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.

gamma-Irradiation of acrolein and other acrylic monomers allowed the synthesis of spherical polyfunctional hydrophilic microparticles in the size range of 50 to 300 nm, on which antigens (immunoglobulins G, chorionic gonadotropin hormone, prealbumin) could be covalently bound. Microsphere-antigen conjugates clustered together in the presence of specific antiserum or monoclonal antibodies and their agglutination was quantified by light-scattering measurement performed with a specially designed nephelometer. Essential factors concerning the conjugate agglutination and its quantitation (size of microsphere, amount of antigen bound on microsphere, concentration of conjugate, concentration of agglutinating reagent, angle of light-scattering observation) were successively studied. A microparticle-enhanced nephelometric immunoassay for prealbumin was finally developed as an example of application. It was based on the inhibition of the immunoagglutination of microspheres-prealbumin conjugate by free prealbumin. This prealbumin immunoassay was easy to perform (one-step assay without washing or phase separation), fast (30 min), reliable (variation coefficients ranged from 3.6% to 7.5% for within- and between-assay determination), and sensitive (1 microgram/L detected). It was correlated with conventional immunonephelometry and radial immunodiffusion (correlation coefficients, 0.98). Microparticle-enhanced nephelometric immunoassay offered many advantages over the last two methods. Its better sensitivity allowed a lower reagent consumption and a larger sample dilution (contrary to the conventional immunonephelometry, sample pretreatment and sample blank measurement were unnecessary). Its inhibition mode induced a total accuracy for sample with high analyte concentration (a risk of underevaluation in antigen excess conditions existed in all method based on a noncompetitive antigen-antibody reaction) and provided the possibility to quantify haptens.(ABSTRACT TRUNCATED AT 250 WORDS)

Summary:Eleven proteins (immunoglobulins IgG, IgA, IgM, orosomucoid, o^-antiproteinase, haptoglobin, ceruloplasmin, C-reactive protein, transferrin, prealbumin and a 2 -macroglobulin) in human serum were quantitated by a new microparticle-enhanced nephelometric immunoassay. This is a one step competitive assay, based on the nephelometric measurement of light scattered by clusters of protein-coated microparticles specially synthesized for that use. Statistical evaluation (precision, recovery and method comparison) shows that the determination of serum proteins is reliable and accurate for wide ranges of concentration and that the method is quite adequate for strongly increased concentrations. This microparticle-enhanced nephelometric immunoassay appears to offer an alternative method for routine measurement of a great variety of serum proteins at high and intermediate concentrations, which are usually quantified by radial immunodiffusion or conventional immunonephelometry. On account of its sensitivity, it can also be used for the determination of relatively low concentrations of analytes.

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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.