Gravidin, an endogenous inhibitor of phospholipase A2 activity, is a secretory component of IgA

Mechanisms of progesterone action in inhibiting prematurity

Progesterone is a steroid hormone that plays an integral role in each step of human pregnancy. In early pregnancy, progesterone produced by the corpus luteum is critical to the maintenance of early pregnancy until the placenta takes over this function at 7 to 9 weeks of gestation, hence its name (pro-gestational steroid hormone). The role of progesterone in later pregnancy, however, is less clear. It has been proposed that progesterone may be important in maintaining uterine quiescence in the latter half of pregnancy by limiting the production of stimulatory prostaglandins and inhabiting the expression of contraction-associated protein genes within the myometrium. Although systemic progesterone withdrawl may not correlate directly with the onset of labour in humans, there is increasing evidence to suggest that progesterone exerts its influence indirectly via a 'functional' withdrawl at the level of the uterus. The molecular mechanisms by which progesterone is able to maintain uterine quiescence and prevent preterm birth in some high-risk women are not clear. Six putative mechanisms have been proposed in the literature by both US and other investigators and are explored in this review.

Defective implantation and placentation: laying the blueprint for pregnancy complications

Normal implantation and placentation is critical for pregnancy success. Many pregnancy-related complications that present late in gestation (such as pre-eclampsia and preterm labour) appear to have their origins early in pregnancy with abnormalities in implantation and placental development. Implantation is characterized by invasion of the maternal tissues of the uterus by fetal trophoblast, and the degree to which trophoblast invades these tissues appears to be a major determinant of pregnancy outcome. Excessive invasion can lead to abnormally firm attachment of the placenta to the myometrium (placenta accreta) with increased maternal and perinatal morbidity. Inadequate invasion, specifically restricted endovascular invasion, has been implicated in the pathophysiology of such conditions as pre-eclampsia (gestational proteinuric hypertension), preterm premature rupture of membranes, preterm labour, and intrauterine growth restriction. The molecular and cellular mechanisms responsible for implantation remain enigmatic. This review will include an overview of implantation followed by a discussion of a number of molecular mechanisms implicated in defective implantation and placentation including the role of decidual prostaglandins and haemorrhage in regulating trophoblast invasion. An improved understanding of the molecular mechanisms responsible for abnormal implantation and placentation will likely improve clinicians' abilities to treat disorders that occur along this continuum, including infertility, recurrent pregnancy loss, pre-eclampsia, and preterm birth.

Secretory component: a potential regulator of endometrial-decidual prostaglandin production in early human pregnancy

OBJECTIVE

We sought to investigate the production of secretory component, an inhibitor of phospholipase A(2), and prostaglandins by human endometrium-decidua.

STUDY DESIGN

The production of secretory component and prostaglandins by explants and dispersed glandular and stromal cells of secretory endometrium and first-trimester and term decidua were measured by enzyme-linked immunosorbent assay and radioimmunoassay, respectively.

RESULTS

Explants of first-trimester decidua produced significantly more secretory component and less prostaglandins than secretory endometrium. Immunohistochemical studies localized secretory component to epithelial glandular cells. At term, when fewer glandular cells are present, both secretory component and prostaglandin production were low. Exposure of first-trimester decidua to progesterone significantly increased secretory component production.

CONCLUSION

Secretory component and prostaglandins localize primarily to epithelial glandular cells in endometrium-decidua, and their production appears to be inversely correlated. The increase in secretory component by first-trimester decidua after progesterone stimulation may account for the down-regulation of endometrial prostaglandin synthesis after implantation, a process thought to be necessary for pregnancy success.

The role of the endogenous anti-inflammatory compound gravidin in pre-eclampsia

OBJECTIVES

The study's aims were to investigate the levels of gravidin, an endogenous phospholipase A2 inhibitor, in pregnancy and pre-eclampsia and to establish its effects on neutrophil function.

STUDY DESIGN

Serum samples were collected from 9 nonpregnant, 15 preeclamptic, and 10 healthy pregnant women and assayed for free gravidin by enzyme-linked immunosorbent assay. Neutrophil phospholipase A2 and respiratory burst activities were determined in the presence of isolated free gravidin by cellular arachidonic acid release and superoxide anion production.

RESULTS

Levels of free gravidin were higher in the healthy pregnant (36.1 +/- 5.5 ng/mL) and preeclamptic (17.8 +/- 2.8 ng/mL) groups than in the nonpregnant control group (3.9 +/- 0.5 ng/mL) and were significantly different between pregnancy groups (P <.01, Mann-Whitney U test). Free gravidin caused a concentration dependent decrease in N-formyl-methionyl-leucyl-phenylalanine-stimulated neutrophil arachidonic acid release (inhibitory concentration of 50% 25 nmol/L) and superoxide anion generation (inhibitory concentration of 50% 32 nmol/L).

CONCLUSIONS

Circulating levels of free gravidin are reduced in pre-eclampsia compared with normal pregnancy. This may encourage an increase in the respiratory burst of neutrophils in pre-eclampsia and could contribute to the oxidative stress and vascular damage that characterize this disease.

Regulation of the polymeric immunoglobulin receptor by water intake and vasopressin in the rat kidney

The polymeric immunoglobulin receptor (pIgR) transports polymeric immunoglobulins (IgA) from the basolateral to the apical surface of epithelial cells. At the apical surface, its amino-terminal domain, termed secretory component (SC), is proteolytically cleaved and released either unbound (free SC) or bound to IgA. We examined the effects of changes in water balance and vasopressin on the production and secretion of the pIgR in the rat kidney in vivo. Water deprivation induced a 2.7-fold increase in the pIgR mRNA and a 2.2-fold increase in intracellular pIgR protein compared with water-loaded animals. Physiological doses of desmopressin reproduced the effects of water deprivation on mRNA and intracellular protein levels, suggesting that pIgR expression may be regulated by a vasopressin-coupled mechanism. Secretion of free SC and secretory IgA in the urine, however, correlated directly with water intake and urine flow. These results suggest that hydration status and vasopressin may affect the mucosal immunity of the kidney by regulating at different steps the epithelial cell production and secretion of the polymeric immunoglobulin transporter/ secretory component.

Secretory component of immunoglobulin A in maternal serum and the prediction of preterm delivery

OBJECTIVE

Our purpose was to determine whether the secretory component of immunoglobulin A in maternal serum predicts delivery before 34 weeks' gestation.

STUDY DESIGN

Primigravid women of an urban population in New Zealand were recruited at booking into a prospective longitudinal nested case control study (n = 1651; after exclusions and withdrawals, n = 1511). Serum was collected at 8 to 12 weeks, 15 to 18 weeks, 21 to 24 weeks, 28 to 30 weeks, and 36 to 38 weeks of gestation and 6 weeks post partum. Concentrations of the secretory component of immunoglobulin A were determined by enzyme-linked immunosorbent assay in all women who were delivered preterm (n = 53) and in controls randomly selected from women delivered at > or =37 weeks' gestation (n = 178).

RESULTS

Serum concentrations of the secretory component of immunoglobulin A were similar in women delivered at term or preterm throughout pregnancy (n = 21 delivered at <34 weeks and n = 32 at 34 to 36.9 weeks, incidence 3.5%). Receiver-operator characteristic curves showed no discriminating ability of the secretory component of immunoglobulin A. Smokers had 50% higher concentrations than nonsmokers did (p < 0.0001 by analysis of variance).

CONCLUSION

The secretory component of immunoglobulin A in maternal serum does not predict preterm delivery in a low-risk population.

Neuroendocrine changes in systemic lupus erythematosus and Sjögren's syndrome

It has become clear that the neuroendocrine and immune systems are closely linked and interdependent. The exact mechanisms of this interaction are only beginning to be unravelled. The complexity of these connections may partly explain why the aetiopathogenesis of autoimmune diseases remains obscure and why genetic, hormonal, microbial, environmental, as well as a host of other factors, have all been put forward as explanations. What has become clear is that a number of neuroendocrine and hormonal factors have important immunomodulatory roles in health and disease.

Secretory component (polymeric immunoglobulin receptor) as an intrinsic inhibitor of biological functions of interferon gamma in keratinocytes

Secretory component (SC) acts as a transmembrane polymeric immunoglobulin receptor of epithelial cells and is known to bind to polymeric IgA and to contribute to the secretion of secretory IgA (sIgA). We describe a new biological function for free SC (FSC) by which the expression of intercellular adhesion molecule-1 (ICAM-1) and HLA-DR induced by interferon gamma (IFN gamma) is inhibited in human keratinocytes. This activity coincided with suppression of adenosine cyclic 3,5-monophosphate (cyclic AMP) production in keratinocytes. Keratinocytes produced SC after stimulation with IFN gamma and this production was suppressed by the addition of H-7 or propranolol. The addition of propranolol resulted in prolongation of ICAM-1 expression on keratinocytes induced by IFN gamma. These results suggest that endogenously produced SC, as well as exogenously added FSC, acts as an inhibitor of IFN gamma. Therefore, our results suggest that SC plays an antiinflammatory role in the pathogenesis of inflammatory skin diseases via inhibition in keratinocytes of IFN gamma induced expression of ICAM-1 and HLA-DR.

Decrease in human plasma gravidin levels after medical abortion

The aim of this study was to determine if loss of pregnancy is associated with a decrease in plasma levels of gravidin, a phospholipase inhibitor thought to maintain pregnancy. Blood was taken from 28 women in the first trimester of pregnancy who had requested an abortion. The progesterone receptor antagonist, RU-486 was given on Day 0 for termination of pregnancy. Plasma gravidin levels were measured on day 0 and on day 2 just before the patients were given misoprostol, a prostaglandin E1 analogue (600 micrograms). In a small group of patients, plasma measurements were continued up to 42 days. By day 2, plasma gravidin levels had fallen significantly (100% to 94%, p = 0.010 in a paired t-test). Following treatment with prostaglandins and pregnancy loss, plasma gravidin levels continued to fall until day 14 when the non pregnant level was reached at 80% of the pregnant level. We conclude that a decrease in plasma gravidin levels is associated with loss of pregnancy. This may occur because progesterone action is blocked.

Gravidin: an endogenous inhibitor of phospholipase A2

Gravidin is a recently discovered protein inhibitor of phospholipase A2 and therefore prostaglandin synthesis. Transformed or rapidly growing cells are unaffected by gravidin, but in slow-growing cells arachidonate release is inhibited. Gravidin may play a physiological role in pregnancy maintenance. This review summarizes our current knowledge of the properties and activity of gravidin.

Serum concentrations of secretory IgA in pregnancies delivering at term or preterm

Secretory component (SC) is a phospholipase A2 inhibitor possibly associated with pregnancy maintenance and in serum is bound either to IgA (sIgA) or IgM (sIgM). To determine if serum secretory component levels a) increase during pregnancy, b) fall as term approaches, c) are low in women who will deliver prematurely, serum sIgA was measured at "booking in" and related to weeks of gestation and length of gestation at subsequent noninduced delivery. Levels of sIgA increased during pregnancy; sIgA increased from a non-pregnant value of 1.6 nM +/- 0.2 (mean +/- SEM) to 2.8 nM +/- 0.3 at the end of the second trimester, then fell significantly between 31-34 weeks. Delivery before 37 weeks was associated with significantly reduced serum sIgA levels, particularly in women who delivered before 32 weeks and in whom sIgA concentrations were similar to those of nonpregnant women.

Decreased inhibition by gravidin of arachidonate release from transformed compared to nontransformed cells

1. Gravidin (a phospholipase A2 inhibitor) reduced the release of arachidonic acid from human lymphocytes by 51% at 10(-8) M. 2. Under normal culture conditions, nanomolar gravidin caused a significant reduction in the release of free arachidonic acid from human lymphocytes or nontransformed fibroblasts but in transformed cells, nanomolar gravidin was ineffective. 3. Inhibition of arachidonate release appeared to be related to rate of growth as inhibitory effects of gravidin on Jurkat cells and HL-29 cells could be observed if the cells were cultured under conditions where DNA synthesis was low. 4. The reported disparate effects of lipocortin on cell phospholipase A2 activity may be reconciled if DNA synthesis is investigated.