title: Evidence for a post-entry barrier to R5 HIV-1 infection of CD4 memory T cells.
abstract: BACKGROUND
  HIV-1 strains R5 and X4 can infect CD4 memory T cells in vivo. Anti-CD3/28 stimulation induces beta-chemokines and CCR5 down-regulation and renders these cells resistant to R5 HIV-1 infection. Here we describe an additional cellular mechanism that blocks productive R5 HIV-1 infection of CD4 memory T cells.
  
  
  METHODS
  Blood-derived CD4 memory T cells and CD4 T-cell clones were infected with primary R5 and X4 HIV-1 strains. Virus replication was correlated with CCR5 expression and beta-chemokine production. Virus entry and infectivity were measured by PCR for early and late products of HIV reverse transcription respectively.
  
  
  RESULTS
  R5 strains were up to 1000-fold less infectious than X4 viruses for CD4 memory T cells. This resistance was independent of CCR5 levels and of the Delta-32 mutation and the CCR2-V64I/CCR5-59653T linked mutations. Blocking endogenous beta-chemokines relieved minimally this restriction. At the single cell level, CD4 memory cells were either permissive or non-permissive for R5 HIV-1 infection. R5 HIV titre was up to 10-fold lower than X4 virus titre even in a permissive clone. However, R5 viruses replicated as efficiently as X4 viruses in the permissive clone when neutralizing anti-beta chemokine antibodies were added. Non-permissive cells blocked a post-entry step of the virus life-cycle and expressed early but not late HIV transcripts. Neutralizing anti-beta chemokine antibodies promoted R5 virus replication marginally in the non-permissive clone.
  
  
  CONCLUSIONS
  Some blood memory CD4 T cells retard R5 HIV-1 replication via endogenous beta-chemokines whereas others block productive R5 HIV-1 infection by an additional mechanism that interferes with a post-entry step of the virus life cycle. These natural barriers might contribute to lower pathogenicity of R5 HIV-1 strains for CD4 memory T cells than X4 viruses that emerge late in disease.
authors.affiliation: Department of Immunology, GKT School of Medicine and Dentistry, The Rayne Institute, London, UK.
authors.forename: A
authors.initials: A
authors.lastname: Vyakarnam
authors.forename: J
authors.initials: J
authors.lastname: Eyeson
authors.forename: I
authors.initials: I
authors.lastname: Teo
authors.forename: M
authors.initials: M
authors.lastname: Zuckerman
authors.forename: K
authors.initials: K
authors.lastname: Babaahmady
authors.forename: H
authors.initials: H
authors.lastname: Schuitemaker
authors.forename: S
authors.initials: S
authors.lastname: Shaunak
authors.forename: T
authors.initials: T
authors.lastname: Rostron
authors.forename: S
authors.initials: S
authors.lastname: Rowland-Jones
authors.forename: G
authors.initials: G
authors.lastname: Simmons
authors.forename: P
authors.initials: P
authors.lastname: Clapham
mesh_terms: D015496:CD4-Positive T-Lymphocytes / Q000821:virology*; D002460:Cell Line; D002478:Cells, Cultured; D019742:Chemokines, CC / Q000096:biosynthesis / Q000494:pharmacology*; D015658:HIV Infections / Q000517:prevention & control / Q000821:virology; D015497:HIV-1 / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology; D006801:Humans; D007156:Immunologic Memory; D011110:Polymorphism, Genetic; D019713:Receptors, CCR5 / Q000235:genetics / Q000378:metabolism; D014779:Virus Replication / Q000187:drug effects
chemical_list: D019742:Chemokines, CC; D019713:Receptors, CCR5