Nephelometric assay of antigens and antibodies with latex particles

Anti-neutrophil cytoplasm antibody IgG subclasses in Wegener's granulomatosis: a possible pathogenic role for the IgG4 subclass

A characteristic feature of Wegener's granulomatosis is the presence of antineutrophil cytoplasm antibodies (ANCA) to proteinase 3 (PR3). In vitro, ANCA activate neutrophils by co-ligating PR3 and FcgammaRIIa/IIIb receptors. ANCA are predominantly of the IgG isotype, and IgG1, IgG3 and IgG4 subclasses are particularly represented. To address the pathogenic role of individual ANCA-IgG subclass antibodies, patients' sera were screened using indirect immunofluorescence, enzyme-linked immunosorbent assay (ELISA) and subclass PR3-ELISA to identify patients with high titres of PR3-ANCA within the IgG1, IgG3 or IgG4 subclasses. Unfractionated ANCA-IgG and subclass fractions were isolated by affinity chromatography and compared for their capacities to stimulate superoxide production by primed human neutrophils. Donor neutrophils were analysed for constitutive and induced FcgammaRI expression by flow cytometry. The IgG1, IgG3 and IgG4 subclass fractions, isolated from three different ANCA sera, each stimulated superoxide production from neutrophils derived from multiple donors. Subsequently, IgG4 subclass fractions isolated from a further four ANCA positive sera demonstrated varying abilities to stimulate release of superoxide; unrelated to PR3-ANCA titre, neutrophil donor, or neutrophil FcgammaRI expression. The stimulation of superoxide release by IgG1- and IgG3-ANCA subclass fractions is consistent with the proposed mechanism of co-ligation of PR3 antigen and FcgammaRIIa/IIIb receptors. However, the demonstration of similar activity for the IgG4-ANCA subclass fractions isolated from some sera was unexpected. This activity was independent of neutrophil donor and expression of FcgammaRI, suggesting it was capable of activating neutrophils via constitutively expressed FcgammaRIIa/IIIb or co-ligation of other, unidentified, cell surface molecules.

A review of factors affecting the performances of latex agglutination tests

The present review describes the different strategies followed to improve the performance of latex agglutination tests. The analysis is mainly focused on the diverse parameters that affect the final colloidal stability of the immunoprotein-latex system. These parameters include: the surface properties of polymer carriers; the different kind of antibodies usually employed; the use of BSA as stabilizer; the co-adsorption of various macromolecules (BSA, surfactants and lipids) and antibodies; recent approaches to colloidal stability at high ionic strengths due to hydration forces; and the covalent coupling of antibodies on functionalized latex particles. Special emphasis is given to the relation between electrophoretic mobility and the colloidal stability of the sensitized particles and how this knowledge can be utilized for a better understanding of the immunoagglutination kinetic.

Latex immunoassays: comparative studies on covalent and physical immobilization of antibodies. I. F(ab')2 fragments

Colloidal particles coated with antibodies are currently used in diagnostic test systems for the detection of antigens in biological fluids. Immobilization is usually carried out by physical adsorption. Covalent coupling of antibodies to particles, however, offers certain advantages. The present research deals with the study of these possible advantages. A sulphonated polystyrene latex has been used to prepare an immunolatex with physically adsorbed antibodies, while a functionalized latex with chloromethyl groups on the surface has been used for the partly covalent coupling of the antibody (F(ab')2 fragments). The immunoreactivity was studied by measuring the variations in scattered light intensity after mixing a solution of CRP antigen and the sensitized latex. The influence on the immunoresponse of the scattering angle (5, 10, and 20 deg), protein coverage and storage time have been studied for both systems.

Particle enhanced immunoassays stabilized by hydration forces: a comparative study between IgG and F(ab)2 immunoreactivity

In previous publications we have discussed the stabilization mechanism of hydration forces as applied to the development of latex agglutination tests. We describe here how we have obtained stable and reactive IgG-latex conjugates in a high-ionic-strength reaction buffer. To this end we have made agglutination tests with polystyrene beads sensitized with IgG, measuring the immunoaggregation reaction with human C-reactive protein in a stopped-flow nephelometer. The results are compared to those obtained with a F(ab')2-latex conjugate with similar antibody molecule coverage. Adsorption isotherms of F(ab')2 and IgG on latex at pH 7.2 were obtained to study the affinity of these antibodies for the surface. The results of the electrokinetic characterization of the antibody-latex conjugates agree satisfactorily with those obtained from stability studies. This research throws light upon the use of hydration forces as a new approach to stabilizing immunoassay reagents that are colloidally unstable in physiological reaction buffers.

A comparative study of optical techniques applied to particle-enhanced assays of C-reactive protein

This work is based on the well-established immunoassay principle of agglutination of latex particles covered by immunoproteins. In our experiments, positively charged particles act as carriers for the F(ab')2 fragment, obtained from rabbit polyclonal IgG, active against C-reactive protein (CRP). The presence of the antigen CRP in the immunolatex system causes agglutination and the aim of the present study was to compare different optical techniques (turbidimetry, nephelometry, angular anisotropy and photon correlation spectroscopy) capable of detecting the agglutination. The sensitivity and detection limit largely depend on the optical method. We have analyzed for each optical technique the following aspects: sensitivity, reproducibility, detection limit, reaction time, amount of sample wasted and availability of the required detection device. The results presented in this paper show that both angular anisotropy and photon correlation spectroscopy offer lower detection limits, and use little reagent, but have longer assay times than the classical optical techniques of turbidimetry and nephelometry.

Synthesis of new hydrophilic microspheres: optimized carriers for microparticle-enhanced nephelometric immunoassays

To optimize antigen-antibody reactions, we have synthesized chemically well-defined hydrophilic microspheres. Proteins or haptens were covalently linked to these carriers. When the microsphere conjugates were agglutinated by the corresponding antiserum, the size of the complex artificially increased during the immunological reaction. After optimizing various parameters such as the hydrophilic character, repulsion charges, and amount of antigen coupled to the microspheres, we developed a rapid and sensitive immunoassay based on laser light scattering by the complexes.

Polyacrylic microspheres as a solid phase for microparticle enhanced nephelometric immunoassay (NEPHELIA (R)) of transferrin

Polyfunctional hydrophilic microspheres (MS) can be produced by copolymerisation with gamma-irradiation of acrylic monomers. Transferrin (TRF) can be covalently bound to these MS by reaction between aldehyde groups of the MS and primary amino groups of the protein. MS-TRF conjugates thus obtained are agglutinated by specific antiserum and this agglutination is inhibited by free TRF. Agglutination and inhibition are quantified by measurement of the light scattered by MS-TRF conjugate clusters with a specially designed nephelometer, a process designated as microparticle enhanced nephelometric immunoassay (NEPHELIA (R)) for TRF. Recovery, correlation and reproducibility studies, simultaneously performed in three different laboratories, show that this TRF immunoassay is accurate for a large concentration range. NEPHELIA (R) may appear as an alternative method for a large variety of molecules.

A novel covalent enzyme-linked immunoassay (CELIA) for simultaneously measuring free and immune complex bound antibodies of defined specificity. I. Application to naturally occurring antipolyamine antibodies in human sera

A simple covalent enzyme-linked immunoassay procedure (CELIA) is described for the routine determination of free and immune complex-bound antibodies in sera. Assays for the latter could not have been performed by adsorption ELISA due to the high ionic strength of the reassociating buffer. For the measurement in human sera of free naturally occurring IgG and IgM antibody directed against the hapten spermine, polycarboxystyrene microtiter plates with covalently coupled spermine were used. For the determination of immune complex-bound antipolyamine IgG and IgM antibody titers, serum was first dissociated at pH 2.3 in tubes and then reassociated at pH 8.1 in the wells of a microtiter plate containing covalently bound spermine. The reactivity of anti-spermine antibodies was increased from 2- to 13-fold after dissociation and reassociation compared to that of non-dissociated area. The apparent reaction constant (Rapp.) of free IgG antibodies to spermine in the sera of 19 bronchopulmonary patients with cancer differed significantly from Rapp. values of IgG antibodies having this specificity in ten other patients with non-malignant disease.

Possible significance of transferrin levels in seminal plasma of fertile and infertile men

Human seminal plasma contains large amounts of transferrin, which is a protein secreted mostly by Sertoli cells. It has been suggested that the concentration of transferrin may serve as a possible clinical marker of Sertoli cell function. Therefore the concentration of this protein in human seminal plasma from fertile and infertile men has been evaluated in order to find a relationship between transferrin concentrations and human semen parameters and plasma FSH levels. Findings show that seminal transferrin in subjects with oligozoospermia or azoospermia is significantly lower than in controls, and that it is strongly related to sperm count. Results also indicate that transferrin secretion can be impaired when plasma FSH levels are still normal, suggesting that seminal transferrin is an early and specific marker of Sertoli cell function. These results, however, do not clarify whether impairment of transferrin secretion by Sertoli cells is due to an organic dysfunction or to an organic secretory alteration.

Measurement of factor VIIIRAg-1. A method for use in the Hyland laser nephelometer

Factor VIIIRAg was measured by laser nephelometry using a new diluent containing a citrate-carbonate buffer, pluronic polyol P94 and triton X100. No pre-treatment of the samples was required, the incubation time was 0.5 to 1.5 hours depending on the antiserum used, and the tests could be read during the following 4 hours (plasma) or 1.5 hours (intermediate purity F VIII). The CV for the assay was less than 10% for plasma or dilutions of plasma in which the minimum detectable amount of factor VIIIRAg was about 0.04 u/ml. A significant correlation was obtained between the nephelometric method and the Laurell rocket method using plasma, but agreement between the methods when therapeutic products were assayed was poor.

Investigation of enzyme immunoassay time courses: development of rapid assay systems

An enzyme immunoassay (EIA) consists of a series of antigen-antibody reactions which result in the binding of an enzyme-labeled antibody to a solid phase. The performance time of an EIA determination is thus largely dependent upon the time required for the antigen-antibody reactions. In an attempt to develop a rapid EIA system, we investigated the time course of an EIA system for the measurement of Haemophilus influenzae type b polysaccharide. We found that, although the use of short incubations led to a decrease in sensitivity, an assay system utilizing 10-min incubation periods was still capable of detecting antigen at a concentration of 1 ng/ml. Important factors in the sensitivity of EIAs with short incubation times were the performance of the reaction at 37 degrees C and the incubation of the solid phase with constant agitation. Utilizing these techniques, we developed an EIA system for the measurement of H. influenzae type b polysaccharide which could be completed in less than 30 min. This system was sufficiently sensitive to detect H. influenzae polysaccharide in the cerebrospinal fluids of nine patients with proven H. influenzae meningitis. Thus, EIA systems utilizing short incubation times might be useful for the rapid detection of infectious antigens in body fluids.

Light scattering and absorption--developments in immunology

Fluid-phase immunoprecipitation analysis has undergone two distinct paths of development. One path utilizes existing absorptiometric equipment while the other relies on apparatus constructed specifically for the measurement of scattered light. The principles and instrumentation employed in light scattering and absorption techniques are reviewed with special reference to their applications in immunology. The main features of available analysers are summarised in the table. Specialised equipment is becoming increasingly sophisticated and expensive and it is important to assess critically the benefits, if any, that such apparatus may offer compared with more conventional devices. The latter are often capable of performing the same function with greater versatility. A good quality bench spectrophotometer is a more appropriate multi-purpose laboratory instrument than a specialised nephelometer with its more limited application. The equipment of choice for automated immunochemical protein quantitation, however, is the centrifugal analyser. The capital outlay is compensated for by high throughput, development potential and reduced consumption of reagents (i.e. antisera).

An automatic continuous flow method for the determination of antipolyamine antibodies in human sera

Latex particles with covalently bound polyamines were used to detect antipolyamine antibodies in human sera in manual and automated nephelometric assays. There was good correlation between the two assays though in the former aggregate size was measured after 24 h incubation whereas in the latter monomer loss was determined after 1 h.

Evidence for natural antibodies (IgG) to polyamines in human sera

Human sera contain IgGs that react with latex-putrescine spheres. Identification of the IgGs has been achieved by polyacrylamide gel electrophoresis and their reaction with peroxidase-labeled antihuman gamma-chain-specific antibodies. The inhibition of IgG fixation to latex-putrescine spheres by free spermine and putrescine provides evidence that these IgGs are specific for polyamines.

The preparation of latex particles with covalently bound polyamines, IgG and measles agglutinins and their use in visual agglutination tests

Carboxylated latex particles were substituted with side arms terminating in primary amine and hydrazine groups. The particles were coupled to aldehyde groups generated on glycoproteins which were treated with sodium periodate. Particles having the alipathic primary amine putrescine hapten as the sole substituent and particles linked to glycoproteins such as measles agglutinins and IgG were used to detect the presence of the corresponding antibodies or antigens in biological fluids by agglutination tests.