Comparison of a multiplex flow cytometric assay with enzyme-linked immunosorbent assay for auantitation of antibodies to tetanus,diphtheria, and Haemophilus influenzae Type b

We developed a multiplexed indirect immunofluorescence assay for antibodies to Haemophilus influenza type b (Hib) polysaccharide and the toxoids of Clostridium tetani (Tet) and Corynebacterium diphtheriae (Dip) based on the Luminex multiple-analyte profiling system. A pooled serum standard was calibrated against World Health Organization standards for Dip and Tet and an international standard for Hib. The multiplexed Luminex assay was compared to individual enzyme-linked immunosorbent assays (ELISAs) for the same analytes. By both methods, 75 (92.6%) of 81 of random serum samples had protective levels of antibody to Tet (> or = 0.1 IU/ml). For Dip, 81.5% of the samples had protective antibody levels (> or = 0.1 IU/ml) by ELISA and 80.2% had protective antibody levels by Luminex. Protective levels (> or = 1.0 microg/ml) of antibody to Hib were found in 45.0% of the samples tested by ELISA and in 39.0% of the samples tested by Luminex. The correlations (R(2)) between ELISA and Luminex of the 81 samples were 0.96, 0.96, and 0.91 for Tet, Dip, and Hib, respectively. There was also similar agreement between Luminex and ELISA for sera collected before and 1 month after Tet, Dip, and Hib vaccine administration. Both methods detected strong postvaccination responses. The Luminex method is an attractive alternative to ELISA since it reduces labor and reagent costs, as well as assay time.     

Analytical sensitivity of four HIV combined antigen/antibody assays using the p24 WHO standard

BackgroundThe Common Technical Specifications for HIV-1 p24 assays published in 2009 fixed the lower limit of detection for obtaining C.E. approval at 2 IU/ml against the WHO standard (first international reference, code NIBSC 90/636); it was previously 50 pg/ml. Some recent fourth generation HIV assays that simultaneously detect antigen and antibody are equivalent to p24 assays, but they were mainly evaluated using p24 antigen standards in pg/ml and little is known of their performance with the IU/ml standard.ObjectivesTo evaluate four of the combined serological assays most commonly used for HIV diagnosis in France against the WHO standard in IU/ml.Study designThe analytical sensitivity of four combined p24 antigen and antibody assays (ARCHITECT HIV Ag/Ab Combo, AxSYM HIV Ag/Ab Combo, VIDAS HIV DUO Quick and VIDAS HIV DUO Ultra) and of one p24 assay (VIDAS HIV p24 II) were determined using dilutions of the WHO standard.ResultsFour of the five assays had a lower limit of detection below 2 IU/ml: 1.24 for ARCHITECT Combo, 0.66 for VIDAS DUO Ultra, 0.43 for VIDAS DUO Quick and 0.73 to 1.15 for VIDAS p24, while that of AxSYM was close to 2 (1.94–2.25).ConclusionsWe have provided the first data on the lower limit of detection of HIV combined assays using the IU/ml WHO standard and demonstrated the need for a single international standard for comparing assays. We recommend the use of this approach in medical laboratory to validate on site their methods.     

One- and two-step non-competitive avidin-biotin immunoassays for monomeric and heterodimeric antigen

In this study of one-step and two different two-step non-competitive avidin-biotin assays (NABAs) were developed for the measurement of a monomeric antigen (lactoferrin, LF) using polyclonal antibodies and the detection of a heterodimeric antigen (lutropin. LH) using monoclonal antibodies. The assays were based on the use of performed complexes of biotinylated antibody and avidin-peroxidase conjugate. The detection limits and intra-assay CVs of the one- and two-step NABAs were 0.1-0.5 mg/ml and 2.6-5.1% for LF, and 0.1-0.2 IU/l and 2.3-3.7% for LH, respectively. The working range was 1-100 ng/ml for the LF assay and 1-100 IU/l for the LH assay. A linear relationship with high correlation coefficients (0.979-0.992 for LF-NABAs: 0.949-0.990 for LH-NABAs) and good agreement was observed between the one- and two-step assays and the corresponding three-step NABAs used as reference methods. However, under stringent conditions the one-step assay for heterodimeric antigen was found to be sensitive to interference. The results indicate that it is possible to perform the multistep NABAs using convenient one- and two-step protocols. The one- and two-step assays also retained the advantages of the avidin-biotin system: rapidity and good sensitivity.     

Comparison of a Multiplex Flow Cytometric Assay with Enzyme-Linked Immunosorbent Assay for Quantitation of Antibodies to Tetanus, Diphtheria, and Haemophilus influenzae Type b

We developed a multiplexed indirect immunofluorescence assay for antibodies to Haemophilus influenza type b (Hib) polysaccharide and the toxoids of Clostridium tetani (Tet) and Corynebacterium diphtheriae (Dip) based on the Luminex multiple-analyte profiling system. A pooled serum standard was calibrated against World Health Organization standards for Dip and Tet and an international standard for Hib. The multiplexed Luminex assay was compared to individual enzyme-linked immunosorbent assays (ELISAs) for the same analytes. By both methods, 75 (92.6%) of 81 of random serum samples had protective levels of antibody to Tet (≥0.1 IU/ml). For Dip, 81.5% of the samples had protective antibody levels (≥0.1 IU/ml) by ELISA and 80.2% had protective antibody levels by Luminex. Protective levels (≥1.0 μg/ml) of antibody to Hib were found in 45.0% of the samples tested by ELISA and in 39.0% of the samples tested by Luminex. The correlations (R²) between ELISA and Luminex of the 81 samples were 0.96, 0.96, and 0.91 for Tet, Dip, and Hib, respectively. There was also similar agreement between Luminex and ELISA for sera collected before and 1 month after Tet, Dip, and Hib vaccine administration. Both methods detected strong postvaccination responses. The Luminex method is an attractive alternative to ELISA since it reduces labor and reagent costs, as well as assay time.     

A novel separation-free assay technique for serum antibodies using antibody bridging assay principle and two-photon excitation fluorometry

A new technique for separation-free detection of antigen-specific antibodies is presented. The new technique employs antibody bridging assay principle and the recently developed ArcDia TPX fluorescence detection technology. According to the assay scheme, antibody molecules from the sample bind with one arm to an antigen on polymer microspheres and with the other arm to a fluorescently labeled secondary antigen reagent. Consequently, fluorescent immunocomplexes are formed on the surface of microspheres in proportion to the concentration of the analyte in the sample. The fluorescence signal from individual microspheres is measured by means of two-photon excited fluorescence detection. In order to demonstrate the applicability of the new assay technique, an assay for anti-adenovirus antibodies was constructed. The function of the assay method was tested both with monoclonal anti-adenovirus antibody preparation (standard analyte), and with positive serum samples. Standard class-specific ELISA was used as a reference method. The new assay method provides comparable sensitivity and precision, and wider dynamic range for IgG antibodies than the ELISA method. The standard curve showed linear response (R(2)=0.999) with a dynamic range of three orders of magnitude, detection limit (mean+3S.D.) of 8 pM, and intra-assay signal precision of 5%. Applicability of the new method for clinical serodiagnostics is discussed.     

Preparation and characterization of polyclonal and monoclonal antibodies against fusarenon‐X

Polyclonal and monoclonal antibodies against fusarenon‐X were prepared by using a fusarenon‐X oxime derivative coupled to human serum albumin as the antigen for the immunization of rabbits and BALB/c mice, respectively. The specificity and sensitivity of these antibodies were tested by using fusarenon‐X oxime coupled to horseradish peroxidase as an enzyme‐linked toxin in a competitive assay with a double antibody solid phase. The relative cross‐reactivities of the polyclonal antiserum with T‐2 toxin, diacetoxyscirpenol, fusarenon‐X and neosolaniol were 3.67, 2.75, 1.0 and 0.58, respectively. The monoclonal antibody, however, showed considerable cross‐reactivity only with neosolaniol (0.28). The detection limit for fusarenon‐X was 150 pg/ml (5 pg per assay) and 300 pg/ml (10 pg per assay), respectively, using the polyclonal and monoclonal antibodies.     

Synthesis of olaquindox metabolite,methyl-3-quinoxaline-2-carboxylic acid for development of an immunoassay

A novel synthesis method of methyl-3-quinoxaline-2-carboxylic acid (MQCA) and the preparation of its hapten were described. MQCA was synthesised involving in two steps with a high purity. For improving the sensitivity of detection, five different haptens were synthesised and corresponding immunogens and coating antigens were prepared. After comparing the sensitivity of immunoassay with different pairs of antibody and coating antigen, a specific immunoassay was obtained using an antibody raised against hapten (four-atom spacer arm) – BSA and a suitable coating antigen with a heterologous spacer arm group. The 50% inhibitory concentration of MQCA by indirect competitive enzyme-linked immunosorbent assay with optimised antibody and coating antigen was 3.84 ng/ml and the limit of detection was 0.25 ng/ml.     

Comparison of two techniques for detecting antibody to HBsAg during a hepatitis B vaccine study

Two assays for the detection of antibody against hepatitis B surface antigen (anti-HBs) were compared. The first was a direct sandwich radioimmunoassay (RIA) which detects, in principle, antibody against any epitope of hepatitis B surface antigen (HBsAg). The second assay was an inhibition enzyme-linked immunosorbent assay (ELISA). In this assay a fixed amount of HBsAg which can be blocked by anti-HBs is measured in a direct sandwich test. Prevaccination screening sera (n = 191) and follow-up sera obtained from high risk groups (n₁ = 85; n₂ = 41) during two hepatitis B vaccine studies were compared in RIA and ELISA. In prevaccination sera either HBsAg or anti-HBs were detected by ELISA. Full agreement between the results of RIA and ELISA for anti-HBs was obtained in sera containing more than 10 IU/1 anti-HBs. Both tests showed variable results at low titres. Experiments with monoclonal anti-HBs indicated that ELISA is less sensitive for subtype specific antibodies (anti-d, anti-y), which may explain that there were consistent differences between RIA and ELISA in a minority of cases.     

Artificial factor VIII deficient plasma: preparation using monoclonal antibodies and its use in one stage coagulation assays.

Monoclonal antibodies to factor VIII antigen (VIII:Ag) and von Willebrand factor (vWf:Ag) were immobilised on Sephacryl S-1000 and tested for their ability to deplete normal human citrated plasma of factor VIII. A combination of two antibodies to VIII:Ag and one antibody to vWf:Ag was required to produce plasma containing less than 0.01 IU/ml. Its performance in the one stage coagulation assay of VIII:C was equivalent to that of congenital VIII deficient plasma for the assay of normal and haemophilic plasma and factor VIII concentrates. Storage of freeze dried aliquots of this product at -20 degrees C, +4 degrees C, and 37 degrees C showed that it could be used as a substrate for at least six months when stored at temperatures +4 degrees C and below.     

化学发光酶免疫分析法在乙肝病毒及核心抗体定性检测中的应用分析

目的 通过对比,探讨了化学发光酶免疫分析法在乙肝病毒及核心抗体定性检测中的应用价值.方法 选取2013年5月至2015年5月在我院的疑似乙型肝炎患者80例,抽取空腹血液样本后都分别进行乙肝病毒以及核心抗体的化学发光酶免疫分析法及ELISA法检测,并对其检测结果进行分析.结果 化学发光酶免疫分析法检出乙型肝炎病毒阳性78例,检出率为97.5％;而ELISA检出乙型肝炎病毒阳性76例,检出率为95.0％,两种方法的检出率对比差异无统计学意义(P＞0.05).化学发光酶免疫分析法对于乙肝病毒核心抗体IgM与IgG的检测阳性率分别为80.0％和70.0％,而ELISA法检测两种抗体的阳性率则分别为18.8％和20.0％,化学发光酶免疫分析法对乙肝核心抗体IgM与IgG的检测阳性率明显高于ELISA法(P＜0.05).ELISA法检出HBc-IgM的最低限为0.135 IU/ml,检出HBc-IgM最低限为0.143 IU/ml;化学发光酶免疫分析法检出HBc-IgM最低限为0.032 IU/ml,检出HBc-IgG最低限为0.038 IU/ml.结论 化学发光酶免疫分析法在乙型肝炎检测中具有高的检出率,尤其对乙肝病毒的核心抗体的检测敏感度较高,值得在临床推广应用.     

Circulating Candida antigens and antibodies: useful markers of candidemia.

To investigate the utility of the 48-kDa antigen from Candida albicans in its commercial form (Directigen; Becton Dickinson) and three other serodiagnostic methods (detection of one antigen by Pastorex Candida [Sanofi Diagnostics Pasteur] and detection of immunoglobulin G [IgG] and IgM antibodies to C. albicans blastoconidia [bioMerieux]) for diagnosis of invasive Candida infection, we conducted a prospective clinical trial among 10 patients with candidemia (group 1), 30 patients colonized by C. albicans (group 2), 20 patients with bacteremia (group 3), and 20 subjects without clinical or microbiological evidence of infection. The Directigen system was positive for at least one serum sample each from eight patients in group 1. In groups 2, 3, and 4, it was positive for only three patients. There was no reaction to the Pastorex system in any of the patients infected with or colonized by C. albicans or in the non-Candida-carrying controls. The IgG antibody concentration oscillated between 100 and 800 (mean, 510 +/- 268) IU/ml for the patients in group 1. In this group, eight patients had IgG antibody levels of > 400 IU/ml. The percentages of persons with IgG antibody levels of > 400 IU/ml in groups 2, 3, and 4 were 43.3, 0, and 0, respectively. Specific IgM antibody was present in all group 1 patients but not in those in groups 2, 3, and 4. The sensitivity and specificity of the Directigen test were 65 and 97.1%, respectively. For the Pastorex test, the sensitivity was 0%. The sensitivity of IgG antibodies was 80%, with a specificity of 81.4%, while the IgM antibodies were 100% specific and sensitive. Both the positive and negative predictive values of specific IgM antibodies appeared to be superior to those of the other three tests.     

Human immune response to botulinum pentavalent (ABCDE) toxoid determined by a neutralization test and by an enzyme-linked immunosorbent assay.

To determine the immune status of persons receiving botulinum pentavalent (ABCDE) toxoid and to evaluate the effectiveness of the vaccine, we surveyed immunized individuals for neutralizing antibodies to type A and to type B botulinum toxins. After the primary series of three immunizations administered at 0, 2, and 12 weeks, 21 of 23 persons tested (91%) had a titer for type A that was greater than or equal to 0.08 international units (IU)/ml, and 18 (78%) had a titer for type B of greater than or equal to 0.02 IU/ml. (One international unit is defined as the amount of antibody neutralizing 10,000 mouse 50% lethal doses of type A or B botulinum toxin). Just before the first annual booster, 10 of 21 (48%) and 14 of 21 (67%) people lacked a detectable titer for type A and for type B, respectively. After the first booster, all individuals tested had a demonstrable titer to both types A and B. Of 77 persons who had previously received from one to eight boosts of the toxoid, 74 (96%) had an A titer of greater than or equal to 0.25 IU/ml and would not require an additional booster, according to the recommendations of the Centers for disease Control. However, only 44 of 77 (57%) had a B titer of greater than or equal to 0.25 IU/ml. In each group by booster number, even the group having had eight boosts, at least one person would require reimmunization on the basis of B titer. There was a wide range of antibody levels among individuals at the same point in the immunization scheme. Results from an enzyme linked immunosorbent assay, with purified type A or type B neurotoxin as the capture antigen, were compared with neutralization test results on 186 serum samples for type A and 168 samples for type B. Statistically, the correlation coefficients for results from the two assays were high (r = 0.69, P < 0.0001, for type A and r = 0.77, P < 0.0001, for type B). However, due to the wide dispersion of values obtained, using enzyme-linked immunosorbent assay results to predict neutralizing antibody levels is unwarranted.     

Solid-phase radioimmunoassay for the measurement of IgG antibodies specific for the house dust mite, Dermatophagoides farinae

The sera from 65 asthmatic patients were studied for the measurement of IgG antibodies specific to the house dust mite, Dermatophagoides farinae (D. farinae) by solid-phase radioimmunoassay using polystyrene tubes coated with the antigen extract. The solid-phase radioimmunoassay had about the same sensitivity as the conventional double antibody antigen-binding assay in the detection of mite-specific IgG antibodies. The mean value of IgG antibodies was 26.1 (+/- 39.8) micrograms/ml in patients hyposensitized with D. farinae, 23.9 (+/- 29.3) micrograms/ml in those hyposensitized with house dust (HD), and 21.6 (+/- 35.6) micrograms/ml in non-treated patients. A significant difference was detected between HD-treated patients and normals (p less than 0.05). The levels of IgG antibody tended to increase with the increment of the maintenance dose of the D. farinae or HD used in immunotherapy. In addition, eight patients were evaluated for their IgG antibody levels before and after immunotherapy. In five of them, IgG antibodies increased about two to threefold above the value before immunotherapy. These results suggest that the measurement of IgG antibodies by solid-phase radioimmunoassay may be clinically useful in evaluating the effectiveness of immunotherapy.     

New, ultrasensitive enzyme immunoassay for detecting vaccine- and disease-induced hepatitis A virus-specific immunoglobulin G in saliva.

Although detection of disease-induced hepatitis A virus (HAV)-specific antibodies in saliva has been successfully utilized in a few epidemiological studies, available assays fail to detect lower salivary anti-HAV levels associated with vaccine-induced immunity. We present a new capture enzyme immunoassay which employs a three-layer antibody recognition system. Evaluation of paired saliva-serum specimens from 1,025 international travellers, 134 other volunteers, and 91 hepatitis A vaccine recipients demonstrated 99.6% (95% confidence interval, 98.4 to 99.9) specificity and 98.7% (95% confidence interval, 97.7 to 99.4) sensitivity of this salivary assay in differentiating between immune and susceptible individuals, compared with serum-based methods. We conclude that this assay is sufficiently sensitive for reliable detection of both vaccine- and infection-induced HAV-specific immunoglobulin G in saliva, even when corresponding anti-HAV levels in serum are very low (< 1 IU/ml).     

Evaluation of the core antigen assay as a second-line supplemental test for diagnosis of active hepatitis C virus infection

The British Columbia Center for Disease Control laboratory performs approximately 95% of all hepatitis C virus (HCV) antibody tests for the province's 4 million inhabitants. In 2002, the laboratory tested 96,000 specimens for anti-HCV antibodies, of which 4,800 (5%) were seroreactive and required confirmation of active infection. Although HCV RNA assays with a sensitivity of 50 IU/ml or less are recommended for the confirmation of active HCV infection, given the large number of seroreactive specimens tested annually, we evaluated the Ortho trak-C assay (OTCA) as a second-line confirmatory test and determined its limit of detection (LoD). Of 502 specimens from treatment-na?ve anti-HCV-positive individuals, 478 had sufficient volumes for evaluation by the OTCA and HCV RNA tests. Core antigen was not detected in 147 of 478 (30.8%) of these specimens, of which 37 of 147 (25.2%) were shown to be viremic by the VERSANT HCV (version 3.0) (branched-DNA) assay and/or the VERSANT HCV qualitative assay. Testing of 144 replicates of a World Health Organization standard dilution series indicated that the LoD of OTCA was approximately 27,000 IU/ml. This LoD is consistent with the inability of OTCA to detect core antigen in clinical specimens with low viral loads. We conclude that OTCA has limited value as a confirmatory test for the diagnosis of active HCV infection because 37 of 367 (10%) of viremic specimens had undetectable core antigen. Qualitative HCV RNA testing remains the present standard for the confirmation of active HCV infection in the diagnostic setting.     

Analysis of human serum immunoglobulin G against O-acetyl-positive and O-acetyl-negative serogroup W135 meningococcal capsular polysaccharide

The capsular polysaccharide of Neisseria meningitidis serogroup W135 is expressed in both O-acetyl-positive (OA+) and O-acetyl-negative (OA-) forms. This study investigates the impact of OA status (OA+ versus OA-) on serological measurements of anti-W135 immunoglobulin G (IgG) antibodies in immunized adults. W135-specific serum antibody assignments were made for 28 postimmunization sera from adults by enzyme-linked immunosorbent assay using the meningococcal standard reference serum CDC1992. The established IgG concentration in micrograms per milliliter ([IgG]microg/ml) for CDC1992 against OA+ antigen (16.2 microg/ml) was used as a reference to assign a concentration of 10.13 microg/ml IgG against OA- antigen by cross-standardization. Overall, the IgG assignments for these sera were higher against OA+ antigen (geometric mean concentration [GMC] = 7.16 microg/ml) than against OA- antigen (GMC = 2.84 microg/ml). However, seven sera showed higher specific [IgG]microg/ml values against the OA+ antigen than against the OA- antigen. These sera were also distinguished by the inability of fluid-phase OA- antigen to compete for antibody binding to OA+ solid-phase antigen. Although there was no overall difference in functional activity measured by complement-mediated serum bactericidal assay (SBA) against OA+ and OA- target bacteria (geometric mean titers of 9,642 and 9,045, respectively), three serum specimens showed a large difference in SBA antibody titers against OA+ versus OA- W135 target bacteria, which may reflect different epitope specificities for these sera. Our data indicate that, for some sera, the agreement in anti-OA+ versus anti-OA- W135 IgG assignments is serum specific and does not reflect the functional (killing) activity in vitro.     

柯萨奇病毒A组16型抗原的ELISA定量检测方法建立

目的:建立柯萨奇病毒A组16型(CA16)抗原的双抗体夹心ELISA定量检测方法,用于CA16灭活疫苗的研发和生产过程的抗原定量检测。方法:以CA16中和单抗T26H12为包被抗体、NA14B9为标酶抗体,构建定量检测CA16抗原的双抗体夹心ELISA方法,并对方法的特异性、灵敏度、精密度、准确性、线性和稳定性进行分析。结果:建立了双抗体夹心定量检测CA16抗原的ELISA方法。方法的线性相关系数R2=0.998,线性范围为8～128 ng/ml,定量限度为8 ng/ml;变异系数CV<15%;回收率介于87.0%～113.8%之间;37℃6天的回收率>80%;与CA16以外的其他样本没有交叉反应。结论:构建的CA16抗原ELISA定量检测方法的各项性能符合定量检测需要,可用于CA16疫苗的研发和生产过程的抗原活性的定量检测。     

Adjuvant effect of bacterial LPS and/or alum precipitation in responses to polysaccharide and protein antigens.

A conjugate of a hapten (NIP) and a strongly antigenic protein chicken gamma globulin (CGG), when injected in soluble form into mice, induced weak primary responses, as weak as responses induced by conjugates of NIP (or other haptens) to polysaccharides Ficoll or alpha (-1-6) dextran. Mean concentrations of anti-hapten antibodies on day 14 varied within the range of 37-105 micrograms/ml (C57BL mice) or 14-38 micrograms/ml (CBA mice). The NIP-protein conjugate administered in alum-precipitated form induced 100 times higher primary antibody responses. Alum-precipitation of NIP-Ficoll made it a modestly stronger antigen than soluble NIP-Ficoll. When lipopolysaccharide (LPS) was injected together with any of the soluble antigens, the mice produced plenty of anti-hapten antibodies regardless of whether the antigen was hapten-polysaccharide or hapten-protein conjugate. Concentrations on day 14 varied from around 400 micrograms/ml to approximately 1600 micrograms/ml. LPS had a similar adjuvant effect on antidextran responses. LPS alone induced a polyclonal immunoglobulin production, and the immunoglobulin produced included 'anti-NIP' or 'anti-dextran' detectable in the solid phase antibody assay. These 'antibodies' induced by LPS alone were almost totally mercapto-ethanol-sensitive and poorly detectable by Farr assay or the bacteriophage assay. The response to the LPS+antigen combination was specific for the antigen and included both mercapto-ethanol-sensitive and resistant antibodies.     

检测类风湿因子ELISA法的建立及其应用

本文建立了测定类风湿因子（ＲＦ）总量的双抗原夹心法和测定ＩｇＧ－ＲＦ的间接法。用于临床检测表明，１００名献血员中有３例ＲＦ总量测定为阳性。９７例类风关患者中７２例阳性（阳性率７５．３％）。１３２例健康老年人中５人阳性（阳性率３．８％）。ＩｇＧ－ＲＦ测定结果：１２０例正常人和１３２例健康老年人均为阴性，９７例类风关病人中有７例阳性（阳性率７．２％）。