[Study of the binding of thyroxine by thyroxine-binding prealbumin by a dialysis method using a fixed free concentration of ligand (author's transl)]. / Etude de la liaison thyroxine-thyroxine-binding prealbumin par une methode de dialyse a concentration libre imposee.

In order to study ligand-protein binding in solution, a dialysis method was used in which the free concentration of ligand can be controlled. The method has certain advantages and was applied to the binding of thyroxine by thyroxine-binding prealbumin, a system about which the results found in the literature are not in good agreement. From the isotherm drawn according to the Scatchard plot, it was found that thyroxine-binding prealbumin only presents a single binding site for thyroxine per molecule, the association constant being 1.7 . 10(8) M-1.

Correlation of free thyroxine index and thyroxine: thyroxine-binding globulin ratio with the free thyroxine concentration as measured by the thyroxine and thyroxine-binding globulin radioimmunoassays.

The concentration of thyroxine-binding globulin in the serum can now be measured by a simple and specific radioimmunoassay. Triiodothyronine uptake and measurement of total thyroxine have been combined to yield a free thyroxine index which has been found to correlate with the clinical state of the patients. An estimate of the free thyroxine concentration, as measured by the thyroxine and thyroxine-binding globulin radioimmunoassays, provided a good correlation with the free thyroxine index and the thyroxine: thyroxine-binding globulin ratio. However, the thyroxine: thyroxine-binding globulin ratio is inaccurate when thyroxine-binding globulin concentrations are high or low.

A method for measuring testosterone-estradiol-binding globulin--new analysis of experimental data and comparison with two commercially available kits.

Some binding assays have been suggested to measure serum testosterone--estradiol-binding globulin (TeBG) concentration. They have led to discrepant results. This study brought to surface the lack of these methods and the interest of a method using an accurate analysis of the binding isotherm. These observations led us to propose an absolute reference method especially suitable for the radioimmunological assays standardization. Our method used Con A Sepharose as a solid phase and DHT as a radioligand. We succeeded in solving the difficulties related to binding methods by evaluating the non-specific binding of the ligand and ligand--albumin binding. A careful analysis of experimental data, by setting equations specific to this DHT-TeBG system permitted the systematic errors to be corrected and allowed a precise determination of the serum TeBG concentration (27.3 +/- 6.0 nmol/l for 30 healthy men; 40 +/- 13 nmol/l for 15 healthy women). Moreover, the affinity constant of the ligand for the protein was accurately evaluated KDHT = (0.7 +/- 0.1)10(9) (mol/l-1) at 20 degrees C, which was not permitted by other methods. Two lines of evidence supported our assumptions and results. On the one hand, using estradiol as a radioligand instead of dihydrotestosterone, we found the same value for serum TeBG concentration; on the other hand, our assay favourably compared with two different kits commercially available. The correlation (r = 0.89) with 3H-SBP kit Merieux was good though this kit was not suitable for correctly assaying serum TeBG concentrations between 30 nmol/l and 60 nmol/l. An excellent correlation (r = 0.97) with SHBG IRMA Kit Farmos was found. This antibody-based assay and our binding assay yielded quite similar values that mutually validated both methods.

Effect of human syncytiotrophoblast plasma membrane-soluble extracts on in vitro mitogen-induced lymphocyte proliferation. A possible inhibition mechanism involving the transferrin receptor.

Transferrin (Tf) binding to lymphocytes and to syncytiotrophoblast plasma membranes (STPM) and their soluble extracts (STPM-SE) was examined, as well as the effect of the latter on mitogen-induced lymphoproliferation. Lymphocytes only express Tf receptors (Rtf) after mitogen (phytohemagglutinin or concanavalin A) stimulation, and the percentage of Tf bound by stimulated lymphocytes increased as a function of contact time with the mitogen, reaching a maximum at 72 hr. Studies of Tf binding to STPM-SE showed that the percentage of bound Tf increased proportionally to the protein concentration, but was additionally enhanced by a factor of three when STPM were pretreated with 3 M KCl. Scatchard analysis of Tf binding to lymphocytes cultured for 72 hr in the presence of mitogen, as well as to STPM and STPM-SE, revealed that this binding was specific and occurs via a single category of identical and independent receptors the numbers and affinity constants (Ka) of which have been determined. The results obtained by using STPM indicate that the Ka does not vary significantly from one preparation to another, but that the number of sites per milligram of protein increases by a factor of 10 when the STPM are pretreated with 3 M KCl (KCl-STPM). Finally, STPM-SE inhibited the mitogen-induced lymphoproliferative response whether or not they were treated with 3 M KCl. This inhibition was not due to lymphocytotoxicity, was dose dependent regardless of the preparation used, but was maximized with the KCl-STPM-SE fraction. The correlation between the inhibitory capacities of the soluble STPM extracts and the numbers of RTf sites present on their membranes leads to the hypothesis that the observed inhibition could involve the RTf. This effect may help in protecting the fetus from the maternal immune system at the time of the semi-allogenic fetal graft.

[Detection of the HBs antigen. Analysis of an interlaboratory of different methods of detection used in the blood banks of the central region]. / Détection de l'antigène HBs. Analyse d'une confrontation interlaboratoires concernant les différentes méthodes de détection utilisées dans les centres de transfusion sanguine de la région Centre.

A one year study has been performed between six blood Banks of the Centre of France in order to evaluate, among a population of donors found to be positive for HBs Ag by a radioimmunoassay, the number of those who were not detected by Enzyme immunoassay or passive hemagglutination. This study provides a good basis for comparing the sensitivities of the different methods used for Hbs Ag testing.

A simple and sensitive solid-phase radioimmunoassay for measuring the transferrin content of human biological fluids: its application to seminal plasma.

A highly sensitive and reproducible radioimmunoassay was established to detect transferrin in human fluids. By this technique, applied to seminal fluid, transferrin levels (micrograms/ml) were found in normozoospermic individuals (64.49 +/- 25.41) at level higher than in oligozoospermic (38.93 +/- 21.35), azoospermic (19.49 +/- 10.23), or vasectomized (19.61 +/- 8.95) subjects. A relationship between transferrin and spermatozoid concentration in sperm was shown. These results reinforce previous findings that seminal transferrin can be used as a reliable clinical marker of Sertoli Cell function.

[Use of radioimmunoassay of "thyroxine binding globulin" to determine the concentration of free plasma thyroxine]. / Application du dosage radio-immunologique de la "thyroxine-binding globulin" à la détermination de la concentration de thyroxine plasmatique libre.

A relationship is proposed for calculating the concentration of free serum thyroxine using the measured values of thyroxine and thyroxine-binding globulin total concentrations. This calculation has been performed on a population of 335 patients. A good discrimination of the different thyroid diseases has been obtained.

[Radioimmunoassay of serum thyroxin-binding-globulin in euthryoid subjects]. / Dosage radio-immunologique de la "thyroxine-binding-globulin" sérique chez les sujets euthyroidiens.

The authors have set up a thyroxine-binding-globulin radio-immunoassay in blood serum. The standard used has been determined by gravimetry, its maximal thyroxine-binding capacity is 0,96 mole of thyroxine per mole of TBG. Serum concentration of TBG has been measured in 159 euthyroid normals. The mean value of the concentration is 20 mg/l.

Investigation of the competition of two ligands for the same binding sites on a protein.

The authors describe an experimentally simple method for investigating the competition of two ligands for the same binding sites on a protein. The free and bound concentrations of one ligand are modified by the presence of the other; binding isotherms are therefore deformed. The authors present a theoretical study based on the analysis of these isotherms obtained with different known concentrations of the competing ligand. It is shown that deformation of the isotherms can be used to obtain the affinity constant of the competitor. The method was applied to competition between different ligands for the binding sites of testosterone-estradiol-binding globulin, a serum protein specific for the transport of steroid hormones as essential as testosterone and estradiol.