Evidence of promiscuous endothelial binding by Plasmodium falciparum-infected erythrocytes.

The adhesion of infected red blood cells (iRBCs) to human endothelium is considered a key event in the pathogenesis of cerebral malaria and other life-threatening complications caused by the most prevalent malaria parasite Plasmodium falciparum. In the past 30 years, 14 endothelial receptors for iRBCs have been identified. Exposing 10 additional surface proteins of endothelial cells to a mixture of P. falciparum isolates from three Ghanaian malaria patients, we identified seven new iRBC receptors, all expressed in brain vessels. This finding strongly suggests that endothelial binding of P. falciparum iRBCs is promiscuous and may use a combination of endothelial surface moieties.

MCP1 haplotypes associated with protection from pulmonary tuberculosis.

BACKGROUND: The monocyte chemoattractant protein 1 (MCP-1) is involved in the recruitment of lymphocytes and monocytes and their migration to sites of injury and cellular immune reactions. In a Ghanaian tuberculosis (TB) case-control study group, associations of the MCP1 -362C and the MCP1 -2581G alleles with resistance to TB were recently described. The latter association was in contrast to genetic effects previously described in study groups originating from Mexico, Korea, Peru and Zambia. This inconsistency prompted us to further investigate the MCP1 gene in order to determine causal variants or haplotypes genetically and functionally. RESULTS: A 14 base-pair deletion in the first MCP1 intron, int1del554-567, was strongly associated with protection against pulmonary TB (OR=0.84, CI 0.77-0.92, Pcorrected=0.00098). Compared to the wildtype combination, a haplotype comprising the -2581G and -362C promoter variants and the intronic deletion conferred an even stronger protection than did the -362C variant alone (OR=0.78, CI 0.69-0.87, Pnominal=0.00002; adjusted Pglobal=0.0028). In a luciferase reporter gene assay, a significant reduction of luciferase gene expression was observed in the two constructs carrying the MCP1 mutations -2581 A or G plus the combination -362C and int1del554-567 compared to the wildtype haplotype (P=0.02 and P=0.006). The associated variants, in particular the haplotypes composed of these latter variants, result in decreased MCP-1 expression and a decreased risk of pulmonary TB. CONCLUSIONS: In addition to the results of the previous study of the Ghanaian TB case-control sample, we have now identified the haplotype combination -2581G/-362C/int1del554-567 that mediates considerably stronger protection than does the MCP1 -362C allele alone (OR=0.78, CI 0.69-0.87 vs OR=0.83, CI 0.76-0.91). Our findings in both the genetic analysis and the reporter gene study further indicate a largely negligible role of the variant at position -2581 in the Ghanaian population studied.

Mycolactone induces cell death by SETD1B-dependent degradation of glutathione.

Mycobacterium ulcerans is a human pathogen that causes a necrotizing skin disease known as Buruli ulcer. Necrosis of infected skin is driven by bacterial production of mycolactone, a diffusible exotoxin targeting the host translocon (Sec61). By blocking Sec61, mycolactone prevents the transport of nascent secretory proteins into the endoplasmic reticulum of host cells. This triggers pro-apoptotic stress responses partially depending on activation of the ATF4 transcription factor. To gain further insight into the molecular pathways mediating the cytotoxic effects of mycolactone we conducted the first haploid genetic screen with the M. ulcerans toxin in KBM-7 cells. This approach allowed us to identify the histone methyltransferase SETD1B as a novel mediator of mycolactone-induced cell death. CRISPR/Cas9-based inactivation of SETD1B rendered cells resistant to lethal doses of the toxin, highlighting the critical importance of this gene's expression. To understand how SETD1B contributes to mycolactone cytotoxicity, we compared the transcriptomes of wild-type (WT) and SETD1B knockout KBM-7 cells upon exposure to the toxin. While ATF4 effectors were upregulated by mycolactone in both WT and SETD1B knockout cells, mycolactone selectively induced the expression of pro-apoptotic genes in WT cells. Among those genes we identified CHAC1, which codes for a major glutathione (GSH)-degrading enzyme, and whose strong upregulation in mycolactone-treated WT cells correlated with a marked reduction in GSH protein level. Moreover, GSH supplementation conferred cells with substantial protection against the toxic effects of mycolactone. Our data thus identify SETD1B/CHAC1/GSH as a novel, epigenetic mechanism connecting Sec61 blockade with apoptotic cell death. They suggest that GSH-based treatments might have the capacity to limit skin necrosis in Buruli ulcer.

No significant impact of IFN-γ pathway gene variants on tuberculosis susceptibility in a West African population.

The concept of interferon-γ (IFN-γ) having a central role in cell-mediated immune defence to Mycobacterium tuberculosis has long been proposed. Observations made through early candidate gene studies of constituents of the IFN-γ pathway have identified moderately associated variants associated with resistance or susceptibility to tuberculosis (TB). By analysing 20 major genes whose proteins contribute to IFN-γ signalling we have assessed a large fraction of the variability in genes that might contribute to susceptibility to TB. Genetic variants were identified by sequencing the promoter regions and all exons of IFNG, IFNGR1, IFNGR2, IRF1, IL12A, IL12B, IL12RB1, IL12RB2, IL23A, IL23R, IL27, EBI3, IL27RA, IL6ST, SOCS1, STAT1, STAT4, JAK2, TYK2 and TBX21 in 69 DNA samples from Ghana. In addition, we screened all exons of IFNGR1 in a Ghanaian study group comprising 1999 TB cases and 2589 controls by high-resolution melting point analysis. The fine-mapping approach allows for a detailed screening of all variants, common and rare. Statistical comparisons of cases and controls, however, did not yield significant results after correction for multiple testing with any of the 246 variants selected for genotyping in this investigation. Gene-wise haplotype tests and analysis of rare variants did not reveal any significant association with susceptibility to TB in our investigation as well. Although this analysis was applied on a plausible set of IFN-γ pathway genes in the largest African TB cohort available so far, the lack of significant results challenges the view that genetic marker of the IFN-γ pathway have an important impact on susceptibility to TB.