Human monoclonal antibodies neutralizing varicella-zoster virus

Hybridomas secreting human monoclonal antibodies to varicella-zoster virus were produced by fusing B cells of a patient recovering from acute varicella infection with a human-mouse cell line. Two hybrid lines have continued to secrete IgG1, one with kappa and the other with lambda chains, for at least 12 months. Each antibody neutralizes virus infectivity between 1-5 micrograms of partially purified immunoglobulin/ml, each shows a different pattern of immunofluorescent staining of virus-infected cells, and one identifies three viral proteins with molecular weights of 60,000, 95,000, and 97,000.     

狂犬病疫苗接种人群中狂犬病病毒中和抗体水平分析

目的 通过分析狂犬病疫苗接种人群中狂犬病病毒RABV中和抗体特征,为狂犬病防控提供依据。方法 收集2019-2020年杭州市职业病防治院犬伤后暴露预防接种门诊抗体检测者信息,经筛选后确定157例RABV中和抗体检测者作为研究对象,采用快速荧光灶抑制试验检测狂犬病毒中和抗体,利用横断面研究方法对狂犬病毒中和抗体水平进行人群特征分析。结果 研究对象中,初种者98人,复种者59人,复种者中2-1-1程序比5针法产生的抗体水平更高,其余特征均无统计学差异(P>0.05)。除1例初种者中和抗体效价低于0.5 IU/mL,其余检测者中和抗体效价均高于0.5 IU/mL。狂犬病毒中和抗体水平时间趋势分析显示,狂犬病毒中和抗体水平与时间呈负相关,回归方程为(F=4.974,P=0.031),标准化回归系数为-0.322(t=-2.230,P=0.031)。结论 复种者狂犬病毒中和抗体水平与免疫程序有关,2-1-1程序对人体再次免疫应答的效果优于5针法。接种疫苗2年后部分个体出现失保护状态,再次暴露有必要全程接种狂犬病疫苗。     

Hepatitis C virus evasion mechanisms from neutralizing antibodies

Hepatitis C virus (HCV) represents a major public health problem, affecting 3% of the world's population. The majority of infected individuals develop chronic hepatitis, which can progress to cirrhosis and hepatocellular carcinoma. To date, a vaccine is not available and current therapy is limited by resistance, adverse effects and high costs. Although it is very well established that cell-mediated immunity is necessary for viral clearance, the importance of host antibodies in clearing HCV infection is being increasingly recognized. Indeed, recent studies indicate that neutralizing antibodies are induced in the early phase of infection by patients who subsequently clear viral infection. Conversely, patients who do not clear the virus develop high titers of neutralizing antibodies during the chronic stage. Surprisingly, these antibodies are not able to control HCV infection. HCV has therefore developed mechanisms to evade immune elimination, allowing it to persist in the majority of infected individuals. A detailed understanding of the mechanisms by which the virus escapes immune surveillance is therefore necessary if novel preventive and therapeutic treatments have to be designed. This review summarizes the current knowledge of the mechanisms used by HCV to evade host neutralizing antibodies.     

Detection of platelet-associated antibodies by flow cytometry in hematological autoimmune disorders

We describe our experience in the evaluation of platelet-associated immunoglobulins (PAIg) by flow cytometry in comparison to solid-phase assay in patients affected by idiopathic thrombocytopenic purpura and by Evans syndrome. Results show that the analysis of PAIg by flow cytometry is easy and reliable and correlates well with data obtained by the solid-phase technique. In addition, flow cytometry allows the evaluation of samples containing small numbers of platelets (<20000/mm³); the analysis is objective, not influenced by personal experience. Moreover, flow cytometry appears simple enough to be performed in a routine laboratory, and data might be retrieved to perform batch analysis. Our results appear to indicate that PAIg flow cytometry might be a sensitive tool for the evaluation of patients with autoimmune thrombocytopenia.     

Vaccine-induced cross-genotype reactive neutralizing antibodies against hepatitis C virus

We detected cross-reactive neutralizing antibodies (NtAb) against hepatitis C virus (HCV) in chimpanzees vaccinated with HCV-1 (genotype 1a) recombinant E1/E2 envelope glycoproteins. Five vaccinated chimpanzees, protected following HCV-1 challenge, were initially studied using the heterologous H77 (genotype 1a) HCVpp assay. All animals had developed NtAb after the second vaccination; 4 animals had reciprocal titers of ≥200 at the time of challenge. Using genotypes 1a-6a HCV pseudoparticles (HCVpp) and cell culture-derived HCV (HCVcc) assays, cross-reactive NtAb were detected against 1a, 4a, 5a, and 6a, with limited reactivity against 2a and 3a. Our study provides encouragement for the development of a recombinant envelope-based vaccine against hepatitis C.     

Virus‐neutralizing antibodies to hepatitis C virus

For a long time, the lack of an appropriate cell culture system has hampered the study of neutralizing antibody responses against hepatitis C virus (HCV). However, the last decade has seen the development of several model systems that have significantly advanced our understanding of viral entry and antibody neutralization. Studies of acutely infected patients suggest that a strong and early production of neutralizing antibodies may contribute to control the virus during the acute phase of HCV infection and facilitate viral elimination by cellular immune responses. It also emerges that the early antibody response mainly targets hypervariable region 1 (HVR1) of the envelope glycoprotein E2. This host response can lead to viral escape from neutralization by rapid amino acid changes in this hypervariable region. In contrast, cross‐reactive neutralizing antibodies seem to appear later during HCV infection, and several mechanisms contribute to reduce their accessibility to their cognate epitopes. These include the masking of major conserved neutralizing epitopes by HVR1, specific N‐linked glycans and the lipid moiety of the viral particle. Other potential mechanisms of evasion from the neutralizing antibody response include a modulation by high‐density lipoproteins and interfering antibodies as well as the capacity of the virus to be transferred by cell‐to‐cell contacts. Finally, the recent identification of several highly conserved neutralizing epitopes provides some opportunities for the design and development of vaccine candidates that elicit a protective humoral immune response.     

Analysis of the insulin receptor by anti-receptor antibodies and flow cytometry.

We characterized insulin receptors on a human lymphoblastoid cell line (IM-9) and studied their regulation using anti-receptor antibodies and fluorescence flow cytometry. The fluorescence intensity distribution of insulin receptors on cells was determined by incubating the cells with one of three different anti-receptor antisera (human serum B-9 containing polyclonal autoantibodies, serum from a rabbit with polyclonal antibodies, and a monoclonal antibody to the receptor produced in mouse hybridomas), followed by incubation with an appropriate fluorescein isothiocyanate-labeled second antibody and analysis on an Epics-V flow cytometer. All three anti-receptor antibodies specifically labeled the insulin receptors. The monoclonal antibody showed the highest level of labeling. Treatment of cells with proteolytic enzymes, such as trypsin or chymotrypsin, produced a dose-dependent loss of 125I-labeled insulin (125I-insulin) binding but a relatively small decrease in the binding of anti-receptor antibodies, suggesting that most antibody binding occurred in domains other than the insulin binding site. Treatment with glycosidic enzymes, such as neuraminidase and beta-galactosidase did not affect the binding of 125I-insulin, and fluorescence was actually enhanced by about 20% in the beta-galactosidase-treated cells. Exposure of IM-9 cells to insulin resulted in a reduction in the number of insulin receptors. Analysis of the down-regulated cells by immunofluorescence revealed a complete correlation between the percent binding of 125I-insulin and percent peak fluorescence. In all cases, receptors were lost proportionally from all cells, yielding a single symmetrical peak by fluorescence analysis. Exposure of IM-9 cells to anti-receptor antibodies at 37 degrees C for 16 hr also produced a down-regulation in the number of insulin receptors. Incubation with human antiserum B-9 caused a 95% loss of both 125I-insulin binding and peak fluorescence, while the monoclonal antibody resulted in a 50% loss of receptors. Incubation of cells with anti-receptor antibodies for 2 hr at 4 degrees C did not produce any receptor loss; however, the human anti-receptor antisera B-2 and B-9 inhibited the binding of the monoclonal anti-receptor antibody by about 50%, suggesting that these antisera contained autoantibodies directed at the monoclonal antibody binding site. These data indicate that insulin receptors can be regulated by both insulin and anti-receptor antibody and demonstrate the utility of immunofluorescence and flow cytometry as a tool for the study of the insulin receptor.     

Liver cell-membrane specific antibodies in autoimmune hepatitis patients detected by flow cytometry

In this study, we identified autoantibody in patients with autoimmune hepatitis against liver cell membrane using flow cytometry. After incubation of one of the hepatoblastoma cell lines, Hep G2, with serum from a patient, and the addition of FITC-labeled anti-human Ig antibody, anti-membrane antibodies were analyzed by flow cytometry. By our method, the antibody in serum can react only with autoantigens on the cell surface. Furthermore, propidium iodide staining enabled us to exclude the possibility of crossreaction of antibodies against dead cells. The relative fluorescence intensity in 12 patients with autoimmune chronic active hepatitis was significantly higher than that in 20 normal subjects, six primary biliary cirrhosis (PBC), 18 chronic viral hepatitis, and 11 systemic lupus erythematosus (SLE). The normal level of fluorescence intensity provided by sera from the SLE patients indicated that antibody binding to the liver cell membrane was not derived from Fc-mediated immune complex capture. These findings demonstrated that this flow cytometric technique provides a simple and accurate method for the detection of autoantibodies against liver cell membrane.     

Development and evaluation of a competitive ELISA for estimation of rabies neutralizing antibodies after post-exposure rabies vaccination in humans.

OBJECTIVES: Currently three tests are approved for the estimation of neutralizing antibodies after rabies vaccination: the mouse neutralization test (MNT), the rapid fluorescent focus inhibition test (RFFIT), and the fluorescent antibody virus neutralization (FAVN) test. Performance of these tests requires a lot of expertise and is generally carried out in reference laboratories and, hence, they are not available to many people. The aim of the present study was to develop and evaluate a competitive ELISA (C-ELISA) for estimation of neutralizing antibodies in order to make this testing more widely available. METHODS: The C-ELISA was designed based on competition between a murine neutralizing monoclonal antibody (Mab) and the antibodies in serum of vaccinated people. The test was initially standardized using known negative and known positive serum samples for determining the optimal dilution of the Mab as well as the cut-off value (%) for ascertaining the level of inhibition. Nine hundred and ninety serum samples were tested from 250 people who had been administered purified chick embryo cell vaccine (PCECV). Serum samples were collected on days 0, 14, 30 and 90 post-vaccination, and were tested by C-ELISA. RESULTS: All the serum samples that were positive by RFFIT were also positive by C-ELISA. The titers obtained with C-ELISA were marginally higher than the RFFIT titers, but a significant correlation was noted between the two tests (r=0.897). None of the negative controls were detected to be positive for rabies antibodies by either of these tests. Therefore the C-ELISA was found to be 100% specific and sensitive in comparison to RFFIT. Further, the initial rise and fall of antibody titers on different days post-vaccination was comparable for both tests. CONCLUSIONS: The C-ELISA described herein can be used to quantify rabies neutralizing antibody levels after vaccination. This test is simple and can be conveniently used under field conditions for monitoring seroconversion after post-exposure rabies vaccination. Moreover it does not require handling of infectious virus by the end user.     

Simple method for differentiating between HLA and platelet-specific antibodies by flow cytometry.

Since platelets express both platelet-specific and class I HLA antigens, serum antiplatelet reactivity assessed by most platelet antibody techniques could be due to antibodies with either or both specificities. Flow cytometric analysis of sera for detection of antiplatelet antibody commonly employs a purified platelet preparation as target cells. A method is described for investigating sera for platelet antibodies by flow cytometry using a mixture of platelets and lymphocytes. The mixture of lymphocytes and platelets as target cells has the advantage of confirming the presence of the HLA antibodies in reactive sera. The concomitant use of platelets and lymphocytes treated with citric acid, pH3, or with chloroquine (to remove or alter surface HLA antigens without affecting platelet specific antigens) may further assist in identifying antiplatelet antibodies in alloimmunized patients. These techniques may also be useful in platelet crossmatching procedures.     

Sensitive detection technique of myeloperoxidase precursor protein by flow cytometry with monoclonal antibodies

This report describes the analysis of culture cells and blast cells separated from the heparinized bone marrow and whole blood of patients with acute leukemias by means of a density-gradient technique (Ficoll-sodium metrizoate d = 1.077 g/cm³). Cell-surface antigens were analyzed by a fluorescence-activated cell sorter using a panel of monoclonal antibodies (MAbs). The blast cells and culture cells were fixed by 3% paraformaldehyde in phosphate-buffered saline. A low level of expression of MPO precursor protein was found in THP−1. K-562 and HEL, MEG-01, erythro-megakaryocytic leukemia cell lines, Jurkat, MOLT-3, MOLT-4, RPMI8402, ATL-5, T-cell leukemia cell lines, Raji, Daudi. BALL-1, B-cell leukemia cell lines, and AGNK1 showed negative reaction. The de novo MPO-negative acute leukemias, middle level of expression of MPO precursor protein, was found in the blasts of MPO-negative AML (AML, M0), which coexpressed CD13, CD33, CD34, and CD38. A high level of expression of MPO protein was found in all cases of AML, M1, and M2. The MPO expression was not found in all cases of acute lymphoblastic leukemia. The highest level of MPO expression was found in cases of AML, M3, and AML, M3v, suggesting the diagnostic value for this type of leukemia. The detection of MPO precursor protein by flow cytometric analysis with monoclonal antibodies is essential for the determination of lineage and precise diagnosis of acute unclassifiable leukemia, and should contribute substantially to the development of an effective form of therapy and cure. Am. J. Hematol. 58:241–243, 1998. © 1998 Wiley-Liss, Inc.     

Virus inactivation by addition of neutralizing antibodies

This study has shown that the principle of virus neutralization by specific antibodies is feasible at least in the case of hepatitis B. Virus neutralization is our preferred method since it entails no loss of functional activity and no risk of induction of neo-antigens in the plasma derivatives. Although double-blind clinical trials have not been performed, this study--in combination with some other studies - brought the conclusive evidence that virus neutralization in the case of hepatitis B transmission is efficacious. The suggested occurrence of side effects related to the formation of immune complexes during or after administration is not borne out by more than 7 years of experience with neutralized plasma derivatives with no reported side effects. Whether this method is useful for other viruses will depend on the availability of specific neutralizing antibodies.     

Enumeration of platelets by multiparameter flow cytometry using platelet-specific antibodies and fluorescent reference particles

Summary The correct enumeration of platelets is still an elusive matter. This is mainly due to the fact that commercial instruments which are used for platelet counting cannot discriminate platelets from other cellular particles and precipitates that cause similar signals. Visual (chamber counting) methods are still frequently used in routine laboratories to verify low automated platelet counts (< 50 × 10/l) despite obvious technical and statistical drawbacks. The following report shows how platelet counts can be measured by multiparameter flow cytometry with the help of reference particles (fluorescent latex beads) and platelet-specific antibodies i.e. anti-GPIIb/IIIa(CD41a), anti-GP Ib-α (CD42b) and anti-GP IIIa (CD61). The linearity of this method was highly satisfactory and the observed imprecision was within acceptable limits. At a platelet concentration of 10 × 10⁹/l the coefficient of variation (CV, n = 10) ranged from 5.3% (PCV = 0.456) to 5.6% (PCV = 0.148). Accuracy was evaluated by comparing results to the ICSH-selected method for platelet counting. The correlation of both methods was significant (P < 0.005) and Passing-Bablok's linear regression analysis showed no systematic differences between the two methods. Comparisons of this new platelet counting technique were also performed with routine visual methods, automated blood analysers (Technicon H-1, Sysmex E-5000) and a different flow cytometric method using only forward and side light scatter properties of platelets for their discrimination. The linear correlation of all methods was significant (P < 0.01) at platelet concentrations above 50 × 10⁹/l. At lower platelet concentrations, our new platelet counting technique correlated significantly only with the visual and the forward/side scatter methods. These findings stress the necessity to confirm low platelet counts by automated blood analysers and suggest that using multiparameter flow cytometry with platelet-specific antibodies may be a proficient way to do so. The possibility of using this technique as a reference method is discussed.