title: Low pH immobilizes and kills human leukocytes and prevents transmission of cell-associated HIV in a mouse model.
abstract: BACKGROUND
  Both cell-associated and cell-free HIV virions are present in semen and cervical secretions of HIV-infected individuals. Thus, topical microbicides may need to inactivate both cell-associated and cell-free HIV to prevent sexual transmission of HIV/AIDS. To determine if the mild acidity of the healthy vagina and acid buffering microbicides would prevent transmission by HIV-infected leukocytes, we measured the effect of pH on leukocyte motility, viability and intracellular pH and tested the ability of an acidic buffering microbicide (BufferGel) to prevent the transmission of cell-associated HIV in a HuPBL-SCID mouse model.
  
  
  METHODS
  Human lymphocyte, monocyte, and macrophage motilities were measured as a function of time and pH using various acidifying agents. Lymphocyte and macrophage motilities were measured using video microscopy. Monocyte motility was measured using video microscopy and chemotactic chambers. Peripheral blood mononuclear cell (PBMC) viability and intracellular pH were determined as a function of time and pH using fluorescent dyes. HuPBL-SCID mice were pretreated with BufferGel, saline, or a control gel and challenged with HIV-1-infected human PBMCs.
  
  
  RESULTS
  Progressive motility was completely abolished in all cell types between pH 5.5 and 6.0. Concomitantly, at and below pH 5.5, the intracellular pH of PBMCs dropped precipitously to match the extracellular medium and did not recover. After acidification with hydrochloric acid to pH 4.5 for 60 min, although completely immotile, 58% of PBMCs excluded ethidium homodimer-1 (dead-cell dye). In contrast, when acidified to this pH with BufferGel, a microbicide designed to maintain vaginal acidity in the presence of semen, only 4% excluded dye at 10 min and none excluded dye after 30 min. BufferGel significantly reduced transmission of HIV-1 in HuPBL-SCID mice (1 of 12 infected) compared to saline (12 of 12 infected) and a control gel (5 of 7 infected).
  
  
  CONCLUSIONS
  These results suggest that physiologic or microbicide-induced acid immobilization and killing of infected white blood cells may be effective in preventing sexual transmission of cell-associated HIV.
authors.affiliation: Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA. olmsted@rand.org
authors.forename: Stuart S
authors.initials: SS
authors.lastname: Olmsted
authors.forename: Kristen V
authors.initials: KV
authors.lastname: Khanna
authors.forename: Erina M
authors.initials: EM
authors.lastname: Ng
authors.forename: Steven T
authors.initials: ST
authors.lastname: Whitten
authors.forename: Owen N
authors.initials: ON
authors.lastname: Johnson
authors.forename: Richard B
authors.initials: RB
authors.lastname: Markham
authors.forename: Richard A
authors.initials: RA
authors.lastname: Cone
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Moench
mesh_terms: D000143:Acids / Q000494:pharmacology; D000818:Animals; D002634:Chemotaxis, Leukocyte / Q000187:drug effects; D004195:Disease Models, Animal; D005260:Female; D015658:HIV Infections / Q000276:immunology / Q000473:pathology / Q000635:transmission* / Q000821:virology*; D015497:HIV-1 / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007962:Leukocytes / Q000187:drug effects / Q000473:pathology* / Q000821:virology*; D008297:Male; D051379:Mice; D016513:Mice, SCID; D013997:Time Factors
chemical_list: D000143:Acids