Soluble forms of Toll-like receptor (TLR)2 capable of modulating TLR2 signaling are present in human plasma and breast milk.
Dysregulation of the initial, innate immune response to bacterial infection may lead to septic shock and death. Toll-like receptors (TLRs) play a crucial role in this innate immune response, and yet the regulatory mechanisms controlling microbial-induced TLR triggering are still to be fully understood. We have therefore sought specific regulatory mechanisms that may modulate TLR signaling. In this study, we tested for the possible existence of a functionally active soluble form of TLR2. We demonstrated the existence of natural soluble forms of TLR2 (sTLR2), which we show to be capable of modulating cell activation. We found that blood monocytes released sTLR2 constitutively and that the kinetics of sTLR2 release increased upon cell activation. Analysis of cells expressing the human TLR2 cDNA or its c-myc-tagged version indicated that sTLR2 resulted from the posttranslational modification of the TLR2 protein in an intracellular compartment. Moreover, an intracellular pool of sTLR2 is maintained. sTLR2 was found naturally expressed in breast milk and plasma. Milk sTLR2 levels mirrored those of the TLR coreceptor soluble CD14. Depletion of sTLR2 from serum resulted in an increased cellular response to bacterial lipopeptide. Notably, serum sTLR2 was lower in tuberculosis patients. Coimmunoprecipitation experiments and computational molecular docking studies showed an interaction between sTLR2 and soluble CD14 in plasma and milk. These findings suggest the existence of a novel and specific innate immune mechanism regulating microbial-induced TLR triggering, and may lead to new therapeutics for the prevention and/or treatment of severe infectious diseases.
LeBouder
Emmanuel
E
Section of Infection and Immunity, University of Wales, College of Medicine, Cardiff, United Kingdom.
Rey-Nores
Julia E
JE
Rushmere
Neil K
NK
Grigorov
Martin
M
Lawn
Stephen D
SD
Affolter
Michael
M
Griffin
George E
GE
Ferrara
Pascual
P
Schiffrin
Eduardo J
EJ
Morgan
B Paul
BP
Labéta
Mario O
MO
D000595:Amino Acid Sequence; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D002478:Cells, Cultured; D003545:Cysteine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D018076:DNA, Complementary / Q000096:biosynthesis; D015536:Down-Regulation / Q000187:drug effects / Q000276:immunology; D005260:Female; D006801:Humans; D007141:Immunoglobulin Fc Fragments / Q000235:genetics; D007424:Intracellular Fluid / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D007774:Lactation; D018950:Lipopolysaccharide Receptors / Q000097:blood / Q000378:metabolism; D008074:Lipoproteins / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008262:Macrophage Activation / Q000187:drug effects / Q000276:immunology; D008562:Membrane Glycoproteins / Q000097:blood* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008895:Milk, Human / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism*; D008969:Molecular Sequence Data; D008985:Monensin / Q000494:pharmacology; D009000:Monocytes / Q000276:immunology / Q000378:metabolism; D010455:Peptides / Q000097:blood / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology; D011233:Precipitin Tests; D020033:Protein Isoforms / Q000097:blood / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000276:immunology; D021381:Protein Transport / Q000276:immunology; D011956:Receptors, Cell Surface / Q000097:blood* / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology*; D012995:Solubility; D051195:Toll-Like Receptor 2; D051193:Toll-Like Receptors
D018076:DNA, Complementary; D007141:Immunoglobulin Fc Fragments; D018950:Lipopolysaccharide Receptors; D008074:Lipoproteins; D008562:Membrane Glycoproteins; D010455:Peptides; D020033:Protein Isoforms; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C495342:TLR2 protein, human; D051195:Toll-Like Receptor 2; D051193:Toll-Like Receptors; C069172:2,3-bis(palmitoyloxy)-2-propyl-1-palmitoylcysteine; D008985:Monensin; D003545:Cysteine