On the role of CD4+ T cells and pathogenic mechanisms in HSV-1-induced ocular disease : herpetic stromal keratitis

Experimental infection of mice by scarification of cornea with HSV exhibits ocular disease pattem similar to the histopathological manifestations seen in man. An experiment in athymic mice that did not succumb to herpetic stromal keratitis (HSK) showed that HSK is an immunopathological manifestation of host T cell mediated immune response. It was confirmed later that following infection of corneas in the murine model with RE strain of HSV-1, the immunopathology is manifested by CD4+T lymphocytes that exhibit the Thl cytokine profile. A prominent cell type present in HSK lesions is the neutrophil (PMN), the infiltration of which is a biphasic event following HSV infection of immunocompetent mice, an initial transient infiltration appeared to be triggered by replicating virus and a second more intense invasion along with other inflammatory cells including CD4+ cells. This secondary PMN invasion episode, seemingly orchestrated by CD4+T cells, is called HSK and is not apparently triggered by replicating virus which remains undetectable at this stage. By taking advantage of cell depletion and adoptive transfer studies, the type of cells involved and sequence of cellular events in initiation and effector phase have been addressed. While some of these approaches could explain one facet of HSK immunopathology, identifying the antigen(s) (viral and/or host) to which T cells respond is another interesting field. Some of the recent observations lend credence to the growing notion that HSK represents an autoreactive inflammatory reaction set off by HSV that unmasks sequestered corneal antigens is normally accessible to the immune system. In this study, experiments were designed to address such issues and hence primarily focussed on elucidating the mechanisms which drive the inflammatory responses in HSV-infected murine cornea. Experiments described in this dissertation are aimed at T cell specificity, role of viral antigens in lesion development and mechanisms that drive the inflammatory response in the infected cornea. The series of experiments described here and their results indicate \u27nonspecific activation of CD4+T cells\u27 as a novel mechanism in herpes-induced stromal keratitis. Following an overview of herpes induced ocular disease in part 1, part 2 in addition to supporting HSK as a T cell-mediated immunoinflammatory disease, the results also show the potential for controlling the disease by coreceptor modulation. In part 3, characterization of a unique mouse model with skewed T cell repertoire (Tg- SCID) has been described which is useful for studying antigen specificity in T cell-mediated immunopathological disorders. Results of experiments described in part 4 propose nonspecific activation of T cells and hence the cytokine milieu by virus replication as a novel mechanism by which CD4+ T cells could orchestrate a virus induced ocular immunopathology. Finally, using adoptive transfer protocols, part 5 examines whether lesion development in Tg-SCID mice is virus replication, persistence and CD4+ T cell dependent. Additionally, in part 5, the differential role of HSV-specific antiserum and CD8+ T cells on virus dissemination was analyzed in the infected cornea

Antibody-Independent Control of γ-Herpesvirus Latency via B Cell Induction of Anti-Viral T Cell Responses

B cells can use antibody-dependent mechanisms to control latent viral infections. It is unknown whether this represents the sole function of B cells during chronic viral infection. We report here that hen egg lysozyme (HEL)-specific B cells can contribute to the control of murine γ-herpesvirus 68 (γHV68) latency without producing anti-viral antibody. HEL-specific B cells normalized defects in T cell numbers and proliferation observed in B cell−/− mice during the early phase of γHV68 latency. HEL-specific B cells also reversed defects in CD8 and CD4 T cell cytokine production observed in B cell−/− mice, generating CD8 and CD4 T cells necessary for control of latency. Furthermore, HEL-specific B cells were able to present virally encoded antigen to CD8 T cells. Therefore, B cells have antibody independent functions, including antigen presentation, that are important for control of γ-herpesvirus latency. Exploitation of this property of B cells may allow enhanced vaccine responses to chronic virus infection

Identification of the In Vivo Role of a Viral bcl-2

Many γ-herpesviruses encode candidate oncogenes including homologues of host bcl-2 and cyclin proteins (v-bcl-2, v-cyclin), but the physiologic roles of these genes during infection are not known. We show for the first time in any virus system the physiologic role of v-bcl-2. A γ-herpesvirus v-bcl-2 was essential for efficient ex vivo reactivation from latent infection, and for both persistent replication and virulence during chronic infection of immunocompromised (interferon [IFN]-γ−/−) mice. The v-cyclin was also critical for the same stages in pathogenesis. Strikingly, while the v-bcl-2 and v-cyclin were important for chronic infection, these genes were not essential for viral replication in cell culture, viral replication during acute infection in vivo, establishment of latent infection, or virulence during acute infection. We conclude that v-bcl-2 and v-cyclin have important roles during latent and persistent γ-herpesvirus infection and that herpesviruses encode genes with specific roles during chronic infection and disease, but not acute infection and disease. As γ-herpesviruses primarily cause human disease during chronic infection, these chronic disease genes may be important targets for therapeutic intervention

Antigen-specific precursor frequency impacts T cell proliferation, differentiation, and requirement for costimulation

After a brief period of antigenic stimulation, T cells become committed to a program of autonomous expansion and differentiation. We investigated the role of antigen-specific T cell precursor frequency as a possible cell-extrinsic factor impacting T cell programming in a model of allogeneic tissue transplantation. Using an adoptive transfer system to incrementally raise the precursor frequency of antigen-specific CD8+ T cells, we found that donor-reactive T cells primed at low frequency exhibited increased cellular division, decreased development of multifunctional effector activity, and an increased requirement for CD28- and CD154-mediated costimulation relative to those primed at high frequency. The results demonstrated that recipients with low CD4+ and CD8+ donor-reactive T cell frequencies exhibited long-term skin graft survival upon CD28/CD154 blockade, whereas simultaneously raising the frequency of CD4+ T cells to ∼0.5% and CD8+ T cells to ∼5% precipitated graft rejection despite CD28/CD154 blockade. Antigenic rechallenge of equal numbers of cells stimulated at high or low frequency revealed that cells retained an imprint of the frequency at which they were primed. These results demonstrate a critical role for initial precursor frequency in determining the CD8+ T cell requirement for CD28- and CD154-mediated costimulatory signals during graft rejection

5'PPP-RNA induced RIG-I activation inhibits drug-resistant avian H5N1 as well as 1918 and 2009 pandemic influenza virus replication

<p>Abstract</p> <p>Background</p> <p>Emergence of drug-resistant strains of influenza viruses, including avian H5N1 with pandemic potential, 1918 and 2009 A/H1N1 pandemic viruses to currently used antiviral agents, neuraminidase inhibitors and M2 Ion channel blockers, underscores the importance of developing novel antiviral strategies. Activation of innate immune pathogen sensor Retinoic Acid Inducible Gene-I (RIG-I) has recently been shown to induce antiviral state.</p> <p>Results</p> <p>In the present investigation, using real time RT-PCR, immunofluorescence, immunoblot, and plaque assay we show that 5'PPP-containing single stranded RNA (5'PPP-RNA), a ligand for the intracytoplasmic RNA sensor, RIG-I can be used as a prophylactic agent against known drug-resistant avian H5N1 and pandemic influenza viruses. 5'PPP-RNA treatment of human lung epithelial cells inhibited replication of drug-resistant avian H5N1 as well as 1918 and 2009 pandemic influenza viruses in a RIG-I and type 1 interferon dependant manner. Additionally, 5'PPP-RNA treatment also inhibited 2009 H1N1 viral replication <it>in vivo </it>in mice.</p> <p>Conclusions</p> <p>Our findings suggest that 5'PPP-RNA mediated activation of RIG-I can suppress replication of influenza viruses irrespective of their genetic make-up, pathogenicity, and drug-sensitivity status.</p

Prevalent, protective, and convergent IgG recognition of SARS-CoV-2 non-RBD spike epitopes

The molecular composition and binding epitopes of the immunoglobulin G (IgG) antibodies that circulate in blood plasma following SARS-CoV-2 infection are unknown. Proteomic deconvolution of the IgG repertoire to the spike glycoprotein in convalescent subjects revealed that the response is directed predominantly (>80%) against epitopes residing outside the receptor-binding domain (RBD). In one subject, just four IgG lineages accounted for 93.5% of the response, including an N-terminal domain (NTD)-directed antibody that was protective against lethal viral challenge. Genetic, structural, and functional characterization of a multi-donor class of “public” antibodies revealed an NTD epitope that is recurrently mutated among emerging SARS-CoV-2 variants of concern. These data show that “public” NTD-directed and other non-RBD plasma antibodies are prevalent and have implications for SARS-CoV-2 protection and antibody escape

The 3′ Untranslated Regions of Influenza Genomic Sequences Are 5′PPP-Independent Ligands for RIG-I

Retinoic acid inducible gene-I (RIG-I) is a key regulator of antiviral immunity. RIG-I is generally thought to be activated by ssRNA species containing a 5′-triphosphate (PPP) group or by unphosphorylated dsRNA up to ∼300 bp in length. However, it is not yet clear how changes in the length, nucleotide sequence, secondary structure, and 5′ end modification affect the abilities of these ligands to bind and activate RIG-I. To further investigate these parameters in the context of naturally occurring ligands, we examined RNA sequences derived from the 5′ and 3′ untranslated regions (UTR) of the influenza virus NS1 gene segment. As expected, RIG-I-dependent interferon-β (IFN-β) induction by sequences from the 5′ UTR of the influenza cRNA or its complement (26 nt in length) required the presence of a 5′PPP group. In contrast, activation of RIG-I by the 3′ UTR cRNA sequence or its complement (172 nt) exhibited only a partial 5′PPP-dependence, as capping the 5′ end or treatment with CIP showed a modest reduction in RIG-I activation. Furthermore, induction of IFN-β by a smaller, U/A-rich region within the 3′ UTR was completely 5′PPP-independent. Our findings demonstrated that RNA sequence, length, and secondary structure all contributed to whether or not the 5′PPP moiety is needed for interferon induction by RIG-I

Antibody to a Lytic Cycle Viral Protein Decreases Gammaherpesvirus Latency in B-Cell-Deficient Mice

While antiviral antibody plays a key role in resistance to acute viral infection, the contribution of antibody to the control of latent virus infection is less well understood. Gammaherpesvirus 68 (γHV68) infection of mice provides a model well suited to defining contributions of specific immune system components to the control of viral latency. B cells play a critical role in regulating γHV68 latency, but the mechanism(s) by which B cells regulate latency is not known. In the experiments reported here, we determined the effect of passively transferred antibody on established γHV68 latency in B-cell-deficient (B-cell(−/−)) mice. Immune antibody decreased the frequency of cells reactivating ex vivo from latency in splenocytes (>10-fold) and peritoneal cells (>100-fold) and the frequency of cells carrying latent viral genome in splenocytes (>5-fold) and peritoneal cells (>50-fold). This effect required virus-specific antibody and was observed when total and virus-specific serum antibody concentrations in recipient B-cell(−/−) mice were <8% of those in normal mice during latent infection. Passive transfer of antibody specific for the lytic cycle γHV68 RCA protein, but not passive transfer of antibody specific for the v-cyclin protein or the latent protein M2, decreased both the frequency of cells reactivating ex vivo from latency and the frequency of cells carrying the latent viral genome. Therefore, antibody specific for lytic cycle viral antigens can play an important role in the control of gammaherpesvirus latency in immunocompromised hosts. Based on these findings, we propose a model in which ongoing productive replication is essential for maintaining high levels of latently infected cells in immunocompromised hosts. We confirmed this model by the treatment of latently infected B-cell(−/−) mice with the antiviral drug cidofovir

Effective Vaccination against Long-Term Gammaherpesvirus Latency

The fundamental question of whether a primed immune system is capable of preventing latent gammaherpesvirus infection remains unanswered. Recent studies showing that vaccination can reduce acute replication and short-term latency but cannot alter long-term latency further call into question the possibility of achieving sterilizing immunity against gammaherpesviruses. Using the murine gammaherpesvirus 68 (γHV68) system, we demonstrate that it is possible to effectively vaccinate against long-term latency. By immunizing mice with a γHV68 mutant virus that is deficient in its ability to reactivate from latency, we reduced latent infection of wild-type challenge virus to a level below the limit of detection. Establishment of latency was inhibited by vaccination regardless of whether mice were challenged intraperitoneally or intranasally. Passive transfer of antibody from vaccinated mice could partially reconstitute the effect, demonstrating that antibody is an important component of vaccination. These results demonstrate the potential of a memory immune response against gammaherpesviruses to alter long-term latency and suggest that limiting long-term latent infection in a clinically relevant situation is an attainable goal