Circulating Soluble Endoglin Levels in Pregnant Women in Cameroon and Malawi—Associations with Placental Malaria and Fetal Growth Restriction

Placental infections with Plasmodium falciparum are associated with fetal growth restriction resulting in low birth weight (LBW). The mechanisms that mediate these effects have yet to be completely described; however, they are likely to involve inflammatory processes and dysregulation of angiogenesis. Soluble endoglin (sEng), a soluble receptor of transforming growth factor (TGF)-β previously associated with preeclampsia in pregnant women and with severe malaria in children, regulates the immune system and influences angiogenesis. We hypothesized that sEng may play a role in development of LBW associated with placental malaria (PM). Plasma levels of sEng were measured in women (i) followed prospectively throughout pregnancy in Cameroon (n = 52), and (ii) in a case-control study at delivery in Malawi (n = 479). The relationships between sEng levels and gravidity, peripheral and placental parasitemia, gestational age, and adverse outcomes of PM including maternal anemia and LBW were determined. In the longitudinal cohort from Cameroon, 28 of 52 women (54%) experienced at least one malaria infection during pregnancy. In Malawi we enrolled two aparasitemic gravidity-matched controls for every case with PM. sEng levels varied over the course of gestation and were significantly higher in early and late gestation as compared to delivery (P<0.006 and P<0.0001, respectively). Circulating sEng levels were higher in primigravidae than multigravidae from both Cameroon and Malawi, irrespective of malarial infection status (p<0.046 and p<0.001, respectively). Peripheral parasitemia in Cameroonian women and PM in Malawian women were each associated with elevated sEng levels following correction for gestational age and gravidity (p = 0.006 and p = 0.033, respectively). Increased sEng was also associated with the delivery of LBW infants in primigravid Malawian women (p = 0.017); the association was with fetal growth restriction (p = 0.003) but not pre-term delivery (p = 0.286). Increased circulating maternal sEng levels are associated with P. falciparum infection in pregnancy and with fetal growth restriction in primigravidae with PM

Congenital Exposure to Plasmodium falciparum Antigens: Prevalence and Antigenic Specificity of In Utero-Produced Antimalarial Immunoglobulin M Antibodies

Congenital Plasmodium falciparum malaria in newborns is uncommon in sub-Saharan Africa. A significant number of infants, however, become infected or exposed to malarial antigens either in utero or at delivery and have the potential to produce antimalarial antibodies and memory cells before their first natural infection. In Yaounde, Cameroon, parasite-specific immunoglobulin M (IgM) was detected in 14% of cord blood samples. The IgM antibodies reacted with a wide range of asexual-stage antigens, with each newborn having its own unique pattern of IgM reactivity. PCR-based detection and genotyping of cord blood parasites found that the prevalence, total number of parasite genotypes, and complexity of infection were higher in newborns who had produced antimalarial IgM than those who had not. Maternal placental malaria and anemia were associated with the production of P. falciparum-specific IgM by the fetus. The effect of early immune priming on acquisition of immunity by infants is unknown and merits further investigation, since a significant proportion of Cameroonian newborns developed a humoral response to malaria before birth

Comparison of the specificity of antibodies to VAR2CSA in Cameroonian multigravidae with and without placental malaria:a retrospective case-control study

BACKGROUND: Antibodies (Ab) to VAR2CSA prevent Plasmodium falciparum-infected erythrocytes from sequestrating in the placenta, i.e., prevent placental malaria (PM). The specificity of Ab to VAR2CSA associated with absence of PM is unknown. Accordingly, differences in the specificity of Ab to VAR2CSA were compared between multigravidae with and without PM who had Ab to VAR2CSA. METHODS: In a retrospective case–control study, plasma collected from Cameroonian multigravidae with (n = 96) and without (n = 324) PM were screened in 21 assays that measured antibody levels to full length VAR2CSA (FV2), individual VAR2CSA DBL domains, VAR2CSA domains from different genetic backgrounds (variants), as well as proportion of high avidity Ab to FV2. RESULTS: Multigravidae with and without PM had similar levels of Ab to FV2, the six VAR2CSA DBL domains and different variants, while the proportion of high avidity Ab to FV2 was significantly higher in women without PM at delivery (p = 0.0030) compared to women with PM. In a logistic regression model adjusted for gravidity and age, the percentage of high avidity Ab to FV2 was associated with reduced likelihood of PM in multigravidae. A 5 % increase in proportion of high avidity Ab to FV2 was associated with a nearly 15 % lower likelihood of PM. CONCLUSION: Ab avidity to FV2 may be an important indicator of immunity to PM. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12936-015-1023-6) contains supplementary material, which is available to authorized users

Timing of the human prenatal antibody response to <i>Plasmodium falciparum</i> antigens

<div><p><i>Plasmodium falciparum</i> (Pf)-specific T- and B-cell responses may be present at birth; however, when during fetal development antibodies are produced is unknown. Accordingly, cord blood samples from 232 preterm (20–37 weeks of gestation) and 450 term (≥37 weeks) babies were screened for IgM to Pf blood-stage antigens MSP1, MSP2, AMA1, EBA175 and RESA. Overall, 25% [95% CI = 22–28%] of the 682 newborns were positive for IgM to ≥1 Pf antigens with the earliest response occurring at 22 weeks. Interestingly, the odds of being positive for cord blood Pf IgM decreased with gestational age (adjusted OR [95% CI] at 20–31 weeks = 2.55 [1.14–5.85] and at 32–36 weeks = 1.97 [0.92–4.29], with ≥37 weeks as reference); however, preterm and term newborns had similar levels of Pf IgM and recognized a comparable breadth of antigens. Having cord blood Pf IgM was associated with placental malaria (adjusted OR [95% CI] = 2.37 [1.25–4.54]). To determine if <i>in utero</i> exposure occurred via transplacental transfer of Pf-IgG immune complexes (IC), IC containing MSP1 and MSP2 were measured in plasma of 242 mother-newborn pairs. Among newborns of IC-positive mothers (77/242), the proportion of cord samples with Pf IC increased with gestational age but was not associated with Pf IgM, suggesting that fetal B cells early in gestation had not been primed by IC. Finally, when cord mononuclear cells from 64 term newborns were cultured <i>in vitro</i>, only 11% (7/64) of supernatants had Pf IgM; whereas, 95% (61/64) contained secreted Pf IgG. These data suggest fetal B cells are capable of making <i>Pf</i>-specific IgM from early in the second trimester and undergo isotype switching to IgG towards term.</p></div

Breadth of Pf IgM response in different gestational age groups.

<p>The 169 Cameroonian newborns who were cord IgM+ to ≥ 1 Pf Ag were included, i.e., n = 75 preterm [n = 14 (20–27 weeks), n = 19 (28–31 weeks), n = 42 (32–36 weeks)] and n = 95 term. For each GA group, the bars show the proportion of Ab-positive newborns who produced IgM recognizing 1, 2, 3, 4 and 5 Pf blood-stage Ags. Whiskers represent the 95% confidence interval of proportions. There were no significant (ns) differences in responders to multiple antigens across GA groups.</p

Influence of gestational age and placental malaria on production of Pf IgM to MSP1 and MSP2 <i>in utero</i>.

<p>Influence of gestational age and placental malaria on production of Pf IgM to MSP1 and MSP2 <i>in utero</i>.</p

Timing of fetal exposure to maternal immune complexes (IC).

<p>Peripheral plasma samples of 77/242 mothers had IC containing MSP1 or MSP2. Cord plasma IC data of the 77 corresponding newborns were analyzed for materno-fetal IC transfer. (<b>A</b>) The percentage of cord blood samples with IC increased with GA, especially after 31 wks. (<b>B</b>) Average levels of Pf-specific IC in cord plasma. P values were calculated using Kruskal-Wallis test with post-test for trend: *p<0.01 and **p<0.001. The 20–27 wks group was excluded in the analysis because of few (<3) data points.</p

Descriptive characteristics of the 682 Cameroonian preterm and term newborns whose samples were used for plasma antibody studies.

<p>Descriptive characteristics of the 682 Cameroonian preterm and term newborns whose samples were used for plasma antibody studies.</p

Model for the timing of fetal exposure and Ab responses to Pf Ags.

<p>The model is an estimate of the likelihood of fetal exposure, and fetal Ab response, to Pf through the second and third trimesters of gestation. On the horizontal gray scales, dark shade = high; and light shade = low. Infected erythrocytes can sequester in the placenta from ~12 wks of gestation when the IVS are formed. The incidence of maternal malaria and the density of Pf parasites in the IVS are high during the second trimester, thus increasing the risk of exposure to Pf in utero. At this time of gestation, the fetus is already capable of making Pf-specific IgM. As gestation advances, fetal B cells receive secondary exposures to Pf Ags and class-switching to Pf IgG production occurs. The proportion of fetuses with Pf IgM drops rapidly at term while the proportion of Pf IgG responders increases to almost 95% at 40 weeks.</p

Timing of the prenatal Pf IgM response.

<p>(<b>A</b>) The percent of newborns (n = 682) positive for IgM to Pf Ags was stratified by gestational age category. The proportion of IgM+ newborns decreased with gestational age, Chi-square test for trend: MSP1 (i.e., positive for IgM to the 3D7 or FVO variant of MSP1), p = 0.008; MSP2 (3D7 or FC27), p = 0.0006; AMA1, ns; EBA175, ns; RESA, p = 0.002; and ≥1 Pf Ag, p = 0.001. For clarity of figures, confidence intervals of proportions are provided in the text but not on the figure. (<b>B</b>) Amount of IgM Ab present for newborns who were Ab positive for the specified antigen. Average IgM levels did not differ significantly with GA for any of the antigens (Kruskal-Wallis).</p