB and RF viruses in vitro, as well as four of nine primary HIV-1 isolates. In competition immunoassays, mAb G3-4 and soluble CD4 were found to inhibit one another in binding to gp120. However, no competition was seen between mAb G3-4 and mAbs directed to the third variable region or the fourth conserved region of gp120. In particular, mAb G3-4 did not compete with our human mAb 15e, which identifies a discontinuous epitope on gp120 involved in group-specific neutralization of HIV-1 and in gp120-CD4 binding. Epitope-mapping studies on mAb G3-4 with synthetic or unglycosylated recombinant peptides were negative, suggesting that its epitope may be discontinuous. Indeed, this hypothesis was confirmed by showing the loss of mAb G3-4 serologic reactivity when gp120 was first denatured. We conclude that the site recognized by mAb G3-4 represents another discontinuous epitope on gp120 important for neutralization of HIV-1.

An epitope on membrane-bound but not secreted IgE: implications in isotype-specific regulation

Immunoglobulins (Igs) on the surface of B lymphocytes are isotype-specific immunological markers of the B-cell subsets expressing them. Since these membrane-bound Igs (mIgs) are antigen receptors, their interaction with antibodies could be explored for modulating the activity of specific B-cell subsets. Targeting mIgs by antibodies in vivo, however, has not been feasible because of the presence of Igs in the circulation and the frequent association of Igs with various cell types via Fc receptors. To circumvent these problems, we proposed that the extracellular portions of the membrane-anchoring segments of the heavy chains of mIgs, referred to as "mIg isotype-specific" or "migis" peptides, may provide the antigenic sites for the isotype-specific targeting of B cells in vivo. Here we describe the exemplary development of monoclonal antibodies (mAbs) recognizing this unique epitope of mIgE.