Endogenous Murine BST-2/Tetherin Is Not a Major Restriction Factor of Influenza A Virus Infection

BST-2 (tetherin, CD317, HM1.24) restricts virus growth by tethering enveloped viruses to the cell surface. The role of BST-2 during influenza A virus infection (IAV) is controversial. Here, we assessed the capacity of endogenous BST-2 to restrict IAV in primary murine cells. IAV infection increased BST-2 surface expression by primary macrophages, but not alveolar epithelial cells (AEC). BST-2-deficient AEC and macrophages displayed no difference in susceptibility to IAV infection relative to wild type cells. Furthermore, BST-2 played little role in infectious IAV release from either AEC or macrophages. To examine BST-2 during IAV infection in vivo, we infected BST-2-deficient mice. No difference in weight loss or in viral loads in the lungs and/or nasal tissues were detected between BST-2-deficient and wild type animals. This study rules out a major role for endogenous BST-2 in modulating IAV in the mouse model of infection.

Hepatitis B virus-like particles access major histocompatibility class I and II antigen presentation pathways in primary dendritic cells

Virus-like particles (VLPs) represent high density displays of viral proteins that efficiently trigger immunity. VLPs composed of the small hepatitis B virus envelope protein (HBsAgS) are useful vaccine platforms that induce humoral and cellular immune responses. Notably, however, some studies suggest HBsAgS VLPs impair dendritic cell (DC) function. Here we investigated HBsAgS VLP interaction with DC subsets and antigen access to major histocompatibility complex (MHC) class I and II antigen presentation pathways in primary DCs. HBsAgS VLPs impaired plasmacytoid DC (pDC) interferon alpha (IFNα) production in response to CpG in vitro, but did not alter conventional DC (cDC) or pDC phenotype when administered in vivo. To assess cellular immune responses, HBsAgS VLPs were generated containing the ovalbumin (OVA) model epitopes OVA(257-264) and OVA(323-339) to access MHCI and MHCII antigen presentation pathways, respectively; both in vitro and following immunisation in vivo. HBsAgS VLP-OVA(257-264) elicited CTL responses in vivo that were not enhanced by inclusion of an additional MHCII helper epitope. HBsAgS VLP-OVA(257-264) administered in vivo was cross-presented by CD8(+) DCs, but not CD8(-) DCs. Therefore, HBsAgS VLPs can deliver antigen to both MHCI and MHCII antigen presentation pathways in primary DCs and promote cytotoxic and helper T cell priming despite their suppressive effect on pDCs.

Targeting antigen to bone marrow stromal cell-2 expressed by conventional and plasmacytoid dendritic cells elicits efficient antigen presentation

Bone marrow stromal cell-2 (BST-2) has major roles in viral tethering and modulation of interferon production. Here we investigate BST-2 as a receptor for the delivery of antigen to dendritic cells (DCs). We show that BST-2 is expressed by a panel of mouse and human DC subsets, particularly under inflammatory conditions. The outcome of delivering antigen to BST-2 expressed by steady state and activated plasmacytoid DC (pDC) or conventional CD8(+) and CD8(-) DCs was determined. T-cell responses were measured for both MHC class I (MHCI) and MHC class II (MHCII) antigen presentation pathways in vitro. Delivering antigen via BST-2 was compared with that via receptors DEC205 or Siglec-H. We show that despite a higher antigen load and faster receptor internalisation, when antigen is delivered to steady state or activated pDC via BST-2, BST-2-targeted activated conventional DCs present antigen more efficiently. Relative to DEC205, BST-2 was inferior in its capacity to deliver antigen to the MHCI cross-presentation pathway. In contrast, BST-2 was superior to Siglec-H at initiating either MHCI or MHCII antigen presentation. In summary, BST-2 is a useful receptor to target with antigen, given its broad expression pattern and ability to access both MHCI and MHCII presentation pathways with relative efficiency.

Influenza epitope-specific CD8+ T cell avidity, but not cytokine polyfunctionality, can be determined by TCRβ clonotype

Cytokine polyfunctionality has recently emerged as a correlate of effective CTL immunity to viruses and tumors. Although the determinants of polyfunctionality remain unclear, there are published instances of a link between the production of multiple effector molecules and the peptide plus MHC class I molecule avidity of T cell populations. Influenza A virus infection of C57BL/6J mice induces CTL populations specific for multiple viral epitopes, each with varying proportions of monofunctional (IFN-γ(+) only) or polyfunctional (IFN-γ(+)TNF-α(+)IL-2(+)) CTLs. In this study, we probe the link between TCR avidity and polyfunctionality for two dominant influenza epitopes (D(b)NP(366) and D(b)PA(224)) by sequencing the TCR CDR3β regions of influenza-specific IFN-γ(+) versus IFN-γ(+)IL-2(+) cells, or total tetramer(+) versus high-avidity CTLs (as defined by the peptide plus MHC class I molecule-TCR dissociation rate). Preferential selection for particular clonotypes was evident for the high-avidity D(b)PA(224)-specific set but not for any of the other subsets examined. These data suggest that factors other than TCRβ sequence influence cytokine profiles and demonstrate no link between differential avidity and polyfunctionality.

Narrowed TCR diversity for immunised mice challenged with recombinant influenza A-HIV Env(311-320) virus

Understanding CD8+ T cell responses generated by live virus vectors is critical for the rational design of next generation HIV CTL-based vaccines. We used recombinant influenza viruses expressing the HIV Env(311-320) peptide in the neuraminidase stalk to study response magnitude, cytokine production and repertoire diversity for the elicited CD8+ D(d)Env(311) CTL set. The insertion of the CD8+ D(d)Env(311) epitope into the NA stalk resulted in a decrease in viral fitness that was reflected in lower lung viral titres. While not affecting the magnitude of endogenous primary influenza-specific responses, the introduction of the D(d)Env(311) CD8+ T cell epitope altered the hierarchy of responses following secondary challenge. The CD8+ K(d)NP(147) response increased 9-fold in the spleen following secondary infection whereas the CD8+ D(d)Env(311) response increased 15-fold in the spleen. Moreover, this study is the first to describe narrowing of CD8+ TCR repertoire diversity in the context of an evolving secondary immune response against influenza A virus. Analysis of Vbeta bias for CD8+ D(d)Env(311) T cell responses showed a narrowing of CD8+ Vbeta8.1/8.2 D(d)Env(311) TCR repertoire diversity. This work further emphasizes the importance of understanding vaccine-induced CD8+ T cell responses.

Granzyme A expression reveals distinct cytolytic CTL subsets following influenza A virus infection

CTL mediate anti-viral immunity via targeted exocytosis of cytolytic granules containing perforin and members of the granzyme (grz) serine protease family. Here, we provide the first analysis of grzA protein expression by murine anti-viral CTL. During the progression of influenza A virus infection, CTL expressed two divergent cytolytic phenotypes: grzA(-)B(+) and grzA(+)B(+). CTL lacked grzA expression during the initial rounds of antigen-driven division. High levels of grzA were expressed by influenza-specific CTL early post infection (day 6), particularly in tissues associated with the infected respiratory tract (bronchoalveolar lavage, lung). Following resolution of influenza infection, a small population of memory CTL expressed grzA. Interestingly, individual influenza A virus-derived epitope-specific CTL expressed different levels of grzA. The grzA expression hierarchy was determined to be K(b)PB1(703)=D(b)F2(62)=K(b)NS2(114)>D(b)NP(366)=D(b)PA(224) and inversely correlated with CTL magnitude. Therefore following influenza infection, a CTL cytolytic hierarchy was established relating to the different profiles of antigen expression and relative immunodominance. Analysis of CTL grzA expression during influenza virus immunity has enabled a more detailed insight into the cytolytic mechanisms of virus elimination.

Transience of MHC Class I-restricted antigen presentation after influenza A virus infection

Antigen expressed as MHC Class I glycoprotein (pMHCI) complexes on dendritic cells is the primary driver of CD8(+) T cell clonal expansion and differentiation. As we seek to define the molecular differences between acutely stimulated cytotoxic T lymphocyte (CTL) effectors and long-lived memory T cells, it is essential that we understand the duration of in vivo pMHCI persistence. Although infectious influenza A virus is readily cleared by mammalian hosts, that does not necessarily mean that all influenza antigen is totally eliminated. An exhaustive series of carefully controlled adoptive transfer experiments using 3 different carboxy fluorescein diacetate succinimidyl ester-labeled T cell receptor-transgenic CTL populations and a spectrum of genetically engineered and wild-type influenza A viruses provided no evidence for pMHCI persistence over the 30-60-d interval after virus challenge. Molecular profiles identified in antigen-specific T cells at this time may thus be considered to reflect established immunologic memory and not recent CTL activation from a persistent pMHCI pool.

Mobilizing for pedestrian safety: an experiment in community action

In contrast to the steady reduction in mortality and morbidity from collisions involving motor vehicle occupants, relatively little progress has been made in controlling motor vehicle/pedestrian collisions. Engineering modifications are the most effective means of reducing such collisions, but mainly because of their cost, and public apathy about pedestrian safety, are too rarely employed. A modest experiment in community action was undertaken by attempting to induce the authorities of 10 small cities to apply for state funds to create a single model pedestrian refuge in their respective communities. Our hope was that this model would later lead to more widespread improvements. The key elements of the campaign were organizing local pedestrian safety task forces, compiling local pedestrian injury statistics, and publicizing the stories of pedestrian injury victims. At the conclusion of the planning process, all 10 target communities submitted grant applications and all 10 received full grant funding. Five projects were completed as planned, two are under construction, and the plans for three were abandoned. Pedestrian safety is not an issue that captures public attention. To make progress, goals must be modest, and a dedicated constituency must be developed. "Victim advocacy" is a vital part of this process. Progress in injury control requires concerted community action.

Drowsiness, counter-measures to drowsiness, and the risk of a motor vehicle crash

OBJECTIVES

Knowledge of how different indicators of drowsiness affect crash risk might be useful to drivers. This study sought to estimate how drowsiness related factors, and factors that might counteract drowsiness, are related to the risk of a crash.

METHODS

Drivers on major highways in a rural Washington county were studied using a matched case-control design. Control (n=199) drivers were matched to drivers in crashes (n=200) on driving location, travel direction, hour, and day of the week.

RESULTS

Crash risk was greater among drivers who felt they were falling asleep (adjusted relative risk (aRR) 14.2, 95% confidence interval (CI) 1.4 to 147) and those who drove longer distances (aRR 2.2 for each additional 100 miles, 95% CI 1.4 to 3.3). Risk was also greater among drivers who had slept nine or fewer hours in the previous 48 hours, compared with those who had slept 12 hours. Crash risk was less for drivers who used a highway rest stop (aRR 0.5, 95% CI 0.3 to 1.0), drank coffee within the last two hours (aRR 0.5, 95% CI 0.3 to 0.9), or played a radio while driving (aRR 0.6, 95% CI .4 to 1.0).

CONCLUSION

Drivers may be able to decrease their risk of crashing if they: (1) stop driving if they feel they are falling asleep; (2) use highway rest stops; (3) drink coffee; (4) turn on a radio; (5) get at least nine hours sleep in the 48 hours before a trip; and (6) avoid driving long distances by sharing the driving or interrupting the trip.