Selective and direct activation of human neutrophils but not eosinophils by Toll-like receptor 8.
BACKGROUND
Granulocytes represent the largest fraction of immune cells in peripheral blood and are directly exposed to circulating Toll-like receptor (TLR) ligands. Although highly relevant for TLR-based therapies, because of the technical challenge, activation of the granulocyte subsets of neutrophils and eosinophils by TLR ligands is less well studied than activation of other immune cell subsets.


OBJECTIVE
The aim of this work was to study direct versus indirect neutrophil and eosinophil activation by TLR7 and TLR8 ligands.


METHODS
We used a new whole-blood assay, single cell-based cytokine detection, and highly purified primary human neutrophils and eosinophils to separate direct and indirect effects on these blood cell subsets.


RESULTS
We found indirect but not direct activation of neutrophils but not eosinophils in whole blood by using unmodified immunostimulatory RNA (isRNA; TLR7/8 ligand). In contrast, direct activation and stimulation of the respiratory burst and degranulation was seen with nuclease-stable isRNA and with the small-molecule TLR8 agonist 3M002 but not 3M001 (TLR7). Neutrophils expressed TLR8 but none of the other 2 RNA-detecting TLRs (TLR3 and TLR7).


CONCLUSIONS
Together, these results demonstrate that neutrophils are directly and fully activated through TLR8 but not TLR7. Furthermore, the results predict that the clinical utility of small-molecule TLR8 ligands or nuclease-stable RNA ligands for TLR8 might be limited because of neutrophil-mediated toxicity and that no such limitation applies for unmodified isRNA, which is known to induce desired T(H)1 activities in other immune cell subsets.
Institute of Clinical Chemistry and Pharmacology, University Hospital, University of Bonn, Bonn, Germany.
Markus
M
Janke
Jens
J
Poth
Vera
V
Wimmenauer
Thomas
T
Giese
Christoph
C
Coch
Winfried
W
Barchet
Martin
M
Schlee
Gunther
G
Hartmann
D039481:CD11b Antigen / Q000276:immunology / Q000378:metabolism; D015550:Cell Degranulation / Q000187:drug effects / Q000276:immunology; D016207:Cytokines / Q000096:biosynthesis / Q000276:immunology; D004804:Eosinophils / Q000166:cytology / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D019041:L-Selectin / Q000276:immunology / Q000378:metabolism; D008024:Ligands; D008070:Lipopolysaccharides / Q000276:immunology; D009504:Neutrophils / Q000166:cytology / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D009843:Oligoribonucleotides / Q000276:immunology; D011804:Quinolines / Q000494:pharmacology; D012313:RNA / Q000276:immunology; D051199:Toll-Like Receptor 7 / Q000819:agonists / Q000276:immunology* / Q000378:metabolism; D051200:Toll-Like Receptor 8 / Q000819:agonists / Q000276:immunology* / Q000378:metabolism
C526116:3M 001; C526117:3M 002; D039481:CD11b Antigen; D016207:Cytokines; C509295:ITGAM protein, human; D007093:Imidazoles; D008024:Ligands; D008070:Lipopolysaccharides; D009843:Oligoribonucleotides; D011804:Quinolines; D051199:Toll-Like Receptor 7; D051200:Toll-Like Receptor 8; D019041:L-Selectin; D012313:RNA