title: Toll-like receptor 9 can be expressed at the cell surface of distinct populations of tonsils and human peripheral blood mononuclear cells.
abstract: Unmethlylated CpG dinucleotides induce a strong T-helper-1-like inflammatory response, presumably mediated by Toll-like receptor 9 (TLR9). However, the nature and cellular localization of TLR9 in primary human cells remain controversial. Here we demonstrate, using flow cytometry and immunofluorescence microscopy techniques, that TLR9 can be expressed at the cell surface. The primary human cell subsets that were positive for TLR9 expression were distinct depending on the tissues analyzed. Specifically, in human peripheral blood mononuclear cells (PBMC) the majority of cell surface TLR9(+) cells were confined to the major histocompatibility complex (MHC) class II(+) CD19(-) populations that express CD11c and/or CD14, whereas in tonsils the same gated population contained primarily MHC class II(+) CD19(+) cells. Cells positive for surface expression represented a minor fraction of the total cell populations examined, varying between 2 and 10%. In addition, we found that TLR9 expression at the surface of PBMC was up-regulated approximately fourfold following stimulation with the gram-negative bacterial cell wall component lipopolysaccharide, suggesting a potential modulatory role of TLR4 agonists on TLR9 expression. Taken together, these data validate human TLR9 expression at the surface of primary cells, in addition to the previously described intracellular localization. Further, our results suggest that human antigen-presenting cells comprise the major cell populations expressing cell surface TLR9.
authors.affiliation: Department of Infectious Diseases, Centocor Inc., 200 Great Valley Parkway, Malvern, PA 19355, USA.
authors.forename: Ashlyn
authors.initials: A
authors.lastname: Eaton-Bassiri
authors.forename: Susan B
authors.initials: SB
authors.lastname: Dillon
authors.forename: Mark
authors.initials: M
authors.lastname: Cunningham
authors.forename: Michael A
authors.initials: MA
authors.lastname: Rycyzyn
authors.forename: Juliane
authors.initials: J
authors.lastname: Mills
authors.forename: Robert T
authors.initials: RT
authors.lastname: Sarisky
authors.forename: M Lamine
authors.initials: ML
authors.lastname: Mbow
mesh_terms: D000595:Amino Acid Sequence; D018941:Antigens, CD19 / Q000032:analysis; D039521:CD11c Antigen / Q000032:analysis; D004268:DNA-Binding Proteins / Q000032:analysis*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D053650:Interleukin-3 Receptor alpha Subunit; D007963:Leukocytes, Mononuclear / Q000737:chemistry*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008969:Molecular Sequence Data; D014066:Palatine Tonsil / Q000737:chemistry*; D011956:Receptors, Cell Surface / Q000032:analysis*; D016185:Receptors, Interleukin-3 / Q000032:analysis; D013194:Staining and Labeling; D051217:Toll-Like Receptor 9
chemical_list: D018941:Antigens, CD19; D039521:CD11c Antigen; D004268:DNA-Binding Proteins; C115022:IL3RA protein, human; D053650:Interleukin-3 Receptor alpha Subunit; D008070:Lipopolysaccharides; D011956:Receptors, Cell Surface; D016185:Receptors, Interleukin-3; C495371:TLR9 protein, human; D051217:Toll-Like Receptor 9