Multiplexing detection of IgG against Plasmodium falciparum pregnancy-specific antigens

Background

Pregnant women exposed to Plasmodium falciparum generate antibodies against VAR2CSA, the parasite protein that mediates adhesion of infected erythrocytes to the placenta. There is a need of high-throughput tools to determine the fine specificity of these antibodies that can be used to identify immune correlates of protection and exposure. Here we aimed at developing a multiplex-immunoassay to detect antibodies against VAR2CSA antigens.

Methods and findings

We constructed two multiplex-bead arrays, one composed of 3 VAR2CSA recombinant-domains (DBL3X, DBL5Ɛ and DBL6Ɛ) and another composed of 46 new peptides covering VAR2CSA conserved and semi-conserved regions. IgG reactivity was similar in multiplexed and singleplexed determinations (Pearson correlation, protein array: R² = 0.99 and peptide array: R² = 0.87). IgG recognition of 25 out of 46 peptides and all recombinant-domains was higher in pregnant Mozambican women (n = 106) than in Mozambican men (n = 102) and Spanish individuals (n = 101; p<0.05). Agreement of IgG levels detected in cryopreserved plasma and in elutions from dried blood spots was good after exclusion of inappropriate filter papers. Under heterogeneous levels of exposure to malaria, similar seropositivity cutoffs were obtained using finite mixture models applied to antibodies measured on pregnant Mozambican women and average of antibodies measured on pregnant Spanish women never exposed to malaria. The application of the multiplex-bead array developed here, allowed the assessment of higher IgG levels and seroprevalences against VAR2CSA-derived antigens in women pregnant during 2003–2005 than during 2010–2012, in accordance with the levels of malaria transmission reported for these years in Mozambique.

Conclusions

The multiplex bead-based immunoassay to detect antibodies against selected 25 VAR2CSA new-peptides and recombinant-domains was successfully implemented. Analysis of field samples showed that responses were specific among pregnant women and dependent on the level of exposure to malaria. This platform provides a high-throughput approach to investigating correlates of protection and identifying serological markers of exposure for malaria in pregnancy.

Changing Trends in P. falciparum Burden, Immunity, and Disease in Pregnancy

BACKGROUND

Prevention of reinfection and resurgence is an integral component of the goal to eradicate malaria. However, the adverse effects of malaria resurgences are not known.

METHODS

We assessed the prevalence of Plasmodium falciparum infection among 1819 Mozambican women who delivered infants between 2003 and 2012. We used microscopic and histologic examination and a quantitative polymerase-chain-reaction (qPCR) assay, as well as flow-cytometric analysis of IgG antibody responses against two parasite lines.

RESULTS

Positive qPCR tests for P. falciparum decreased from 33% in 2003 to 2% in 2010 and increased to 6% in 2012, with antimalarial IgG antibody responses mirroring these trends. Parasite densities in peripheral blood on qPCR assay were higher in 2010-2012 (geometric mean [±SD], 409±1569 genomes per microliter) than in 2003-2005 (44±169 genomes per microliter, P=0.02), as were parasite densities in placental blood on histologic assessment (50±39% of infected erythrocytes vs. 4±6%, P<0.001). The malaria-associated reduction in maternal hemoglobin levels was larger in 2010-2012 (10.1±1.8 g per deciliter in infected women vs. 10.9±1.7 g per deciliter in uninfected women; mean difference, -0.82 g per deciliter; 95% confidence interval [CI], -1.39 to -0.25) than in 2003-2005 (10.5±1.1 g per deciliter vs. 10.6±1.5 g per deciliter; difference, -0.12 g per deciliter; 95% CI, -0.67 to 0.43), as was the reduction in birth weight (2863±440 g in women with past or chronic infections vs. 3070±482 g in uninfected women in 2010-2012; mean difference, -164.5 g; 95% CI, -289.7 to -39.4; and 2994±487 g vs. 3117±455 g in 2003-2005; difference, -44.8 g; 95% CI, -139.1 to 49.5).

CONCLUSIONS

Antimalarial antibodies were reduced and the adverse consequences of P. falciparum infections were increased in pregnant women after 5 years of a decline in the prevalence of malaria. (Funded by Malaria Eradication Scientific Alliance and others.).

Efficacy and safety of intermittent preventive treatment with sulfadoxine-pyrimethamine for malaria in African infants: a pooled analysis of six randomised, placebo-controlled trials

BACKGROUND

Intermittent preventive treatment (IPT) is a promising strategy for malaria control in infants. We undertook a pooled analysis of the safety and efficacy of IPT in infants (IPTi) with sulfadoxine-pyrimethamine in Africa.

METHODS

We pooled data from six double-blind, randomised, placebo-controlled trials (undertaken one each in Tanzania, Mozambique, and Gabon, and three in Ghana) that assessed the efficacy of IPTi with sulfadoxine-pyrimethamine. In all trials, IPTi or placebo was given to infants at the time of routine vaccinations delivered by WHO's Expanded Program on Immunization. Data from the trials for incidence of clinical malaria, risk of anaemia (packed-cell volume <25% or haemoglobin <80 g/L), and incidence of hospital admissions and adverse events in infants up to 12 months of age were reanalysed by use of standard outcome definitions and time periods. Analysis was by modified intention to treat, including all infants who received at least one dose of IPTi or placebo.

FINDINGS

The six trials provided data for 7930 infants (IPTi, n=3958; placebo, n=3972). IPTi had a protective efficacy of 30.3% (95% CI 19.8-39.4, p<0.0001) against clinical malaria, 21.3% (8.2-32.5, p=0.002) against the risk of anaemia, 38.1% (12.5-56.2, p=0.007) against hospital admissions associated with malaria parasitaemia, and 22.9% (10.0-34.0, p=0.001) against all-cause hospital admissions. There were 56 deaths in the IPTi group compared with 53 in the placebo group (rate ratio 1.05, 95% CI 0.72-1.54, p=0.79). One death, judged as possibly related to IPTi because it occurred 19 days after a treatment dose, was subsequently attributed to probable sepsis. Four of 676 non-fatal hospital admissions in the IPTi group were deemed related to study treatment compared with five of 860 in the placebo group. None of three serious dermatological adverse events in the IPTi group were judged related to study treatment compared with one of 13 in the placebo group.

INTERPRETATION

IPTi with sulfadoxine-pyrimethamine was safe and efficacious across a range of malaria transmission settings, suggesting that this intervention is a useful contribution to malaria control.

FUNDING

Bill & Melinda Gates Foundation.

System and market failures: the unavailability of magnesium sulphate for the treatment of eclampsia and pre-eclampsia in Mozambique and Zimbabwe

Low cost and effective drugs, such as magnesium sulphate, need to be included in initiatives to improve access to essential medicines in Africa

Influence of salt intake on the daytime-nighttime blood pressure variation in normotensive and hypertensive black subjects

OBJECTIVE

To evaluate the influence of different salt-intake regimens on the circadian rhythm of blood pressure (daytime-night-time relationship) in normotensive and hypertensive black subjects with different patterns of salt sensitivity.

METHODS

Randomized, cross-over study. Twenty normotensive (NT) and 27 hypertensive (HT) black subjects were kept on a low-sodium diet (30 mmol sodium/d, LS) and on a high-sodium diet (300 mmol sodium/d, HS) for 1 week each. On the last day of each regimen, 24 hour ambulatory blood pressure monitoring was performed.

RESULTS

Eight normotensives were classified as salt-sensitive (SS), all with haptoglobin phenotypes (FeHap) 1,1 or 1,2, and 12 as salt resistant (SR), 5 with FeHap 2,2. Seventeen hypertensives were classified as SS, all with FeHap 1,1 or 1,2, and 11 as SR, 2 with FeHap 2,2. Salt sensitivity criterium was: difference > 5 mmHg of 24 h mean blood pressure from low sodium to high sodium. The pattern of daytime-nighttime blood pressure relationship between LS and HS was only modified (respectively from dipper to non-dipper) in HT-SS, but not in NT-SS, NT-SR and HT-SR. The percentual drop in nighttime mean blood pressure was about 10% in HT-SR and in NT-SR either under LS or HS. In NT-SS, the percentual night-time drop in mean blood pressure was lower than that of NT-RS (i.e. about 7-8%), but it was not different on LS and on HS. In contrast, in HT-SS, the percentual nighttime drop in mean blood pressure on HS (6%) was significantly lower than that on LS (10%, p < 0.01). In the 27 HT, but not in the NT, changes in the nocturnal drop in mean blood pressure induced by salt restriction correlated positively with the degree of salt sensitivity (r = 0.45, p < 0.05).

CONCLUSIONS

In black subjects, the pattern of nighttime-daytime blood pressure relationship appears to be modified from LS to HS diets (or vice-versa) only in SS hypertensive subjects, but neither in NT-SS nor in NT-SS and HT-SR. Only in HT-SS, but not in the other groups, salt restriction shifts the circadian rhythm of blood pressure from a non-dipper to a dipper pattern. We conclude that in black salt-sensitive hypertensives, salt restriction improves the circadian rhythm of blood pressure. This may have important therapeutic consequences on target organ damage associated with non-dipper patterns.

Nifedipine-retard versus nifedipine-capsules for the therapy of hypertensive crisis in black patients

In a randomized parallel-group placebo-controlled study, we compared the short-term hypotensive efficacy and the safety of a single administration of nifedipine-retard (20-mg tablets) with that of two administrations 6 h apart of nifedipine capsules (10 mg) in 10 and 11 black patients, respectively, with acute severe hypertension. Both groups had similar pretreatment blood-pressure (BP) values. Blood pressure was recorded at 10-min intervals for 12 h by using an automated device. In the first 3 h of treatment, nifedipine capsules induced a faster and greater hypotensive effect than nifedipine retard, which was associated with an increase in heart rate. At 2 h after treatment, nifedipine capsules decreased BP to levels (159 +/- 5/105 +/- 3 mm Hg) that were significantly lower than those reached by nifedipine-retard (175 +/- 4/118 +/- 4 mm Hg; p < 0.05). Both preparations induced a similar maximal BP decrease of approximately 30% of the placebo values, but the peak decrease of BP occurred significantly later with nifedipine-retard (283 +/- 31 min after administration) than with nifedipine capsules (100 +/- 14 min; p < 0.01). Four hours after administration, the hypotensive effect of nifedipine capsules was blunted, and a second administration was necessary, whereas nifedipine-retard reduced BP slowly and continuously for < or =12 h and more smoothly. Flush and headache were more frequently found with nifedipine capsules. We conclude that in black patients with hypertensive crisis, nifedipine capsules produce an abrupt decrease in BP that may be potentially harmful. Thus for patients suitable for treatment with nifedipine, nifedipine-retard is preferable because it effectively reduces BP for > or =12 h while achieving a rapid enough effect without critical short-term decreases in BP.

Efficacy of captopril and nifedipine in black and white patients with hypertensive crisis

We examined the antihypertensive efficacy of: (1) sublingual-oral single doses of captopril (25 mg) and nifedipine-capsules (10 mg) in 9 + 9 white patients and in 9 + 8 black patients with hypertensive crisis; and (2) a single oral dose of the slow-acting preparation of nifedipine-retard (20 mg) in another 10 black patients. Blood pressure (BP) was assessed at 10 min intervals for 6 h after administration. After 6 h, the BP falls induced by these drugs were still significantly lower than the baseline placebo values. Hypotensive effect of nifedipine-capsules was established more rapidly than that of captopril in both white and black patients, and of nifedipine-retard in black patients. Considering the area under the curve of BP values during the 6-h treatment, the overall hypotensive effect of nifedipine-capsules was similar to captopril in white patients, but significantly more pronounced than captopril and nifedipine-retard in black patients. In white patients similar maximal drops of BP (mean+/-s.e.m.) were obtained with nifedipine-capsules (71+/-4/52+/-4 mm Hg) and with captopril (69+/-4/50+/-3 mm Hg). In black patients the maximal drop of BP of nifedipine-capsules (70+/-4/52+/-4 mm Hg) was greater (P < 0.02) than that of captopril (48+/-4/32+/-3 mm Hg) but similar to that of nifedipine-retard (71+/-4/49+/-4 mm Hg). However, in contrast to nifedipine-capsules and captopril, nifedipine-retard produced a slower drop in BP. The time of peak drop in BP of both nifedipine-capsules and captopril occurred within the first 2 h whereas with nifedipine-retard it occurred only between 4 and 6 h after administration. Fewer patients reported side effects with nifedipine-retard as compared with the other two preparations. We conclude that single doses of captopril and nifedipine reduces BP for at least 6 h in both white and black patients with hypertensive crisis, but nifedipine is more potent than captopril in black patients. The slow release form of nifedipine-retard effectively and safely lowers BP while achieving a rapid enough effect without the critical rapid falls in BP that occur with nifedipine-capsules.