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

Microparticle-enhanced nephelometric immunoassay for caseinomacropeptide in milk

A microparticle-enhanced nephelometric immunoassay has been developed for the determination of caseinomacropeptide (CMP) in bovine milk. It is based on the nephelometric quantification of the competitive immunoagglutination of a microparticle–CMP conjugate with an anti-κ-casein (κ-CN) antiserum. This one step immunoassay was sensitive (detection limit in reaction mixture, 16μg/l), accurate (linear recovery of CMP in dilution overloading) and reproducible (CV 7–14% for within and between run precision). Because of the specificity of the polyclonal antiserum used, it was necessary to separate CMP from κ-CN by ultrafiltration before the quantification of bovine milk CMP. Under the conditions of milk ultrafiltration used, κ-CN was entirely retained (> 99·5%) but the concentration of CMP measured in milk ultrafiltrates was underestimated (by ∼25%) compared with its concentration in whole milk. Microparticle-enhanced nephelometric immunoassay of CMP, with a calibration range from 0·32 to 20 mg/1 for 20- fold diluted milk ultrafiltrate, allowed contamination of bovine milk by rennet whey as low as 5 ml/1 to be detected. Applied to ultrafiltrates from milk stored at 4 °C, this immunoassay also detected proteolysis of κ-CN not revealed by measurement of κ-CN concentration in milk. A statistical lower limit of 3·21 mg/1 was determined as the increase in CMP concentration in milk ultrafiltrates that indicated probable κ-CN proteolysis in the milk sample. Previously demonstrated to be an easy to perform method for assaying the main proteins of bovine milk, microparticle-enhanced nephelometric immunoassay thus also appeared to be appropriate to quantify CMP so as to detect slight contamination of milk by whey and to indicate the proteolysis of κ-CN during milk storage at low temperature.

Poly(styrene/α-tert-butoxy-ω-vinylbenzylpolyglycidol) Microspheres for Immunodiagnostics. Principle of a Novel Latex Test Based on Combined Electrophoretic Mobility and Particle Aggregation Measurements

The principle of a novel latex agglutination test based on combined results of electrophoretic mobility and particle aggregation measurements is described. Poly(styrene/alpha-tert-butoxy-omega-vinylbenzylpolyglycidol) (P(S/PGL)) microspheres were synthesized by a one step soap-free emulsion copolymerization of styrene and alpha-tert-butoxy-omega-vinylbenzylpolyglycidol macromonomer with number average molecular weight Mn = 2700 (polydispersity [Mw]/[Mn] = 1.10). Particles with monomodal size distribution (number average diameter Dn = 220 nm) and surface fraction of polyglycidol equal to f = 0.42 mol % were obtained. Human serum albumin (HSA) was covalently bound onto the surface of P(S/PGL) microspheres activated with 1,3,5-trichlorotriazine. In a model immunodiagnostic assay for anti-HSA, in which P(S/PGL) particles with covalently bound HSA have been used, the electrophoretic mobility and aggregation of microspheres were measured simultaneously. This approach allowed detection of anti-HSA in the serum in the range of anti-HSA concentrations from 0.1 to 150 microg/mL. The highest changes in electrophoretic mobility were registered for microspheres with surface concentration of immobilized HSA equal to Gamma = 9.2 x 10(-4) g/m2.

Changes in lactoferrin and lysozyme levels in human milk during the first twelve weeks of lactation

Changes in the lactoferrin and lysozyme concentration of human milk during lactation were determined by microparticle-enhanced nephelometric immunoassays of 360 milk samples collected from 64 lactating volunteers. These 360 samples were colostrum from days 1 to 5 postpartum (142 samples), transitional milk from days 6 to 14 (106 samples), and 112 mature milk samples obtained from days 15 to 28 (34 samples), from days 29 to 56 (50 samples) and from days 57 to 84 postpartum (28 samples). The concentration and percentage of lactoferrin vs. total protein were found to be significantly higher in colostrum (5.8 g/L, 27%) than in transitional milk (3.1 g/L, 22%) or day 15 to 28 mature milk (2.0 g/L, 19%), then increased in day 29 to 56 mature milk (2.2 g/L, 22%) and day 57 to 84 mature milk (3.3 g/L, 30%). The concentration of lysozyme decreased from colostrum (0.37 g/L) to transitional milk (0.27g/L) and day 15 to 28 mature milk (0.24 g/L), then increased in day 29 to 56 mature milk (0.33 g/L) and was highest in day 57 to 84 mature milk (0.89 g/L). The percentage of lysozyme vs. total protein was found to be always rising during lactation: colostrum, 2%; transitional milk, 2%; days 15 to 28, 2%; days 29 to 56, 3%; and days 57 to 84 mature milk, 8%.

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.

Measurement of nine human milk proteins by nephelometric immunoassays: application to the determination of mature milk protein profile

OBJECTIVES

Microparticle-enhanced nephelometric immunoassays for six human milk proteins (beta-casein, kappa-casein, alpha-lactalbumin, serum albumin, lactoferrin, and lysozyme) and conventional immunonephelometry assays for immunoglobulin A, C3, and C4 complement proteins were developed and characterized.

DESIGN AND METHODS

Microparticle-enhanced nephelometric immunoassays are competitive assays based on the nephelometric quantification of the inhibition of microparticle-protein conjugates immunoagglutination by the proteins to be assayed.

RESULTS

High precision (CVs ranged from 1% to 14% in within- and between-assays) and recovery (linear recovery in dilution-overloading assay) ensure a reliable determination of the main human milk proteins by single-step homogeneous nephelometric immunoassays, accurate over wide ranges of concentration. These immunoassays were easily applied to a large number of mature human milk samples (between 373 and 503 according to the proteins tested).

CONCLUSIONS

The immunoassays developed could be applied to the fast determination of human milk protein profile usable for nursery milk bank and fortification.

Forces acting on particle-enhanced immunoassays

The aim of the present work is to study the role of the different forces involved in the agglutination of immuno gamma-globulin (IgG) covered latex particles due to antigen-antibody reaction. An experimental investigation on the adsorption of IgG molecules on three latexes with different surface charge densities is described. Photon correlation spectroscopy was used to determine the hydrodynamic layer thickness of the IgG molecules adsorbed on the latexes. In order to get an insight into the forces acting between two antibody-covered particles approaching each other, the colloidal stability and immunoreactivity of these biocomplexes were studied. They can be stabilized by electrostatic or hydration forces. The immunological agglutination of IgG-immobilized latex particles due to the addition of the antigen was quantified through scattered light intensity measurements. The immunoresponse increases with ionic strength of the medium until a maximum value is achieved. Above this maximum, the immunoreactivity decreases.

Immunological and nutritional composition of human milk in relation to prematurity and mother's parity during the first 2 weeks of lactation

BACKGROUND

To investigate the effect of prematurity and parity on the dynamics of the major immunologic and nutritional proteins of human milk over the first 2 weeks of lactation.

METHODS

Microparticle-enhanced nephelometric immunoassays were developed for the quantification of alpha-lactalbumin, beta-casein, serum albumin, lactoferrin, and lysozyme in human milk. These components, immunoglobulin A, and total proteins were assayed in 368 individual samples collected from 74 mothers.

RESULTS

The dynamics of the major immunologic and nutritional proteins in early lactation presented similar patterns in preterm and term human milks. In comparison with term milk, preterm milk was globally characterized by higher concentrations of immune proteins and lower concentrations of nutritive proteins. These differences were increased by the degree of prematurity, which, however, influenced the absolute and relative protein concentrations differently, depending on the stage of lactation. The protein composition of term milk was similar, whatever the mother's parity. Conversely, the influence of prematurity on the levels of milk proteins during the first days of lactation was even greater in primiparous mothers.

CONCLUSIONS

This precise description of the composition of preterm and term milk, regarding the main nutritional and immunologic proteins, confirms the influence of both prematurity and parity on milk components and demonstrates the combined effect of these two conditions.

Microparticle-enhanced nephelometric immunoassay of lysozyme in milk and other human body fluids

Quantitation of lysozyme in human milk was performed by a microparticle-enhanced nephelometric immunoassay based on the measurement of the light scattered during the competitive immunoagglutination of a microparticle–lysozyme conjugate with an anti-lysozyme antiserum. This immunoassay has a detection limit of 8 μg/L of reaction mixture and can be performed using diluted milk (1:6000, in reaction mixture), excluding sample pretreatment. Human milk lysozyme can be quantified over the concentration range 0.09–1.50 g/L, with within- and between-run coefficients of variation <5%. Changes in the lysozyme concentration of human milk during lactation were determined in 636 samples. Lysozyme concentrations (mean ± SE) decreased from colostrum (0.36 ± 0.02 g/L) to transitional milk (0.30 ± 0.01 g/L) and mature milk during days 15–42 (0.30 ± 0.01 g/L), then increased in the mature milk during days 43–56 (0.35 ± 0.01 g/L) and especially during days 57–84 (0.83 ± 0.05 g/L). The proportion of lysozyme contributing to total protein was found to rise during lactation and was as follows: colostrum (1.7%), transitional milk (2.3%), and mature milk from days 15–28 (2.7%), days 29–42 (3.1%), days 43–56 (3.8%), and days 57–84 (7.3%). The assay developed for milk was also suitable for the determination of lysozyme in other human body fluids.

Microparticle-enhanced nephelometric immunoassay of alpha-lactalbumin in human milk

A microparticle-enhanced nephelometric immunoassay was developed for alpha-lactalbumin quantitation in human milk. It is based on the nephelometric measurement of the light scattered during the competitive immunoagglutination of a microparticle-alpha-lactalbumin conjugate with an anti-alpha-lactalbumin antiserum. This immunoassay is sensitive (detection limit in reaction mixture, 1.5 micrograms/L) and could be performed in high dilution of milk, excluding any interference or sample pretreatment. It allowed the quantification of alpha-lactalbumin on a large range of concentrations (0.5-16.9 g/L) with accuracy (linear recovery in dilution-overloading assay) and precision (within- and between-run coefficients of variation from 1 to 7%). Changes in the alpha-lactalbumin concentration of human milk during lactation were determined in 162 samples. The concentration and ratio of alpha-lactalbumin total protein were found to be significantly lower in colostrum (4.9 g/l, 27%) than in transitional milk (5.2 g/L, 40%), then decreased in mature milk (3.4 g/L, 31%).

Microparticle-enhanced nephelometric immunoassay of human plasminogen

A microparticle-enhanced nephelometric immunoassay was developed for plasminogen quantitation in human plasma. It is based on the nephelometric measurement of the light scattered by microparticle clusters formed during a sandwich reaction between plasminogen, microparticle--anti-plasminogen conjugate, and the free antibodies of anti-plasminogen rabbit antiserum. This immunoassay was sensitive (detection limit in reaction mixture, 34 micrograms/L) and could be performed in 500-fold diluted human plasma, excluding any interference or sample pretreatment. It allowed the quantitation of plasminogen on a large range of concentrations (17-550 mg/L), with a security in antigen excess reaching 1,100 mg/L, with accuracy (linear recovery in dilution-overloading assay and correlation with conventional immunonephelometry), and precision (within- and between-run coefficients of variation lower than 8%). A normal reference range from 54 to 148 mg/L (mean +/- 2 SD) was calculated from plasminogen concentration in plasma from 130 adults. Easy to perform (no washing or phase separation) and rapid (two steps of 30 minutes then 1 hour of incubation at room temperature), this microparticle-enhanced nephelometric immunoassay could be an interesting alternative method for human plasminogen quantitation.

Interactions of complement fraction C1q, fibronectin, and immunoglobulin G with polyacrylic microparticles used as solid-phase in immunoassay

A microparticle-enhanced nephelometric immunoassay was recently described, where polyacrylic, hydrophilic, and polyfunctional microparticles are used as the solid phase. It is a one-step immunoassay based on the nephelometric quantification of microparticle agglutination. In such assays, the measurement of analytes at low concentration may be impaired by the need of using undiluted biological samples. This leads to work with high concentrations of several proteins liable to interfere with the agglutination process. In this paper, we report on a study performed with human serum and purified proteins, which were assayed by classical analytical methods. This work identified three major components of human serum specifically involved in yielding polyacrylic microparticle instability: complement fraction C1q, fibronectin, and immunoglobulins G. In this order of importance, they all showed a marked ability to be adsorbed on the microparticle's surface. Pretreatment of human serum with microparticles decreased the concentrations in C1q (82%), fibronectin (16%), and immunoglobulin G (4%) very unequally. However, it allowed the elimination of microparticle instability, consequently providing the possible use of such polyacrylic microparticles in a one-step nephelometric immunoassay of analytes at low concentration in biological samples, without washes or phase separation.