Maternal origin of nucleated erythrocytes in peripheral venous blood of pregnant women

We studied the origin of nucleated red blood cells (NRBC) in peripheral venous blood samples from 40 pregnant women carrying a male fetus, using a technique that allows direct chromosomal analysis by in situ hybridisation on immunologically and morphologically classified cells. Samples from ten nulligravid women were studied as controls. NRBC were enriched by negative magnetic activated cell sorting (miniMACS) using anti-CD45 monoclonal antibody. NRBC were detected by alkaline phosphatase anti-alkaline phosphatase immunostaining using a monoclonal anti-glycophorin A antibody. The origin of the NRBC was determined by fluorescence in situ hybridisation using X and Y specific probes. NRBC were found in 37 of the 40 pregnant women at a range of 1 to 230 per 20 ml of venous blood and in 6 of the 10 controls at a range of 1 to 3 per 20 ml of venous blood. All NRBC detected in the pregnant women were evidently of maternal origin, and in the pregnant women the number of NRBC was significantly higher (P < 0.05) than in the controls. Pregnancy per se seems to induce the appearance of maternal NRBC in the circulation, and it cannot therefore be assumed that NRBC isolated from the maternal blood are of fetal origin on the basis of morphology alone. Discrimination of fetal NRBC must occur for prenatal diagnosis of fetal genetic disorders.

Determination of human tumour necrosis factor-alpha (TNF-alpha) by time-resolved immunofluorometric assay

We have developed a 'sandwich'-type time-resolved immunofluorometric assay (IFMA) for tumour necrosis factor alpha (TNF-alpha) using two monoclonal antibodies (mAb) and the streptavidin/biotin (SAB) system. In this simple and fast streptavidin/biotin IFMA (SAB-IFMA) we used streptavidin coated wells to which we added biotinylated mAb for 3 h. After washing, the serum sample was added and incubated for 2 h followed by washing. Another monoclonal europium-labelled tracer antibody was added and incubated for 1 h, the wells were washed and the fluorescence of Eu measured. We tested various assay conditions in order to optimize the assay for sensitivity and measuring range. Purification of the labelled antibody by hydrophobic interaction chromatography was found to be essential to improve sensitivity. With a sample volume of 50 microliters the detection limit was 6 ng l-1 and the analytical range large, i.e. 10,000-fold. The median concentration in serum from healthy subjects was 12 ng l-1 and the reference range < 39 ng l-1. The mean analytical recovery in plasma was 76% and in serum 83%. Separation of serum by gel filtration and assay of TNF-alpha in fractions showed that the assay also measured the high molecular weight (MW) form of TNF-alpha, apparently corresponding to its complex with soluble receptors. Advantages of our SAB-IFMA were high sensitivity and low consumption of mAb. The assay performance of the SAB-IFMA was compared to two commercially available enzyme immunoassays also using the SAB system.

Optimization of a time-resolved immunofluorometric assay for tumor-associated trypsin inhibitor (TATI) using the streptavidin-biotin system

We have developed two 'sandwich'-type time-resolved immunofluorometric assays (IFMA) for tumor-associated trypsin inhibitor (TATI) using monoclonal and polyclonal antibodies. In the standard assay the monoclonal antibody was immobilized onto the walls of polystyrene microstrip wells and the polyclonal reagent was labeled with a europium chelate. We tested various assay conditions in order to optimize the assay for sensitivity and measuring range. Purification of the labeled antibody by hydrophobic interaction chromatography was found to be the most important single factor affecting sensitivity. Assay sensitivity and range were also improved by acid treatment of the solid phase antibody. To improve the sensitivity further the streptavidin/biotin (SAB) system was incorporated into the IFMA technique. In this simple and fast streptavidin/biotin IFMA (SAB-IFMA) we used streptavidin-coated wells to which we added biotinylated monoclonal antibody and a serum or urine sample. After incubation for 1.5 h and washing, the polyclonal europium-labeled tracer antibody was added. After incubation for 1 h the wells were washed and the Eu fluorescence measured. The assay performance of the SAB-IFMA was compared to the standard IFMA and radioimmunoassay (RIA). The detection limit was 0.05 microgram/l and the analytical range 3000-fold. The mean analytical recovery was 101%. Other advantages of the SAB-IFMA were high sensitivity and the low amounts of monoclonal antibody required, only 1/50 of that used in the standard IFMA.