The Role of the st313-td Gene in Virulence of Salmonella Typhimurium ST313

Multidrug-resistant Salmonella enterica serovar Typhimurium ST313 has emerged in sub-Saharan Africa causing severe infections in humans. Therefore, it has been speculated that this specific sequence type, ST313, carries factors associated with increased pathogenicity. We assessed the role in virulence of a gene with a yet unknown function, st313-td, detected in ST313 through comparative genomics. Additionally, the structure of the genomic island ST313-GI, harbouring the gene was determined. The gene st313-td was cloned into wild type S. Typhimurium 4/74 (4/74-C) as well as knocked out in S. Typhimurium ST313 02-03/002 (Δst313-td) followed by complementation (02-03/002-C). Δst313-td was less virulent in mice following i.p. challenge than the wild type and this phenotype could be partly complemented in trans, indicating that st313-td plays a role during systemic infection. The gene st313-td was shown not to affect invasion of cultured epithelial cells, while the absence of the gene significantly affects uptake and intracellular survival within macrophages. The gene st313-td was proven to be strongly associated to invasiveness, harboured by 92.5% of S. Typhimurium blood isolates (n = 82) and 100% of S. Dublin strains (n = 50) analysed. On the contrary, S. Typhimurium isolates of animal and food origin (n = 82) did not carry st313-td. Six human, non-blood isolates of S. Typhimurium from Belarus, China and Nepal harboured the gene and belonged to sequence types ST398 and ST19. Our data showed a global presence of the st313-td gene and in other sequence types than ST313. The gene st313-td was shown to be expressed during logarithmic phase of growth in 14 selected Salmonella strains carrying the gene. This study reveals that st313-td plays a role in S. Typhimurium ST313 pathogenesis and adds another chapter to understanding of the virulence of S. Typhimurium and in particular of the emerging sequence type ST313

Leukocyte counts and lymphocyte subsets in relation to pregnancy and HIV infection in Malawian women.

PROBLEM: We investigated leukocyte and lymphocyte subsets in HIV-infected or HIV-uninfected, pregnant or non-pregnant Malawian women to explore whether HIV infection and pregnancy may act synergistically to impair cellular immunity. METHOD OF STUDY: We recruited 54 pregnant and 48 non-pregnant HIV-uninfected women and 24 pregnant and 20 non-pregnant HIV-infected Malawian women. We compared peripheral blood leukocyte and lymphocyte subsets between women in the four groups. RESULTS: Parturient HIV-infected and HIV-uninfected women had more neutrophils (each P<.0001), but fewer lymphocytes (P<.0001; P=.0014) than non-pregnant women. Both groups had fewer total T cells (P<.0001; P=.002) and CD8(+) T cells (P<.0001; P=.014) than non-pregnant women. HIV-uninfected parturient women had fewer CD4(+) and γδ T cells, B and NK cells (each P<.0001) than non-pregnant women. Lymphocyte subset percentages were not affected by pregnancy. CONCLUSION: Malawian women at parturition have an increased total white cell count due to neutrophilia and an HIV-unrelated pan-lymphopenia

Monocyte activation and cytokine production in Malawian children presenting with P. falciparum malaria

Malaria in malaria-naïve adults is associated with an inflammatory response characterised by expression of specific activation markers on innate immune cells. Here we investigate activation and adhesion marker expression, and cytokine production in monocytes from children presenting with cerebral malaria (CM, n=36), severe malarial anaemia (SMA, n=42) or uncomplicated malaria (UM, n= 66), and healthy aparasitemic children (n=52) in Blantyre, Malawi. In all malaria groups, but particularly in the two severe malaria groups, monocyte expression of CD11b, CD11c, CD18, HLA-DR and CD86, and percentages of TNFα and IL-6-producing monocytes were lower than in healthy controls, while expression of CD11a, TLR2 and TLR4 was lower in children with severe malaria compared with controls. These levels mostly normalised during convalescence, but percentages of cytokine-producing monocytes remained suppressed in children with SMA. In all malaria groups, especially the SMA group, a greater proportion of monocytes were loaded with haemozoin than among controls. In a P. falciparum hyperendemic area, monocytes in children with acute symptomatic malaria have reduced expression of adhesion molecules and activation markers and reduced inflammatory cytokine production. This immune suppression could be due to accumulation of haemozoin and/or previous exposure to P. falciparum. This article is protected by copyright. All rights reserved

HIV infection compounds the lymphopenia associated with cerebral malaria in Malawian children

Aim: Cerebral malaria (CM), unlike severe malarial anemia (SMA), has previously been characterized by pan-lymphopenia that normalizes in convalescence, while HIV infection is associated with depletion of CD4+ T cells. In this study, we investigate whether HIV infection in Malawian children exacerbates the pan-lymphopenia associated with CM. Methods: We investigated the absolute and percentage lymphocyte-subset counts and their activation and memory status in Malawian children presenting with either CM who were HIV-uninfected (n=29), HIV-infected (n=9), or SMA who were HIV-uninfected (n=30) and HIV-infected (n=5) in comparison with HIV-uninfected children without malaria (n=42) and HIV-infected children without malaria (n=4). Results: HIV-infected CM cases had significantly lower absolute counts of T cells (P=0.006), CD4+ T cells (P=0.0008), and B cells (P=0.0014) than HIV-uninfected CM cases, and significantly lower percentages of CD4+ T cells than HIV-uninfected CM cases (P=0.005). HIV-infected SMA cases had significantly lower percentages of CD4+ T cells (P=0.001) and higher CD8+ T cells (P=0.003) in comparison with HIV-uninfected SMA cases. HIV-infected SMA cases had higher proportions of activated T cells (P=0.003) expressing CD69 than HIV-uninfected SMA cases. Conclusion: HIV infection compounds the perturbation of acute CM and SMA on lymphocytes, exacerbating subset-specific lymphopenia in CM and increasing activation status in SMA, potentially exacerbating host immunocompromise

HIV infection compounds the lymphopenia associated with cerebral malaria in Malawian children

Wilson L Mandala,1–3 Esther N Gondwe,1,† Tonney S Nyirenda,1,4 Mark Drayson,5 Malcolm E Molyneux,1,6 Calman A MacLennan1,7 1Malawi Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, Blantyre, Malawi; 2Biomedical Sciences Department, College of Medicine, Blantyre, Malawi; 3Academy of Medical Sciences, Malawi University of Science and Technology, Thyolo, Malawi; 4Pathology Department, College of Medicine, Blantyre, Malawi; 5Institute of Immunology and Immunotherapy, College of Medicine and Dental Sciences, University of Birmingham, Birmingham, UK; 6Liverpool School of Tropical Medicine, Liverpool, UK; 7Jenner Institute, Nuffield Department of Medicine, University of Oxford, Oxford, UK †Esther N Gondwe passed away on April 5, 2018 Aim: Cerebral malaria (CM), unlike severe malarial anemia (SMA), has previously been characterized by pan-lymphopenia that normalizes in convalescence, while HIV infection is associated with depletion of CD4+ T cells. In this study, we investigate whether HIV infection in Malawian children exacerbates the pan-lymphopenia associated with CM. Methods: We investigated the absolute and percentage lymphocyte-subset counts and their activation and memory status in Malawian children presenting with either CM who were HIV-uninfected (n=29), HIV-infected (n=9), or SMA who were HIV-uninfected (n=30) and HIV-infected (n=5) in comparison with HIV-uninfected children without malaria (n=42) and HIV-infected children without malaria (n=4). Results: HIV-infected CM cases had significantly lower absolute counts of T cells (P=0.006), CD4+ T cells (P=0.0008), and B cells (P=0.0014) than HIV-uninfected CM cases, and significantly lower percentages of CD4+ T cells than HIV-uninfected CM cases (P=0.005). HIV-infected SMA cases had significantly lower percentages of CD4+ T cells (P=0.001) and higher CD8+ T cells (P=0.003) in comparison with HIV-uninfected SMA cases. HIV-infected SMA cases had higher proportions of activated T cells (P=0.003) expressing CD69 than HIV-uninfected SMA cases. Conclusion: HIV infection compounds the perturbation of acute CM and SMA on lymphocytes, exacerbating subset-specific lymphopenia in CM and increasing activation status in SMA, potentially exacerbating host immunocompromise. Keywords: HIV, cerebral malaria, severe malarial anemia, Malawian childre

Cytokine profiles during invasive nontyphoidal Salmonella disease predict outcome in African children.

Nontyphoidal Salmonella is a leading cause of sepsis in African children. Cytokine responses are central to the pathophysiology of sepsis and predict sepsis outcome in other settings. In this study, we investigated cytokine responses to invasive nontyphoidal Salmonella (iNTS) disease in Malawian children. We determined serum concentrations of 48 cytokines with multiplexed immunoassays in Malawian children during acute iNTS disease (n = 111) and in convalescence (n = 77). Principal component analysis and logistic regression were used to identify cytokine signatures of acute iNTS disease. We further investigated whether these responses are altered by HIV coinfection or severe malnutrition and whether cytokine responses predict inpatient mortality. Cytokine changes in acute iNTS disease were associated with two distinct cytokine signatures. The first is characterized by increased concentrations of mediators known to be associated with macrophage function, and the second is characterized by raised pro- and anti-inflammatory cytokines typical of responses reported in sepsis secondary to diverse pathogens. These cytokine responses were largely unaltered by either severe malnutrition or HIV coinfection. Children with fatal disease had a distinctive cytokine profile, characterized by raised mediators known to be associated with neutrophil function. In conclusion, cytokine responses to acute iNTS infection in Malawian children are reflective of both the cytokine storm typical of sepsis secondary to diverse pathogens and the intramacrophage replicative niche of NTS. The cytokine profile predictive of fatal disease supports a key role of neutrophils in the pathogenesis of NTS sepsis

Bactericidal immunity to salmonella in Africans and mechanisms causing its failure in HIV infection

Nontyphoidal strains of Salmonella are a leading cause of death among HIV-infected Africans. Antibody-induced complement-mediated killing protects healthy Africans against Salmonella, but increased levels of anti-lipopolysaccharide (LPS) antibodies in some HIV-infected African adults block this killing. The objective was to understand how these high levels of anti-LPS antibodies interfere with the killing of Salmonella.Sera and affinity-purified antibodies from African HIV-infected adults that failed to kill invasive S. Typhimurium D23580 were compared to sera from HIV-uninfected and HIV-infected subjects with bactericidal activity. The failure of sera from certain HIV-infected subjects to kill Salmonella was found to be due to an inherent inhibitory effect of anti-LPS antibodies. This inhibition was concentration-dependent and strongly associated with IgA and IgG2 anti-LPS antibodies (p<0.0001 for both). IgG anti-LPS antibodies, from sera of HIV-infected individuals that inhibit killing at high concentration, induced killing when diluted. Conversely, IgG, from sera of HIV-uninfected adults that induce killing, inhibited killing when concentrated. IgM anti-LPS antibodies from all subjects also induced Salmonella killing. Finally, the inhibitory effect of high concentrations of anti-LPS antibodies is seen with IgM as well as IgG and IgA. No correlation was found between affinity or avidity, or complement deposition or consumption, and inhibition of killing.IgG and IgM classes of anti-S. Typhimurium LPS antibodies from HIV-infected and HIV-uninfected individuals are bactericidal, while at very high concentrations, anti-LPS antibodies of all classes inhibit in vitro killing of Salmonella. This could be due to a variety of mechanisms relating to the poor ability of IgA and IgG2 to activate complement, and deposition of complement at sites where it cannot insert in the bacterial membrane. Vaccine trials are required to understand the significance of lack of in vitro killing by anti-LPS antibodies from a minority of HIV-infected individuals with impaired immune homeostasis

Les affaires d'etat d'abord, l'amite apres France, out of Africa?

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