CIITA enhances HIV-1 attachment to CD4+ T cells leading to enhanced infection and cell depletion.

Activated CD4(+) T cells are more susceptible to HIV infection than resting T cells; the reason for this remains unresolved. Induction of CIITA and subsequent expression of the MHC class II isotype HLA-DR are hallmarks of CD4(+) T cell activation; therefore, we investigated the role of CIITA expression in T cells during HIV infection. CIITA-expressing SupT1 cells display enhanced virion attachment in a gp160/CD4-dependent manner, which results in increased HIV infection, virus release, and T cell depletion. Although increased attachment and infection of T cells correlated with HLA-DR surface expression, Ab blocking, transient expression of HLA-DR without CIITA, and short hairpin RNA knockdown demonstrate that HLA-DR does not directly enhance susceptibility of CIITA-expressing cells to HIV infection. Further analysis of the remaining MHC class II isotypes, HLA-DP and HLA-DQ, MHC class I isotypes, HLA-A, HLA-B, and HLA-C, and the class II Ag presentation genes, invariant chain and HLA-DM, demonstrate that these proteins likely do not contribute to CIITA enhancement of HIV infection. Finally, we demonstrate that in activated primary CD4(+) T cells as HLA-DR/CIITA expression increases there is a corresponding increase in virion attachment. Overall, this work suggests that induction of CIITA expression upon CD4(+) T cell activation contributes to enhanced attachment, infection, virus release, and cell death through an undefined CIITA transcription product that may serve as a new antiviral target.

Overview of varicella-zoster virus glycoproteins gC, gH and gL.

The VZV genome is smaller than the HSV genome and only encodes nine glycoproteins. This chapter provides an overview of three VZV glycoproteins: gH (ORF37), gL (ORF60), and gC (ORF14). All three glycoproteins are highly conserved among the alpha herpesviruses. However, VZV gC exhibits unexpected differences from its HSV counterpart gC. In particular, both VZV gC transcription and protein expression are markedly delayed in cultured cells. These delays occur regardless of the virus strain or the cell type, and may account in part for the aberrant assembly of VZV particles. In contrast to VZV gC, the general properties of gH and gL more closely resemble their HSV homologs. VZV gL behaves as a chaperone protein to facilitate the maturation of the gH protein. The mature gH protein in turn is a potent fusogen. Its fusogenic activity can be abrogated when infected cultures are treated with monoclonal anti-gH antibodies.

Diagnostic accuracy of rapid antigen tests for COVID-19 compared to the viral genetic test in adults: a systematic review protocol.

OBJECTIVE: The objective of this diagnostic accuracy review is to evaluate the effectiveness of rapid antigen tests versus viral genetic PCR-based tests on COVID-19 diagnostic accuracy in adults 18 years and over. INTRODUCTION: Due to the rapidly changing nature of the COVID-19 pandemic, it is imperative that clinicians have access to the most relevant and effective tools and information required to combat this disease. Testing strategies are being developed continuously and need to be evaluated to ensure their appropriate implementation into clinical practice. INCLUSION CRITERIA: This systematic review will include publications that are in the English language (originally or translated) and any gray literature pertaining to the tests of interest. All races, ages over 18, and geographic locations will be considered. METHODS: MEDLINE (PubMed), Embase (Elsevier), Scopus (Elsevier), Qinsight (Quertle), and WHO COVID-19 database (World Health Organization) will be searched. Scopus, Qinsight, and WHO COVID-19 include gray literature. Studies in English published from November 2019 to the present will be considered. Animal studies and studies including pregnant women will be excluded. Retrieval of full-text studies, data extraction, and assessment of methodological quality will be performed independently by two reviewers. A custom data extraction table will be used. Findings will be graphically represented with two forest plots, one for sensitivity and the other for specificity. The strategy for meta-analysis includes producing a summary receiver operating characteristic curve and estimating the summary sensitivity/specificity for each threshold provided in the articles. SYSTEMATIC REVIEW REGISTRATION NUMBER: PROSPERO CRD42020224250.

HIV-1 replication and pathogenesis in the human thymus.

How HIV replicates and causes destruction of the thymus, and how to restore thymic function, are among the most important questions of HIV-1 pathogenesis and therapy in adult as well as pediatric patients. The thymus appears to function, albeit at reduced levels, throughout the life of adults, to respond to T cell depletion induced by HIV and to be suppressed by HIV. In this review, we summarize recent findings concerning HIV replication and pathogenesis in the human thymus, focusing on mechanistic insights gleaned from studies in the SCID-hu Thy/Liv mouse and human fetal-thymus organ culture (HF-TOC) models. First, we discuss HIV viral determinants and host factors involved in the replication of HIV in the thymus. Second, we consider evidence that both viral factors and host factors contribute to HIV-induced thymocyte depletion. We thus propose that multiple mechanisms, including depletion and suppression of progenitor cells, paracrine and direct lytic depletion of thymocytes, and altered thymocyte selection are involved in HIV-induced pathology in the thymus. With the SCID-hu Thy/Liv mouse and HF-TOC models, it will be important in the coming years to further clarify the virological, cell biological, and immunological mechanisms of HIV replication and pathogenesis in human thymus, and to correlate their significance in HIV disease progression.

Class II transactivator (CIITA) enhances cytoplasmic processing of HIV-1 Pr55Gag.

BACKGROUND: The Pr55(gag) (Gag) polyprotein of HIV serves as a scaffold for virion assembly and is thus essential for progeny virion budding and maturation. Gag localizes to the plasma membrane (PM) and membranes of late endosomes, allowing for release of infectious virus directly from the cell membrane and/or upon exocytosis. The host factors involved in Gag trafficking to these sites are largely unknown. Upon activation, CD4+ T cells, the primary target of HIV infection, express the class II transcriptional activator (CIITA) and therefore the MHC class II isotype, HLA-DR. Similar to Gag, HLA-DR localizes to the PM and at the membranes of endosomes and specialized vesicular MHC class II compartments (MIICs). In HIV producer cells, transient HLA-DR expression induces intracellular Gag accumulation and impairs virus release. METHODOLOGY/PRINCIPAL FINDINGS: Here we demonstrate that both stable and transient expression of CIITA in HIV producer cells does not induce HLA-DR-associated intracellular retention of Gag, but does increase the infectivity of virions. However, neither of these phenomena is due to recapitulation of the class II antigen presentation pathway or CIITA-mediated transcriptional activation of virus genes. Interestingly, we demonstrate that CIITA, apart from its transcriptional effects, acts cytoplasmically to enhance Pr160(gag-pol) (Gag-Pol) levels and thereby the viral protease and Gag processing, accounting for the increased infectivity of virions from CIITA-expressing cells. CONCLUSIONS/SIGNIFICANCE: This study demonstrates that CIITA enhances HIV Gag processing, and provides the first evidence of a novel, post-transcriptional, cytoplasmic function for a well-known transactivator.

The HIV1 protein Vpr acts to promote G2 cell cycle arrest by engaging a DDB1 and Cullin4A-containing ubiquitin ligase complex using VprBP/DCAF1 as an adaptor.

The roles of the HIV1 protein Vpr in virus replication and pathogenesis remain unclear. Expression of Vpr in dividing cells causes cell cycle arrest in G(2). Vpr also facilitates low titer infection of terminally differentiated macrophages, enhances transcription, promotes apoptosis, and targets cellular uracil N-glycosylase for degradation. Using co-immunoprecipitation and tandem mass spectroscopy, we found that HIV1 Vpr engages a DDB1- and cullin4A-containing ubiquitin-ligase complex through VprBP/DCAF1. HIV2 Vpr has two Vpr-like proteins, Vpr and Vpx, which cause G(2) arrest and facilitate macrophage infection, respectively. HIV2 Vpr, but not Vpx, engages the same set of proteins. We further demonstrate that the interaction between Vpr and the ubiquitin-ligase components as well as further assembly of the ubiquitin-ligase are necessary for Vpr-mediated G(2) arrest. Our data support a model in which Vpr engages the ubiquitin ligase to deplete a cellular factor that is required for cell cycle progression into mitosis. Vpr, thus, functions like the HIV1 proteins Vif and Vpu to usurp cellular ubiquitin ligases for viral functions.

Characterization of a thymus-tropic HIV-1 isolate from a rapid progressor: role of the envelope.

Loss of T cell homeostasis usually precedes the onset of AIDS. We hypothesized that rapid progressors may be transmitted with HIV-1 that is particularly able to perturb T cell homeostasis. To this end, we have tested two transmitted, syncytium-inducing (SI) viral isolates from a rapid progressor in two thymus models. One of the isolates (R3A) exhibited markedly rapid kinetics of replication and thymocyte depletion. These phenotypes mapped to the envelope, as a recombinant NL4-3 virus encoding the R3A envelope had similar phenotypes, even in the absence of nef. Notably, the viruses with high pathogenic activity in the thymus (R3A and NL4-R3A) did not show enhanced replication or cytopathicity in PHA-stimulated PBMCs. Furthermore, NL4-R3A did not enhance replication of the coinfected NL4-3 virus in the thymus, suggesting an intrinsic advantage of the R3A envelope. The R3A envelope showed higher entry activity in infecting human T cells and in depleting CD4+ thymocytes when expressed in trans. These data suggest that SI viruses with unique envelope functions which can overcome barriers to transmission may hasten disease progression by perturbing T cell homeostasis.

Wild-type Kaposi's sarcoma-associated herpesvirus isolated from the oropharynx of immune-competent individuals has tropism for cultured oral epithelial cells.

Based on the observation that wild-type Kaposi's sarcoma-associated herpesvirus (KSHV) DNA can be detected in the oral cavity of healthy, immunocompetent individuals, we hypothesized that epithelial cells could be infected in vitro by wild-type (WT) KSHV isolated from immunocompetent individuals. Primary oral epithelial (P-EPI) cells and telomerase-immortalized oral epithelial cells were generated from human gingival tissue and were then infected in vitro with WT KSHV isolated from throat wash samples. Markers of lytic and latent KSHV infection were detected in cultures by 24 h postinfection by immunofluorescence confocal microscopic assays. The infectivity of the WT and BCBL virus was blocked by neutralizing antibodies against KSHV gB. The presence of KSHV DNA in these cells was confirmed by real-time PCR amplification of different regions of the viral genome. The significant in vitro viral replication that had occurred was inhibited by ganciclovir and by neutralizing antibodies against gB. When infected cultures were examined by scanning electron microscopy, thousands of KSHV particles were clearly visible across the surfaces of P-EPI cells. The detection of enveloped particles indicated that the infectious cycle had proceeded through assembly and egress. We thus demonstrated that oral WT KSHV isolated from immunocompetent individuals was able to infect and replicate in vitro in a relevant primary cell type. Furthermore, our results provide compelling evidence for KSHV transmission within infected oral epithelial cells derived from healthy, immunocompetent populations.