The ability to detect recent natural selection in the human population would have profound implications for the study of human history and for medicine. Here, we introduce a framework for detecting the genetic imprint of recent positive selection by analysing long-range haplotypes in human populations. We first identify haplotypes at a locus of interest (core haplotypes). We then assess the age of each core haplotype by the decay of its association to alleles at various distances from the locus, as measured by extended haplotype homozygosity (EHH). Core haplotypes that have unusually high EHH and a high population frequency indicate the presence of a mutation that rose to prominence in the human gene pool faster than expected under neutral evolution. We applied this approach to investigate selection at two genes carrying common variants implicated in resistance to malaria: G6PD and CD40 ligand. At both loci, the core haplotypes carrying the proposed protective mutation stand out and show significant evidence of selection. More generally, the method could be used to scan the entire genome for evidence of recent positive selection.

Plasmodium falciparum malaria, an infectious disease caused by a parasitic protozoan, claims the lives of nearly a million children each year in Africa alone and is a top public health concern. Evidence is accumulating that resistance to artemisinin derivatives, the frontline therapy for the asexual blood stage of the infection, is developing in southeast Asia. Renewed initiatives to eliminate malaria will benefit from an expanded repertoire of antimalarials, including new drugs that kill circulating P. falciparum gametocytes, thereby preventing transmission. Our current understanding of the biology of asexual blood-stage parasites and gametocytes and the ability to culture them in vitro lends optimism that high-throughput screenings of large chemical libraries will produce a new generation of antimalarial drugs. There is also a need for new therapies to reduce the high mortality of severe malaria. An understanding of the pathophysiology of severe disease may identify rational targets for drugs that improve survival.

Interleukin-8 (IL8) is believed to play a role in the pathogenesis of bronchiolitis, a common viral disease of infancy, and a recent U.K. family study identified an association between this disease and the IL8-251A allele. In the present study we report data, from a different set of families, which replicate this finding; combined analysis of 194 nuclear families through use of the transmission/disequilibrium test gives P = .001. To explore the underlying genetic cause, we identified nine single-nucleotide polymorphisms (SNPs) in a 7.6-kb segment spanning the IL8 gene and its promoter region and used six of these SNPs to define the haplotypic structure of the IL8 locus. The IL8-251A allele resides on two haplotypes, only one of which is associated with disease, suggesting that this may not be the functional allele. Europeans show an unusual haplotype genealogy that is dominated by two common haplotypes differing at multiple sites, whereas Africans have much greater haplotypic diversity. These marked haplotype-frequency differences give an F(ST) of.25, and, in the European sample, both Tajima's D statistic (D = 2.58, P = .007) and the Hudson/Kreitman/Aguade test (chi(2) = 4.9, P = .03) reject neutral equilibrium, suggesting that selective pressure may have acted on this locus.

Stimulation of the NF-B pathway often causes p65-p50 and p50-p50 dimers to be simultaneously present in the cell nucleus. A natural polymorphism at nucleotide ؊863 in the human TNF promoter (encoding tumor necrosis factor [TNF]) region provides an opportunity to dissect the functional interaction of p65-p50 and p50-p50 at a single NF-B binding site. We found that this site normally binds both p65-p50 and p50-p50, but a single base change specifically inhibits p50-p50 binding. Reporter gene analysis in COS-7 cells expressing both p65-p50 and p50-p50 shows that the ability to bind p50-p50 reduces the enhancer effect of this NF-B site. Using an adenoviral reporter assay, we found that the variant which binds p50-p50 results in a reduction of lipopolysaccharide-inducible gene expression in primary human monocytes. This finding adds to a growing body of experimental evidence that p50-p50 can inhibit the transactivating effects of p65-p50 and illustrates the potential for genetic modulation of inflammatory gene regulation in humans by subtle nucleotide changes that alter the relative binding affinities of different forms of the NF-B complex.The NF-B/Rel family of transcription factors is involved in many physiological processes, including regulation of a wide range of inflammatory mediators (2). Inflammation is a critical component of host defense, but it is also responsible for many of the clinical symptoms of infection and injury and can be fatal if elicited in excess. This raises the fundamental question of how the level of response to NF-B is optimized across a large number of different inflammatory genes. Often this may involve functional interactions between NF-B and other transcription factors (24). This paper considers another mechanism, which has received relatively little attention, namely, through variation in the composition of NF-B dimers that bind to a specific regulatory site. The canonical form of NF-B is a heterodimer comprising a p65 subunit, containing both a DNA binding domain and a domain that is essential for transcriptional activation, plus a p50 subunit which has a DNA binding domain but no activation domain. The biological role of p50 was initially thought to relate solely to its DNA binding properties within the active p65-p50 complex, but more recent evidence suggests that p50-p50 homodimers are capable of acting as transcriptional repressors. For example, artificial overexpression of p50 acts to suppress the transactivating effects of p65 at some NF-B sites (15,17), and this mechanism has been implicated in the downregulation of major histocompatibility complex expression (16) and in viral postinduction repression of the beta interferon gene (23). Since the optimal binding sequences for p65 and p50 are similar but not identical (12,15,23), it is possible that NF-B-induced responses might be fine-tuned by minor sequence variations that alter the relative binding of p65-p50 and p50-p50 to different regulatory elements. To examine this question, we have investigated the functional properties o...

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SummaryThere has been much debate about the relative merits of population-and family-based strategies for testing genetic association, yet there is little empirical data that directly compare the two approaches. Here we compare case-control and transmission/disequilibrium test (TDT) study designs using a well-established genetic association, the protective effect of the sickle-cell trait against severe malaria. We find that the two methods give similar estimates of the level of protection (case-control odds ratio = 0.10, 95% confidence interval 0.03-0.23; family-based estimate of the odds ratio = 0.11, 95% confidence interval 0.04-0.25) and similar statistical significance of the result (case-control: χ 2 = 41.26, p = 10 − 10 , TDT: χ 2 = 39.06, p = 10 − 10 ) when 315 TDT cases are compared to 583 controls. We propose a family plus population control study design, which allows both case-control and TDT analysis of the cases. This combination is robust against the respective weaknesses of the case-control and TDT study designs, namely population structure and segregation distortion. The combined study design is especially cost-effective when cases are difficult to ascertain and, when the case-control and TDT results agree, offers greater confidence in the result.

Objectives The coagulation-inflammation cycle has been implicated as a critical component in malaria pathogenesis. Defibrotide (DF), a mixture of DNA aptamers, displays anticoagulant, anti-inflammatory, and endothelial cell (EC)-protective activities and has been successfully used to treat comatose children with veno-occlusive disease. DF was investigated here as a drug to treat cerebral malaria (CM). Methods and Results DF blocks tissue factor (TF) expression by ECs incubated with parasitized red blood cells (pRBCs), attenuates prothrombinase activity, platelet aggregation, and complement activation. In contrast, it does not affect nitric oxide bioavailability. We also demonstrated that Plasmodium falciparum glycosylphosphatidylinositol (Pf-GPI) induces TF expression in ECs and cytokine production by dendritic cells (DCs). Notably, DCs – known to modulate coagulation and inflammation systemically – were identified as a novel target for DF. Accordingly, DF inhibits Toll-like receptor (TLR) ligand-dependent DCs activation by a mechanism that is blocked by adenosine receptor (AR) antagonist (8-p-sulfophenyltheophylline), but not reproduced by synthetic poly-A,-C,-T,-G. These results imply that aptameric sequences and AR mediate DCs responses to the drug. DF also prevents rosetting formation, RBC invasion by P. falciparum and abolishes oocysts formation in Anopheles gambiae. In a murine model of CM, DF affected parasitemia, decreased IFN-γ levels, and ameliorated clinical score (day 5) with a trend for increased survival. Conclusions Therapeutic use of DF in malaria is proposed.

Plasmodium falciparum (Pf) infection remodels the human erythrocyte with new membrane systems, including a modified host erythrocyte membrane (EM), a parasitophorous vacuole membrane (PVM), a tubulovesicular network (TVN), and Maurer's clefts (MC). Here we report on the relative cholesterol contents of these membranes in parasitized normal (HbAA) and hemoglobin S-containing (HbAS, HbAS) erythrocytes. Results from fluorescence lifetime imaging microscopy (FLIM) experiments with a cholesterol-sensitive fluorophore show that membrane cholesterol levels in parasitized erythrocytes (pRBC) decrease inwardly from the EM, to the MC/TVN, to the PVM, and finally to the parasite membrane (PM). Cholesterol depletion of pRBC by methyl-β-cyclodextrin treatment caused a collapse of this gradient. Lipid and cholesterol exchange data suggest that the cholesterol gradient involves a dilution effect from non-sterol lipids produced by the parasite. FLIM signals from the PVM or PM showed little or no difference between parasitized HbAA vs HbS-containing erythrocytes that differed in lipid content, suggesting that malaria parasites may regulate the cholesterol contents of the PVM and PM independently of levels in the host cell membrane. Cholesterol levels may affect raft structures and the membrane trafficking and sorting functions that support Pf survival in HbAA, HbAS and HbSS erythrocytes.