HLA-associated protection of lymphocytes during influenza virus infection.

BACKGROUND: Heterozygosity at HLA class I loci is generally considered beneficial for host defense. We report here an element of HLA class I homozygosity that may or may not help preserve its existence in populations but which could indicate a new avenue for antiviral research. METHODS: Lymphocytes from serologically HLA-homozygous or -heterozygous donors were examined for synthesis of influenza virus proteins and RNA after exposure to virus as peripheral blood mononuclear cells. The virus-exposed lymphocytes were also examined for internalization of the virus after exposure, and for susceptibility to virus-specific cytotoxic T lymphocytes in comparison with virus-exposed monocytes/macrophages and unseparated peripheral blood mononuclear cells. Results were compared using two-tailed Fisher's exact test. RESULTS: Serologically-defined HLA-A2-homozygous lymphocytes, in contrast to heterozygous lymphocytes, did not synthesize detectable influenza virus RNA or protein after exposure to the virus. HLA-A2-homozygous lymphocytes, including both homozygous and heterozygous donors by genetic sequence subtyping, did internalize infectious virus but were not susceptible to lysis by autologous virus-specific cytotoxic T lymphocytes ("fratricide"). Similar intrinsic resistance to influenza virus infection was observed with HLA-A1- and HLA-A11-homozygous lymphocytes and with HLA-B-homozygous lymphocytes. CONCLUSIONS: A significant proportion of individuals within a population that is characterized by common expression of HLA class I alleles may possess lymphocytes that are not susceptible to influenza virus infection and thus to mutual virus-specific lysis. Further study may identify new approaches to limit influenza virus infection.

Influenza Virus Infection of Human Lymphocytes Occurs in the Immune Cell Cluster of the Developing Antiviral Response.

Monocytes-macrophages and lymphocytes are recruited to the respiratory tract in response to influenza virus challenge and are exposed to the virus during the establishment of immune defenses. The susceptibility of human lymphocytes to infection was assessed. The presence of monocytes-macrophages was required to attain infection of both resting and proliferating lymphocytes. Lymphocyte infection occurred in the context of immune cell clusters and was blocked by the addition of anti-intercellular adhesion molecule-1 (ICAM-1) antibody to prevent cell clustering. Both peripheral blood-derived and bronchoalveolar lymphocytes were susceptible to infection. Both CD4⁺ and CD8⁺ T lymphocytes were susceptible to influenza virus infection, and the infected CD4⁺ and CD8⁺ lymphocytes served as infectious foci for other nonpermissive or even virus-permissive cells. These data show that monocytes-macrophages and both CD4⁺ and CD8⁺ lymphocytes can become infected during the course of an immune response to influenza virus challenge. The described leukocyte interactions during infection may play an important role in the development of effective anti-influenza responses.

Contributions of neurotropic human herpesviruses herpes simplex virus 1 and human herpesvirus 6 to neurodegenerative disease pathology.

Human herpesviruses (HVs) have developed ingenious mechanisms that enable them to traverse the defenses of the central nervous system (CNS). The ability of HVs to enter a state of latency, a defining characteristic of this viral family, allows them to persist in the human host indefinitely. As such, HVs represent the most frequently detected pathogens in the brain. Under constant immune pressure, these infections are largely asymptomatic in healthy hosts. However, many neurotropic HVs have been directly connected with CNS pathology in the context of other stressors and genetic risk factors. In this review, we discuss the potential mechanisms by which neurotropic HVs contribute to neurodegenerative disease (NDD) pathology by highlighting two prominent members of the HV family, herpes simplex virus 1 (HSV-1) and human herpesvirus 6 (HHV-6). We (i) introduce the infectious pathways and replicative cycles of HSV-1 and HHV-6 and then (ii) review the clinical evidence supporting associations between these viruses and the NDDs Alzheimer's disease (AD) and multiple sclerosis (MS), respectively. We then (iii) highlight and discuss potential mechanisms by which these viruses exert negative effects on neurons and glia. Finally, we (iv) discuss how these viruses could interact with other disease-modifying factors to contribute to the initiation and/or progression of NDDs.

Leishmania induces survival, proliferation and elevated cellular dNTP levels in human monocytes promoting acceleration of HIV co-infection.

Leishmaniasis is a parasitic disease that is widely prevalent in many tropical and sub-tropical regions of the world. Infection with Leishmania has been recognized to induce a striking acceleration of Human Immunodeficiency Virus Type 1 (HIV-1) infection in coinfected individuals through as yet incompletely understood mechanisms. Cells of the monocyte/macrophage lineage are the predominant cell types coinfected by both pathogens. Monocytes and macrophages contain extremely low levels of deoxynucleoside triphosphates (dNTPs) due to their lack of cell cycling and S phase, where dNTP biosynthesis is specifically activated. Lentiviruses, such as HIV-1, are unique among retroviruses in their ability to replicate in these non-dividing cells due, at least in part, to their highly efficient reverse transcriptase (RT). Nonetheless, viral replication progresses more efficiently in the setting of higher intracellular dNTP concentrations related to enhanced enzyme kinetics of the viral RT. In the present study, in vitro infection of CD14+ peripheral blood-derived human monocytes with Leishmania major was found to induce differentiation, marked elevation of cellular p53R2 ribonucleotide reductase subunit and R2 subunit expression. The R2 subunit is restricted to the S phase of the cell cycle. Our dNTP assay demonstrated significant elevation of intracellular monocyte-derived macrophages (MDMs) dNTP concentrations in Leishmania-infected cell populations as compared to control cells. Infection of Leishmania-maturated MDMs with a pseudotyped GFP expressing HIV-1 resulted in increased numbers of GFP+ cells in the Leishmania-maturated MDMs as compared to control cells. Interestingly, a sub-population of Leishmania-maturated MDMs was found to have re-entered the cell cycle, as demonstrated by BrdU labeling. In conclusion, Leishmania infection of primary human monocytes promotes the induction of an S phase environment and elevated dNTP levels with notable elevation of HIV-1 expression in the setting of coinfection.

Infection of murine oligodendroglial precursor cells with Human Herpesvirus 6 (HHV-6)--establishment of a murine in vitro model.

BACKGROUND: Human Herpesvirus 6 was previously demonstrated to infect human oligodendroglial precursor cells (OPCs) in vitro causing cell cycle arrest and premature differentiation with consequent loss of the precursor pool. OBJECTIVES: To develop an in vitro murine OPC model to study the cell cycle and differentiation effects of HHV-6 in more readily available, genetically well-defined cells free of the risk of contamination with human herpesviruses. STUDY DESIGN: Murine OPCs were exposed to infectious HHV-6A or HHV-6B and analyzed for production of viral transcripts, particles, and replicating virus. FACS analysis and specific markers were used to evaluate effects on cell cycling and differentiation. RESULTS: HHV-6 infection of murine OPCs resulted in production of both immediate-early and some late transcripts but no replicating virus by TaqMan quantitative PCR or electron microscopy. Both a specific G1/S cell cycle arrest and premature loss of OPCs through differentiation into oligodendrocytes as previously seen with human precursors were recapitulated. CONCLUSIONS: Infection of murine OPCs by HHV-6 reproduces the critical phenotypes of cell cycle arrest and altered differentiation seen in human cells. The murine system provides a highly defined, accessible, and reproducible source of cells permitting the elucidation of specific viral and cell cycle genes involved in CNS viral infections of OPCs.

Infection with an endemic human herpesvirus disrupts critical glial precursor cell properties.

Human herpesvirus 6 (HHV-6), a common resident virus of the human CNS, has been implicated in both acute and chronic inflammatory--demyelinating diseases. Although HHV-6 persists within the human CNS and has been described to infect mature oligodendrocytes, nothing is known about the susceptibility of glial precursors, the ancestors of myelin-producing oligodendrocytes, to viral infection. We show that HHV-6 infects human glial precursor cells in vitro. Active infection was demonstrated by both electron microscopy and expression of viral gene transcripts and proteins, with subsequent formation of cell syncytia. Infection leads to alterations in cell morphology and impairment of cell replication but not increased cell death. Infected cells showed decreased proliferation as measured by bromodeoxyuridine uptake, which was confirmed by blunting of the cell growth rate of infected cells compared with uninfected controls over time. The detailed analysis using novel, fluorescent-labeled HHV-6A or HHV-6B reagents demonstrated strong G1/S phase inhibition in infected precursor cells. Cell cycle arrest in HHV-6-infected cells was associated with a profound decrease in the expression of the glial progenitor cell marker A2B5 and a corresponding increase in the oligodendrocyte differentiation marker GalC. These data demonstrate for the first time that infection of primary human glial precursor cells with a neurologically relevant human herpesvirus causes profound alterations of critical precursor cell properties. In light of recent observations that repair of CNS demyelination is dependent on the generation of mature oligodendrocytes from the glial precursor cell pool, these findings may have broad implications for both the ineffective repair seen in demyelinating diseases and the disruption of normal glial maturation.

Human herpesvirus 6 genome and antigen in acute multiple sclerosis lesions.

Evidence for a candidate multiple sclerosis (MS) virus, human herpesvirus 6 (HHV-6), was sought in biopsy specimens of acute lesions that presented clinically as cerebral tumors obtained from 5 patients. Histopathology, magnetic resonance imaging, and clinical course confirmed the diagnosis of MS in each case. A sensitive in situ polymerase chain reaction (ISPCR) method was used to detect HHV-6 genome, in conjunction with immunocytochemical staining (ICC) to detect viral and cellular antigens. ISPCR revealed numerous oligodendrocytes, lymphocytes, and microglia containing HHV-6 genome within all lesions, whereas ICC showed only the HHV-6 glycoprotein 116 antigen in some reactive astrocytes and microglia. High frequencies of neuroglial and inflammatory cells containing HHV-6 genome were present in acute-phase lesion tissue from patients who were free of the effects of chronic MS and had not been received immunomodulatory therapy for MS. The prevalence of HHV-6 genome-containing cells, including oligodendrocytes, in each lesion suggests that HHV-6 plays a role in the demyelinative pathogenesis of MS; the significance of the discrepant expression of viral antigens remains uncertain.