title: Human metapneumovirus SH and G glycoproteins inhibit macropinocytosis-mediated entry into human dendritic cells and reduce CD4+ T cell activation.
abstract: Human metapneumovirus (HMPV) is a major etiologic agent of respiratory disease worldwide. HMPV reinfections are common in healthy adults and children, suggesting that the protective immune response to HMPV is incomplete and short-lived. We used gene-deletion viruses to evaluate the role of the attachment G and small hydrophobic SH glycoproteins on virus uptake by primary human monocyte-derived dendritic cells (MDDC) in vitro and on subsequent MDDC maturation and activation of autologous T cells. HMPV with deletion of G and SH (ΔSHG) exhibited increased infectivity but had little effect on MDDC maturation. However, MDDC stimulated with ΔSHG induced increased proliferation of autologous Th1-polarized CD4(+) T cells. This effect was independent of virus replication. Increased T cell proliferation was strictly dependent on contact between virus-stimulated MDDC and CD4(+) T cells. Confocal microscopy revealed that deletion of SH and G was associated with an increased number of immunological synapses between memory CD4(+) T cells and virus-stimulated MDDC. Uptake of HMPV by MDDC was found to be primarily by macropinocytosis. Uptake of wild-type (WT) virus was reduced compared to that of ΔSHG, indicative of inhibition by the SH and G glycoproteins. In addition, DC-SIGN-mediated endocytosis provided a minor alternative pathway that depended on SH and/or G and thus operated only for WT. Altogether, our results show that SH and G glycoproteins reduce the ability of HMPV to be internalized by MDDC, resulting in a reduced ability of the HMPV-stimulated MDDC to activate CD4(+) T cells. This study describes a previously unknown mechanism of virus immune evasion.
  
  
  OBJECTIVE
  Human metapneumovirus (HMPV) is a major etiologic agent of respiratory disease worldwide. HMPV reinfections are common in healthy adults and children, suggesting that the protective immune response to HMPV is incomplete and short-lived. We found that HMPV attachment G and small hydrophobic SH glycoproteins reduce the ability of HMPV to be internalized by macropinocytosis into human dendritic cells (DC). This results in a reduced ability of the HMPV-stimulated DC to activate Th1-polarized CD4(+) T cells. These results contribute to a better understanding of the nature of incomplete protection against this important human respiratory virus, provide new information on the entry of HMPV into human cells, and describe a new mechanism of virus immune evasion.
authors.affiliation: RNA Viruses Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Cyril
authors.initials: C
authors.lastname: Le Nouën
authors.forename: Philippa
authors.initials: P
authors.lastname: Hillyer
authors.forename: Linda G
authors.initials: LG
authors.lastname: Brock
authors.forename: Christine C
authors.initials: CC
authors.lastname: Winter
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Rabin
authors.forename: Peter L
authors.initials: PL
authors.lastname: Collins
authors.forename: Ursula J
authors.initials: UJ
authors.lastname: Buchholz
mesh_terms: D000704:Analysis of Variance; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D015815:Cell Adhesion Molecules / Q000276:immunology; D003713:Dendritic Cells / Q000276:immunology / Q000821:virology*; D005434:Flow Cytometry; D006023:Glycoproteins / Q000276:immunology*; D006801:Humans; D057131:Immune Evasion / Q000276:immunology*; D054992:Immunological Synapses / Q000276:immunology; D037181:Lectins, C-Type / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology; D029121:Metapneumovirus / Q000235:genetics / Q000276:immunology*; D018613:Microscopy, Confocal; D010873:Pinocytosis / Q000276:immunology*; D011956:Receptors, Cell Surface / Q000276:immunology; D015682:Retroviridae Proteins, Oncogenic / Q000276:immunology*; D014764:Viral Proteins / Q000276:immunology*; D053586:Virus Internalization; D000099215:DC-Specific ICAM-3 Grabbing Nonintegrin
chemical_list: D015815:Cell Adhesion Molecules; D006023:Glycoproteins; D037181:Lectins, C-Type; D011956:Receptors, Cell Surface; D015682:Retroviridae Proteins, Oncogenic; D014764:Viral Proteins; D000099215:DC-Specific ICAM-3 Grabbing Nonintegrin; C484233:G glycoprotein, human metapneumovirus; C056150:small hydrophobic protein, virus