Trogocytosis by Entamoeba histolytica contributes to cell killing and tissue invasion.

Entamoeba histolytica is the causative agent of amoebiasis, a potentially fatal diarrhoeal disease in the developing world. The parasite was named "histolytica" for its ability to destroy host tissues, which is probably driven by direct killing of human cells. The mechanism of human cell killing has been unclear, although the accepted model was that the parasites use secreted toxic effectors to kill cells before ingestion. Here we report the discovery that amoebae kill by ingesting distinct pieces of living human cells, resulting in intracellular calcium elevation and eventual cell death. After cell killing, amoebae detach and cease ingestion. Ingestion of human cell fragments is required for cell killing, and also contributes to invasion of intestinal tissue. The internalization of fragments of living human cells is reminiscent of trogocytosis (from Greek trogo, nibble) observed between immune cells, but amoebic trogocytosis differs because it results in death. The ingestion of live cell material and the rejection of corpses illuminate a stark contrast to the established model of dead cell clearance in multicellular organisms. These findings change the model for tissue destruction in amoebiasis and suggest an ancient origin of trogocytosis as a form of intercellular exchange.

Effect of the leptin receptor Q223R polymorphism on the host transcriptome following infection with Entamoeba histolytica.

Resistance to amebiasis is associated with a polymorphism in the leptin receptor. Previous studies demonstrated that humans with the ancestral Q223 leptin receptor allele were nearly four times less likely to be infected with Entamoeba histolytica than those carrying the mutant R223 allele. We hypothesized that the Q223 allele protected against E. histolytica via STAT3-mediated transcription of genes required for mucosal immunity. To test this, mice containing the humanized LEPR Q or R allele at codon 223 were intracecally infected with E. histolytica. Susceptibility to amebiasis was assessed, and cecal tissues were analyzed for changes in gene expression. By 72 h postchallenge, all Q223 mice had cleared E. histolytica, whereas 39% of 223R mice were infected. Thirty-seven genes were differentially expressed in response to infection at 72 h, including proinflammatory genes (CXCL2, S100A8/9, PLA2G7, ITBG2, and MMP9) and functions pertaining to the movement and activity of immune cells. A comparison at 12 h postchallenge of infected Q223 versus R223 mice identified a subset of differentially expressed genes, many of which were closely linked to leptin signaling. Further analyses indicated that the Q223 gene expression pattern was consistent with a suppressed apoptotic response to infection, while 223R showed increased cellular proliferation and recruitment. These studies are the first to illuminate the downstream effects of leptin receptor polymorphisms on intestinal infection by E. histolytica. As such, they are important for the insight that they provide into this previously uncharacterized mechanism of mucosal immunity.

Regulation of Staphylococcus aureus immunodominant antigen B (IsaB).

Staphylococcus aureus is a leading cause of nosocomial and community-acquired infections and increased prevalence of antibiotic resistance has necessitated the search for novel therapeutic targets. The immunodominant antigen B induces an antibody response during septicemia and has therefore been proposed as a vaccine target. Because it appears to be expressed during infection but not during colonization, we sought to characterize the regulation of isaB expression by internal transcription factors and external stimuli. We found that expression of isaB was stimulated by glucose, human serum, and plasma. Furthermore isaB transcript levels increased in the absence of the global staphylococcal accessory regulator SarA and decreased in the absence of the carbon catabolite regulator CcpA. Interestingly, glucose and CcpA-mediated isaB expression appeared to be related to the decrease in pH subsequent to carbon metabolism, rather than a direct response to the carbon source and could be prevented by buffering the growth medium.

Amoebic dysentery.

INTRODUCTION: Amoebic dysentery is caused by the protozoan parasite Entamoeba histolytica. It is transmitted in areas where poor sanitation allows contamination of drinking water and food with faeces. In these areas, up to 40% of people with diarrhoea may have amoebic dysentery. METHODS AND OUTCOMES: We conducted a systematic review and aimed to answer the following clinical question: What are the effects of drug treatments for amoebic dysentery in endemic areas? We searched: Medline, Embase, The Cochrane Library, and other important databases up to April 2010 (Clinical Evidence reviews are updated periodically; please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). RESULTS: We found 6 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. CONCLUSIONS: In this systematic review, we present information relating to the effectiveness and safety of the following interventions: diiodohydroxyquinoline (iodoquinol), diloxanide, emetine, metronidazole, nitazoxanide, ornidazole, paromomycin, secnidazole, and tinidazole.

Staphylococcus aureus immunodominant surface antigen B is a cell-surface associated nucleic acid binding protein.

BACKGROUND: Staphylococcus aureus immunodominant surface antigen B (IsaB) elicits an immune response during septicemia and is generally classified as a virulence factor, but its biological function remains completely undefined. In an attempt to identify staphylococcal RNA-binding proteins, we designed an RNA Affinity Chromatography assay and subsequently isolated IsaB. RESULTS: Western analysis indicated that IsaB was both secreted and cell-surface associated. Gel Shift analysis confirmed the RNA binding activity but revealed that IsaB bound to any nucleic acid without sequence specificity. IsaB exhibited the highest affinity for double-stranded DNA followed by single-stranded DNA and RNA. Because extracellular DNA has been shown to play a role in biofilm formation, we investigated the biofilm-forming capacity of an isogenic isaB deletion mutant but we found that IsaB did not contribute to biofilm formation under any conditions tested. CONCLUSION: IsaB is an extracellular nucleic acid binding protein, with little to no sequence specificity, but its role in virulence remains unclear.