A Plasmodium Whole-Genome Synteny Map: Indels and Synteny Breakpoints as Foci for Species-Specific Genes

Whole-genome comparisons are highly informative regarding genome evolution and can reveal the conservation of genome organization and gene content, gene regulatory elements, and presence of species-specific genes. Initial comparative genome analyses of the human malaria parasite Plasmodium falciparum and rodent malaria parasites (RMPs) revealed a core set of 4,500 Plasmodium orthologs located in the highly syntenic central regions of the chromosomes that sharply defined the boundaries of the variable subtelomeric regions. We used composite RMP contigs, based on partial DNA sequences of three RMPs, to generate a whole-genome synteny map of P. falciparum and the RMPs. The core regions of the 14 chromosomes of P. falciparum and the RMPs are organized in 36 synteny blocks, representing groups of genes that have been stably inherited since these malaria species diverged, but whose relative organization has altered as a result of a predicted minimum of 15 recombination events. P. falciparum-specific genes and gene families are found in the variable subtelomeric regions (575 genes), at synteny breakpoints (42 genes), and as intrasyntenic indels (126 genes). Of the 168 non-subtelomeric P. falciparum genes, including two newly discovered gene families, 68% are predicted to be exported to the surface of the blood stage parasite or infected erythrocyte. Chromosomal rearrangements are implicated in the generation and dispersal of P. falciparum-specific gene families, including one encoding receptor-associated protein kinases. The data show that both synteny breakpoints and intrasyntenic indels can be foci for species-specific genes with a predicted role in host-parasite interactions and suggest that, besides rearrangements in the subtelomeric regions, chromosomal rearrangements may also be involved in the generation of species-specific gene families. A majority of these genes are expressed in blood stages, suggesting that the vertebrate host exerts a greater selective pressure than the mosquito vector, resulting in the acquisition of diversity

The Tuberculin Skin Test (TST) Is Affected by Recent BCG Vaccination but Not by Exposure to Non-Tuberculosis Mycobacteria (NTM) during Early Life

The tuberculin skin test (TST) is widely used in TB clinics to aid Mycobacterium tuberculosis (M.tb) diagnosis, but the definition and the significance of a positive test in very young children is still unclear. This study compared the TST in Gambian children at 4½ months of age who either received BCG vaccination at birth (Group 1) or were BCG naïve (Group 2) in order to examine the role of BCG vaccination and/or exposure to environmental mycobacteria in TST reactivity at this age. Nearly half of the BCG vaccinated children had a positive TST (≥5 mm) whereas all the BCG naïve children were non-reactive, confirming that recent BCG vaccination affects TST reactivity. The BCG naïve children demonstrated in vitro PPD responses in peripheral blood in the absence of TST reactivity, supporting exposure to and priming by environmental mycobacterial antigens. Group 2 were then vaccinated at 4½ months of age and a repeat TST was performed at 20–28 months of age. Positive reactivity (≥5 mm) was evident in 11.1% and 12.5% infants from Group 1 and Group 2 respectively suggesting that the timing of BCG vaccination had little effect by this age. We further assessed for immune correlates in peripheral blood at 4½ months of age. Mycobacterial specific IFNγ responses were greater in TST responders than in non-responders, although the size of induration did not correlate with IFNγ. However the IFNγ: IL-10 ratio positively correlated with TST induration suggesting that the relationship between PPD induced IFNγ and IL-10 in the peripheral blood may be important in controlling TST reactivity. Collectively these data provide further insights into how the TST is regulated in early life, and how a positive response might be interpreted

Placental Malaria is associated with reduced early life weight development of affected children independent of low birth weight

<p>Abstract</p> <p>Background</p> <p>Infection with <it>Plasmodium falciparum </it>during pregnancy contributes substantially to the disease burden in both mothers and offspring. Placental malaria may lead to intrauterine growth restriction or preterm delivery resulting in low birth weight (LBW), which, in general, is associated with increased infant morbidity and mortality. However, little is known about the possible direct impact of the specific disease processes occurring in PM on longer term outcomes such as subsequent retarded growth development independent of LBW.</p> <p>Methods</p> <p>In an existing West-African cohort, 783 healthy infants with a birth weight of at least 2,000 g were followed up during their first year of life. The aim of the study was to investigate if <it>Plasmodium falciparum </it>infection of the placenta, assessed by placental histology, has an impact on several anthropometric parameters, measured at birth and after three, six and 12 months using generalized estimating equations models adjusting for moderate low birth weight.</p> <p>Results</p> <p>Independent of LBW, first to third born infants who were exposed to either past, chronic or acute placental malaria during pregnancy had significantly lower weight-for-age (-0.43, 95% CI: -0.80;-0.07), weight-for-length (-0.47, 95% CI: -0.84; -0.10) and BMI-for-age z-scores (-0.57, 95% CI: -0.84; -0.10) compared to infants born to mothers who were not diagnosed with placental malaria (p = 0.019, 0.013, and 0.012, respectively). Interestingly, the longitudinal data on histology-based diagnosis of PM also document a sharp decline of PM prevalence in the Sukuta cohort from 16.5% in 2002 to 5.4% in 2004.</p> <p>Conclusions</p> <p>It was demonstrated that PM has a negative impact on the infant's subsequent weight development that is independent of LBW, suggesting that the longer term effects of PM have been underestimated, even in areas where malaria transmission is declining.</p

Placental malaria is associated with attenuated CD4 T-cell responses to tuberculin PPD 12 months after BCG vaccination

Abstract Background Placental malaria (PM) is associated with prenatal malaise, but many PM+ infants are born without symptoms. As malaria has powerful immunomodulatory effects, we tested the hypothesis that PM predicts reduced T-cell responses to vaccine challenge. Methods We recruited healthy PM+ and PM- infants at birth. At six and 12 months, we stimulated PBMCs with tuberculin purified protein derivative (PPD) and compared expression of CD154, IL-2 and IFNγ by CD4 T-cells to a negative control using flow cytometry. We measured the length, weight and head circumference at birth and 12 months. Results IL-2 and CD154 expression were low in both groups at both timepoints, without discernable differences. Expression of IFNγ was similarly low at 6 months but by 12 months, the median response was higher in PM- than PM + infants (p = 0.026). The PM+ infants also had a lower weight (p = 0.032) and head circumference (p = 0.041) at 12 months, indicating lower growth rates. At birth, the size and weight of the PM+ and PM- infants were equivalent. By 12 months, the PM+ infants had a lower weight and head circumference than the PM- infants. Conclusions Placental malaria was associated with reduced immune responses 12 months after immune challenge in infants apparently healthy at birth.</p