engleski

Extracellular expression of otherwise intracellular Toll-like receptors

Toll-like receptors (TLRs) are a family of germ-line encoded proteins involved in host defense by their ability to recognize conserved components of different microorganisms. According to current data, TLRs that recognize bacterial and fungal cell wall structures (TLR1, -2, -4, -5, -6) are expressed on the cell surface, and TLRs that recognize nuclear acids (TLR3, -7, -8, -9) are located inside the cell, in endosomal compartment. Biological significance of this difference in localization is thought to lie in discrimination between foreign and self nucleic acids (1). However, some studies that indicate intracellular TLRs can be expressed on cell surface of certain subpopulations of antigen-presenting cells both in steady-state (2) and upon activation (3). Here we analyzed surface expression of TLR3, TLR8 and TLR9 after short-term culture with their specific ligands (poly(I:C) for TLR3, gardiquimod for TLR8 and CpG DNA for TLR9), other TLR ligand (LPS) and non-TLR-specific activator (phorbol-12-myristate-13-acetate and ionomycin). TLR expression was measured by 5-color flow cytometry on CD3+, CD19+ and CD14+ subpopulations of freshly isolated human peripheral blood mononuclear cells. The results of the study will be discussed. (1) Barton GM, Kagan JC, Medzhitov R. Intracellular localization of TLR9 prevents recognition of self DNA but facilitates access to viral DNA. Nat Immunol 2006 ; 7:49-56. (2) Eaton-Bassiri A et al. TLR9 can be expressed at the cell surface of distinct populations of tonsils and human PBMCs. Infect Immunity 2004 ; 72:7202– 211. (3) Saikh KU et al. Human monocytes infected with Yersinia pestis express cell surface TLR9 and differentiate into dendritic cells. J Immunol 2004 ; 173:7426– 34.

Toll-like receptors; intracellular staining; flow cytometry

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