Blood-stage Plasmodium infection induces CD8+ T lymphocytes to parasite-expressed antigens, largely regulated by CD8α+ dendritic cells

Although CD8+ T cells do not contribute to protection against the blood stage of Plasmodium infection, there is mounting evidence that they are principal mediators of murine experimental cerebral malaria (ECM). At present, there is no direct evidence that the CD8+ T cells mediating ECM are parasite-specific or, for that matter, whether parasite-specific CD8+ T cells are generated in response to blood-stage infection. To resolve this and to define the cellular requirements for such priming, we generated transgenic P. berghei parasites expressing model T cell epitopes. This approach was necessary as MHC class I-restricted antigens to blood-stage infection have not been defined. Here, we show that blood-stage infection leads to parasite-specific CD8+ and CD4+ T cell responses. Furthermore, we show that P. berghei-expressed antigens are cross-presented by the CD8α+ subset of dendritic cells (DC), and that this induces pathogen-specific cytotoxic T lymphocytes (CTL) capable of lysing cells presenting antigens expressed by blood-stage parasites. Finally, using three different experimental approaches, we provide evidence that CTL specific for parasite-expressed antigens contribute to ECM.

CD8+ T cells from a novel T cell receptor transgenic mouse induce liver-stage immunity that can be boosted by blood-stage infection in rodent malaria

To follow the fate of CD8+ T cells responsive to Plasmodium berghei ANKA (PbA) infection, we generated an MHC I-restricted TCR transgenic mouse line against this pathogen. T cells from this line, termed PbT-I T cells, were able to respond to blood-stage infection by PbA and two other rodent malaria species, P. yoelii XNL and P. chabaudi AS. These PbT-I T cells were also able to respond to sporozoites and to protect mice from liver-stage infection. Examination of the requirements for priming after intravenous administration of irradiated sporozoites, an effective vaccination approach, showed that the spleen rather than the liver was the main site of priming and that responses depended on CD8α+ dendritic cells. Importantly, sequential exposure to irradiated sporozoites followed two days later by blood-stage infection led to augmented PbT-I T cell expansion. These findings indicate that PbT-I T cells are a highly versatile tool for studying multiple stages and species of rodent malaria and suggest that cross-stage reactive CD8+ T cells may be utilized in liver-stage vaccine design to enable boosting by blood-stage infections.

Disentangling the stigma of HIV/AIDS from the stigmas of drugs use, commercial sex and commercial blood donation - a factorial survey of medical students in China

Background
HIV/AIDS related stigma interferes with the provision of appropriate care and support for people living with HIV/AIDS. Currently, programs to address the stigma approach it as if it occurs in isolation, separate from the co-stigmas related to the various modes of disease transmission including injection drug use (IDU) and commercial sex (CS). In order to develop better programs to address HIV/AIDS related stigma, the inter-relationship (or 'layering') between HIV/AIDS stigma and the co-stigmas needs to be better understood. This paper describes an experimental study for disentangling the layering of HIV/AIDS related stigmas.

Methods
The study used a factorial survey design. 352 medical students from Guangzhou were presented with four random vignettes each describing a hypothetical male. The vignettes were identical except for the presence of a disease diagnosis (AIDS, leukaemia, or no disease) and a co-characteristic (IDU, CS, commercial blood donation (CBD), blood transfusion or no co-characteristic). After reading each vignette, participants completed a measure of social distance that assessed the level of stigmatising attitudes.

Results
Bivariate and multivariable analyses revealed statistically significant levels of stigma associated with AIDS, IDU, CS and CBD. The layering of stigma was explored using a recently developed technique. Strong interactions between the stigmas of AIDS and the co-characteristics were also found. AIDS was significantly less stigmatising than IDU or CS. Critically, the stigma of AIDS in combination with either the stigmas of IDU or CS was significantly less than the stigma of IDU alone or CS alone.

Conclusion
The findings pose several surprising challenges to conventional beliefs about HIV/AIDS related stigma and stigma interventions that have focused exclusively on the disease stigma. Contrary to the belief that having a co-stigma would add to the intensity of stigma attached to people with HIV/AIDS, the findings indicate the presence of an illness might have a moderating effect on the stigma of certain co-characteristics like IDU. The strong interdependence between the stigmas of HIV/AIDS and the co-stigmas of IDU and CS suggest that reducing the co-stigmas should be an integral part of HIV/AIDS stigma intervention within this context.

The significance of transfusion in the past as a risk for current hepatitis B and Hepatitis C infection: a study in endoscopy patients

BACKGROUND: The objective was to determine the contribution of transfusion in the past to the risk of current infection with hepatitis B or C among patients attending a large hospital for endoscopic procedures.
STUDY DESIGN AND METHODS: Blood samples had been tested for hepatitis markers by routine methods. Patients completed a comprehensive risk factor questionnaire and results were analyzed using computer software.
RESULTS: Twenty-seven percent of the 2120 participants in the study received transfusions in the past. There was no increase in prevalence of hepatitis B among those transfused. Compared with nontransfused participants, recipients of blood before the implementation of hepatitis C virus (HCV) screening in 1990 had a 4.6-fold increased risk of HCV infection, whereas those transfused with screened blood had a 3-fold increased risk. The difference between the odds ratios for patients before and after screening was not significant.
CONCLUSIONS: Because screening has almost completely eliminated HCV from the blood supply, our finding of a continuing association of HCV infection with transfusion was unexpected. It implies that there are significant other nosocomial risks for hepatitis C transmission associated with the clinical situations where patients received blood. These should be actively investigated.

A new rodent model to assess blood stage immunity to the plasmodium falciparum antigen merozoite surface protein 119 reveals a protective role for invasion inhibitory antibodies

Antibodies capable of inhibiting the invasion of Plasmodium merozoites into erythrocytes are present in individuals that are clinically immune to the malaria parasite. Those targeting the 19-kD COOH-terminal domain of the major merozoite surface protein (MSP)-119 are a major component of this inhibitory activity. However, it has been difficult to assess the overall relevance of such antibodies to antiparasite immunity. Here we use an allelic replacement approach to generate a rodent malaria parasite (Plasmodium berghei) that expresses a human malaria (Plasmodium falciparum) form of MSP-119. We show that mice made semi-immune to this parasite line generate high levels of merozoite inhibitory antibodies that are specific for P. falciparum MSP-119. Importantly, protection from homologous blood stage challenge in these mice correlated with levels of P. falciparum MSP-119–specific inhibitory antibodies, but not with titres of total MSP-119–specific immunoglobulins. We conclude that merozoite inhibitory antibodies generated in response to infection can play a significant role in suppressing parasitemia in vivo. This study provides a strong impetus for the development of blood stage vaccines designed to generate invasion inhibitory antibodies and offers a new animal model to trial P. falciparum MSP-119 vaccines.

Systemic activation of dendritic cells by toll-like receptor ligands or malaria infection impairs cross-presentation and antiviral immunity

The mechanisms responsible for the immunosuppression associated with sepsis or some chronic blood infections remain poorly understood. Here we show that infection with a malaria parasite (Plasmodium berghei) or simple systemic exposure to bacterial or viral Toll-like receptor ligands inhibited cross-priming. Reduced cross-priming was a consequence of downregulation of cross-presentation by activated dendritic cells due to systemic activation that did not otherwise globally inhibit T cell proliferation. Although activated dendritic cells retained their capacity to present viral antigens via the endogenous major histocompatibility complex class I processing pathway, antiviral responses were greatly impaired in mice exposed to Toll-like receptor ligands. This is consistent with a key function for cross-presentation in antiviral immunity and helps explain the immunosuppressive effects of systemic infection. Moreover, inhibition of cross-presentation was overcome by injection of dendritic cells bearing antigen, which provides a new strategy for generating immunity during immunosuppressive blood infections.

Frequency of Anti-HBc & HBV DNA detection in blood donors of Kerman province, Iran

Hepatitis B is a serious global infection disease and a major cause of mortality and morbidity worldwide. However, data on Occult Hepatitis B in Iran are scare. The current study assessed the frequency of Anti-HBc and HBV DNA in serum sample of healthy blood donors negative for HBsAg stratified by sex and age; and also investigated the relationship between detection of HBV-DNA and anti-HBc positivity. Since anti-HBc screening is not performed in Iranian Blood Bank, we assessed whether anti-HBc could be adopted as a screening assay for the donated blood. The study included a total of 1525 blood samples of blood donors negative for hepatitis B virus surface antigen ( 87% male with a mean age ± SD: of 31±8yr; and 13% female with a mean age ± SD of 30±6yr). Eight percent (121 out of 1525) of the blood samples with negative HBs-Ag were positive for Anti-HBc and were all from males. HBV-DNA was detected in 36 out of 121 anti-HBc+ specimens (29.7%). The study found a positive relation between anti-HBc positivity and detection of HBV-DNA in serum samples of HBs-Ag negative blood donors. Findings from this study suggest that, introducing anti HBc screening in Iran maybe very practical in order to limit the transmission risk of Occult Hepatitis B virus through blood transfusion.

You are what you eat : influence of host ecology on infection risk in populations and individuals

It is widely accepted that wild aquatic birds are the major reservoir for Avian Influenza viruses (AIV), and also play a significant role as vectors for the disease. However, despite intensive surveillance, we still know very little about the role individual wild birds (and their populations) play in the transmission and maintenance of these viruses. Traditionally, combinations of single-location surveillance and historical migration patterns have been used to estimate the degree to which different species may be involved. However, this broad scale approach tends to neglect the ecology of the virus, and just as importantly, the ecology of the host. Over 100 species have been found infected with these viruses worldwide, with many more purportedly negative for the disease. Using data from ten years of wild bird surveillance in the Netherlands we catalogued the ecological properties of each species sampled, in order to determine whether infected species are ecologically separated from those that are not. Using stable isotope analysis of feathers and blood components, we also examine whether infection risk of individuals within a species known to be infected by AIV can be attributable to antecedent foraging habitats. The use of an aquatic habitat is strongly associated with infection risk at all levels analysed, including individuals and populations of a single species, and between species. These unique findings underscore the usefulness of stable isotope methods in disease ecology, particularly when compared to broader-scale inter-species patterns, and the potential role of host ecology in transmission and maintenance of AIV.

HIV infection of dendritic cells subverts the IFN induction pathway via IRF-1 and inhibits type 1 IFN production

Many viruses have developed mechanisms to evade the IFN response. Here, HIV-1 was shown to induce a distinct subset of IFN-stimulated genes (ISGs) in monocyte-derived dendritic cells (DCs), without detectable type I or II IFN. These ISGs all contained an IFN regulatory factor 1 (IRF-1) binding site in their promoters, and their expression was shown to be driven by IRF-1, indicating this subset was induced directly by viral infection by IRF-1. IRF-1 and -7 protein expression was enriched in HIV p24 antigen-positive DCs. A HIV deletion mutant with the IRF-1 binding site deleted from the long terminal repeat showed reduced growth kinetics. Early and persistent induction of IRF-1 was coupled with sequential transient up-regulation of its 2 inhibitors, IRF-8, followed by IRF-2, suggesting a mechanism for IFN inhibition. HIV-1 mutants with Vpr deleted induced IFN, showing that Vpr is inhibitory. However, HIV IFN inhibition was mediated by failure of IRF-3 activation rather than by its degradation, as in T cells. In contrast, herpes simplex virus type 2 markedly induced IFNβ and a broader range of ISGs to higher levels, supporting the hypothesis that HIV-1 specifically manipulates the induction of IFN and ISGs to enhance its noncytopathic replication in DCs.

The dimer initiation sequence stem-loop of human immunodeficiency virus type 1 is dispensable for viral replication in peripheral blood mononuclear cells

Human immunodeficiency virus type 1 (HIV-1) contains two copies of genomic RNA that are noncovalently linked via a palindrome sequence within the dimer initiation site (DIS) stem-loop. In contrast to the current paradigm that the DIS stem or stem-loop is critical for HIV-1 infectivity, which arose from studies using T-cell lines, we demonstrate here that HIV-1 mutants with deletions in the DIS stem-loop are replication competent in peripheral blood mononuclear cells (PBMCs). The DIS mutants contained either the wild-type (5′GCGCGC3′) or an arbitrary (5′ACGCGT3′) palindrome sequence in place of the 39-nucleotide DIS stem-loop (NLCGCGCG and NLACGCGT). These DIS mutants were replication defective in SupT1 cells, concurring with the current model in which DIS mutants are replication defective in T-cell lines. All of the HIV-1 DIS mutants were replication competent in PBMCs over a 40-day infection period and had retained their respective DIS mutations at 40 days postinfection. Although the stability of the virion RNA dimer was not affected by our DIS mutations, the RNA dimers exhibited a diffuse migration profile when compared to the wild type. No defect in protein processing of the Gag and GagProPol precursor proteins was found in the DIS mutants. Our data provide direct evidence that the DIS stem-loop is dispensable for viral replication in PBMCs and that the requirement of the DIS stem-loop in HIV-1 replication is cell type dependent.

Community-onset Escherichia coli infection resistant to expanded- spectrum cephalosporins in low-prevalence countries

Background
By global standards the prevalence of community onset expanded-spectrum cephalosporin resistant Escherichia coli (ESC-R-EC) remains low in Australia and New Zealand. Of concern, our countries are in a unique position with high extramural resistance pressure from close population and trade links to Asia-Pacific neighbours with high ESC-R-EC rates. We aim to characterize the risks and dynamics of community onset ESC-R-EC in our low-prevalence region.

Methods
A case-control methodology was used. Patients with ESC-R-EC or susceptible E. coli isolated from blood or urine were recruited at six geographically dispersed tertiary hospitals in Australia and New Zealand. Epidemiological data was prospectively collected and bacteria were retained for analysis.

Results
In total, 182 patients (91 cases and 91 controls) were recruited. Multivariate logistic regression identified risk factors for ESC-R amongst E. coli including birth on the Indian subcontinent (OR=11.13, 2.17-56.98, p=0.003), urinary tract infection in the past year (per infection OR=1.430, 1.13-1.82, p=0.003), travel to South East Asia, China, Indian subcontinent, Africa and the Middle East (OR=3.089, 1.29-7.38, p=0.011), prior exposure to trimethoprim+/-sulfamethoxazole &/or an expanded-spectrum cephalosporin (OR=3.665, 1.30-10.35, p=0.014) and healthcare exposure in the previous six months (OR=3.16, 1.54-6.46, p=0.02).

Amongst our ESC-R-EC the blaCTX-M ESBLs was dominant (83% of ESC-R-EC), and the worldwide pandemic clone ST-131 was frequent (45% of ESC-R-EC).

Conclusion
In our low prevalence setting, ESC-R amongst community onset E. coli may be associated with both ‘export’ from healthcare facilities into the community and direct ‘import’ into the community from high-prevalence regions.

Foot-and-mouth disease in red deer - experimental infection and test methods performance

Summary: The aim of this study was to evaluate a number of foot-and-mouth disease (FMD) test methods for use in red deer. Ten animals were intranasally inoculated with the FMD virus (FMDV) O UKG 11/2001, monitored for clinical signs, and samples taken regularly (blood, serum, oral swabs, nasal swabs, probang samples and lesion swabs, if present) over a 4-week period. Only one animal, deer 1103, developed clinical signs (lesions under the tongue and at the coronary band of the right hind hoof). It tested positive by 3D and IRES real-time reverse transcription polymerase chain reaction (rRT-PCR) in various swabs, lesion materials and serum. In a non-structural protein (NSP) in-house ELISA (NSP-ELISA-IH), one commercial ELISA (NSP-ELISA-PR) and a commercial antibody NSP pen side test, only deer 1103 showed positive results from day post-inoculation (dpi) 14 onwards. Two other NSP-ELISAs detected anti-NSP serum antibodies with lower sensitivity. It also showed rising antibody levels in the virus neutralization test (VNT), the in-house SPO-ELISA-IH and the commercial SPO-ELISA-PR at dpi 9, and in another two commercial SPO-ELISAs at dpi 12 (SPO-ELISA-IV) and dpi 19 (SPO-ELISA-IZ), respectively. Six of the red deer that had been rRT-PCR and antibody negative were re-inoculated intramuscularly with the same O-serotype FMDV at dpi 14. None of these animals became rRT-PCR or NSP-ELISA positive, but all six animals became positive in the VNT, the in-house SPO-ELISA-IH and the commercial SPO-ELISA-PR. Two other commercial SPO-ELISAs were less sensitive or failed to detect animals as positive. The rRT-PCRs and the four most sensitive commercial ELISAs that had been used for the experimentally inoculated deer were further evaluated for diagnostic specificity (DSP) using 950 serum samples and 200 nasal swabs from non-infected animals. DSPs were 100% for the rRT-PCRs and between 99.8 and 100% for the ELISAs.

The PTEX component EXP2 is critical for establishing a patent malaria infection in mice

Export of most malaria proteins into the erythrocyte cytosol requires the Plasmodium Translocon of Exported proteins (PTEX) and a cleavable Plasmodium Export Element (PEXEL). In contrast, the contribution of PTEX in the liver stages and export of liver stage proteins is unknown. Here, using the FLP/FRT conditional mutatagenesis system, we generate transgenic P. berghei parasites deficient in EXP2, the putative pore-forming component of PTEX. Our data reveal that EXP2 is important for parasite growth in the liver and critical for parasite transition to the blood, with parasites impaired in their ability to generate a patent blood-stage infection. Surprisingly, whilst parasites expressing a functional PTEX machinery can efficiently export a PEXEL-bearing GFP reporter into the erythrocyte cytosol during a blood stage infection, this same reporter aggregates in large accumulations within the confines of the parasitophorous vacuole membrane during hepatocyte growth. Notably HSP101, the putative molecular motor of PTEX, could not be detected during the early liver stages of infection, which may explain why direct protein translocation of this soluble PEXEL-bearing reporter or indeed native PEXEL proteins into the hepatocyte cytosol has not been observed. This suggests that PTEX function may not be conserved between the blood and liver stages of malaria infection. This article is protected by copyright. All rights reserved.