No abstract

Plasmodium falciparum-infected erythrocytes often are sequestered in the placenta and stimulate the accumulation of maternal mononuclear cells. In this study, the role that chemokines and cytokines play in mediating the inflammatory response was investigated. Placental parasites elicited a statistically significant increase in the levels of interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-10, in plasma collected from the intervillous space. Explants of fetal tissue from malaria-positive placentas also secreted significantly enhanced amounts of IFN-gamma. Culture supernatant of maternal intervillous leukocytes obtained from infected placentas contained significantly higher levels of TNF-alpha, IL-10, monocyte chemotactic protein-1, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, and IFN-gamma inducible protein-10 than did cultures of white blood cells obtained from uninfected placentas. Taken together, these results show that both fetal and maternal cells secrete inflammatory and immunoregulatory cytokines in response to P. falciparum and suggest that beta-chemokines produced by maternal cells contribute to the accumulation of macrophages in the intervillous space.

Between 1996 and 2001, the prevalence of placental malaria in pregnant women living in Yaounde, Cameroon and its effect on pregnancy outcome were evaluated with respect to gravidity and maternal age. Results showed that 19.9% of the women had placental malaria at delivery. After adjusting for relevant covariates, the major risk factor for placental malaria was an age < 25 years old. Placental malaria significantly increased the prevalence of anemia in women regardless of gravidity or age. In addition, the mean infant birth weight was lower and the percentage of pre-term deliveries (PTDs) and low birth weight (LBW) babies were higher in primigravidae and women < 20 years of age who had placental malaria. However, in a multivariate regression model taking relevant covariates into consideration, the major risk factor for PTDs was maternal anemia, and maternal anemia as well as first and second pregnancies were important risk factors for LBW babies.

Polymerase chain reaction (PCR)-based methods were used to investigate malaria in pregnant women residing in Yaounde, Cameroon. Microscopy and species-specific PCR-based diagnosis show that at delivery 82.4% of the women were infected with Plasmodium falciparum (27.5% blood-smear positive and 54.9% submicroscopic infections). The prevalence of P. malariae and P. ovale was 7.6% and 2.5%, respectively, with 9.4% infected with more than one species. Based on genotyping of the merozoite surface protein 1 (msp-1) and msp-2 alleles, the mean number of genetically different P. falciparum parasites in peripheral blood was 3.4 (range = 1-9) and 3.5 (range 1-8) in the placenta. Plasmodium falciparum detected by microscopy and PCR as well as mixed-species infections were significantly higher in women < or = 20 years old and paucigravidae, but maternal anemia was associated only with microscopic detection of parasites. Neither submicroscopic infections nor number of parasite genotypes decreased significantly with age or gravidity. Thus, pregnancy-associated immunity helps reduce malaria to submicroscopic levels, but does not reduce the number of circulating parasite genotypes.

Antibodies to Plasmodium falciparum are classically measured using the enzyme-linked immunosorbent assay (ELISA). Although highly sensitive, this technique is labor-intensive when large numbers of samples must be screened against multiple antigens. The suspension array technology (SAT) might be an alterative to ELISA, as it allows measurement of antibodies against multiple antigens simultaneously with a small volume of sample. This study sought to adapt the new SAT multiplex system for measuring antibodies against nine malarial vaccine candidate antigens, including recombinant proteins from two variants of merozoite surface protein 1, two variants of apical merozoite antigen 1, erythrocyte binding antigen 175, merozoite surface protein 3, and peptides from the circumsporozoite protein, ring erythrocyte surface antigen, and liver-stage antigen 1. Various concentrations of the antigens were coupled to microspheres with different spectral addresses, and plasma samples from Cameroonian adults were screened by SAT in mono-and multiplex formats and by ELISA. Optimal amounts of protein required to perform the SAT assay were 10-to 100-fold less than that needed for ELISA. Excellent agreement was found between the single and multiplex formats (R > 0.96), even when two variants of the same antigen were used. The multiplex assay was rapid, reproducible, required less than 1 l of plasma, and had a good correlation with ELISA. Thus, SAT provides an important new tool for studying the immune response to malaria rapidly and efficiently in large populations, even when the amount of plasma available is limited, e.g., in studies of neonates or finger-prick blood.