Suppression of virus-specific antibody production by CD8+ class I-restricted antiviral cytotoxic T cells in vivo.

The question of whether virus-induced immunosuppression includes the antibody response against the infecting virus itself was evaluated in a model situation. Transgenic mice expressing the T-cell receptor (TCR) specific for peptide 32-42 of lymphocytic choriomeningitis virus (LCMV) glycoprotein 1 presented by Db reacted with a strong transgenic cytotoxic T-lymphocyte (CTL) response starting on day 3 after infection with a high dose (10(6) PFU intravenously [i.v.]) of the WE strain of LCMV (LCMV-WE); LCMV-specific antibody production in the spleen was suppressed in these mice. Low-dose (10(2) PFU i.v.) infection resulted in an antiviral antibody response comparable to that of the transgene-negative littermates. The induction of suppression of LCMV-specific antibody responses was specifically mediated by CD8+ TCR transgenic CTLs, since the LCMV-8.7 variant virus (which is not recognized by transgenic TCR-expressing CTLs because of a point mutation) did not induce suppression. In addition, treatment with CD8 monoclonal antibody in vivo abrogated suppression. Once suppression had been established, it was found to be nonspecific. The abrogation of antibody responses depended on the relative kinetics of the antibody response involved and the kinetics of the anti-LCMV CTL response. Analysis of T- and B-cell subpopulations showed no significant changes, but immunohistochemical analysis of spleens revealed extensive destruction of follicular organization in lymphoid tissue by day 4 in transgenic mice infected with LCMV-WE but not in those infected with the CTL escape mutant LCMV-8.7. Impairment of antigen presentation rather than of T or B cells was also suggested by adoptive transfer experiments, showing that transferred infected macrophages may improve the anti-LCMV antibody response in LCMV-immunosuppressed transgenic recipients; also, T and B cells from suppressed transgenic mice did respond in irradiated and virus-infected nontransgenic mice with antibody formation to LCMV. Such virus-triggered, T-cell-mediated immunopathology causing the suppression of B cells and of protective antibody responses, including those against the infecting virus itself, may permit certain viruses to establish persistent infections.     

Adding Content to Contacts: Measurement of High Quality Contacts for Maternal and Newborn Health in Ethiopia,North East Nigeria,and Uttar Pradesh,India

BackgroundFamilies in high mortality settings need regular contact with high quality services, but existing population-based measurements of contacts do not reflect quality. To address this, in 2012, we designed linked household and frontline worker surveys for Gombe State, Nigeria, Ethiopia, and Uttar Pradesh, India. Using reported frequency and content of contacts, we present a method for estimating the population level coverage of high quality contacts.ConclusionsMeasuring content of care to reflect the quality of contacts can reveal missed opportunities to deliver best possible health care.     

Lymphoid follicle destruction and immunosuppression after repeated CpG oligodeoxynucleotide administration

DNA containing unmethylated cytidyl guanosyl (CpG) sequences, which are underrepresented in mammalian genomes but prevalent in prokaryotes, is endocytosed by cells of the innate immune system, including macrophages, monocytes and dendritic cells, and activates a pathway involving Toll-like receptor-9 (TLR9). CpG-containing oligodeoxynucleotides (CpG-ODN) are potent stimulators of innate immunity, and are currently being tested as adjuvants of antimicrobial, antiallergic, anticancer and antiprion immunotherapy. Little is known, however, about the consequences of repeated CpG-ODN administration, which is advocated for some of these applications. Here we report that daily injection of 60 microg CpG-ODN dramatically alters the morphology and functionality of mouse lymphoid organs. By day 7, lymphoid follicles were poorly defined; follicular dendritic cells (FDC) and germinal center B lymphocytes were suppressed. Accordingly, CpG-ODN treatment for > or =7 d strongly reduced primary humoral immune responses and immunoglobulin class switching. By day 20, mice developed multifocal liver necrosis and hemorrhagic ascites. All untoward effects were strictly dependent on CpG and TLR9, as neither the CpG-ODN treatment of Tlr9(-/-) mice nor the repetitive challenge of wild-type mice with nonstimulatory ODN (AT-ODN) or with the TLR3 agonist polyinosinic:cytidylic acid (polyI:C) were immunotoxic or hepatotoxic.     

Complement facilitates early prion pathogenesis

New-variant Creutzfeldt-Jakob disease and scrapie are typically initiated by extracerebral exposure to the causative agent, and exhibit early prion replication in lymphoid organs. In mouse scrapie, depletion of B-lymphocytes prevents neuropathogenesis after intraperitoneal inoculation, probably due to impaired lymphotoxin-dependent maturation of follicular dendritic cells (FDCs), which are a major extracerebral prion reservoir. FDCs trap immune complexes with Fc-gamma receptors and C3d/C4b-opsonized antigens with CD21/CD35 complement receptors. We examined whether these mechanisms participate in peripheral prion pathogenesis. Depletion of circulating immunoglobulins or of individual Fc-gamma receptors had no effect on scrapie pathogenesis if B-cell maturation was unaffected. However, mice deficient in C3, C1q, Bf/C2, combinations thereof or complement receptors were partially or fully protected against spongiform encephalopathy upon intraperitoneal exposure to limiting amounts of prions. Splenic accumulation of prion infectivity and PrPSc was delayed, indicating that activation of specific complement components is involved in the initial trapping of prions in lymphoreticular organs early after infection.     

Reactive oxygen species delay control of lymphocytic choriomeningitis virus

Cluster of differentiation (CD)8⁺ T cells are like a double edged sword during chronic viral infections because they not only promote virus elimination but also induce virus-mediated immunopathology. Elevated levels of reactive oxygen species (ROS) have been reported during virus infections. However, the role of ROS in T-cell-mediated immunopathology remains unclear. Here we used the murine lymphocytic choriomeningitis virus to explore the role of ROS during the processes of virus elimination and induction of immunopathology. We found that virus infection led to elevated levels of ROS producing granulocytes and macrophages in virus-infected liver and spleen tissues that were triggered by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Lack of the regulatory subunit p47phox of the NADPH oxidase diminished ROS production in these cells. While CD8⁺ T cells exhibited ROS production that was independent of NADPH oxidase expression, survival and T-cell function was elevated in p47phox-deficient (Ncf1^−/−) mice. In the absence of p47phox, enhanced T-cell immunity promoted virus elimination and blunted corresponding immunopathology. In conclusion, we find that NADPH-mediated production of ROS critically impairs the immune response, impacting elimination of virus and outcome of liver cell damage.     

Contribution of SecDF to <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>resistance and expression of virulence factors

Background  

SecDF is an accessory factor of the conserved Sec protein translocation machinery and belongs to the resistance-nodulation-cell division (RND) family of multidrug exporters. SecDF has been shown in Escherichia coli and Bacillus subtilis to be involved in the export of proteins. RND proteins can mediate resistance against various substances and might be of relevance in antimicrobial therapy. The role of RND proteins in Staphylococcus aureus has not yet been determined.     

Streptococcal SpeB Cleaved PAR-1 Suppresses ERK Phosphorylation and Blunts Thrombin-Induced Platelet Aggregation

Background

The family of 4 related protease-activated receptors (PAR-1, 2, 3 & 4) expressed by mammalian cells allow to sense for and react to extracellular proteolytic activity. Since major human bacterial pathogens secret a wide array of protease(-s) we investigated whether they interfere with human PAR function.

Methodology/Principal Findings

Supernatants from cultures of major human bacterial pathogens were assayed for the presence of protease(-s) capable to cleave overexpressed human PAR-1, 2, 3 and 4 reporter constructs. Group A streptococcus (GAS) was found to secret a PAR-1-cleaving protease. Experiments involving genetical and pharmacological gain and loss of function identified streptococcal pyrogenic exotoxin B SpeB as the protease responsible. On the host’s side analysis of overexpressed PAR-1 carrying alanine substitutions and deletions showed the amino acid residue leucine₄₄ on PAR-1’s extracellular N-terminus to be the only cleavage site. Complementary studies on endogenously expressed PAR-1 using PAR-1 blocking antibodies further supported our conclusion. Through PAR-1 cleavage SpeB efficiently blunted thrombin-induced induction of the ERK-pathway in endothelial cells and prevented platelets aggregation in response to thrombin.

Conclusions/Significance

Our results identify a novel function of the streptococcal virulence factor SpeB. By cleaving human PAR-1 at the N-terminal amino acid residue leucine₄₄ SpeB rendered endothelial cells unresponsive to thrombin and prevented human platelets from thrombin-induced aggregation. These results suggest that by blunting PAR-1 signaling, SpeB modulates various innate host responses directed against invasive GAS potentially helping the invasive bacteria to escape. This may allow to tailor additional treatments in the future since upon invasion of the blood stream endothelial cells as well as platelets and mononuclear cells respond to PAR-1 agonists aiming to prevent further bacterial dissemination.     

Porphyromonas gingivalis Regulates TREM-1 in Human Polymorphonuclear Neutrophils via Its Gingipains

The Triggering Receptor Expressed on Myeloid cells 1 (TREM-1) is a cell surface receptor of the immunoglobulin superfamily, with the capacity to amplify pro-inflammatory cytokine production and regulate apoptosis. Polymorphonuclear neutrophils (PMNs) are the first line of defence against infection, and a major source of TREM-1. Porphyromonas gingivalis is a Gram-negative anaerobe highly implicated in the inflammatory processes governing periodontal disease, which is characterized by the destruction of the tooth-supporting tissues. It expresses a number of virulence factors, including the cysteine proteinases (or gingipains). The aim of this in vitro study was to investigate the effect of P. gingivalis on TREM-1 expression and production by primary human PMNs, and to evaluate the role of its gingipains in this process. After 4 h of challenge, P. gingivalis enhanced TREM-1 expression as identified by quantitative real-time PCR. This was followed by an increase in soluble (s)TREM-1 secretion over a period of 18 h, as determined by ELISA. At this time-point, the P. gingivalis-challenged PMNs exhibited diminished TREM-1 cell-membrane staining, as identified by flow cytometry and confocal laser scanning microscopy. Furthermore engagement of TREM-1, by means of anti-TREM-1 antibodies, enhanced the capacity of P. gingivalis to stimulate interleukin (IL)-8 production. Conversely, antagonism of TREM-1 using a synthetic peptide resulted in reduction of IL-8 secretion. Using isogenic P. gingivalis mutant strains, we identified the Arg-gingipain to be responsible for shedding of sTREM-1 from the PMN surface, whereas the Lys-gingipain had the capacity to degrade TREM-1. In conclusion, the differential regulation of TREM-1 by the P. gingivalis gingipains may present a novel mechanism by which P. gingivalis manipulates the host innate immune response helping to establish chronic periodontal inflammation.     

B cell activation state-governed formation of germinal centers following viral infection

Germinal centers are structures that promote humoral memory cell formation and affinity maturation, but the triggers for their development are not entirely clear. Activated extrafollicular B cells can form IgM-producing plasmablasts or enter a germinal center reaction and differentiate into memory or plasma cells, mostly of the IgG isotype. Vesicular stomatitis virus (VSV) induces both types of response, allowing events that promote each of these pathways to be studied. In this work, extrafollicular vs germinal center responses were examined at a cellular level, analyzing VSV-specific B cells in infected mice. We show that VSV-specific germinal centers are transiently formed when insufficient proportions of specific T cell help is available and that strong B cell activation in cells expressing high levels of the VSV-specific BCR promoted their differentiation into early blasts, whereas moderate stimulation of B cells or interaction with Th cells restricted extrafollicular responses and promoted germinal center formation.