Abstracts (complete list) - Wissenschaft Online

Markus Janke, Jens Poth, Thomas Giese, Gunther Hartmann
Effects of immunostimulatory RNA on human granulocyte
populations
Immunostimulatory RNA (isRNA) is known to stimulate plasmacytoid dendritic cells
(PDC) and other immune cells via TLR7 or TLR8, which then produce large amounts of
type I interferon and other cytokines, followed by induction of immune responses of
potential therapeutical relevance. The expression of TLR7 and TLR8 on granulocytes is
not doubtlessly clarified and the response to isRNA is still unclear. In this study we
analyzed the effect of isRNA 9.2s on neutrophils and eosinophils as the largest fraction
of white blood cells.
To analyze potential activation of neutrophils and eosinophils we studied upregulation of
CD11b and downregulation of CD62L as granulocyte activation markers in whole blood
assays after stimulation with isRNA 9.2s by FACS. TLR expression profile and direct
effects were analyzed on highly purified neutrophils. Quantification of expressed
cytokines and chemokines after stimulation was performed by cytometric bead array
(CBA). For functional analysis of purified neutrophils we tested the impact of isRNA
stimulation on degranulation and respiratory burst activity.
We found that neutrophils but not eosinophils are activated after isRNA stimulation in
human whole blood. This stimulatory effect of isRNA 9.2s was shown to be indirect and
TLR7 dependent. The only ribonucleic acid recognizing TLR expressed on neutrophils
was TLR8, which showed functional activity on purified cells. Thus direct neutrophil
activation via isRNA 9.2s should be restricted to TLR8 but not TLR7 but purified
neutrophils responded with cytokine and chemokine release, respiratory burst and
degranulation only after stimulation with synthetic TLR-8 agonists. IsRNA 9.2s did not
induce any direct effects.
In conclusion this study clearly shows that neutrophils express only TLR8 but not TLR7
for nucleic acid recognition. IsRNA 9.2s had no direct influence on neutrophil or
eosinophil activation. Thus side effects that could emanate from direct activation of
granulocytes seem to be improbable when isRNA 9.2s is used in prospective
therapeutical approaches.