Adjacent Uninfected Cells Research Articles

Herpes simplex virus spreads rapidly in human foreskin, partly driven by chemokine-induced redistribution of Nectin-1 on keratinocytes.

HSV infects keratinocytes in the epidermis of skin via nectin-1. We established a human foreskin explant infection model to investigate HSV entry and spread. HSV1 entry could only be achieved by the topical application of virus via high density microarray projections (HD-MAPs) to the epidermis, which penetrated beyond one third of its thickness, simulating in vivo microtrauma. Rapid lateral spread of HSV1 to a mean of 13 keratinocytes wide occurred after 24 hours and free virus particles were observed between keratinocytes, consistent with an intercellular route of spread. Nectin-1 staining was markedly decreased in foci of infection in the epidermis and in the human keratinocyte HaCaT cell line. Nectin-1 was redistributed, at the protein level, in adjacent uninfected cells surrounding infection, inducible by CCL3, IL-8 (or CXCL8), and possibly CXCL10 and IL-6, thus facilitating spread. These findings provide the first insights into HSV1 entry and spread in human inner foreskin in situ.

Extragenic suppression of an HSV-1 UL34 nuclear egress mutant reveals role for pUS9 as an inhibitor of epithelial cell-to-cell spread.

Herpesviruses are able to disseminate in infected hosts despite development of a strong immune response. Their ability to do this relies on a specialized process called cell-to-cell spread in which newly assembled virus particles are trafficked to plasma membrane surfaces that abut adjacent uninfected cells. The mechanism of cell-to-cell spread is obscure, and little is known about whether or how it is regulated in different cells. We show here that a viral protein with a well-characterized role in promoting spread from neurons has an opposite, inhibitory role in other cells.

IM-4 Impact of oHSV activated NOTCH signaling in tumor microenvironment and its impact on anti-tumor immunity

Oncolytic herpes simplex virus-1 (oHSV) is novel FDA-approved immunotherapy for advanced melanoma patients in US. Also, oHSV is recently approved for the treatment of recurrent GBM in Japan. We have shown that oHSV treatment of GBM cells induces NICD cleavage and NOTCH activation in adjacent uninfected glioma cells via HSV-1 microRNA-H16 (Otani Y and Yoo JY, Clin Cancer Res, 2020), however, the consequences of NOTCH on immunotherapy in GBM is unknow. Here we have investigated the impact of oHSV-induced NOTCH signaling on the tumor microenvironment (TME). Analysis of TCGA GBM data and experimental murine models revealed NOTCH induced immunosuppressive myeloid cell recruitment and limited anti-tumor immunity. In oHSV treated tissue, viral infection educated tumor associated macrophages to secrete CCL2 which recruited monocytic myeloid derived suppressor cell (MDSC) that attenuated anti-tumor immunity. Consistent with this, CCL2 induction was also observed in serum of recurrent GBM patients treated with oHSV (NCT03152318). Importantly, blockade of NOTCH signaling reduced the oHSV induced immunosuppressive environment and activated a CD8 dependent anti-tumor memory response. These findings present the opportunities for combination therapies that can help improve therapeutic benefit and anti-tumor immunity in GBM.

TAMI-11. IMPACT OF oHSV ACTIVATED NOTCH SIGNALING IN TUMOR MICROENVIRONMENT, AND ITS IMPACT ON ANTI-TUMOR IMMUNITY

Abstract NOTCH signaling is a method of cell-cell communication where membrane bound NOTCH ligands on signal-sending cells can bind to and initiate cleavage of the NOTCH receptor, releasing NICD which can initiate signal transduction in adjacent “signal-receiving” cells. We have recently shown that oHSV treatment of GBM cells induces NICD cleavage and NOTCH activation in adjacent uninfected glioma cells. RNA sequencing of GBM cells post-infection also uncovered Gene Ontology NOTCH signaling pathway to be significantly upregulated. This activation was induced by viral miRNA-H16, which represses FIH-1 expression. FIH-1 was found to be a negative regulator of Mib1, a ubiquitin ligase, which activates NOTCH ligand-mediated activation of adjacent signal-receiving cells bearing the NOTCH receptor (Otani et al Clin. Can. Res. 2020). Here we have investigated the impact of oHSV-induced NOTCH signaling on the tumor microenvironment. Treatment of brain tumors in immune competent mice with oHSV and NOTCH blocking gamma secretase inhibitor (GSI) induced an anti-tumor memory immune response. Long term survivors in mice treated with the combination also completely rejected subsequent tumor re-challenge in the other hemisphere. UMAP of flow cytometry of tumor-bearing hemispheres and functional analysis of isolated cellular fractions from treated mice showed a significant influx of MDSC cells after oHSV treatment that was rescued in mice treated with oHSV and GSI. Ongoing mechanistic studies are uncovering a significant induction of NOTCH in tumor associated macrophages that aids in recruitment of MDSC cells. Overall these studies have uncovered a significant impact of oHSV therapy on GBM tumor microenvironment and presents opportunities for combination therapies that can help improve therapeutic benefit and anti-tumor immunity.

Pathogenesis of ocular toxoplasmosis.

Ocular toxoplasmosis is a retinitis -almost always accompanied by vitritis and choroiditis- caused by intraocular infection with Toxoplasma gondii. Depending on retinal location, this condition may cause substantial vision impairment. T. gondii is an obligate intracellular protozoan parasite, with both sexual and asexual life cycles, and infection is typically contracted orally by consuming encysted bradyzoites in undercooked meat, or oocysts on unwashed garden produce or in contaminated water. Presently available anti-parasitic drugs cannot eliminate T. gondii from the body. In vitro studies using T. gondii tachyzoites, and human retinal cells and tissue have provided important insights into the pathogenesis of ocular toxoplasmosis. T. gondii may cross the vascular endothelium to access human retina by at least three routes: in leukocyte taxis; as a transmigrating tachyzoite; and after infecting endothelial cells. The parasite is capable of navigating the human neuroretina, gaining access to a range of cell populations. Retinal Müller glial cells are preferred initial host cells. T. gondii infection of the retinal pigment epithelial cells alters the secretion of growth factors and induces proliferation of adjacent uninfected epithelial cells. This increases susceptibility of the cells to parasite infection, and may be the basis of the characteristic hyperpigmented toxoplasmic retinal lesion. Infected epithelial cells also generate a vigorous immunologic response, and influence the activity of leukocytes that infiltrate the retina. A range of T. gondii genotypes are associated with human ocular toxoplasmosis, and individual immunogenetics -including polymorphisms in genes encoding innate immune receptors, human leukocyte antigens and cytokines- impacts the clinical manifestations. Research into basic pathogenic mechanisms of ocular toxoplasmosis highlights the importance of prevention and suggests new biological drug targets for established disease.

Use of cell fusion proteins to enhance adenoviral vector efficacy as an anti-cancer therapeutic.

Oncolytic viruses are designed to replicate in and kill cancer cells, and have shown tremendous promise in preclinical and clinical studies. Indeed, several oncolytic viruses are available to patients in a number of different countries around the world. However, most oncolytic viruses show a poor ability to spread throughout the tumor mass, frequently leading to only a partial response and regrowth of the tumor. One approach to improve spread of the viral effect throughout the tumor mass is to arm the oncolytic virus with a fusogenic protein. In this manner, a single infected cell can fuse with many adjacent uninfected cells, essentially amplifying the anti-tumor effects. In this review, we discuss the development and use of fusogenic proteins to enhance the efficacy of human adenovirus-based vectors for cancer therapy.

Molecular Basis of The Retinal Pigment Epithelial Changes That Characterize The Ocular Lesion in Toxoplasmosis.

When a person becomes infected with Toxoplasma gondii, ocular toxoplasmosis is the most common clinical presentation. The medical literature describes retinitis with surrounding hyperpigmentation secondary to proliferative changes in the retinal pigment epithelium, which is sufficiently characteristic that investigation often is not needed to make the diagnosis. We aimed to establish the frequency of “typical” ocular toxoplasmosis and delineate its molecular basis. Among 263 patients presenting consecutively with ocular toxoplasmosis to Ribeirão Preto General Hospital in Brazil, where T. gondii infection is endemic, 94.2% of 345 eyes had retinal hyperpigmentation. In ARPE-19 and primary human retinal pigment epithelial cell monolayers exposed to minimal numbers of T. gondii tachyzoites, the proliferation marker–KI-67–was increased in uninfected cells, which also were rendered more susceptible to infection. RT-qPCR and ELISA detected increased expression of vascular endothelial growth factor A (VEGF) and insulin-like growth factor (IGF)1, and decreased expression of thrombospondin (TSP)1 by infected cells. Blockade of VEGF and IGF1—or supplementation of TSP1—reversed the proliferation phenotype in uninfected cells. Our findings confirm that hyperpigmentation is a characteristic feature of retinitis in ocular toxoplasmosis, and demonstrate that T. gondii-infected human retinal pigment epithelial cells secrete VEGF and IGF1, and reduce production of TSP1, to promote proliferation of adjacent uninfected cells and create this disease-specific appearance.

Dual RNA-seq identifies human mucosal immunity protein Mucin-13 as a hallmark of Plasmodium exoerythrocytic infection

The exoerythrocytic stage of Plasmodium infection is a critical window for prophylactic intervention. Using genome-wide dual RNA sequencing of flow-sorted infected and uninfected hepatoma cells we show that the human mucosal immunity gene, mucin-13 (MUC13), is strongly upregulated during Plasmodium exoerythrocytic hepatic-stage infection. We confirm MUC13 transcript increases in hepatoma cell lines and primary hepatocytes. In immunofluorescence assays, host MUC13 protein expression distinguishes infected cells from adjacent uninfected cells and shows similar colocalization with parasite biomarkers such as UIS4 and HSP70. We further show that localization patterns are species independent, marking both P. berghei and P. vivax infected cells, and that MUC13 can be used to identify compounds that inhibit parasite replication in hepatocytes. This data provides insights into host-parasite interactions in Plasmodium infection, and demonstrates that a component of host mucosal immunity is reprogrammed during the progression of infection.

CX43 is essential for optimal cGAS function during cytosolic DNA-sensing

Abstract During intracellular Chlamydia infection, cytosolic DNA is sensed by cyclic GMP-AMP synthase (cGAS) that catalyzes the synthesis of cGAMP from ATP and GTP. cGAMP is a key mediator of IFN beta expression during DNA sensing and can also transfer to adjacent uninfected cells through intercellular connexin gap-junctions to induce intrinsic immunity. In this study, we investigated the role of gap junction protein connexin 43 (CX43) during Chlamydia infection. Using RNA-in situ hybridization, we discovered a distinct intracellular contribution of CX43 in IFN beta expression in the infected cells and cells transfected with DNA, a function distinct from its intercellular gap-junction role affecting IFN beta expression in adjacent uninfected cell. CX43 is essential for IFN beta expression during DNA-sensing upstream of STING activation, but not required during RNA-sensing. CX43 co-localized with transfected DNA and on the chlamydial inclusion membrane with cGAS. CX43-depleted cells showed significantly reduced cGAMP production during DNA-sensing. CX43 forms hemichannels on intracellular membrane, which open and close to allow nucleotide transfer. Blocking this transport across CX43 hemichannel reduced IFN beta expression during infection and DNA-sensing, without altering CX43 localization. These results uncover a novel role of CX43 in cGAMP synthesis by cGAS during cytosolic DNA-sensing.

Dengue virus activates cGAS through the release of mitochondrial DNA

Cyclic GMP-AMP synthetase (cGAS) is a DNA-specific cytosolic sensor, which detects and initiates host defense responses against microbial DNA. It is thus curious that a recent study identified cGAS as playing important roles in inhibiting positive-sense single-stranded RNA (+ssRNA) viral infection, especially since RNA is not known to activate cGAS. Using a dengue virus serotype 2 (DENV-2) vaccine strain (PDK53), we show that infection creates an endogenous source of cytosolic DNA in infected cells through the release of mitochondrial DNA (mtDNA) to drive the production of cGAMP by cGAS. Innate immune responses triggered by cGAMP contribute to limiting the spread of DENV to adjacent uninfected cells through contact dependent gap junctions. Our result thus supports the notion that RNA virus indirectly activates a DNA-specific innate immune signaling pathway and highlights the breadth of the cGAS-induced antiviral response.

A novel role for Connexin 43 in IFN beta expression during Chlamydia trachomatis infection and cytosolic DNA-sensing

Abstract Background The DNA sensor cGAS is essential for IFNβ expression in cells infected with Chlamydia. cGAMP generated during DNA sensing can also transfer via intercellular gap-junction proteins, connexins CX43/45 leading to IFNβ expression in adjacent uninfected cells. Present study highlights a novel role for CX43 in IFNβ expression during DNA-sensing and during Chlamydia infection, independent of its gap junction function. Methods Total IFNβ transcripts were measured by qRT-PCR following CX43 or CX45 siRNA mediated knockdown (KD). Single cell RNA-ISH method view RNA™ was used to visualize IFNβ mRNA in infected HeLa cells. CX43 localization was studied using IF and confocal microscopy. Results CX43-KD in HeLa cells reduced IFNβ expression by >90% (p<0.001) compared to control or CX45 KD, as measured by qRT-PCR. CX43-KD also reduced IFNβ mRNA in dsDNA transfected cells (p<0.001) but not with poly IC RNA. RNA-ISH showed IFNβ mRNA transcripts in infected cells (>90%) and in adjacent uninfected (~10%) cells, but not in distal uninfected cells, suggesting cell contact is required for adjacent-cell effect. Surprisingly, RNA-ISH of CX43-KD cells showed >85% reduction in IFNβ transcripts (p<0.0001) in infected cells, in addition to the loss of transcripts in cells adjacent to infected cells. CX43 localized proximal to the chlamydial inclusion membrane. Co-localization of CX43 was also observed with transfected dsDNA, but not dsRNA. Conclusion CX43 depletion has been shown to increase autophagy in cells. Here we show that CX43 depletion decreases IFNβ induction during DNA sensing. Our results suggest that like STING, CX43 could be a key player in both DNA sensing and autophagy, but with opposing roles. (Funded by NIAID R01-AI067678 to UN).

Varicella-Zoster Virus Downregulates Programmed Death Ligand 1 and Major Histocompatibility Complex Class I in Human Brain Vascular Adventitial Fibroblasts, Perineurial Cells, and Lung Fibroblasts.

Here, we provide the first demonstration that VZV downregulates PD-L1 expression in infected HBVAFs, HPNCs, and HFLs, which, together with the noted VZV-mediated downregulation of MHC-I, might foster persistent inflammation in vessels, leading to pathological vascular remodeling during VZV vasculopathy and persistent inflammation in infected lungs to promote subsequent infection of T cells and hematogenous virus spread. Identification of a potential mechanism by which persistent inflammation in the absence of effective viral clearance occurs in VZV vasculopathy and VZV infection of the lung is a step toward targeted therapy of VZV-induced disease.

Visualization of IFN-β mRNA in Chlamydia-infected and adjacent uninfected cells and the contribution of CX43 in intercellular transfer of cGAMP

Abstract Background IFNβ has been implicated a key effector of oviduct pathology after genital chlamydial infection in mice. We reported that the host DNA sensor cGAS (cGAMP synthase) is essential for IFNβ expression during Chlamydia trachomatis infection. Sensing during infection leads to generation of the second messenger, 2′3-cGAMP, which can migrate to uninfected adjacent cells via gap-junction mediated transfer. cGAMP binding to central adaptor molecule, STING drives IFNβ induction. The goals of this study were to visualize the mechanism of c-GAMP transfer and to identify the DNA source triggering this response. Methods cGAMP production was detected by mass spectrometry. The contribution of gap junction proteins, connexins CX43 and CX45 in intercellular transfer of cGAMP was assayed by siRNA depletion and subsequent co-culture experiments. view RNATM methodology was used to detect IFNβ mRNA transcripts in Hela cells. Mitochondrial DNA as IFNβ inducer was assessed in mtDNA depleted cell lines. Results Mass spectroscopy confirmed cGAMP in infected host cytosol. Connexin depletion studies revealed that CX43 but not CX45 was essential for optimal IFNβ expression during infection. IFNβ mRNA transcripts were visualized in infected and adjacent, uninfected cells. In contrast, distal uninfected cells lacking cell-cell contact were negative. IFNβ induction after chlamydia infection was unchanged in mtDNA depleted cells. Conclusion Overall, our results confirm the production of cGAMP in chlamydia-infected cells and its transfer via CX43 to adjacent cells resulting in IFNβ production. Our studies exclude mtDNA as a potential source initiating this response. We are currently investigating the role of Chlamydial-DNA as an initiator.

The DNA sensor, cyclic GMP-AMP synthase, is essential for induction of IFN-β during Chlamydia trachomatis infection.

IFN-β has been implicated as an effector of oviduct pathology resulting from genital chlamydial infection in the mouse model. In this study, we investigated the role of cytosolic DNA and engagement of DNA sensors in IFN-β expression during chlamydial infection. We determined that three-prime repair exonuclease-1, a host 3' to 5' exonuclease, reduced IFN-β expression significantly during chlamydial infection using small interfering RNA and gene knockout fibroblasts, implicating cytosolic DNA as a ligand for this response. The DNA sensor cyclic GMP-AMP synthase (cGAS) has been shown to bind cytosolic DNA to generate cyclic GMP-AMP, which binds to the signaling adaptor stimulator of IFN genes (STING) to induce IFN-β expression. We determined that cGAS is required for IFN-β expression during chlamydial infection in multiple cell types. Interestingly, although infected cells deficient for STING or cGAS alone failed to induce IFN-β, coculture of cells depleted for either STING or cGAS rescued IFN-β expression. These data demonstrate that cyclic GMP-AMP produced in infected cGAS(+)STING(-) cells can migrate into adjacent cells via gap junctions to function in trans in cGAS(-)STING(+) cells. Furthermore, we observed cGAS localized in punctate regions on the cytosolic side of the chlamydial inclusion membrane in association with STING, indicating that chlamydial DNA is most likely recognized outside the inclusion as infection progresses. These novel findings provide evidence that cGAS-mediated DNA sensing directs IFN-β expression during Chlamydia trachomatis infection and suggest that effectors from infected cells can directly upregulate IFN-β expression in adjacent uninfected cells during in vivo infection, contributing to pathogenesis.

Plasmodesmata without callose and calreticulin in higher plants – open channels for fast symplastic transport?

Plasmodesmata (PD) represent membrane-lined channels that link adjacent plant cells across the cell wall. PD of higher plants contain a central tube of endoplasmic reticulum (ER) called desmotubule. Membrane and lumen proteins seem to be able to move through the desmotubule, but most transport processes through PD occur through the cytoplasmic annulus (Brunkard etal., 2013). Calreticulin (CRT), a highly conserved Ca2+-binding protein found in all multicellular eukaryotes, predominantly located in the ER, was shown to localize to PD, though not all PD accumulate CRT. In nitrogen-fixing actinorhizal root nodules of the Australian tree Casuarina glauca, the primary walls of infected cells containing the microsymbiont become lignified upon infection. TEM analysis of these nodules showed that during the differentiation of infected cells, PD connecting infected cells, and connecting infected and adjacent uninfected cells, were reduced in number as well as diameter (Schubert etal., 2013). In contrast with PD connecting young infected cells, and most PD connecting mature infected and adjacent uninfected cells, PD connecting mature infected cells did not accumulate CRT. Furthermore, as shown here, these PD were not associated with callose, and based on their diameter, they probably had lost their desmotubules. We speculate that either this is a slow path to PD degradation, or that the loss of callose accumulation and presumably also desmotubules leads to the PD becoming open channels and improves metabolite exchange between cells.

The CuZn superoxide dismutase from Sclerotinia sclerotiorum is involved with oxidative stress tolerance, virulence, and oxalate production

One of the earliest plant responses to pathogens is the induced accumulation of reactive oxygen species (ROS). The superoxide ion is an important intermediate in the generation of ROS having a key regulatory function during plant–microbe interactions and is an important component in fungal development. The superoxide dismutase (SOD) family contributes to frontline defense via detoxification of reactive superoxide radical anions. Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic fungal pathogen with a broad host range. S. sclerotiorum produces the non-specific phytotoxin and key pathogenicity factor, oxalic acid (OA). We have identified an S. sclerotiorum SOD (Sssod1) with high similarity to CuZnSODs. Sssod1 contains an open reading frame of 908 bp in length and is predicted to encode a protein of 155 amino acids that harbors the entire hallmark motifs associated with SOD function. Treatment with the CuZnSOD inhibitor diethyldithiocarbamate (DETC) resulted in delayed hyphal growth and sclerotial development in a dose-dependent manner. Mutants generated carrying an Sssod1 deletion (ΔSssod1) exhibited morphological defects similar to those observed with the inhibitor treatment. Moreover, ΔSssod1 was more sensitive than wild-type to menadione, a redox cycling agent. Expression of Sssod1 was induced following treatment with oxidizing agents and during interaction with plant host tissue the ΔSssod1 mutant was significantly reduced in virulence on both tomato and tobacco plants compared to wild-type. Interestingly, pathogenicity of the superoxide dismutase mutant was mostly restored following supplementation with oxalate. We also observed that ΔSssod1 was reduced in oxalate production by half. In accordance with reduced virulence, ΔSssod1 induced a host oxidative burst in adjacent uninfected cells, a phenotype indicative of active pathogen recognition by the host. Intriguingly, during wild-type infection, host ROS production was significantly reduced. These results suggest that wild-type Sclerotinia suppresses host defense responses during infection.

Tamiflu-Resistant but HA-Mediated Cell-to-Cell Transmission through Apical Membranes of Cell-Associated Influenza Viruses

The infection of viruses to a neighboring cell is considered to be beneficial in terms of evasion from host anti-virus defense systems. There are two pathways for viral infection to “right next door”: one is the virus transmission through cell-cell fusion by forming syncytium without production of progeny virions, and the other is mediated by virions without virus diffusion, generally designated cell-to-cell transmission. Influenza viruses are believed to be transmitted as cell-free virus from infected cells to uninfected cells. Here, we demonstrated that influenza virus can utilize cell-to-cell transmission pathway through apical membranes, by handover of virions on the surface of an infected cell to adjacent host cells. Live cell imaging techniques showed that a recombinant influenza virus, in which the neuraminidase gene was replaced with the green fluorescence protein gene, spreads from an infected cell to adjacent cells forming infected cell clusters. This type of virus spreading requires HA activation by protease treatment. The cell-to-cell transmission was also blocked by amantadine, which inhibits the acidification of endosomes required for uncoating of influenza virus particles in endosomes, indicating that functional hemagglutinin and endosome acidification by M2 ion channel were essential for the cell-to-cell influenza virus transmission. Furthermore, in the cell-to-cell transmission of influenza virus, progeny virions could remain associated with the surface of infected cell even after budding, for the progeny virions to be passed on to adjacent uninfected cells. The evidence that cell-to-cell transmission occurs in influenza virus lead to the caution that local infection proceeds even when treated with neuraminidase inhibitors.

The Interferon-Inducible Gene viperin Restricts West Nile Virus Pathogenesis

Type I interferon (IFN) signaling coordinates an early antiviral program in infected and uninfected cells by inducing IFN-stimulated genes (ISGs) that modulate viral entry, replication, and assembly. However, the specific antiviral functions in vivo of most ISGs remain unknown. Here, we examined the contribution of the ISG viperin to the control of West Nile virus (WNV) in genetically deficient cells and mice. While modest increases in levels of WNV replication were observed for primary viperin(-/-) macrophages and dendritic cells, no appreciable differences were detected in deficient embryonic cortical neurons or fibroblasts. In comparison, viperin(-/-) adult mice infected with WNV via the subcutaneous or intracranial route showed increased lethality and/or enhanced viral replication in central nervous system (CNS) tissues. In the CNS, viperin expression was induced in both WNV-infected and adjacent uninfected cells, including activated leukocytes at the site of infection. Our experiments suggest that viperin restricts the infection of WNV in a tissue- and cell-type-specific manner and may be an important ISG for controlling viral infections that cause CNS disease.

The Host Phosphoinositide 5-Phosphatase SHIP2 Regulates Dissemination of Vaccinia Virus

After fusing with the plasma membrane, enveloped poxvirus virions form actin-filled membranous protrusions, called tails, beneath themselves and move toward adjacent uninfected cells. While much is known about the host and viral proteins that mediate formation of actin tails, much less is known about the factors controlling release. We found that the phosphoinositide 5-phosphatase SHIP2 localizes to actin tails. Localization requires phosphotyrosine, Abl and Src family tyrosine kinases, and neural Wiskott-Aldrich syndrome protein (N-WASP) but not the Arp2/Arp3 complex or actin. Cells lacking SHIP2 have normal actin tails but release more virus. Moreover, cells infected with viral strains with mutations in the release inhibitor A34 release more virus but recruit less SHIP2 to tails. Thus, the inhibitory effects of A34 on virus release are mediated by SHIP2. Together, these data suggest that SHIP2 and A34 may act as gatekeepers to regulate dissemination of poxviruses when environmental conditions are conducive.

Humoral and Cellular Immunity to Varicella‐Zoster Virus: An Overview

Under conditions of naturally acquired primary varicella-zoster virus (VZV) infection, the first response of the naive host is mediated by the innate immune system through antiviral cytokines and the activation of NK cells [1]. These responses are likely to be important for the initial control of VZV at mucosal sites of inoculation and to trigger the induction and amplification of adaptive, VZV-specific immunity. NK cells can lyse VZV-infected targets [2], and activated NK cells are a major source of interferon (IFN)–g production, which enhances the clonal expansion of antigen-specific T cells. IFN-a inhibits VZV replication in vitro, and treatment with exogenous type I IFN-a reduced the severity of varicella in immunocompromised children with varicella [3]. In addition, VZV replication in skin is associated with extensive production of IFN-a by adjacent uninfected epidermal cells in the SCIDhu model of VZV pathogenesis; blocking this IFN-a response caused a dramatic increase in VZV spread in skin [4]. Innate mechanisms of immune control have the capacity to maintain the host-virus equilibrium, despite the VZV immune evasion strategies that inhibit both class I and class II major histocompatibility complex (MHC) mechanisms for antigen presentation to T cells while the virus is being transferred to skin and in early stages of cutaneous infection [4–6]. These strategies