Molecular insights into evolution, mutations and receptor-binding specificity of influenza A and B viruses from outpatients and hospitalized patients in Singapore

BACKGROUND

This study compared the genomes of influenza viruses that caused mild infections among outpatients and severe infections among hospitalized patients in Singapore, and characterized their molecular evolution and receptor-binding specificity.

METHODS

The complete genomes of influenza A/H1N1, A/H3N2 and B viruses that caused mild infections among outpatients and severe infections among inpatients in Singapore during 2012-2015 were sequenced and characterized. Using various bioinformatics approaches, we elucidated their evolutionary, mutational and structural patterns against the background of global and vaccine strains.

RESULTS

The phylogenetic trees of the 8 gene segments revealed that the outpatient and inpatient strains overlapped with representative global and vaccine strains. We observed a cluster of inpatients with A/H3N2 strains that were closely related to vaccine strain A/Texas/50/2012(H3N2). Several protein sites could accurately discriminate between outpatient versus inpatient strains, with site 221 in neuraminidase (NA) achieving the highest accuracy for A/H3N2. Interestingly, amino acid residues of inpatient but not outpatient isolates at those sites generally matched the corresponding residues in vaccine strains, except at site 145 of hemagglutinin (HA). This would be especially relevant for future surveillance of A/H3N2 strains in relation to their antigenicity and virulence. Furthermore, we observed a trend in which the HA proteins of influenza A/H3N2 and A/H1N1 exhibited enhanced ability to bind both avian and human host cell receptors. In contrast, the binding ability to each receptor was relatively stable for the HA of influenza B.

CONCLUSIONS

Overall, our findings extend our understanding of the molecular and structural evolution of influenza virus strains in Singapore within the global context of these dynamic viruses.

High Viral Diversity and Mixed Infections in Cerebral Spinal Fluid From Cases of Varicella Zoster Virus Encephalitis

Background

Varicella zoster virus (VZV) may cause encephalitis, both with and without rash. Here we investigate whether viruses recovered from the central nervous system (CNS; encephalitis or meningitis) differ genetically from those recovered from non-CNS samples.

Methods

Enrichment-based deep sequencing of 45 VZV genomes from cerebral spinal fluid (CSF), plasma, bronchoalveolar lavage (BAL), and vesicles was carried out with samples collected from 34 patients with and without VZV infection of the CNS.

Results

Viral sequences from multiple sites in the same patient were identical at the consensus level. Virus from vesicle fluid and CSF in cases of meningitis showed low-level diversity. By contrast, plasma, BAL, and encephalitis had higher numbers of variant alleles. Two CSF-encephalitis samples had high genetic diversity, with variant frequency patterns typical of mixed infections with different clades.

Conclusions

Low viral genetic diversity in vesicle fluid is compatible with previous observations that VZV skin lesions arise from single or low numbers of virions. A similar result was observed in VZV from cases of VZV meningitis, a generally self-limiting infection. CSF from cases of encephalitis had higher diversity with evidence for mixed clade infections in 2 cases. We hypothesize that reactivation from multiple neurons may contribute to the pathogenesis of VZV encephalitis.

High Yield of HIV Testing in Dengue-Like Febrile Illness in Singapore

Where dengue virus infections are endemic, acute febrile illness is often managed as dengue fever (DF) without diagnostic testing. In a prospective study of 140 patients with clinical features of DF, 3 (2.1%) had acute HIV infection (AHI). We recommend testing for AHI in dengue-like febrile illness.

Bitten by a bug or a bag? Transfusion-transmitted dengue: a rare complication in the bleeding surgical patient

BACKGROUND

Blood-borne infections remain a risk of blood transfusions. While routine screening of donated blood products has greatly reduced the risk of human immunodeficiency virus, hepatitis B, and hepatitis C transmission, arboviruses such as dengue, chikungunya, and the West Nile virus remain significant risks especially during outbreaks.

CASE REPORT

We report a rare case of dengue documented to be acquired through a blood transfusion, which resulted in severe thrombocytopenia prolonging admission in hospital in a neurosurgical patient.

RESULTS

The donor of one of the units of red blood cells presented with dengue fever 2 days after donating. Sanger sequencing confirmed DENV-2 (dengue virus, Serotype 2) in both the donor and the patient samples and showed 100% nucleotide sequence identity between the two viruses, confirming transfusion-transmitted dengue infection.

CONCLUSION

This case highlights the importance of arboviral screening of donor blood, especially for populations in endemic areas during outbreaks.

Plumbagin inhibits invasion and migration of breast and gastric cancer cells by downregulating the expression of chemokine receptor CXCR4

Background

Increasing evidence indicates that the interaction between the CXC chemokine receptor-4 (CXCR4) and its ligand CXCL12 is critical in the process of metastasis that accounts for more than 90% of cancer-related deaths. Thus, novel agents that can downregulate the CXCR4/CXCL12 axis have therapeutic potential in inhibiting cancer metastasis.

Methods

In this report, we investigated the potential of an agent, plumbagin (5-hydroxy-2-methyl-1, 4-naphthoquinone), for its ability to modulate CXCR4 expression and function in various tumor cells using Western blot analysis, DNA binding assay, transient transfection, real time PCR analysis, chromatin immunoprecipitation, and cellular migration and invasion assays.

Results

We found that plumbagin downregulated the expression of CXCR4 in breast cancer cells irrespective of their HER2 status. The decrease in CXCR4 expression induced by plumbagin was not cell type-specific as the inhibition also occurred in gastric, lung, renal, oral, and hepatocellular tumor cell lines. Neither proteasome inhibition nor lysosomal stabilization had any effect on plumbagin-induced decrease in CXCR4 expression. Detailed study of the underlying molecular mechanism(s) revealed that the regulation of the downregulation of CXCR4 was at the transcriptional level, as indicated by downregulation of mRNA expression, inhibition of NF-κB activation, and suppression of chromatin immunoprecipitation activity. In addition, using a virtual, predictive, functional proteomics-based tumor pathway platform, we tested the hypothesis that NF-κB inhibition by plumbagin causes the decrease in CXCR4 and other metastatic genes. Suppression of CXCR4 expression by plumbagin was found to correlate with the inhibition of CXCL12-induced migration and invasion of both breast and gastric cancer cells.

Conclusions

Overall, our results indicate, for the first time, that plumbagin is a novel blocker of CXCR4 expression and thus has the potential to suppress metastasis of cancer.

Missed diagnosis of influenza B virus due to nucleoprotein sequence mutations, Singapore, April 2011

A new influenza B variant was discovered in Singapore in April 2011 during diagnostic testing of a 3-year-old boy with respiratory symptoms. Influenza B virus was isolated from culture and confirmed by standard immunofluorescence testing, but was not detected by the routine, in-house influenza screening reverse-transcription polymerase chain reaction assay that targets the nucleoprotein (NP) gene. Subsequent sequencing investigations demonstrated that several other published assays targeting NP could also fail to detect this novel variant.

Missed diagnosis of influenza B virus due to nucleoprotein sequence mutations, Singapore, April 2011

A new influenza B variant was discovered in Singapore in April 2011 during diagnostic testing of a 3-year-old boy with respiratory symptoms. Influenza B virus was isolated from culture and confirmed by standard immunofluorescence testing, but was not detected by the routine, in-house influenza screening reverse-transcription polymerase chain reaction assay that targets the nucleoprotein (NP) gene. Subsequent sequencing investigations demonstrated that several other published assays targeting NP could also fail to detect this novel variant.

An international standardization programme towards the application of gene expression profiling in routine leukaemia diagnostics: the Microarray Innovations in LEukemia study prephase

Gene expression profiling has the potential to enhance current methods for the diagnosis of haematological malignancies. Here, we present data on 204 analyses from an international standardization programme that was conducted in 11 laboratories as a prephase to the Microarray Innovations in LEukemia (MILE) study. Each laboratory prepared two cell line samples, together with three replicate leukaemia patient lysates in two distinct stages: (i) a 5-d course of protocol training, and (ii) independent proficiency testing. Unsupervised, supervised, and r² correlation analyses demonstrated that microarray analysis can be performed with remarkably high intra-laboratory reproducibility and with comparable quality and reliability.

Compound heterozygous familial hypercholesterolemia and familial defective apolipoprotein B-100 produce exaggerated hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) and familial defective apolipoprotein B-100 (FDB) represent ligand-receptor disorders that are complementary. Individuals with both FH and FDB are unusual. We report a family with both disorders and the impact of the mutations on the phenotypes of the family members.

METHODS

We used single strand conformation polymorphism (SSCP) and denaturing gradient gel electrophoresis (DGGE) for genetic analysis of all 18 exons and the promoter region of the LDL receptor and DGGE for genetic analysis of the apolipoprotein B-100 (apo B-100) gene. The functional significance of the apo B-100 mutation was studied using a U937 cell proliferation assay. Fasting serum lipid profiles were determined for the index case and seven first-degree relatives.

RESULTS

One of the patient's sisters had a missense mutation (Asp(407)-->Lys) in exon 9 of the LDL receptor and a serum LDL-cholesterol concentration of 4.07 mmol/L. Four other first-degree relatives had hyperlipidemia but no LDL-receptor mutation. However, these subjects had a mutation of the apo B-100 gene (Arg(3500)-->Trp). The cell proliferation rate of U937 cells fed with LDL from other subjects with the same mutation was fourfold less than that of controls. The index case had both FH- and FDB-related mutations. Her serum LDL-cholesterol (9.47 mmol/L) was higher than all other relatives tested.

CONCLUSIONS

Existence of both FH and FDB should be considered in families with LDL-receptor mutations in some but not all individuals with hypercholesterolemia or when some individuals in families with FH exhibit exaggerated hypercholesterolemia.

Prevalence of primary aldosteronism among Asian hypertensive patients in Singapore

Recent studies using the ratio of plasma aldosterone concentration (PAC) to PRA as the screening test for primary aldosteronism in hypertensive populations suggested that the prevalence may be as high as 5-15%, with well over half of the subjects having normal serum potassium concentrations. Despite an increasing clinical awareness of this entity, many clinicians are reluctant to consider routine screening for primary aldosteronism in essential hypertensive patients because there are few community-based prevalence studies of primary aldosteronism in different populations. Furthermore, genetic and environmental differences may affect the prevalence and presentation of primary aldosteronism in distinct populations. This study was designed to determine the prevalence of primary aldosteronism in the predominantly Chinese population in Singapore. Three hundred and fifty unselected adult hypertensive patients attending two primary care clinics had random ambulatory measurements for PAC (nanograms per dL) and PRA (nanograms per mL/h). Serum urea, creatinine, and electrolyte measurements were obtained simultaneously. Subjects with renal insufficiency (serum creatinine, >140 micromol/L) and those treated with glucocorticoids or spironolactone were excluded. Screening was considered positive if the PAC: PRA ratio was more than 20 and the PAC was more than 15 ng/dL (>416 pmol/L). Primary aldosteronism was confirmed with the determination of PAC after 2 L saline administered iv over 4 h. Adrenal computed tomographic (CT) scans were performed in biochemically confirmed cases of primary aldosteronism. Further localization with adrenal vein sampling was carried out in selected patients with equivocal findings on adrenal CT scan. Sixty-three (18%) of the 350 hypertensive patients (215 women and 135 men; age range, 23-75 yr) were screened positive for primary aldosteronism. Only 13 of these 63 subjects (21%) were hypokalemic (serum potassium, <3.5 mmol/L). Confirmatory studies were carried out in 56 (89%) of the subjects with a positive PAC:PRA ratio. Using a PAC above 10 ng/dL (>277 pmol/L) after saline infusion as the diagnostic cut-off, 16 of the 56 patients had biochemically confirmed primary aldosteronism. Hypokalemia was found in 6 of the 16 patients (37.5%) with primary aldosteronism. Subtype evaluation with adrenal CT scan and adrenal vein sampling indicated that half of the patients with primary aldosteronism may have had potentially curable unilateral adrenal adenoma. Our data suggest that primary aldosteronism occurs in at least 5% of the adult Asian hypertensive population, and approximately half of these individuals may have potentially curable, unilateral, aldosterone-producing adrenal adenoma. Our findings also confirm the poor predictive value of hypokalemia in both the diagnosis and the exclusion of primary aldosteronism.

Effects of intragenic variability at 3 polymorphic sites of the apolipoprotein B gene on serum lipids and lipoproteins in a multiethnic Asian population

We determined the allelic (X+/X-, M+/M-, and E+/E-) distribution frequencies of the XbaI, MspI, and EcoRI restriction fragment length polymorphisms (RFLPs) in the apolipoprotein B gene in a control group of 374 healthy Chinese, Malays, and Indians and in a hyperlipidemic cohort of 131 Chinese patients. Covariability between the RFLPs and serum lipid, lipoprotein, and apolipoprotein concentrations was also studied. We found a lower frequency (average 0.0829) of the X+ allele and higher frequencies of the E+ (average 0.9452) and M+ (average 0.9772) alleles in our study population compared with frequencies reported in other populations. The 3 polymorphic sites did not contribute to significant variations in lipid levels (p > 0.1 in all cases). Also, there was no significant variation in genotype frequencies between the control subjects and the hyperlipidemic subjects. Despite their relative close proximity within the APOB gene sequence, the 3 polymorphic sites did not show any significant linkage disequilibrium. However, the presence of the X+ cutting site was in linkage disequilibrium with the Del allele of the 5' insertion-deletion polymorphism and the E-allele was in linkage disequilibrium with the 3' VNTR located near the 3' end of the coding region of the APOB gene.

Apolipoprotein B 5'-Ins/Del and 3'-VNTR polymorphisms in Chinese, malay and Indian singaporeans

The allele frequencies for the apolipoprotein B (apo B) 5'-Ins/Del and 3'-VNTR polymorphisms varied significantly (p < 0.01) among Singaporeans of Chinese, Malay and Indian descent. We calculated the unbiased expected heterozygosities for the 5'-Ins/Del polymorphism as 0.3357, 0.1984 and 0.2418, and for the 3'-VNTR as 0.5980, 0.5260 and 0.6749, respectively, in the Chinese, Malays and Indians. Compared to heterozygosities reported for other populations, the Singaporeans differed from most Caucasians in having significantly lower values but were closely related to other non-Caucasians. Thirteen alleles, with a bimodal distribution, were observed at the 3'-VNTR polymorphic locus; the alleles occurring most frequently among the Chinese and Malays were of 35 or 53 repeats, and among the Indians, of 37 or 47 repeats. The Del allele was associated with elevated serum cholesterol (p = 0.023), LDL-cholesterol (LDL-C) (p = 0.001) in the Chinese, and apo B (p = 0.007) in the Indians. Likewise, the larger 3'-VNTR alleles (> 41 repeats) were associated with raised cholesterol (p = 0.018), LDL-C (p = 0.025), and triglyceride (p = 0.001) in the Chinese. The two polymorphisms were not in significant linkage disequilibrium (D = -0.0029, p = 0.494) in the three ethnic groups.

The StuI polymorphism on exon 8 of the low density lipoprotein (LDL) receptor gene: prevalence and impact on serum lipid levels in an Asian cohort

A single nucleotide (A-->G) substitution in codon 370 (exon 8) of the low density lipoprotein (LDL) receptor gene results in loss of a StuI restriction site and an amino acid change (Ala370-->Thr) in the translated protein. This biallelic polymorphism has been associated with significant variations in plasma lipid concentrations in several Caucasian populations. We investigated its prevalence and impact on lipid metabolism in 539 Singaporeans of Chinese, Malay and Indian descent. The average frequency of 0.003 for the Thr370 allele and heterozygosity of 0.0056 were 10- to 20-fold lower than those reported in Caucasians (range 0.075 to 0.107). Distribution of the genotypes satisfied the Hardy-Weinberg equilibrium (chi 2 = 0.004, P = 0.948). We also found ethnic variation in the allele frequencies of Thr370 among the three races studied (0.009 in Indians, 0.007 in Malays, and 0.003 in Chinese). However, this needs to be confirmed with larger numbers. No significant correlation between genotype and serum concentrations of total cholesterol, triglyceride, high density lipoprotein (HDL)-cholesterol, LDL-cholesterol, lipoprotein(a), apolipoprotein A and apolipoprotein B was found in our study. This argues strongly against a major contribution or impact of this intragenic polymorphic locus on modulating the serum lipid profiles of the study subjects.

Denaturing gradient-gel electrophoresis screening of familial defective apolipoprotein B-100 in a mixed Asian cohort: two cases of arginine3500-->tryptophan mutation associated with a unique haplotype

The Arg-to-Trp substitution at codon 3500 in the apolipoprotein (apo) B-100 gene is established as a cause of familial defective apo B-100 (FDB), a functional mutation, resulting in reduced LDL receptor binding and manifest hypercholesterolemia. In a search for similar mutations in 163 Malaysians, we screened the putative receptor-binding region (codons 3456-3553) of the apo B-100 gene by PCR amplification and denaturing gradient-gel electrophoresis. Four single-base mutations were detected and confirmed by DNA sequencing. Two females, a Chinese and a Malay, had the same CGG3500-->TGG mutation, resulting in an Arg3500-to-Trp substitution. This is the second published report of such an independent mutation involving the same codon as the established Arg3500-to-Gln mutation. The two other mutations detected, CTT3517-->CTG and GCC3527-->GCT, resulted in degenerate codons with no amino acid substitutions. All four mutations were associated with a unique apo B haplotype, different from those found in Caucasian FDB patients but concurring with that previously reported for two other Asians with FDB.

The prevalence of isolated unconjugated hyperbilirubinaemia (Gilbert's syndrome) in subjects attending a health screening programme in Singapore

We retrospectively studied the prevalence of hyperbilirubinaemia in 1,296 consecutive subjects attending a hospital health screening programme over an eighteen-month period. Sixty-four subjects (5%) had elevated bilirubin levels. Forty-one subjects (3.2%) had isolated unconjugated hyperbilirubinaemia. These subjects probably had Gilbert's syndrome. Recognition of this common benign condition is important to avoid unnecessary investigations.

The Bio-Rad Diamat Analyser: an automated liquid chromatography system for haemoglobin A 1c (HbA 1c) determination

The measurement of glycosylated haemoglobin is a relatively new clinical tool, the assays for their determination having become increasingly available since their introduction in the late seventies. The clinical usefulness of these assays in the long-term monitoring of diabetics, especially the pregnant diabetics, appears to be generally accepted. There remains, however, considerable confusion amongst clinicians as to their reliability and interpretation. This is largely engendered by the diversity of the diagnostic methods in current usage, many of which are not specific for the HbA1c moiety, which is the subfraction comprising haemoglobin molecules with attached glucose molecules at the amino terminal valine sites, and which has been shown to be increased in the blood of diabetic patients. This paper describes an evaluation of one of the most specific methods currently available, using state-of-the-art technology. In addition to specificity, the method appears attractive in being precise, automatable (and thus operator-independent), and rapid.

Serum fructosamine determination as an index of glycaemic control: comparison between an automated and manual method, and the effect of serum storage

The measurement of glycated serum proteins was recently introduced as an alternative index of diabetic control of glycated haemoglobin. Manual and automated serum fructosamine colorimetric assays are available for glycated serum proteins determination. We have assessed two serum fructosamine assays, an automated and a manual method, and compared them with a glycated haemoglobin assay. We also studied the effect of serum storage on serum fructosamine concentrations. Serum fructosamine at four different concentrations measured by automated method gave an inner-assay of a 2% (range 1.29 - 1.56%) and an inter-assay variation of 3% (range 1.63-2.92%). There was a good correlation between the automated and manual methods, with a coefficient of r = 0.944. Serum fructosamine by either method is a sample assay to perform and is relatively inexpensive. With automated analysis, a large number of tests can be performed more rapidly. Comparing serum fructosamine with glycated haemoglobin, coefficients = 0.54 (automated) and r = 0.50 (manual) were obtained. An increase in serum fructosamine by 5-20% occurred when the assay is performed on serum samples stored for more than two weeks. It is recommended therefore that test should be performed soon after blood collection, preferably within one week.

Plasma lipid profiles: the expanding repertoire of tests, their clinical significance and pitfalls

Hyperlipidaemia and in particular hypercholesterolaemia is the best established cause of atherosclerosis. As awareness of this association grows amongst a more informed populace, there will be an increasing demand for plasma lipid screening. The traditional measurements of total plasma cholesterol and triglycerides for the assessment of hyperlipidaemia and its attendant CHD risk are now augmented by the availability of routine methods for separating and quantitating the different plasma lipoproteins, thus vastly improving diagnostic sensitivity. Because it is the major carrier of cholesterol in plasma and because the mechanistic evidence relating it to atherogenesis is strongest, elevated levels of the low density lipoproteins (LDL) are undesirable: high levels of high density lipoproteins (HDL), on the other hand, decrease the risk. Currently, plasma LDL and HDL concentrations are most frequently assessed by measuring their cholesterol content. However, the measurement of apolipoproteins, the protein components of the lipoproteins, may yet prove to be superior in predictive value, though they can hardly be expected to replace the older tests as first line screening tests by virtue of their relative costs and sophistication in terms of instrumentation and techniques. Additional diagnostic tests have been developed and newer ones will no doubt continue to evolve with further technical advancements and a better understanding of the pathogenesis of atheromas and vessel disease. The current lineup includes HDL subfractions, unique lipoproteins such as Lp(a) and beta-migrating VLDL and apolipoprotein E variants.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered fibrinolysis in DVT: influence of site of sampling

Alteration of the fibrinolytic system is considered to be important in the development of deep venous thrombosis (DVT). Using specific assays for tissue plasminogen activator (t-PA) activity, t-PA inhibitor (PAI) and t-PA antigen, we measured these activities in 16 women who developed DVT during their pregnancies. A group of 24 healthy females of comparable age was studied as controls. PAI was increased in 87% of these patients compared to the healthy controls. In some of these patients a defect in release of t-PA from vascular endothelium was found as well. The site at which blood was sampled for analysis appeared to be an important criterion in the ex vivo assessment of functional t-PA reserve and PAI levels, though relatively less so for the latter measurement. The unaffected lower limbs, relative to the unaffected upper limbs, showed an increase in PAI and a demonstrable decrease in t-PA release, both representing increased risk factors for rethrombosis. The affected lower limbs showed similar but more accentuated changes in these parameters.

Immunocytochemical localization of prolactin and relaxin C-peptide in human decidua and placenta

The production of PRL by the human decidua is generally accepted, but the production of relaxin by this tissue is not. The two hormones were localized in decidual tissue using the avidin-biotin immunoperoxidase procedure with antisera to human PRL and to a synthetic 14-amino acid sequence of the connecting peptide of human relaxin (hCp14). The object of using the hCp14 antiserum was to verify relaxin production by the detection of C-peptide and/or prorelaxin. Cells of the parietal decidua adherent to the fetal membranes stained with both antisera, and immunostaining for both hormones in the same cell was seen. Also, the decidua-like cells of the placental basal plate stained with both antisera. The chorionic cytotrophoblast stained with the antiserum to hCp14, but not the antiserum to human PRL, whereas the placental syncytiotrophoblast stained for PRL and/or human placental lactogen (hPL), but not hCp14. The PRL staining in all tissues was lost when anti-PRL serum absorbed with human placental lactogen (hPL) was used. This finding suggests that the antiserum to PRL could not distinguish between PRL and hPL. It appears, therefore, that the parietal decidua cells and the decidua-like cells of the placental basal plate may be capable of producing both relaxin and PRL, while the syncytiotrophoblast produces hPL and possibly PRL.

The human fetal membranes: a target tissue for relaxin

The purpose of this study was to adduce further evidence for a paracrine role for human decidual relaxin (Rlx) in the remodelling of collagen in the fetal membranes in the peripartal period. The binding of [125I]porcine Rlx to membrane-enriched fractions from fetal membranes as well as from dispersed cells from the fetal membranes was used to demonstrate the presence of specific Rlx receptors. Rlx added in vitro to cultured amnion/chorion cells increased the release of plasminogen activator and collagenase into the medium. Rlx had no effect on the release of beta-glucuronidase. An in vivo correlate of these in vitro results was obtained, the detection of plasminogen activator and collagenase in amniotic fluids. The active fraction of collagenase was increased in amniotic fluids collected after spontaneous rupture of the membranes. PRL, hCG, estrogen, and progesterone added in equimolar amounts to cultured amnion/chorion cells from elective cesarean sections and normal term deliveries also effected the release of plasminogen activator and collagenase. The greatest effects were found in cells from cesarean section tissue, in terms of the stimulation of plasminogen activator release by Rlx and PRL and of collagenase release by prostaglandin F2 alpha and, to a lesser extent, by Rlx, PRL, and hCG. We conclude that human fetal membranes are targets for a number of hormones, including the decidual paracrine hormones Rlx, PRL, and prostaglandin F2 alpha as well as estrogen, progesterone, and hCG. These hormones act to release or inhibit the enzymes involved in collagen breakdown before rupture of the fetal membranes.

Immunocytochemical localization of relaxin in human decidua and placenta

Specimens from 20 human term placentas were stained with 4 different antisera produced against porcine relaxin (Rlx) using the avidin-biotin immunoperoxidase procedure. Cells of the parietal decidua adherent to the fetal membranes, cells of the chorionic cytotrophoblast, as well as cells of the placental basal plate consistently stained with all 4 anti-Rlx sera. Occasionally, Rlx was detected in epithelial cells lining the amniotic membrane. The syncytiotrophoblast stained for Rlx in 2 specimens only. This response was seen only in syncytiotrophoblast that lined villi in close proximity to the basal plate. Syncytiotrophoblast of the chorionic villi either did not stain at all or gave very weak positive immunostaining with the anti-Rlx sera in all specimens. No difference was noted in staining patterns among placentas delivered by elective cesarean section or vaginal delivery.

Relaxin stimulates collagenase and plasminogen activator secretion by dispersed human amnion and chorion cells in vitro

Dispersed cells from human amnion and chorion were cultured with and without relaxin. The addition of this hormone caused an increased secretion of both collagenase and plasminogen activator into the culture medium over a 32 h period, but had no effect on proteoglycanase or beta-glucuronidase secretion. The increase in plasminogen activator was dose-related to the amount of relaxin added in vitro. The results show that the fetal membranes are a novel target tissue for relaxin in the human, and suggest that relaxin in vivo may cause a similar release of collagenolytic enzymes, leading to the weakening and eventual rupture of the fetal membranes.