A method for preparation of immunosorbents by direct coupling of dissociated immune complexes

Fetal antigen 2: an amniotic protein identified as the aminopropeptide of the alpha 1 chain of human procollagen type I

Fetal antigen (FA2) was purified from second trimester human amniotic fluid by immunospecific chromatography, gel filtration and reversed-phase chromatography. Gel filtration revealed two molecular forms of FA2 eluting at volumes corresponding to an M(r) of approximately 100 kDa and 30 kDa. SDS-PAGE analysis gave an M(r) = 27 kDa under reducing and non-reducing conditions for both forms, whereas the exact M(r) determined by mass spectrometry was 14,343 +/- 3 Da. FA2 was N-terminally blocked and after tryptic digestion the amino acid composition and sequences of the peptides showed identity with the aminopropeptide of the alpha 1 chain of human procollagen type I as determined by nucleotide sequences. After oxidative procedures normally employed for radio-iodination (iodogen and chloramine-T), FA2 lost its immunoreactivity. An antigen which cross-reacted with polyclonal rabbit anti-human FA2 was demonstrated in fetal calf serum. Gel filtration with analysis of fractions by inhibition ELISA showed that the bovine homologue was present in the same molecular forms as those in human amniotic fluid, and immunohistochemical analysis with anti-human FA2 showed that its distribution in bovine skin was identical to that of FA2 in human skin. FA2 is a circulating form of the aminopropeptide of the alpha 1 chain of procollagen type I, and this is the first description of its isolation and structural characterization in humans.

Foetal antigen 2 (FA2) in relation to wound healing and fibroblast proliferation

During wound healing of human skin the deposition of foetal antigen 2 (FA2) and basement membrane (BM) components collagen type IV and collagen VII was followed. FA2 appeared on day 8 in the cytoplasm of proliferating fibroblasts and around newly formed blood vessels. As granulation tissue was formed, FA2 was seen diffusely in the loose matrix and in proliferating fibroblasts. Re-establishment of FA2 as a broad diffuse band along the BM at the dermo-epidermal junction was seen on day 22. In contrast, type IV and VII collagen were found along the BM and in the basal cells of the newly formed epithelium and a continuous linear BM distribution of these two components were re-established by days 12 and 14, respectively. The molecular weight (Mr) analysis of FA2, isolated from human skin fibroblast culture supernatants using SDS-PAGE, revealed a Mr of 27 kDa, corresponding to that of FA2 isolated from amniotic fluid. The presence of FA2 in proliferating fibroblasts and diffusely in the newly formed matrix of granulation tissue, as well as its late appearance at the BM after this had become established, suggests that FA2 takes part in connective tissue metabolism and perhaps tissue morphogenesis.

Zinc ions inhibit factor I-mediated release of CR1-bound immune complexes and degradation of cell-bound complement factors C3b and C4b

ZnCl2 exerted a dose-dependent inhibition of citrate-phosphate-dextrose (CPD) plasma-induced release of 125I-labelled BSA-anti-BSA immune complexes (IC) bound to complement receptor type 1 (CR1, CD35) in human whole blood. Maximal inhibition was observed at 10 mM of ZnCl2. Furthermore, the release of IC bound to erythrocyte (E)-CR1 by purified factor I, factor I-deficient serum plus purified factor I, or normal human serum was reduced by approximately 90%, 64%, and 52%, respectively, in the presence of 10 mM ZnCl2. The effect of ZnCl2 on factor I-mediated degradation of cell-bound C3b/C4b was also investigated employing CPD blood or E from a factor I-deficient donor. These cells expressed covalently bound C3b and C4b as demonstrated by a simple agglutination technique. Upon incubation of CPD whole blood with purified factor I, or of E with purified factor I or normal CPD plasma, the C-fragments were cleaved and the cells were no longer agglutinated by antibodies to C3c and C4c. The presence of ZnCl2 prevented this factor I-mediated degradation of C3b and C4b, as evidenced by the unaffected agglutination of the cells by the antibodies. We conclude that ZnCl2 inhibited factor I activity since: (1) release of complement-preopsonized IC from E-CR1 by purified factor I was markedly inhibited (90%) in the presence of ZnCl2, (2) preincubation of the cells with ZnCl2 caused only a moderate inhibition (32-38%) of the IC release, and (3) degradation by purified factor I of covalently cell-bound C3b and C4b was abrogated in the presence of 10 mM ZnCl2.

Two fetal antigens (FA-1 and FA-2) and endometrial proteins (PP12 and PP14) isolated from amniotic fluid; preliminary observations in fetal and maternal tissues

Rabbit antihuman antibodies were derived by the injection of fractions of second trimester amniotic fluid known to contain proteins of endometrial/decidual origin. Using standard separation and absorption procedures, two antibody preparations were generated which demonstrated specificities against two and three proteins, respectively, in line immunoelectrophoresis and crossed immunoelectrophoresis. Analysis against proteins of fetal, maternal, endometrial and placental origin revealed that the bispecific antiserum reacted only with placental protein 14 (PP14; also known as progestagen-dependent endometrial protein, PEP) and one other hitherto undescribed antigen referred to as Fetal Antigen 1 (FA-1) molecular mass 60 kDa; electrophoretic mobility: slow; alpha 1-alpha 2; fast, albumin. The trispecific antiserum demonstrated specifities against placental protein 12 (PP12), alpha-fetoprotein (AFP) and another previously undescribed antigen referred to as Fetal Antigen 2 (FA-2) molecular mass 35 and 140 kDa; electrophoretic mobility: albumin. Following purification, monospecific antisera against each of these proteins (with the exception of AFP) were derived in new rabbits. Maternal and fetal blood, amniotic fluid and aqueous extracts from endometrial/decidual and placental tissues were analysed in rocket immunoelectrophoresis using these antisera to examine the distribution in these tissues. The analyses demonstrated a pattern of distribution typical for proteins of endometrial/decidual origin in these compartments in the case of PP12 and PP14, but suggested that the primary source of origin of FA-1 and FA-2 may be the fetus.

Release of immune complexes bound to erythrocyte complement receptor (CR1), with particular reference to the role of factor I

The release of 125I-bovine serum albumin (BSA)-anti-BSA immune complexes (IC) bound to human erythrocyte complement receptors (E-CR1) was studied. IC were complement-solubilized in normal human serum (NHS), and reacted with human erythrocytes at conditions optimal for binding of the IC to E-CR1. E-CR1-bound IC could be released by the addition of NHS or purified factor I. Factor I-deficient or I-depleted serum mediated no release, and addition of purified factor I restored the release. Factor H was not required for the release of IC. The kinetics of IC release was influenced by the NHS concentration, the presence of EDTA, and the time of prior storage of the erythrocytes at 4 degrees C. NHS (1:5 to 1:10) in the presence of EDTA caused nearly maximal release within 10-20 min at 37 degrees C. In the absence of EDTA the NHS-induced IC release was markedly slower. IC released within the first 30 min showed significant rebinding to new E. The release of IC was not associated with loss of the IC binding activity of E-CR1. The NHS-mediated release of IC could be inhibited by rabbit anti-CR1 and by a mixture of protease inhibitors. Release induced by purified factor I was also inhibited by protease inhibitors. The affinity of IC binding to E-CR1 was reduced after cleavage of CR1-bound C3b-IC to iC3b-IC by factor I.

Antigenic determinants of pregnancy-associated alpha 2-glycoprotein and alpha 2-macroglobulin defined by poly- and monoclonal antibodies

Human alpha 2-macroglobulin and pregnancy-associated alpha 2-glycoprotein (PA alpha 2G) share several physicochemical characteristics. By the use of unabsorbed or absorbed polyclonal antibodies to these antigens, the existence of common epitopes in these molecules were demonstrated in crossed immunoelectrophoresis. Two monoclonal antibodies out of 9 raised against purified PA alpha 2G were demonstrated to react with both antigens, indicating close immunochemical relatedness between these macroglobulins. The findings might have functional implications.

The selection of antibodies with defined desorption properties from precipitated immune complexes for use in immunoadsorption procedures

A general method for preparing immunosorbents with preselected antibody avidity is described. The method, which is a modification of a method described previously, also includes immunospecific purification of the ligand prior to coupling on the gel matrix. Polyclonal anti-alpha-1-fetoprotein antibodies in precipitated immune complexes were separated according to their avidity (low, intermediate and high) by dissociation with agents of increasing efficiency. After solid-phase coupling the antigen binding activity of the separated antibody preparations was examined according to recovery, capacity and binding strength. Antibodies of intermediate avidity derived from the immune complexes demonstrated optimal properties for preparative affinity chromatography.

Comparison of immunoradiometric assays of Bacillus anthracis spores immobilised on multispot slides and on microtitre plates

Indirect immunoradiometric assays (IRMA) for Bacillus anthracis spores are described in which the spores were heat fixed either on multispot microscope slides or on polyvinyl or polystyrene microtitre plates. Assays on plastic plates sometimes suffered from poor intra-experiment reproducibility. Signals were higher in assays in flat-bottomed microtitre wells than in assays in slides, but assay noise, due to non-specific absorption of antibody, was higher also, giving an overall disadvantage in signal-to-noise ratio. Elution of antibody with acid gave up to a doubling in signal-to-noise ratio. When small volumes of antibody reagents were used in assays in round-bottomed plastic wells, signal and noise characteristics were similar to those of the slide assay. While the assays on plastic wells tended to be less sensitive in terms of anti-spore antibody concentration or the number of spores detectable, the larger volume of antigen suspension that could be used in plastic wells gave them an advantage in terms of the minimum antigen concentration detectable.

Inter-alpha-trypsin-inhibitor (ITI): use of immunoadsorbents for preparation of anti-ITI antiserum, ITI-free human serum and purified ITI

Immunoaffinity chromatography was used to prepare various reagents required for studies of inter-alpha-trypsin-inhibitor (ITI), a human protease inhibitor. To absorb an initially polyspecific anti-ITI antiserum, a mixture of all serum proteins except ITI was prepared as follows: normal human serum was gel filtered (Sephacryl S-300) and the part of peak II containing normal ITI was removed; another aliquot of serum was heated, gel filtered, and peak I which contained all ITI molecules in aggregated form was discarded. The remaining fractions from both gel filtrations were immobilized on gel and used as an immunoadsorbent. The monospecific anti-ITI antiserum thus obtained was immobilized on gel and could bind ITI from human serum. Under conditions chosen to weaken non-specific adsorptions and desorb ITI without denaturation, this immunoadsorbent made it possible to prepare ITI-free serum and purified ITI with biological activity.

Purification of pregnancy-associated plasma protein-A by a two step affinity chromatographic procedure

A high molecular weight pregnancy specific protein (PAPP-A) was purified by immunospecific affinity chromatography. The purification procedure was based on a new method for affinity chromatography using direct coupling of precipitable immune complexes to the gel matrix. The procedure was performed in two steps: a positive immunospecific affinity chromatography followed by a negative affinity chromatography in which balanced amounts of anti-contaminant antibodies were used as ligant. The purified material at a concentration of 300 microgram/ml was tested by immunoelectrophoretic methods and no contaminants were detectable. WHO beta-1 SP1 reference material 78610 contained 45 microgram PAPP-A/ml.