Immunohistochemical demonstration of pregnancy-associated plasma protein A (PAPP-A) in the syncytiotrophoblast of the normal placenta at different gestational ages

Further Evidence that an Episode of Premature Labor Is a Pathologic State: Involvement of the Insulin-Like Growth Factor System

INTRODUCTION

Approximately 47% of women with an episode of preterm labor deliver at term; however, their infants are at greater risk of being small for gestational age and for neurodevelopmental disorders. In these cases, a pathologic insult may disrupt the homeostatic responses sustaining pregnancy. We tested the hypothesis of an involvement of components of the insulin-like growth factor (IGF) system.

METHODS

This is a cross-sectional study in which maternal plasma concentrations of pregnancy-associated plasma protease (PAPP)-A, PAPP-A2, insulin-like growth factor-binding protein 1 (IGFBP-1), and IGFBP-4 were determined in the following groups of women: (1) no episodes of preterm labor, term delivery (controls, n = 100); (2) episode of preterm labor, term delivery (n = 50); (3) episode of preterm labor, preterm delivery (n = 100); (4) pregnant women at term not in labor (n = 61); and (5) pregnant women at term in labor (n = 61). Pairwise differences in maternal plasma concentrations of PAPP-A, PAPP-A2, IGFBP-1, and IGFBP-4 among study groups were assessed by fitting linear models on log-transformed data and included adjustment for relevant covariates. Significance of the group coefficient in the linear models was assessed via t-scores, with p < 0.05 deemed a significant result.

RESULTS

Compared to controls, (1) women with an episode of premature labor, regardless of a preterm or a term delivery, had higher mean plasma concentrations of PAPP-A2 and IGFBP-1 (each p < 0.05); (2) women with an episode of premature labor who delivered at term also had a higher mean concentration of PAPP-A (p < 0.05); and (3) acute histologic chorioamnionitis and spontaneous labor at term were not associated with significant changes in these analytes.

CONCLUSION

An episode of preterm labor involves the IGF system, supporting the view that the premature activation of parturition is a pathologic state, even in those women who delivered at term.

Clinical Importance of Low Level of PAPP-A in First Trimester of Pregnancy - An Obstetrical Dilemma in Chromosomally Normal Fetus

BACKGROUND:

A variety of recent evidence exists about the clinical implication of low level of Pregnancy-associated plasma protein A (PAPP-A) in pregnancy. This glycoprotein is a protease, which releases the Insulin-like growth factor from IGFBP 4. Its role is a trophoblastic invasion of decidua, stimulation of cell mitosis and differentiation. It has an immunosuppressive effect in the placenta, inhibition of coagulation and complex role for integration of all these processes in the placenta. Level of PAPP-A (under 0.4 MoM-Multiple of Medians) in first-trimester screening in chromosomally and morphologically normal fetuses, could influence fetal weight, preeclampsia, premature birth and stillbirth. As a result of the complications mentioned above, there is implication on timing, mode of delivery and condition of the newborn.

AIM:

The study aims to evaluate the influence of low PAPP-A, measured in the first trimester on the outcome of pregnancy, with accent disorders which are the result of placental insufficiency. Also, gestational week, mode of delivery and condition of newborn secondary underlying conditions will be evaluated.

MATERIAL AND METHODS:

After given information and consultation about the expectation from the screening, pregnant women with a singleton pregnancy were tested for First Trimester Screening to estimate the risk for Trisomy 21, 13, 18- the most frequent chromosomopathies. After exclusion of chromosomopathies and congenital malformations, one hundred and fourteen patients enrolled in the study. The target group (n = 64) with PAPP-A below 0.4 MoM and control group (n = 50) with PAPP-A equal and above 0.4 MoM. An assessment of mode and time of delivery and presence of small for gestational age newborns, preeclampsia, premature birth and newborn condition at delivery was made.

RESULTS:

The percentage of the patients delivered in term was similar between the target group (n = 64) and the control group (n = 50), 82.81% vs 82.0% respectively. The rate of cesarean section was 29.7 % in the target group vs 32% in the control group. A significant difference was found about elective vs urgent cesarean section in favour of the target group. The difference was present about the complication in pregnancy before delivery, 56% vs 22%, p = 0.023, which were the main indication for cesarean section. The difference in newborn outcome was not significant.

CONCLUSION:

There is a difference in frequency of complications, in the cases with PAPP-A under 0.4 MoM, such as premature birth, preeclampsia compound with SGA fetuses versus the control group. The difference for SGA newborn and premature birth among the groups has statistical significance. The patients delivered with cesarean section were with the main indications SGA or elevated blood pressure, often occurred combined with prematurity. Apgar score and birth weight were similar in target and control group, but the newborns with a birth weight under 2500 g. were more frequent in the target group. Because these results did not show another significance among two groups, probably lower cut-off is needed, combining with another test (Doppler of uterine arteries in the first trimester, biochemical test). Presence of other diseases which could hurt placental function should be emphasised.

Clinical Importance of Low Level of PAPP-A in First Trimester of Pregnancy - An Obstetrical Dilemma in Chromosomally Normal Fetus

BACKGROUND:

Idiopathic epiretinal membrane (iERM) is an avascular proliferation of different types of cells between the posterior vitreous cortex and the internal limiting membrane. That causes visual impairment including blurry, distortion, scotoma. Many studies of iERM were done to describe the clinical characteristics and investigate the histopathology of this disease. Nonetheless, there has not been a study of iERM histopathology in Vietnam.

AIM:

To describe clinical characteristics and histopathological results of idiopathic retinal membrane and the association between them.

METHODS:

A cross sectional decriptive study of 35 iERMs (33 patients) in Vietnam National Institute of Ophthalmology (VNIO).

RESULTS:

High morbidity incidence was in group age >50 years (32/35), female gender (26/35), limited movement works (27/35), and high educational levels (28/35). Distortion was the highest (77.14%), scotoma and floater was less frequent (28.5%, 45.7%). Macular edema in all cases and PVD and exudate were high frequent (65.7%, 62.8%). Symptom duration was 8.2 ± 4.7 months, (1-21 months). Mean of central macular thickness was 468.51 ± 97.24 µm (656-274 µm). Six types of cell were detected, including glial cell (35/35), fibroblast (23/35), myofibroblast (23/35), macrophage (13/35), lymphocyte (5/35) and neutrophil (2/35). The number of cell types in one sample ranged from 1-5 types (2.85 ± 1.28 cell types). Number of cell types were correlated to symptom duration (r = 0.47, p = 0.004, Pearson’s test) and central macular thickness (r = 0.72, p < 0.001, Pearson’s test).

CONCLUSION:

There were 6 types of cells in iERM. Glial cell was the most frequent cell, inflammatory cells (macrophage, lymphocyte, neutrophil) was also detected. The number of cell types was stastitically correlated to symptom duration and CMT.

Obstetric Outcome in Pregnant Patients with Low Level of Pregnancy-Associated Plasma Protein A in First Trimester

BACKGROUND

Pregnancy-associated plasma protein A (PAPP-A), is a protease which releases Insulin-like growth factor. The role of this factor is stimulation of cell mitosis, differentiation and trophoblastic invasion of deciduas. Identification of patients with low PAPP-A (under 0.4 MoM in the first trimester has an influence on birth weight, attenuation of fetal growth, preeclampsia, birth and fetal demise.

AIM

The main issue in the study is evaluating an influence of PAPP-A, calculated in the first trimester on the unfavourable outcome of pregnancy.

MATERIAL AND METHODS

Seventy pregnant women with singleton pregnancy underwent first-trimester biochemical screening. The target group were women with PAPP-A below 0.4 MoM, and in control group, PAPP-A were over 0.4 MoM. There was an assessment of the influence on the mode of delivery, gestational week, the presence of intrauterine growth restriction, preeclampsia, temporary birth, intrauterine fetal demise and newborn condition.

RESULTS

In target group, consisted of 35 patients, 16 were delivered at term. From 28 to 37 g.w.- were 7 patient, 22-28 g.w.- 4 and 8 patients were under the 22 g.w (all with fetal demise) there were 19 pretemporary deliveries - 9 with Cesarean Section (SC). In the target group: 5 newborn were with IUGR, 6 women had preeclampsia, 1 had placental abruption. In control group were 35 patients: 28 delivered at term, 9 with SC, 26 vaginal deliveries; with IUGR were 4 newborns. Two newborns were hypertrophic.

CONCLUSION

There is a significant difference in unfavourable outcome in the cases with PAPP-A under 0.4 Mom, particular in the group, with a PAPP-A value under 0.2 MoM. The patients delivered with SC with the main indications in utero hypoxia, growth restriction and elevated blood pressure had PAPP-A between 0.3-0.4 MoM. The patients with intrauterine fetal death and placental abruption in the most of the cases have PAPP-A value under 0.2 MoM. There is a need to be aware in these pregnancies to achieve the preventions of adverse outcome, to decrease perinatal morbidity and mortality.

Whole-transcriptome analysis delineates the human placenta gene network and its associations with fetal growth

BACKGROUND

The placenta is the principal organ regulating intrauterine growth and development, performing critical functions on behalf of the developing fetus. The delineation of functional networks and pathways driving placental processes has the potential to provide key insight into intrauterine perturbations that result in adverse birth as well as later life health outcomes.

RESULTS

We generated the transcriptome-wide profile of 200 term human placenta using the Illumina HiSeq 2500 platform and characterized the functional placental gene network using weighted gene coexpression network analysis (WGCNA). We identified 17 placental coexpression network modules that were dominated by functional processes including growth, organ development, gas exchange and immune response. Five network modules, enriched for processes including cellular respiration, amino acid transport, hormone signaling, histone modifications and gene expression, were associated with birth weight; hub genes of all five modules (CREB3, DDX3X, DNAJC14, GRHL1 and C21orf91) were significantly associated with fetal growth restriction, and one hub gene (CREB3) was additionally associated with fetal overgrowth.

CONCLUSIONS

In this largest RNA-Seq based transcriptome-wide profiling study of human term placenta conducted to date, we delineated a placental gene network with functional relevance to fetal growth using a network-based approach with superior scale reduction capacity. Our study findings not only implicate potential molecular mechanisms underlying fetal growth but also provide a reference placenta gene network to inform future studies investigating placental dysfunction as a route to future disease endpoints.

Using RNA sequencing for identifying gene imprinting and random monoallelic expression in human placenta

Given the possible critical importance of placental gene imprinting and random monoallelic expression on fetal and infant health, most of those genes must be identified, in order to understand the risks that the baby might meet during pregnancy and after birth. Therefore, the aim of the current study was to introduce a workflow and tools for analyzing imprinted and random monoallelic gene expression in human placenta, by applying whole-transcriptome (WT) RNA sequencing of placental tissue and genotyping of coding DNA variants in family trios. Ten family trios, each with a healthy spontaneous single-term pregnancy, were recruited. Total RNA was extracted for WT analysis, providing the full sequence information for the placental transcriptome. Parental and child blood DNA genotypes were analyzed by exome SNP genotyping microarrays, mapping the inheritance and estimating the abundance of parental expressed alleles. Imprinted genes showed consistent expression from either parental allele, as demonstrated by the SNP content of sequenced transcripts, while monoallelically expressed genes had random activity of parental alleles. We revealed 4 novel possible imprinted genes (LGALS8, LGALS14, PAPPA2 and SPTLC3) and confirmed the imprinting of 4 genes (AIM1, PEG10, RHOBTB3 and ZFAT-AS1) in human placenta. The major finding was the identification of 4 genes (ABP1, BCLAF1, IFI30 and ZFAT) with random allelic bias, expressing one of the parental alleles preferentially. The main functions of the imprinted and monoallelically expressed genes included: i) mediating cellular apoptosis and tissue development; ii) regulating inflammation and immune system; iii) facilitating metabolic processes; and iv) regulating cell cycle.

Adverse pregnancy outcome in patients with low pregnancy-associated plasma protein-A: The Indian Experience

AIM

The aim of our study was to examine the association of low pregnancy-associated plasma protein-A (PAPP-A) with adverse pregnancy outcome.

MATERIAL AND METHODS

A total of 1640 consecutive pregnant women between 9(+5) and 13(+6) weeks of pregnancy were recruited. One hundred and thirty women with PAPP-A levels < 0.4 multiple of median were followed till delivery and the outcome information was obtained for fetal loss, birthweight, growth restriction, preterm birth, reduced liquor and development of pre-eclampsia.

RESULTS

During the study period, 130 (7.92%) women had low PAPP-A and were considered as cases and 200 women with normal PAPP-A were controls. Intrauterine growth restriction was observed in 28 (21.54%) cases as compared to 10 (5%) controls. Pre-eclampsia presented in 24 (18.46%) cases and in 18 (9%) controls. Twenty (15.38%) cases had preterm delivery compared to 12 (6%) controls. Fifty-six (43.08%) cases delivered low-birthweight babies compared to 22 (11%) controls. Thus, the incidence of intrauterine growth restriction, preterm birth and low birthweight was significantly more in the cases as compared to the control group.

CONCLUSIONS

PAPP-A is a valuable analyte for predicting risk of adverse pregnancy outcome and women with low serum PAPP-A levels would benefit from closer surveillance.

Pattern of secretion of pregnancy-associated plasma protein-A (PAPP-A) during pregnancies complicated by fetal aneuploidy, in vivo and in vitro

BACKGROUND

Pregnancy-associated placental protein-A (PAPP-A) is a metalloprotease which circulates as an hetero-tetramer in maternal blood. Its maternal serum concentration in fetal trisomy 21 is decreased during the first trimester, so that PAPP-A is a useful screening biomarker. However, the regulation of PAPP-A placental secretion is unclear. We therefore investigated the secretion of PAPP-A in pregnancies complicated by fetal aneuploidies, both in vivo and in vitro.

METHODS

Maternal serum collected between 10 WG and 33 WG during 7014 normal pregnancies and 96 pregnancies complicated by fetal trisomy 21, 18, and 13 were assayed for PAPP-A using the Immulite 2000xpi system®. The pregnancies were monitored using ultrasound scanning, fetal karyotyping and placental analysis. Villous cytotrophoblasts were isolated from normal and trisomic placenta and cultured to investigate PAPP-A secretion in vitro (n=6).

RESULTS

An increased nuchal translucency during the first trimester is a common feature of many chromosomal defect but each aneuploidy has its own syndromic pattern of abnormalities detectable at the prenatal ultrasound scanning and confirmed at the fetal examination thereafter. PAPP-A levels rise throughout normal pregnancy whereas in trisomy 21, PAPP-A levels were significantly decreased, but only during the first trimester. PAPP-A levels were decreased in trisomy 13 and sharply in trisomy 18, whatever the gestational age. In vitro, PAPP-A secretion was decreased in aneuploidy, and associated with decreased hCG secretion in Trisomy 21 and 18. These biochemical profiles did not appear to be linked to any specific histological lesions affecting the placenta.

CONCLUSIONS

These profiles may reflect different quantitative and qualitative placental dysfunctions in the context of these aneuploidies.

A sensitive time-resolved fluoroimmunoassay for determination of median levels of pregnancy-associated plasma protein a in pregnant women in China

Pregnancy-associated plasma protein A (PAPP-A) is an important serum marker for first trimester screening. Its weekly median value varies with ethnicity. A one-step time-resolved fluoroimmunoassay (TRFIA) using two monoclonal antibodies against PAPP-A with Eu(3+) chelates as labels has been developed. Using the assay described here, we evaluated 5,301 normal serum samples from Chinese women at 7-13 weeks of gestation. The detection limit using this assay was 1.2 mIU/L, and the maximum detection range was up to 10,000 mIU/L. The intra-assay and inter-assay coefficients of variation were <3.0% and <5.0%, respectively, and the mean recovery rate was 98.0%. PAPP-A concentrations measured in 516 maternal serum samples correlated well with those obtained by Dissociation-Enhanced Lanthanide Fluorescent Immunoassay (DELFIA) PAPP-A assay (r=0.988, P<0.001). The medians for 7-13 weeks of maternal serum PAPP-A were higher in the women from China compared to reports from other countries. The present assay possesses accuracy and high sensitivity and exhibits great potential for the clinical analysis of PAPP-A. Our investigation on the median concentrations of PAPP-A will help establish reference values that are specific for China and study the importance of ethnic factors in biochemical screening.

First-trimester prediction of preeclampsia in nulliparous women at low risk

OBJECTIVE

To identify clinical characteristics and biochemical markers in first-trimester samples that would possibly predict the subsequent development of preeclampsia.

METHODS

We conducted a multicenter observational study in 2,434 nulliparous women at low risk to identify biomarkers that possibly predict preeclampsia. Clinical history, complete blood count, and biochemical markers were assessed in the first trimester. The trophoblast and angiogenesis markers ADAM-12, pregnancy-associated plasma protein-A, placental protein 13, placental growth factor, soluble fms-like tyrosine kinase-1, and endoglin were measured in a case-control subset of 174 women with preeclampsia and 509 women in the control group.

RESULTS

Univariable analysis revealed maternal age, race, marital status, years of education, source of medical payment, prenatal caregiver, body mass index (BMI, calculated as weight (kg)/[height (m)]), and systolic blood pressure at enrollment were significantly associated with preeclampsia. Mean platelet volume was greater at enrollment in women who later had development of preeclampsia (median 9.4 compared with 9.0 femtoliter (fl); P=.02). First-trimester concentrations (multiples of the median) of ADAM-12 (1.14 compared with 1.04; P=.003), pregnancy-associated plasma protein-A (0.94 compared with 0.98; P=.04), and placental growth factor (0.83 compared with 1.04; P<.001) were significantly different in women who had development of preeclampsia compared with women in the control group. The optimal multivariable model included African American race, systolic blood pressure, BMI, education level, ADAM-12, pregnancy-associated plasma protein-A, and placental growth factor, and yielded an area under the curve of 0.73 (95% confidence interval 0.69-0.77) and a sensitivity of 46.1% (95% confidence interval 38.3-54.0) for 80% specificity.

CONCLUSION

A multivariable analysis of clinical data and biochemical markers in the first trimester did not identify a model that had clinical utility for predicting preeclampsia in a nulliparous population at low risk.

LEVEL OF EVIDENCE

II.

Optimisation of sandwich ELISA based on monoclonal antibodies for the specific measurement of pregnancy-associated plasma protein (PAPP-A) in acute coronary syndrome

OBJECTIVES

PAPP-A has become the principal biochemical serum marker in first trimester screening for Down syndrome, the original data being based on results of a radioimmunoassay (RIA). Recent observations using sandwich ELISA technology have proposed PAPP-A as a potential marker in patients with acute coronary syndrome (ACS). The aims of the present study were to demonstrate (i) the importance of antibody specificity, (ii) the potential pitfalls in changing assay technology, (iii) the importance of strict definition of technology, and (iv) the application of a well-defined assay technology on sera from patients with ACS.

DESIGN AND METHODS

Candidate monoclonal antibodies (Mab) were identified by immunohistochemistry, Western blot and the absence of positive signals (ELISA) with normal, non-pregnant serum as antigen source. The ELISA technology was standardized against the original PAPP-A RIA and the WHO reference preparation (WHO 78/610). Results different from those obtained by the original RIA led to ELISA modifications with respect to dilution buffer and enzymatic digestion of the Mab.

RESULTS

The first generation ELISA revealed serum measurements from a pool of non-pregnant (n=103) individuals which, compared to the RIA, seemed to be false positive. The false positive reaction was abolished by addition of bovine serum (BS) to the dilution buffer. Subsequent analysis of individual sera (n=103) indicated that 7/103 were still false positive. This reaction was eliminated by introduction of F(ab')(2)-fragment of the indicator antibody. This modified ELISA revealed that serum PAPP-A levels in ACS were statistically significantly higher than in controls (p<0.001). Moreover, serum PAPP-A in ACS patients with ST-segment elevation (STEMI) were higher (p<0.001) compared to patients without ST-segment elevation (NSTEMI). Immunohistochemical analysis failed to identify PAPP-A in the atherosclerotic plaques.

Pregnancy-associated plasma protein-E (PAPP-E)

A full-length cDNA encoding a novel human protein was cloned from placenta cDNA. The corresponding 1542 amino acid protein sequence was termed 'pregnancy-associated plasma protein-E' (PAPP-E) as it shows a 62% homology to the human pregnancy-associated plasma protein-A (PAPP-A) that is a diagnostic marker for trisomies, especially Down syndrome. The conserved domain structure contains five motifs related to the short consensus repeats of complement proteins and selectins, three motifs related to the lin-notch motifs of proteins regulating early tissue differentiation, and a putative zinc-binding motif and active site of the metzincin-superfamily of metalloproteases. The PAPP-E gene was localized to chromosome 1q23-25. Northern blot analysis showed that PAPP-E is predominantly expressed in placenta.

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)

Comparison of different antibody preparations against pregnancy-associated plasma protein-A (PAPP-A) for use in localization and immunoassay studies

Four antibody preparations against pregnancy-associated plasma protein (PAPP-A) were compared in order to find an explanation for the contradictory results published on tissue localization, clinical usefulness and biological function of PAPP-A. One of the preparations studied was a rabbit anti-PAPP-A antiserum which has been offered for general scientific use (Bischof et al. 1979). Only the IgG fraction of anti-PAPP-A antisera which appeared to be monospecific and had been further absorbed with fetal connective tissue gave specific uniform staining of the cytoplasm of the syncytiotrophoblast exclusively. Circulating PAPP-A could not be detected by RIA employing this IgG preparation in the non-pregnant state, or before 18 days after conception. Circulating PAPP-A could be detected in all seven pregnant women studied within 4 weeks after conception. Identical results were obtained with a commercially available IgG fraction against PAPP-A.

Immunohistochemical aspects of immunological cross-reaction and masking of epitopes for localization studies on pregnancy-associated plasma protein A

The influence of antibody absorption procedures and proteolytic pre-treatment of formaldehyde-fixed placental tissue on the localization of pregnancy-associated plasma protein A by immunoperoxidase technique was examined. Apparently monospecific IgG fraction of the anti-plasma protein applied directly on fixed tissue resulted in staining of connective tissue and a thin apical rim of the syncytiotrophoblast. Further absorption of the antibody with foetal connective tissue abolished this staining reaction. Pre-treatment of the fixed placental tissue with trypsin prior to application of the antibody, which had been absorbed with connective tissue, resulted in staining within the cytoplasm of the syncytiotrophoblast exclusively. Identical staining was seen when this IgG preparation was used directly on frozen placental tissue. The results point to the importance of the specificity of the antibody preparations and of proteolytic unmasking of epitopes when fixed tissues are used for localization studies of pregnancy-associated plasma protein A by immunoperoxidase technique.

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.

In vitro production of pregnancy-associated plasma protein-A (PAPP-A) by trophoblastic cells

Pregnancy-associated plasma protein-A (PAPP-A) a high molecular weight glycoprotein, is found in high concentration in the maternal circulation during pregnancy. Immunohistochemically, PAPP-A can be localized in the trophoblast and in the decidua. Short term cultures of trophoblastic and decidual explants produce PAPP-A in vitro. It was thus of interest to see if long term cultures of primary monolayers of human trophoblast cells were capable of producing PAPP-A. Under our in vitro conditions, trophoblastic monolayers were producing both PAPP-A and beta hCG. During the first 3 days of culture PAPP-A levels increased in the medium whereas beta hCG levels decreased. The production of both proteins could be inhibited by cycloheximide. These results strongly suggest that the trophoblast is a source of PAPP-A in vivo.

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.

The localization of pregnancy proteins (hPL, SP1 and PAPP-A) in intra- and extrauterine pregnancies

The localization of human placental lactogen (hPL), pregnancy-specific beta-1 glycoprotein (Schwangerschaftsprotein 1, SP1) and pregnancy-associated protein A (PAPP-A) was examined in intrauterine and tubal ectopic gestation (n = 5) by the immunoperoxidase technique. The distribution of hPL and SP1 was identical in placental tissues obtained from intra- and extrauterine pregnancies, being uniformly seen throughout the syncytiotrophoblast. hPL and SP1 were not demonstrated in uterine decidual tissue from ectopic pregnancies. During early (week 8) intrauterine pregnancy, PAPP-A was not restricted to the mature syncytiotrophoblast, being observed also in some trophoblast-like cells adjacent to islands of syncytiotrophoblast. In contrast, in ectopic gestation, PAPP-A was observed in these cells at six weeks' gestation only. We were unable to detect PAPP-A in trophoblastic tissue of chorionic villi and uterine decidual tissue from ectopic gestation.