Studies on human pregnancy-associated plasma protein A. Purification by affinity chromatography and structural comparisons with alpha 2-macroglobulin

Complete cDNA sequence of the preproform of human pregnancy-associated plasma protein-A. Evidence for expression in the brain and induction by cAMP

A cDNA that encodes the prepropeptide of pregnancy-associated plasma protein-A (preproPAPP-A), a putative metalloproteinase, has been cloned and sequenced. PAPP-A is synthesized in the placenta as a 1627-residue precursor preproprotein with a putative 22-residue signal peptide and a highly basic propeptide of 58 residues. The prepro-PAPP-A-encoding transcript contains a region with an extremely high G+C content and has an unusually long 5' untranslated region with several upstream short ORF. No alternatively spliced products could be identified by means of Northern blotting experiments or with rapid amplification of 5' cDNA ends experiments. A stretch within the 5' untranslated region shows sequence identities to a partial cDNA isolated from brain and a to cAMP-inducible sequence from a choriocarcinoma cell line.

Interaction of human pregnancy-associated plasma protein-A with serine proteinases

Human pregnancy-associated plasma protein A (PAPP-A) inhibited significantly the proteolytic activity of bovine trypsin and human plasmin. Trypsin or plasmin treatment of PAPP-A resulted in the generation of a major 85 kDa component and the rapid cleavage of internal thiol esters. The results indicated that both of these serine proteinases bound in a 1:1 stoichiometry to PAPP-A. The PAPP-A-bound enzymes were found to be enzymatically active towards small synthetic substrates and inaccessible to inactivation by soybean trypsin inhibitor and alpha 1-proteinase inhibitor. The mechanism of proteinase inhibition was likely to be entrapment, as described for alpha 2-macroglobulin.

Isolation and characterization of circulating complex between human pregnancy-associated plasma protein-A and proform of eosinophil major basic protein

The plasma protein previously known as pregnancy associated plasma protein-A (PAPP-A) and believed to contain only one kind of polypeptide chain has recently been shown to be a complex containing two different chains in equimolar amounts. One of the chains is now defined as the PAPP-A subunit, and the other has been identified as the proform of eosinophil major basic protein (proMBP) (Oxvig et al. (1993) J. Biol. Chem. 268, 12243-12246). A procedure for large scale preparation of the circulating complex (PAPP-A/proMBP) from pooled pregnancy serum is described. The amino acid and carbohydrate compositions of the isolated reduced and carboxymethylated PAPP-A (199 kDa) and proMBP subunits (38 kDa), and of the intact PAPP-A/proMBP have been determined. The PAPP-A and proMBP subunits contain 13.4% (w/w) and 38.6% (w/w) carbohydrate, respectively, and the intact complex contains 17.4% (w/w) carbohydrate. The PAPP-A subunit contains N-bound carbohydrate groups. In contrast, the proMBP subunit contains both N- and O-bound groups as well as glycosaminoglycan, previously found among plasma proteins only in inter-alpha-trypsin inhibitor and pre-alpha-trypsin inhibitor. It is shown that PAPP-A/proMBP can competitively inhibit human leucocyte elastase (KI = (5-10) x 10(-9) M) at an ionic strength of 0.075, but the inhibition is negligible at ionic strengths greater than 0.15. Human cathepsin G is also competitively inhibited (KI approx. 1 x 10(-6) M). The inhibition of both enzymes is most likely due to interactions with the glycosaminoglycan moiety of PAPP-A/proMBP. It is concluded that PAPP-A/proMBP is neither a potent nor a specific inhibitor of human leucocyte elastase.

Biochemical properties, activities, and presence in biologic fluids of eosinophil granule major basic protein

The existence of a proform of MBP is predicted from the sequence of MBP cDNA clones. ProMBP has been purified from the supernatants of CHO cells transfected with cDNA encoding prepro MBP. Purification involved heparin-Sepharose affinity purification followed by two sequential size fractionation steps over Sephadex G-100 and yielded proMBP with a molecular mass of 33 kd. Recombinant proMBP from the heparin-Sepharose column was subjected to isoelectric focusing followed by SDS-PAGE and Western blot analysis. The results indicated that most of the 33 kd form of proMBP focused predominantly between pI 4.2 and 5.1, with a major peak at a pI of approximately 4.9. Analyses of the carbohydrates associated with the purified 33 kd form of recombinant proMBP indicated the addition of 4856 to 5150 Da by carbohydrates characteristic of the complex type. Consistent with the hypothesis that the function of the propiece is to neutralize MBP toxicity during granule processing, proMBP lacked MBP cytostimulatory properties and actually blocked the effect of MBP in two different systems, basophil histamine release and neutrophil activation. In addition, as a measure of toxicity, proMBP did not inhibit protein synthesis, whereas MBP markedly reduced protein synthesis. The mechanisms by which MBP exerts its actions both as a cytostimulant and as a toxin are not known; however, it is known that cationic MBP readily reacts with acidic lipids. Using artificial liposomes as targets, MBP caused a disordering of the lipid bilayer membrane, resulting in fusion and lysis. Therefore, MBP may act both as a cytostimulant and as a toxin because of its marked cationicity and its ability to disorder lipid membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of alpha 2-macroglobulin and alpha 1-acid glycoprotein mRNA shows regional specialization in rat decidua

In situ hybridization histochemistry was used to detect mRNA coding for the plasma proteins alpha 1-acid glycoprotein and alpha 2-macroglobulin in the rat decidua during the period when the chorioallantoic placenta is established. It was found that alpha 1-acid glycoprotein mRNA was localized to a subpopulation of decidual cells predominantly found in the decidua capsularis but extending into the decidua basalis at later times. The highest levels of alpha 2-macroglobulin mRNA were found in the decidua basalis where there was some overlap with regions containing alpha 1-acid glycoprotein mRNA. No alpha 2-macroglobulin mRNA could be found in the inner part of the decidua capsularis where the highest levels of alpha 1-acid glycoprotein mRNA were found. However, a thin outer layer of compressed stromal cells, adjacent to the myometrium expressed the alpha 2-macroglobulin gene which surrounded the cells containing alpha 1-acid glycoprotein mRNA. This distribution of alpha 2-macroglobulin mRNA is consistent with the hypothesis that the protein is produced locally to prevent non-specific proteolysis which may otherwise result from catabolic processes involved in tissue remodelling. The function of alpha 1-acid glycoprotein is unknown but this protein is also likely to be involved in the maintenance of homeostasis during the period when contact between maternal and fetal systems is being established within the chorioallantoic placenta.

Molecular characterization of pregnancy-associated plasma protein-A by electrophoresis

Gradient polyacrylamide gel electrophoresis, isoelectric focusing and multidimensional immunoelectrophoretic techniques have been applied in order to physico-chemically characterize pregnancy-associated plasma protein-A (PAPP-A). By lectin affinity immunoelectrophoresis, PAPP-A contained sialic acid, glucose/mannose and N-acetyl-alpha-D-galactosamine. Immunoelectrophoretic analyses after incubation with various glycolases confirmed these findings and demonstrated that PAPP-A contained glucuronic acid, perhaps in chondroitin sulphate moities, thus indicating that PAPP-A may be a proteoglycan rather than a glycoprotein. Analysis by metal chelate and dye ligand affinity immunoelectrophoresis demonstrated many similarities between PAPP-A and alpha 2-macroglobulin (alpha 2M). However, unlike alpha 2M, PAPP-A did not form immunologically reactive complexes when incubated with proteases. Furthermore, as demonstrated by autoradiographic studies, PAPP-A did not contain internal thiolester groups, thus indicating that PAPP-A cannot inhibit proteases by molecular entrapment and, despite the homotetrameric molecular conformation, PAPP-A and alpha 2M may not have evolved from a common ancestral protein.

A two-site monoclonal enzyme immunoassay for pregnancy-associated alpha 2-glycoprotein

A two-site monoclonal enzyme immunoassay (MEIA) was developed for the determination of pregnancy-associated alpha 2-glycoprotein (PA alpha 2G) in serum. The minimum detectable level was 35 ng/ml. No immunochemical interaction with the closely related alpha 2-macroglobulin was found. Serum levels in 145 normal healthy males and non-pregnant females were 1.8 +/- 2.8 micrograms/ml (mean +/- SD), respectively, both significantly lower than previously reported. The distribution in the normal population was characteristically different when males and females were compared. No increase with age was found. During pregnancy, a significant increase in serum concentration was observed with average levels of 320 +/- 200 micrograms/ml at term (mean +/- SD), a 50-fold increase in concentration. As a tumor marker for breast and ovarian cancer, PA alpha 2G was found to be of no value. The present study emphasizes that a reevaluation of PA alpha 2G levels must be undertaken in order to assess the clinical and biological significance of this protein.

Structural relationships between the isoenzymes of human placental alkaline phosphatase: a serum factor converts M-PLAP to A- and B-PLAP

A protein factor has been found in serum which converts the M form of placental alkaline phosphatase (PLAP) to the A and B forms. The identity of the conversion products has been confirmed by analysis of their dimers and polypeptides. Proteolysis is not implicated in this phenomenon. This report establishes microvillous M-PLAP as the precursor of the A and B forms.

New placental proteins: chemistry, physiology and clinical use

In the past decade, several new placental proteins have been isolated and studied. The 'pregnancy-specific' beta 1-glycoprotein (SP1) is a major placental product with unusual physicochemical properties that has been extensively investigated, but its biological function remains uncertain. Pregnancy-associated plasma protein A (PAPP-A), a glycoprotein of mol. wt 400,000, has effects in vitro on the coagulation and complement cascades, probably by its properties of protease inhibition. Placental protein 5 (PP5) may be involved in the coagulation and fibrinolytic systems, and in follicle maturation and semen liquefaction. 'Placental protein 12' (PP12) is not a product of the placenta at all; it appears to be produced in the female genital tract under the influence of progesterone and may also be produced by proliferating liver cells. Further study may reveal new roles for these placental proteins beyond their traditional roles as tumour markers.

Pulsatile secretion of pregnancy-associated plasma protein-A (PAPP-A) in non-pregnant women

No changes in PAPP-A levels could be detected when plasma samples were obtained every second day throughout the entire menstrual cycle in three healthy women. But when measured every 30 min throughout 12 consecutive hours, in four healthy women, PAPP-A followed a pulsatile pattern which may originate in the endometrium since no PAPP-A pulses were detected in a long-term hysterectomized woman, or in two men. The pulses were not related to levels of oestradiol, progesterone, FSH or LH.

In vitro release of pregnancy-associated plasma protein-A (PAPP-A) by human endometrial cells

Evidence has now accumulated to sustain the idea that pregnancy-associated plasma protein-A (PAPP-A) is not pregnancy specific: it can be localized immunohistochemically in nonpregnant human endometrium. Thus, it was of interest to see if a primary cell culture of human endometrial cells was capable of producing PAPP-A. Immunoreactive PAPP-A-like material was detected in the culture medium of glandular as well as stromal cells. The presence of PAPP-A in endometrial culture medium was specific and could not be attributed to a nonspecific protease effect on the tracer used in radioimmunoassay. The production rate of PAPP-A by stromal cells could be enhanced by the addition of medroxyprogesterone acetate (MPA). Estradiol (E2) alone or in combination with MPA did not modify the production rate of PAPP-A. The production rate of PAPP-A by glandular cells remained unchanged after treatment with MPA and/or E2. These results confirm that in nonpregnant women PAPP-A is a progesterone-dependent protein produced by the endometrium.

Binding of pregnancy-associated plasma protein-A (PAPP-A) to placental subfractions

Pregnancy-associated plasma protein-A (PAPP-A) has been shown to exert immunosuppressive effects both on complement and on lymphoblastogenesis. It was of interest to see whether this protein could bind to syncytiotrophoblast microvillous membranes since these represent the effective interface between fetal tissue and the immunocompetent mother. Placental subfractions were prepared according to established techniques. PAPP-A was purified from different sources (pregnancy serum and plasma, retroplacental serum, placental extracts) and labelled with radioactive iodine. It could be shown that radioactive PAPP-A, irrespective of its biological origin was primarily binding to brush border membrane preparations but that significant binding was also seen with plasma membrane preparations. The binding was specific since alpha 2-macroglobulin (a structurally related protein to PAPP-A) was unable to displace bound radioactive PAPP-A. Scatchard plot representation of the data indicated that the affinity of PAPP-A for its binding site was of the same order of magnitude as reported for the insulin or GnRH receptors of the trophoblast (Ka 2 10(7)-2.5 10(8) M-1). These results are in agreement with the immunohistochemical localization of PAPP-A on the trophoblast providing that the small binding to plasma membrane preparations is due to contamination.

Placental alkaline phosphatase integrates via its carboxy-terminus into the microvillous membrane: its allotypes differ in conformation

Human placental microvillous alkaline phosphatase (M-PLAP) was extracted from microvilli either by butanol extraction or subtilisin proteolysis. The data indicate that subtilisin cleavage of PLAP removes a membrane-binding domain of approximately 2000 molecular weight, leaving the catalytic site intact and the protein in solution. Sequencing studies on the N-terminal 13 amino acids of both the subtilisin-cleaved and uncleaved forms of M-PLAP indicate that the enzyme is anchored to the plasma membranes by its carboxy-terminus. The N-terminal 13 amino acids of A-PLAP were the same as those of M-PLAP. Trypsin solubilization failed to release M-PLAP from these membranes and it appears to cleave a portion of molecular weight of about 9K from the amino terminus, leaving an enzymatically active portion of PLAP associated with the membrane. On SDS gels, subtilisin-cleaved M-PLAP showed an apparent dimeric molecular size larger than that of the original uncleaved enzyme, presumably due to the generation of a less compact conformational state. On starch gels, cleaved M-PLAP showed a single zone of enzyme activity with a mobility sightly greater than that of A-PLAP, which did not require the presence of Triton X-100 to enter the gel. Variations in the apparent molecular sizes of the different allelic forms of PLAP were also observed.

The development and validation of a radioimmunoassay for human pregnancy-associated plasma protein A (PAPP-A)

A specific and sensitive radioimmunoassay for human pregnancy-associated plasma protein A (PAPP-A) is described. This assay utilized tracer repurified by affinity chromatography on heparin-Sepharose. The most sensitive assay developed had a detection limit of 5 microliters PAPP-A in serum, and this protein could not be detected in sera from non-pregnant subjects. During pregnancy, mean circulating levels rose from 0.6 mg/l at 6 weeks gestation to 110 mg/l at term, and PAPP-A was detected in 44 of 101 umbilical blood samples. The use of the anticoagulants EDTA and acid citrate dextrose resulted in significantly different results in the plasma compared to the corresponding serum sample. PAPP-A was also measured in amniotic fluid.

The disappearance rate of pregnancy-associated plasma protein-A (PAPP-A) after the end of normal and abnormal pregnancies

PAPP-A is a macromolecular glycoprotein associated with human pregnancy. In vitro, PAPP-A is produced by explant cultures of trophoblast and decidua. The present work was undertaken to see if the presence of decidua had any effect on the disappearance rate of PAPP-A after removal of the placenta either by surgery or by spontaneous delivery. PAPP-A was measured before and at different times after a normal delivery (n = 6), after a termination of early pregnancy (n = 11) and after surgery for ectopic pregnancy (n = 8). The half life of PAPP-A after normal delivery (52.9 +/- 25.8 h, SD) was significantly (p less than 0.03) less than after a first trimester termination (93.9 +/- 41.6 h). After surgery for ectopic pregnancy in patients with curetted decidua, PAPP-A disappeared significantly faster (p less than 0.005) then in patients with intact decidua (84.1 +/- 17.8 vs 241.2 +/- 81.5 h). These results indicate that PAPP-A continues to be produced by the decidua after removal of the trophoblast in early pregnancy.

Pregnancy-associated plasma protein-A (PAPP-A): concentration in uterine fluid and immunohistochemical localization in the endometrium

Pregnancy-associated plasma protein-A (PAPP-A) was localized immunohistochemically in the endometrium and measured in uterine fluid of non-pregnant women. The variations of PAPP-A concentrations in uterine fluid during the menstrual cycle paralleled those found in the endometrium. In patients receiving hormone therapy there was a significant correlation between the uterine fluid PAPP-A concentration and the progestogen to oestrogen potency ratio of the hormonal treatment. The presence of PAPP-A in the uterine fluid cannot simply be explained by blood contamination or cell damage. These results are interpreted as indirect evidence for an exocrine as well as an endocrine secretion of PAPP-A by the endometrium which might be influenced by hormones.

Pregnancy-associated plasma protein A: purification under mild conditions, peptide mapping and tests for possible interactions with trypsin, plasmin and complement

Pregnancy-associated plasma protein A (PAPP-A) has been obtained in an enriched state under mild conditions of purification involving cibacron blue dye-ligand chromatography, negative antibody-affinity chromatography and gel filtration. The product was a mixture of PAPP-A and alpha-2-macroglobulin (alpha 2M). The ability of these proteins to bind 125I-trypsin and 125I-plasmin was studied. In contrast to previous studies by others, there was no evidence that PAPP-A could bind either protease. It is pointed out that protease-inhibitory activity in samples of PAPP-A can be due to the presence of very small amounts of contaminating alpha 2M in the preparations of PAPP-A. In further experiments PAPP-A did not inhibit the complement-induced lysis of sensitized red cells. Finally, cyanogen bromide peptide mapping experiments failed to yield evidence of structural homologies between PAPP-A and alpha 2M.

A high molecular weight species of placental alkaline phosphatase in human syncytiotrophoblast microvilli

A high molecular weight form of human placental alkaline phosphatase has been detected in extracts of placenta at term by electrophoresis in starch gels containing 0.5 per cent Triton X-100. The enzyme has a mobility intermediate between the previously described A and B forms of the enzyme and has been called the 'M' form of placental alkaline phosphatase. The M form is the major form of the enzyme found in microvilli extracted from syncytiotrophoblast, though trace amounts of membrane-associated M form can be found in extracts of placentae which had previously been experimentally depleted of microvilli. The M form is present in both of the two recently described subfractions of placental microvilli (see Davies, Parry and Sutcliffe, 1981; Truman, Wakefield and Ford, 1981). A variety of experiments show that the M form is not an artefact of extraction. The characteristic mobility of the M form in starch/Triton gels is the same, whether the microvilli are extracted in butanol, chloroform/methanol, Nonidet P40, Triton X-100 or Na deoxycholate. Serological, heat-stability and genetic studies showed that the A and M forms contain the same enzymatic polypeptide. Gel filtration of butanol/H2O and butanol/saline extracts of microvilli provided an estimated molecular weight of the A form of 127000 and of the M form of 725000; these values were unaffected by the presence of Triton in the medium.

In vitro production of pregnancy-associated plasma protein A by human decidua and trophoblast

Immunohistochemical techniques and direct measurements of pregnancy-associated plasma protein A (PAPP-A) have demonstrated the presence of PAPP-A in trophoblast and decidua. The purpose of the present study was to investigate the possibility that these tissues are capable of producing PAPP-A in vitro. Trophoblast and decidua were obtained from term deliveries and from legal surgical terminations of pregnancy (7 to 12 weeks). In addition to trophoblast and decidua, myometrium was also obtained during two hysterectomies in the first trimester of pregnancy. Tissues were incubated in medium 199 at 37 degrees C under an oxygen/carbon dioxide atmosphere. Media containing either pregnancy-associated serum or non-pregnancy-associated serum were changed after 8 hours of incubation in medium 199 alone. In addition to PAPP-A, human placental lactogen (hPL) and prolactin (Prl) were measured in homogenates and media by radioimmunoassays in order to confirm the viability of the cultured tissues. Addition of pregnancy-associated serum to the media induced a significant release of PAPP-A from trophoblast and decidua when compared to that in control cultures. Non-pregnancy-associated serum had no effect. Myometrium did not release any measurable PAPP-A into the medium even in the presence of pregnancy-associated serum. Cycloheximide added to pregnancy-associated serum significantly inhibited the release of PAPP-A from trophoblast and decidua. These last tissues, irrespective of the culture condition, released significantly more PAPP-A as well as hPL and Prl than was initially present in the tissue. These data demonstrate that PAPP-A is released in vitro by trophoblast and decidua (but not by myometrium) and that this release can be magnified by a factor present only in pregnancy-associated serum. The release of PAPP-A, hPL, and Prl is considered as a de novo production since concentration of these proteins are higher in media and tissues after incubation compared to concentrations initially present in the tissue before culture and since cycloheximide significantly inhibits the release of PAPP-A, Prl, and hPL from the cultured tissues.

Pregnancy-associated plasma protein A (PAPP-A) specifically inhibits the third component of human complement (C3)

Pregnancy-associated plasma protein A (PAPP-A), a macromolecular glycoprotein associated with pregnancy, was shown to inhibit complement-induced haemolysis and to bind heparin reversibly. Because of the inhibitory effects of heparin on the complement cascade it was not clear if the inhibition of complement activity observed with PAPP-A (isolated from heparin plasma) was attributable to the heparin moiety bound to PAPP-A. This work demonstrates that heparin exerts an inhibitory effect on complement activity but that heparin-free PAPP-A is also inhibitory. PAPP-A specifically inhibits C3 by binding to this complement subcomponent and not by inhibiting C3 convertase as demonstrated for C3 inactivator.

Autolytic fragmentation of complement components C3 and C4 and its relationship to covalent binding activity

The autolytic cleavage reaction of C3 and C4 and the covalent binding reaction of these proteins, are both aspects of the reactivity of an activated thiolester within these proteins. Autolytic cleavage occurs by internal nucleophilic attack on one face of the planar thiolester, while the covalent binding reaction of the activated proteins follows exposure of the opposite face of the thiolester to attack by external nucleophiles. Although the autolytic cleavage reaction does not occur under physiological conditions, the study of this phenomenon has provided valuable evidence in support of the mechanisms postulated for the physiological covalent binding reactions. The ease with which autolysis can be induced and observed in C3, C4, and alpha 2 M has provided a valuable method for detecting the active forms of these proteins in circumstances where other assays are impracticable, as, for example, in the examination of the uptake of active C3 by lymphocytes. Autolytic cleavage has also been used by Karp and colleagues to produce fragments used in characterizing genetic and biosynthetic variants of mouse C4 and the mouse protein Slp, which is structurally similar to C4. Gross structural comparisons made among C3, C4, and alpha 2 M on the basis of alignment of the autolytic cleavage sites and the protease-activation sites in these proteins were useful in predicting how the alpha-, beta-, and gamma-chains of C4, or the alpha- and beta-chains of C3, were aligned in the single polypeptide chain pro-forms of these proteins. The beta-alpha-gamma alignment deduced for C4 was also found by Goldberger and Colten. Similar alignments of cleavage sites have been used as a basis for evolutionary comparisons of complement proteins and alpha 2 M from species other than man. Although autolytic cleavage has been described only for C3, C4, alpha 2 M, and Slp, it is likely that other proteins will be found that exhibit this phenomenon. A possible candidate is pregnancy-associated plasma protein A (PAPP-A) which resembles alpha 2 M in many respects. The autolytic cleavage reaction will serve as a useful indicator in the detection of other proteins that undergo covalent binding by the mechanism discussed above.

Distribution of acute-phase alpha 2-macroglobulin in rat fetomaternal compartments

Rat acute-phase alpha 2-macroglobulin (AP alpha 2M) concentration was measured by radioimmunoassay in maternal serum, fetal plasma, maternal liver, fetal liver, and amniotic fluid as a function of gestational and neonatal age. The concentration profiles of AP alpha 2M in maternal serum and fetal plasma displayed two peaks, one in early gestation and another during late gestation. Synthesis of AP alpha 2M was confirmed by the immunoprecipitation of [35S]methionine incorporated into cultures of selected tissues. The following observations were made. 1) Maternal serum concentrations of AP alpha 2M were higher than those observed in fetal plasma in early gestation. This was attributable to a high level of maternal AP alpha 2M synthesis in metrial gland which was absent in liver and moderate in yolk sac. 2) In late gestation fetal plasma concentrations of AP alpha 2M greatly exceeded those observed in maternal serum. This could be explained by the pronounced synthesis of AP alpha 2M in fetal liver that was not apparent in maternal liver or yolk sac. 3) During labor, a transient increase in AP alpha 2M concentration was observed in maternal serum and fetal plasma. 4) During lactation a moderately elevated maternal serum concentration of AP alpha 2M was maintained. 5) Amniotic fluid concentration of AP alpha 2M was very low throughout gestation, which indicated that the fetal glomerulus was relatively impermeable to this large protein. It is concluded that in early gestation a principal maternal source of AP alpha 2M appears to be the metrial gland, whereas in late gestation fetal liver is a major source of AP alpha 2M appearing in fetal plasma from where some of this macroglobulin is speculated to be transported to the maternal circulation.

Development of a radioimmunoassay for pregnancy-associated plasma protein A and establishment of normal levels in the first trimester of pregnancy

An accelerated double antibody method has been developed for the radioimmunoassay of pregnancy-associated plasma protein A (PAPP-A) in serum. The workable range for the assay was 0.04-1.8 mg/l of serum. PAPP-A levels were determined in single serum samples from 110 women with prospective normal pregnancies of between 7 and 14 weeks' gestation. The level of pregnancy specific beta 1 glycoprotein (SP1) was also measured in these samples and normal ranges for PAPP-A and SP1 were constructed from the results obtained.

Measurement of plasma placental proteins and estriol in the detection of intrauterine growth retardation

This study was designed as an assessment of the clinical value of total estriol, placental lactogen (hPL), pregnancy specific glycoprotein (SP1), pregnancy-associated plasma protein-A (PAPP-A) and placental protein 5 (PP5), measured in a single sample of maternal serum, in the detection of intrauterine growth retardation (IUGR) in a large series of high risk pregnancies. Our results show the highest detection rate with SP1 (51%) and second highest with hPL (35%); estriol was less useful while PAPP-A and PP5 were of no value. However, there was 31% of false positives with SP1 compared with 14% for hPL. The best combination of the five parameters for the diagnosis of IUGR was achieved by measurement of both SP1 and hPL, with a low concentration of either protein indicating IUGR (sensitivity 63%, specificity 63%).

Studies on the concentration of pregnancy-associated plasma protein-A during normal and complicated pregnancy

Pregnancy-associated plasma protein-A was assayed in the blood of 347 women during pregnancy, using a new primary standard of PAPP-A as reference. The protein was assayed by antibody-antigen crossed electrophoresis with the lower limit of confident assay being 9.5 micrograms PAPP-A/ml (13 pmol/ml). PAPP-A was first detected at 14 weeks of gestation; by term it had risen to within the range 20 to 320 micrograms/ml. There was an indication that pregnancies involving a male baby had higher PAPP-A levels in blood than did those involving female babies. In 51 blood samples from 30 patients with gestational diabetes (taken between 28 weeks of pregnancy and term) there was no significant alteration in PAPP-A values compared with controls. In 35 blood samples from 15 patients with insulin-dependent diabetes, levels of PAPP-A were significantly lower than in controls or in gestational diabetes. In 43 blood samples from 35 patients with babies affected with intrauterine growth retardation (between 28 weeks and term), there was no significant difference in PAPP-A levels compared with controls. The effect of insulin on the blood levels of PAPP-A suggests that the concentration of PAPP-A is capable of altering significantly in response to certain physiological changes associated with the control of carbohydrate metabolism.

Immunological studies of the human placenta: functional and morphological analysis of pregnancy-associated plasma protein A (PAPP-A)

A blood protein, pregnancy-associated plasma protein A (PAPP-A), has been isolated from the plasma of pregnant women. An antiserum to this protein has been prepared and used to localize the protein within the placenta by immunofluorescence. It was found to be inconstantly present in the syncytiotrophoblast and intervillous fibrin. Neither antiserum nor antigen exerts a cytotoxic effect on peripheral blood lymphocytes, and neither affected blastogenic responses of lymphocytes to mitogens or in mixed lymphocyte culture reactions.