Benjamin M. Chain

Reactive oxygen species activate human peripheral blood dendritic cells.

This study investigates the effects of hydrogen peroxide, a potent oxygen free radical donor, on the phenotype and function of dendritic cells differentiated from peripheral blood precursors. We report that hydrogen peroxide induces an up-regulation of several dendritic cell surface markers involved in interaction with T cells, including MHC Class II molecules (DQ and DR) and the co-stimulatory molecules CD40 and CD86. Moreover we have observed that H2O2-treated dendritic cells are more efficient in promoting T cell proliferation than normal dendritic cells and that this enhancement can be blocked using the free radical scavenger agent N-acetylcysteine. Oxygen free radicals are a common by-product of inflammation, and our results suggest they may play an important role in activation of sentinel dendritic cells, linking tissue damage to the initiation of an adaptive immune response.

The injured cell: the role of the dendritic cell system as a sentinel receptor pathway.

A major unresolved paradox in immunology remains: how do we avoid harm, despite the abundant opportunities for induction of immune responses against self-proteins? Here, Mohammad Ibrahim, Benjamin Chain and David Katz extend Janeways proposed explanation, arguing that adaptive immune responses are initiated not only by conserved microbial products, but also by microenvironmental tissue injury. They suggest that the key step is local dendritic cell activation, followed by upregulation of T-cell costimulatory molecules on these cells, and migration, leading to antigen presentation.

Dengue Virus NS5 Inhibits Interferon-α Signaling by Blocking Signal Transducer and Activator of Transcription 2 Phosphorylation

Type I interferons (interferon [IFN]-alpha/beta) are key mediators of innate antiviral responses. Inhibition of IFN-mediated signal transduction by dengue viruses (DENVs), mosquito-borne flaviviruses of immense global health importance, probably plays a crucial role in determining the outcome of the virus-host interaction. Understanding the molecular basis of IFN antagonism by DENV would therefore provide critical insight into disease pathogenesis and new opportunities for development of antiviral therapies and rationally attenuated vaccines. Here we examine the effects of expression of DENV nonstructural proteins on cellular IFN responses. We show that expression of nonstructural protein 5 (NS5) alone inhibits IFN-alpha, but not IFN-gamma, signaling. Expression of the polymerase domain of NS5 is sufficient to inhibit IFN-alpha signaling. NS5 binds signal transducer and activator of transcription 2 (STAT2) and inhibits its phosphorylation. NS5 alone did not, however, induce degradation of STAT2, which occurs when all nonstructural proteins are expressed together. We conclude that DENV NS5 is a potent and specific type I IFN antagonist.

The sequence of sequencers: The history of sequencing DNA

Determining the order of nucleic acid residues in biological samples is an integral component of a wide variety of research applications. Over the last fifty years large numbers of researchers have applied themselves to the production of techniques and technologies to facilitate this feat, sequencing DNA and RNA molecules. This time-scale has witnessed tremendous changes, moving from sequencing short oligonucleotides to millions of bases, from struggling towards the deduction of the coding sequence of a single gene to rapid and widely available whole genome sequencing. This article traverses those years, iterating through the different generations of sequencing technology, highlighting some of the key discoveries, researchers, and sequences along the way.

Hypochlorous Acid: A Natural Adjuvant That Facilitates Antigen Processing, Cross-Priming, and the Induction of Adaptive Immunity

The production of hypochlorous acid (HOCl) is a characteristic of granulocyte activation, a hallmark of the early phase of innate immune responses. In this study, we show that, in addition to its well-established role as a microbicide, HOCl can act as a natural adjuvant of adaptive immunity. HOCl enhances the T cell responses to the model Ag OVA, facilitating the processing and presentation of this protein via the class II MHC pathway. HOCl modification also enhances cross-presentation of the tumor Ag tyrosinase-related protein 2 via class I MHC. The adjuvant effects of HOCl are independent of TLR signaling. The enhanced presentation of HOCl-modified OVA is mediated via modification of the N-linked carbohydrate side chain rather than formation of protein aldehydes or chloramines. HOCl-modified OVA is taken up more efficiently by APCs and is degraded more efficiently by proteinases. Atomic force microscopy demonstrated that enhanced uptake is mediated via specific receptor binding, one candidate for which is the scavenger receptor lectin-like oxidized low-density lipoprotein receptor, which shows enhanced binding to chlorinated OVA. A function of HOCl is therefore to target glycoprotein Ags to scavenger receptors on the APC surface. This additional mechanism linking innate and adaptive immunity suggests novel strategies to enhance immunity to vaccines.

Herpes Simplex Virus Infection of Dendritic Cells: Balance among Activation, Inhibition, and Immunity

Several lines of evidence suggest that dendritic cells (DCs), the most potent antigen-presenting cells known, play a role in the immunological control of herpes simplex virus (HSV) infections. HSV infection of DCs induced submaximal maturation, but DCs failed to mature further in response to lipopolysaccharide (LPS). LPS induced interleukin (IL)-12 secretion, and the induction of primary and secondary T cell responses were impaired by infection. Ultimately, DC infection resulted in delayed, asynchronous apoptotic cell death. However, infected DCs induced HSV recall responses in some individuals. Furthermore, soluble factors secreted by DCs after infection induced DC maturation and primed for IL-12 secretion after LPS stimulation. These data support a pathogenetic model of HSV infection, in which initial delay in the generation of immune responses to HSV at peripheral sites is mediated by disruption of DC function but is overcome by bystander DC maturation and cross-presentation of HSV antigens.

Effects of oxidised low density lipoprotein on dendritic cells: a possible immunoregulatory component of the atherogenic micro-environment?

OBJECTIVE The objective of this study was to explore the relationship between low density lipoprotein (LDL) and dendritic cell (DC) activation, based upon the hypothesis that reactive oxygen species (ROS)-mediated modification of proteins that may be present in local DC microenvironments could be important as mediators of this activation. Although LDL are known to be oxidised in vivo, and taken up by macrophages during atherogenesis; their effect on DC has not been explored previously. METHODS Human DCs were prepared from peripheral blood monocytes using GM-CSF and IL-4. Plasma LDLs were isolated by sequential gradient centrifugation, oxidised in CuSO(4), and oxidation arrested to yield mild, moderate and highly oxidised LDL forms. DCs exposed to these LDLs were investigated using combined phenotypic, functional (autologous T cell activation), morphological and viability assays. RESULTS Highly-oxidised LDL increased DC HLA-DR, CD40 and CD86 expression, corroborated by increased DC-induced T cell proliferation. Both native and oxidised LDL induced prominent DC clustering. However, high concentrations of highly-oxidised LDL inhibited DC function, due to increased DC apoptosis. CONCLUSIONS This study supports the hypothesis that oxidised LDL are capable of triggering the transition from sentinel to messenger DC. Furthermore, the DC clustering-activation-apoptosis sequence in the presence of different LDL forms is consistent with a regulatory DC role in immunopathogenesis of atheroma. A sequence of initial accumulation of DC, increasing LDL oxidation, and DC-induced T cell activation, may explain why local breach of tolerance can occur. Above a threshold level, however, supervening DC apoptosis limits this, contributing instead to the central plaque core.

The role of reactive oxygen species in triggering proliferation and IL-2 secretion in T cells

This paper examines the hypothesis that reactive oxygen species (ROS) play an important role as second messengers in T cell activation. Activation of T cells with phorbol ester in combination with either calcium ionophore, or anti-CD3 antibody results in a large rapid flux of ROS activity. In contrast, co-stimulation with CD28 does not enhance ROS activity. The ROS signal was sensitive to ascorbic acid, desferrioxamine and dimethyl sulfoxide, suggesting that the major active species being generated was the hydroxyl radical, probably by iron-catalyzed decomposition of hydrogen peroxide. The generation of ROS in T cells was regulated by an accessory population within the peripheral blood. An anti-CD2 antibody induced a strong ROS flux, suggesting that the CD2/LFA-3 interaction may be important in this regulation. T cell activation was inhibited by the same panel of anti-oxidants as ROS generation, but much higher concentrations were required for inhibition of proliferation and IL-2 release than those required to block ROS generation. These data imply that ROS are not obligate second messengers for initiation of T cell activation. The results are compatible, however, with a role for activation-dependent T cell ROS generation in modulating the overall T cell response via autocrine and paracrine signalling pathways.

The antigen-presenting environment in normal and human papillomavirus (HPV)-related premalignant cervical epithelium

The activation of HPV‐specific T cells within the cervical microenvironment is likely to play an important part in the natural history of cervical intraepithelial neoplasia (CIN). The extent and the type of T cell activation will depend critically on the expression of MHC, costimulatory cell surface molecules and cytokines by keratinocytes and Langerhans cells within the cervical lesion. Expression of MHC class II (HLA‐DR and ‐DQ), costimulatory/adhesion molecules (CD11a/18, CD50, CD54, CD58 and CD86) and cytokines (tumour necrosis factor‐alpha (TNF‐α) and IL‐10) was therefore investigated by immunohistochemistry in normal squamous epithelium (n = 12), low‐grade (n = 23) and high‐grade (n = 18) squamous intraepithelial lesions of the cervix. CIN progression was associated with de novo expression of HLA‐DR and CD54, and increased expression of CD58 by keratinocytes. However, significantly, there was no expression of any adhesion/costimulation molecule by epithelial Langerhans cells in any cervical biopsy studied. Furthermore, TNF‐α, a potent activator of Langerhans cells, was expressed constitutively by basal keratinocytes in normal cervix (12+/12), but expression of this cytokine was absent in a number of CIN samples (20+/23 for low‐grade, 12+/18 for high‐grade CIN). Conversely, the suppressive cytokine IL‐10 was absent in normal epithelium (0+/12), but was up‐regulated in a number of CIN lesions (12+/23 for low‐grade, 8+/18 for high‐grade CIN). The restricted expression of costimulation/adhesion molecules and the nature of the cytokine microenvironment within the epithelium may act to limit effective immune responses in some CIN lesions.

Understanding HSV-1 entry glycoproteins.

Herpes Simplex Virus‐1 is a common infectious agent, but the precise detail of entry and infection of cells has only now begun to be clarified. Four viral surface glycoproteins (gB, gD, gH and gL) are required. This review summarises the known structure and function of each of these essential viral envelope glycoproteins, and explores what is known about their close cooperation with each other in mediating cellular membrane fusion. It is suggested that, following gD binding to one of its entry receptors, membrane fusion is mediated by gB and the heterodimer gH/gL. Significantly, these four entry glycoproteins also play a key role in the interaction between HSV and the host immune system. The glycoproteins serve an important role as targets of adaptive immunity. However, recent studies have demonstrated that the same proteins also play a key role in initiating the early innate immune response to HSV. Understanding the complex functions of these HSV proteins may be essential for successful development of vaccines for HSV. Copyright