After birth, the alveolar capillary network expands to increase gas exchange surface area and endothelial-derived signals promote alveolarization. Lung capillaries are comprised of two distinct subsets, one with proliferative potential to facilitate growth and repair (Cap1), and the other serving a specialized role in gas exchange (Cap2). However, the molecular mechanisms directing capillary speciation, developmental plasticity, and fate transitions during development and repair are not well understood. Here, we show that Cap2 are absent in late embryonic life but rapidly appear and expand immediately after birth. We show that Cap1 progenitors first transition to a novel, intermediate cell state (CapINT), characterized by co-expression of Cap1 and Cap2 markers, and heightened proliferation. CapINT are present in both the developing mouse and human lung. Hyperoxia, an experimental model of bronchopulmonary dysplasia (BPD), a chronic lung disease marked by impaired alveolarization, increases CapINT abundance and persistence and expands Cap2 EC. CapINT EC are also increased in human infants dying with active BPD. Using genetic lineage tracing, single cell transcriptomics, ATAC-sequencing and a mouse model that permits inducible deletion of VEGFR2 in CapINT and Cap2 EC, we show that postnatal abrogation of VEGFR2 markedly increases CapINT EC abundance, blocks Cap2 terminal differentiation, impairs alveolarization, and activates alveolar fibroblasts. Finally, we identify ERG as a putative VEGFR2-downstream mechanism that promotes CapINT to Cap2 differentiation. Taken together, our data show that Cap1-Cap2 differentiation is a two-step process that only requires VEGFR2 for the second step. Elucidation of the physiologic and molecular pathways that control the initial transition of Cap1 to CapINT EC has the potential to reveal new therapeutic targets for lung diseases that disrupt the alveolar capillary formation and integrity.

Rapid expansion of the pulmonary microvasculature through angiogenesis drives alveolarization, the final stage of lung development that occurs postnatally and dramatically increases lung gas-exchange surface area. Disruption of pulmonary angiogenesis induces long-term structural and physiologic lung abnormalities, including bronchopulmonary dysplasia, a disease characterized by compromised alveolarization. Although endothelial cells are primary determinants of pulmonary angiogenesis, mesenchymal cells (MC) play a critical and dual role in angiogenesis and alveolarization. Therefore, we performed single cell transcriptomics and in-situ imaging of the developing lung to profile mesenchymal cells during alveolarization and in the context of lung injury. Specific mesenchymal cell subtypes were present at birth with increasing diversity during alveolarization even while expressing a distinct transcriptomic profile from more mature correlates. Hyperoxia arrested the transcriptomic progression of the MC, revealed differential cell subtype vulnerability with pericytes and myofibroblasts most affected, altered cell to cell communication, and led to the emergence of Acta1 expressing cells. These insights hold the promise of targeted treatment for neonatal lung disease, which remains a major cause of infant morbidity and mortality across the world.

Rationale: Worldwide, the incidence of both preterm births and chronic lung disease of infancy, or bronchopulmonary dysplasia (BPD), remains high. Infants with BPD have larger and fewer alveoli, pathology that can persist into adulthood. Though hypoxia inducible factor-1α (HIF-1α) plays a significant role in mediating pulmonary angiogenesis and alveolarization, the cell specific role of HIF-1α remains incompletely understood. Objectives: To determine whether HIF-1α, in a mesenchymal cells (MC) subset, mediates postnatal alveolarization. Methods: We generated mice with cell-specific deletion of HIF-1α by crossing SM22α-promoter-driven Cre mice with HIF-1αflox/flox mice (SM22α- HIF-1α-/-), determined SM22α-expressing cell identity using single cell RNA-seq, and interrogated clinical samples from preterm infants. Measurement and Main Outcomes: Deletion of HIF-1α in SM22α expressing cells had no effect on lung structure at day (d) 3 of life. However, at 8d there were fewer and larger alveoli, a difference that persisted into adulthood. Microvascular density, elastin organization, and peripheral branching of the lung vasculature were decreased in SM22α-HIF-1α-/-, compared to control, mice. Single cell RNA-seq demonstrated that 3 MC subtypes (myofibroblasts, airway and vascular smooth muscle cells (VSMC)) express SM22α. Pulmonary VSMC from SM22α- HIF-1α-/- had decreased angiopoetin 2 expression and, in co-culture experiments, a diminished capacity to promote angiogenesis that was rescued by angiopoetin-2. Angiopoetin-2 expression in the tracheal aspirates of preterm infants was inversely correlated with overall time on mechanical ventilation, a marker of disease severity. Conclusions: SM22α-specific HIF-1α expression drives peripheral angiogenesis and alveolarization in the lung, perhaps by promoting angiopoetin-2 expression.

At birth, the lung is still immature, heightening susceptibility to injury but enhancing regenerative capacity. Angiogenesis drives postnatal lung development. Therefore, we profiled the transcriptional ontogeny and sensitivity to injury of pulmonary endothelial cells (EC) during early postnatal life. Although subtype speciation was evident at birth, immature lung EC exhibited transcriptomes distinct from mature counterparts, which progressed dynamically over time. Gradual, temporal changes in aerocyte capillary EC (CAP2) contrasted with more marked alterations in general capillary EC (CAP1) phenotype, including distinct CAP1 present only in the early alveolar lung expressing Peg3, a paternally imprinted transcription factor. Hyperoxia, an injury that impairs angiogenesis induced both common and unique endothelial gene signatures, dysregulated capillary EC crosstalk, and suppressed CAP1 proliferation while stimulating venous EC proliferation. These data highlight the diversity, transcriptomic evolution, and pleiotropic responses to injury of immature lung EC, possessing broad implications for lung development and injury across the lifespan.

In a mouse model wherein hypoxia-inducible factor 1 alpha (HIF-1α) is stabilized in vascular smooth muscle cells, we found that HIF-1α regulates vasoconstriction by limiting phosphorylation of myosin light chain and regulates vascular remodeling through p27 induction. These findings highlight a cell-specific role for HIF-1α in the inhibition of pulmonary vasoconstriction and vascular remodeling.

Though survival rates for preterm infants are improving, the incidence of chronic lung disease of infancy, or bronchopulmonary dysplasia (BPD), remains high. Histologically, BPD is characterized by larger and fewer alveoli. Hypoxia-inducible factors (HIFs) may be protective in the context of hyperoxia-induced lung injury, but the cell-specific effects of HIF expression in neonatal lung injury remain unknown. Thus, we sought to determine whether HIF stabilization in SM22α-expressing cells can limit hyperoxia-induced neonatal lung injury. We generated SM22α-specific HIF-1α-stabilized mice ( SM22α-PHD1/2−/− mice) by cross-breeding SM22α-promotor-driven Cre recombinase mice with prolyl hydroxylase PHD1flox/flox and PHD2flox/flox mice. Neonatal mice were randomized to 21% O2 (normoxia) or 80% O2 (hyperoxia) exposure for 14 days. For the hyperoxia recovery studies, neonatal mice were recovered from normoxia for an additional 10 wk. SM22α-specific HIF-1α stabilization mitigated hyperoxia-induced lung injury and preserved microvessel density compared with control mice for both neonates and adults. In SM22α-PHD1/2−/− mice, pulmonary artery endothelial cells (PAECs) were more proliferative and pulmonary arteries expressed more collagen IV compared with control mice, even under hyperoxic conditions. Angiopoietin-2 (Ang2) mRNA expression in pulmonary artery smooth muscle cells (PASMC) was greater in SM22α-PHD1/2−/− compared with control mice in both normoxia and hyperoxia. Pulmonary endothelial cells (PECs) cocultured with PASMC isolated from SM22α-PHD1/2−/− mice formed more tubes and branches with greater tube length compared with PEC cocultured with PASMC isolated from SM22α-PHD1/2+/+ mice. Addition of Ang2 recombinant protein further augmented tube formation for both PHD1/2+/+ and PHD1/2−/− PASMC. Cell-specific deletion of PHD1 and 2 selectively increases HIF-1α expression in SM22α-expressing cells and protects neonatal lung development despite prolonged hyperoxia exposure. HIF stabilization in SM22α-expressing cells preserved endothelial cell proliferation, microvascular density, increased angiopoietin-2 expression, and lung structure, suggesting a role for cell-specific HIF-1α stabilization to prevent neonatal lung injury.

Lung mesenchymal cells play an essential role in development and at birth, as the lung moves from a fluid-filled to an oxygen-rich environment with a stable gas-liquid interface. The molecular details and cellular changes accompanying this highly coordinated process remain incompletely understood. Therefore, we performed single cell transcriptomics and in-situ imaging of the developing lung in both health and disease to characterize the spectrum of mesenchymal cell states prior to the onset of air-breathing life through late alveolarization to gain insight into their role in orchestrating tissue maturation. We found that cell type diversity in the mesenchymal compartment increases rapidly during normal development but is delayed during neonatal exposure to 80% O 2 hyperoxia, a model for bronchopulmonary dysplasia. This study identifies the molecular transitions between populations of mesenchymal cells at discrete developmental time points across fibroblast, smooth muscle, and mural compartments and elucidates the global and cell type-specific effects of neonatal hyperoxia, including the emergence of Acta1 + cells which are absent in normoxic neonatal lungs. These granular insights hold the promise of targeted treatment for neonatal lung disease, which remains a major cause of infant morbidity and mortality across the world.

Background Endothelial cells (EC) sit at the forefront of dramatic physiologic changes occurring in the pulmonary circulation during late embryonic and early postnatal life. First, as the lung moves from the hypoxic fetal environment to oxygen-rich postnatal environment, marked changes in pulmonary EC structure and function facilitate a marked increase in blood flow from the placenta to the lungs. Subsequently, pulmonary angiogenesis expands the microvasculature to drive exponential distal lung growth during early postnatal life. Yet, how these marked physiologic changes alter distinct EC subtypes to facilitate the transition of the pulmonary circulation and regulate vascular growth and remodeling remains incompletely understood. Methods In this report, we employed single cell RNA-transcriptomics and in situ RNA imaging to profile pulmonary EC in the developing mouse lung from just before birth through this period of rapid postnatal growth. Results Multiple, transcriptionally distinct macro- and microvascular EC were identified in the late embryonic and early postnatal lung, with gene expression profiles distinct from their adult EC counterparts. A novel arterial subtype, unique to the developing lung localized to the distal parenchyma and expressed genes that regulate vascular growth and patterning. Birth particularly heightened microvascular diversity, inducing dramatic shifts in the transcriptome of distinct microvascular subtypes in pathways related to proliferation, migration and antigen presentation. Two distinct waves of EC proliferation were identified, including one just prior to birth, and a second during early alveolarization, a time of exponential pulmonary angiogenesis. Chronic hyperoxia, an injury that impairs parenchymal and vascular growth, induced a common gene signature among all pulmonary EC, unique alterations to distinct microvascular EC subtypes, and disrupted EC-EC and EC-immune cell cross talk. Conclusions Taken together, these data reveal tremendous diversity of pulmonary EC during a critical window of postnatal vascular growth, and provide a detailed molecular map that can be used to inform both normal vascular development and alterations in EC diversity upon injury. These data have important implications for lung diseases marked by dysregulated angiogenesis and pathologic pulmonary vascular remodeling.

At birth, the lungs rapidly transition from a pathogen-free, hypoxic environment to a pathogen-rich, rhythmically distended air-liquid interface. Although many studies have focused on the adult lung, the perinatal lung remains unexplored. Here, we present an atlas of the murine lung immune compartment during early postnatal development. We show that the late embryonic lung is dominated by specialized proliferative macrophages with a surprising physical interaction with the developing vasculature. These macrophages disappear after birth and are replaced by a dynamic mixture of macrophage subtypes, dendritic cells, granulocytes, and lymphocytes. Detailed characterization of macrophage diversity revealed an orchestration of distinct subpopulations across postnatal development to fill context-specific functions in tissue remodeling, angiogenesis, and immunity. These data both broaden the putative roles for immune cells in the developing lung and provide a framework for understanding how external insults alter immune cell phenotype during a period of rapid lung growth and heightened vulnerability.

VZV IE62 is an essential, immediate-early, tegument protein and consists of five domains. We generated recombinant viruses carrying mutations in the first three IE62 domains and tested their influence on VZV replication kinetics. The mutations in domain I did not affect replication kinetics while domain II mutations, disrupting the DNA binding and dimerization domain (DBD), were lethal for VZV replication. Mutations in domain III of the nuclear localization signal (NLS) and the two phosphorylation sites S686A/S722A resulted in slower growth in early and late infection respectively and were associated with IE62 accumulation in the cytoplasm and nucleus respectively. This study mapped the functional domains of IE62 in context of viral infection, indicating that DNA binding and dimerization domain is essential for VZV replication. In addition, the correct localization of IE62, whether nuclear or cytoplasmic, at different points in the viral life cycle, is important for normal progression of VZV replication.

ABSTRACT The tegument proteins encoded by ORF11 and ORF9 of varicella-zoster virus (VZV) are conserved among all alphaherpesvirus. We previously demonstrated that the ORF9 gene is essential, whereas ORF11 is dispensable in vitro but its deletion severely impairs VZV infection of skin xenografts in the SCID mouse model in vivo . Here we report that ORF11 protein interacts with ORF9 protein in infected cells as well as in the absence of other viral proteins, and we have mapped the ORF11 protein domain involved in their interaction. Although ORF11 is an RNA binding protein, the interaction between ORF11 and ORF9 proteins was not mediated by RNA or DNA bridging. VZV recombinants with mutations preventing ORF11 protein binding to ORF9 protein had no effect on 6-day growth kinetics based on plaque numbers, but plaque sizes were reduced in vitro . However, disruption of the ORF11 and ORF9 protein interaction was associated with failure to replicate in skin xenografts in vivo . Further, we demonstrate that in the absence of their interaction, the ORF9 protein displays an identical cellular localization, accumulating in the trans -Golgi region, whereas the ORF11 protein exhibits aberrant localization, dispersing throughout the cytoplasm. Overall, our observations suggest that while complete tegument assembly may not be necessary for VZV replication in vitro , the interaction between the ORF11 and ORF9 proteins appears to be critical for the proper localization of ORF11 protein to the assembly complex and for production of infectious virus during VZV pathogenesis in skin.

The tropism of herpes simplex virus (HSV-1) for human sensory neurons infected in vivo was examined using dorsal root ganglion (DRG) xenografts maintained in mice with severe combined immunodeficiency (SCID). In contrast to the HSV-1 lytic infectious cycle in vitro, replication of the HSV-1 F strain was restricted in human DRG neurons despite the absence of adaptive immune responses in SCID mice, allowing the establishment of neuronal latency. At 12 days after DRG inoculation, 26.2% of human neurons expressed HSV-1 protein and 13.1% expressed latency-associated transcripts (LAT). Some infected neurons showed cytopathic changes, but HSV-1, unlike varicella-zoster virus (VZV), only rarely infected satellite cells and did not induce fusion of neuronal and satellite cell plasma membranes. Cell-free enveloped HSV-1 virions were observed, indicating productive infection. A recombinant HSV-1-expressing luciferase exhibited less virulence than HSV-1 F in the SCID mouse host, enabling analysis of infection in human DRG xenografts for a 61-day interval. At 12 days after inoculation, 4.2% of neurons expressed HSV-1 proteins; frequencies increased to 32.1% at 33 days but declined to 20.8% by 61 days. Frequencies of LAT-positive neurons were 1.2% at 12 days and increased to 40.2% at 33 days. LAT expression remained at 37% at 61 days, in contrast to the decline in neurons expressing viral proteins. These observations show that the progression of HSV-1 infection is highly restricted in human DRG, and HSV-1 genome silencing occurs in human neurons infected in vivo as a consequence of virus-host cell interactions and does not require adaptive immune control.

MxA is an antiviral protein induced by interferon (IFN)-α/β that is known to inhibit the replication of many RNA viruses. In these experiments, the 76-kDa MxA protein expressed in IFN-α-treated cells was shown to have antiviral activity against herpes simplex virus-1 (HSV-1), a human DNA virus. However, MxA was expressed as a 56-kDa protein in HSV-1-infected cells in the absence of IFN-α. This previously unrecognized MxA isoform was produced from an alternatively spliced MxA transcript that had a deletion of Exons 14–16 and a frame shift altering the C-terminus. The variant MxA (varMxA) isoform was associated with HSV-1 regulatory proteins and virions in nuclear replication compartments. varMxA expression enhanced HSV-1 infection as shown by a reduction in infectious virus titers from cells in which MxA had been inhibited by RNA interference and by an increase in HSV-1 titers when the 56-kDa varMxA was expressed constitutively. Thus, the human MxA gene encodes two MxA isoforms, which are expressed differentially depending on whether the stimulus is IFN-α or HSV-1. These findings show that alternative splicing of cellular mRNA can result in expression of a novel isoform of a host defense gene that supports instead of restricting viral infection.

The deletion of ORF11 severely impaired VZV infection of human skin xenografts. Here, we investigate the characteristics and functions of the ORF11 gene product. ORF11 is expressed as a 118 kDa polypeptide in VZV-infected cells; the protein is present in the nucleus and cytoplasm and is incorporated into VZ virions. Although ORF11 had little effect in transactivating VZV gene promoters in transfection assays, deleting ORF11 from the virus was associated with reduced expression of immediate early proteins IE4, IE62 and IE63, and the major glycoprotein, gE. ORF11 was identified as an RNA binding protein and its RNA binding domain was defined. However, disrupting the ORF11 RNA binding domain did not affect skin infection, indicating that RNA binding capacity, conserved among the alphahepesviruses homologues, is not essential while the contribution of ORF11 to the expression of the IE proteins and gE may be required for VZV pathogenesis in skin in vivo.

Varicella-zoster virus (VZV) is a human α-herpesvirus that causes varicella (chickenpox) during primary infection and zoster (shingles) upon reactivation. Like other viruses, VZV must subvert the intrinsic antiviral defenses of differentiated human cells to produce progeny virions. Accordingly, VZV inhibits the activation of the cellular transcription factors IFN regulatory factor 3 (IRF3) and signal transducers and activators of transcription 1 (STAT1), thereby downregulating antiviral factors, including IFNs. Conversely, in this study, we found that VZV triggers STAT3 phosphorylation in cells infected in vitro and in human skin xenografts in SCID mice in vivo and that STAT3 activation induces the anti-apoptotic protein survivin. Small-molecule inhibitors of STAT3 phosphorylation and survivin restrict VZV replication in vitro, and VZV infection of skin xenografts in vivo is markedly impaired by the administration of the phospho-STAT3 inhibitor S3I-201. STAT3 and survivin are required for malignant transformation caused by γ-herpesviruses, such as Kaposi's sarcoma virus. We show that STAT3 activation is also critical for VZV, a nononcogenic herpesvirus, via a survivin-dependent mechanism. Furthermore, STAT3 activation is critical for the life cycle of the virus because VZV skin infection is necessary for viral transmission and persistence in the human population. Therefore, we conclude that takeover of this major cell-signaling pathway is necessary, independent of cell transformation, for herpesvirus pathogenesis and that STAT3 activation and up-regulation of survivin is a common mechanism important for the pathogenesis of lytic as well as tumorigenic herpesviruses.

MxA is an antiviral protein induced by interferon (IFN)‐α/β that is known to inhibit the replication of many RNA viruses. In these experiments, the 76‐kDa MxA protein expressed in IFN‐α‐treated cells was shown to have antiviral activity against herpes simplex virus‐1 (HSV‐1), a human DNA virus. However, MxA was expressed as a 56‐kDa protein in HSV‐1‐infected cells in the absence of IFN‐α. This previously unrecognized MxA isoform was produced from an alternatively spliced MxA transcript that had a deletion of Exons 14–16 and a frame shift altering the C‐terminus. The variant MxA (varMxA) isoform was associated with HSV‐1 regulatory proteins and virions in nuclear replication compartments. varMxA expression enhanced HSV‐1 infection as shown by a reduction in infectious virus titers from cells in which MxA had been inhibited by RNA interference and by an increase in HSV‐1 titers when the 56‐kDa varMxA was expressed constitutively. Thus, the human MxA gene encodes two MxA isoforms, which are expressed differentially depending on whether the stimulus is IFN‐α or HSV‐1. These findings show that alternative splicing of cellular mRNA can result in expression of a novel isoform of a host defense gene that supports instead of restricting viral infection.

Varicella-zoster virus (VZV) is a medically important human alphaherpesvirus that causes varicella and zoster. VZV initiates primary infection by inoculation of the respiratory mucosa. In the course of primary infection, VZV establishes a life-long persistence in sensory ganglia; VZV reactivation from latency may result in zoster in healthy and immunocompromised patients. The VZV genome has at least 70 known or predicted open reading frames (ORFs), but understanding how these gene products function in virulence is difficult because VZV is a highly human-specific pathogen. We have addressed this obstacle by investigating VZV infection of human tissue xenografts in the severe combined immunodeficiency mouse model. In studies relevant to the pathogenesis of primary VZV infection, we have examined VZV infection of human T cell (thymus/liver) and skin xenografts. This work supports a new paradigm for VZV pathogenesis in which VZV T cell tropism provides a mechanism for delivering the virus to skin. We have also shown that VZV-infected T cells transfer VZV to neurons in sensory ganglia. The construction of infectious VZV recombinants that have deletions or targeted mutations of viral genes or their promoters and the evaluation of VZV mutants in T cell and skin xenografts has revealed determinants of VZV virulence that are important for T cell and skin tropism in vivo.

ABSTRACT Varicella-zoster virus (VZV) is an alphaherpesvirus that is restricted to humans. VZV infection of differentiated cells within the host and establishment of latency likely require evasion of innate immunity and limited secretion of antiviral cytokines. Since interferons (IFNs) severely limit VZV replication, we examined the ability of VZV to modulate the induction of the type I IFN response in primary human embryonic lung fibroblasts (HELF). IFN-β production was not detected, and transcription of two interferon response factor 3 (IRF3)-dependent interferon-stimulated genes (ISGs), ISG54 and ISG56, in response to poly(I:C) stimulation was downregulated in VZV-infected HELF. Inhibition of IRF3 function did not require VZV replication; the viral immediate-early protein 62 (IE62) alone was sufficient to produce this effect. IE62 blocked TBK1-mediated IFN-β secretion and IRF3 function, as shown in an IFN-stimulated response element (ISRE)-luciferase reporter assay. However, IRF3 function was preserved if constitutively active IRF3 (IRF3-5D) was expressed in VZV-infected or IE62-transfected cells, indicating that VZV interferes with IRF3 phosphorylation. IE62-mediated inhibition was mapped to blocking phosphorylation of at least three serine residues on IRF3. However, IE62 binding to TBK1 or IRF3 was not detected and IE62 did not perturb TBK1-IRF3 complex formation. IE62-mediated inhibition of IRF3 function was maintained even if IE62 transactivator activity was disrupted. Thus, IE62 has two critical but discrete roles following VZV entry: to induce expression of VZV genes and to disarm the IFN-dependent antiviral defense through a novel mechanism that prevents IRF3 phosphorylation.

Varicella-zoster virus (VZV) is an alphaherpesvirus that infects skin, lymphocytes, and sensory ganglia. VZV glycoprotein E (gE) has a unique N-terminal region (aa1-188), which is required for replication and includes domains involved in secondary envelopment, efficient cell-cell spread, and skin infection in vivo. The nonconserved N-terminal region also mediates binding to the insulin-degrading enzyme (IDE), which is proposed to be a VZV receptor. Using viral mutagenesis to make the recombinant rOka-DeltaP27-G90, we showed that amino acids in this region are required for gE/IDE binding in infected cells; this deletion reduced cell-cell spread in vitro and skin infection in vivo. However, a gE point mutation, linker insertions, and partial deletions in the aa27-90 region, and deletion of a large portion of the unique N-terminal region, aa52-187, had similar or more severe effects on VZV replication in vitro and in vivo without disrupting the gE/IDE interaction. VZV replication in T cells in vivo was not impaired by deletion of gE aa27-90, suggesting that these gE residues are not essential for VZV T cell tropism. However, the rOka-DeltaY51-P187 mutant failed to replicate in T cell xenografts as well as skin in vivo. VZV tropism for T cells and skin, which is necessary for its life cycle in the human host, requires this nonconserved region of the N-terminal region of VZV gE.

Type I interferon induced MxA has antiviral activity against RNA viruses. Here we demonstrate a previously unrecognized MxA isoform induced by herpes simplex virus‐1 (HSV‐1) in human fibroblasts. Transcript encoding MxA splice variant has a deletion in Exons 14–16 which encode a central interactive domain associated with recognition of viral nucleocapsids and is predicted to encode a novel peptide sequence at the C‐terminal region as compared with IFN ‐induced MxA prototype. Polyclonal antiserum raised in rabbit against C‐terminal half of MxA splice variant demonstrated that HSV‐1 induced variant MxA undergoes nuclear translocation associated with viral replication compartment. Infection of variant MxA‐overexpressing fibroblasts with HSV‐1 resulted in the enhancement of viral yields but the yields were decreased in MxA‐knockdown cell by siRNA, suggesting that HSV‐1 induced MxA splice variant enhances viral replication. Both IFN‐ α and HSV‐1 are able to activate the promoter of MxA in luciferase reporter assay; however, only the MxA variant is translated in virus‐infected cells. Thus, differential expression of MxA controlled by IFN‐α or HSV‐1 could result in the increase of host resistance or favoring viral replication, depending on stimulating event. In summary, modulation of cellular mRNA could be a novel mechanism for human alphaherpesviruses to avoid innate immune detection.