Toll-like receptor responses in IRAK-4-deficient neutrophils.
van Bruggen R., Drewniak A., Tool ATJ., Jansen M., van Houdt M., Geissler J., van den Berg TK., Chapel H., Kuijpers TW.
Human neutrophils were found to express all known Toll-like receptors (TLRs) except TLR3 and TLR7. IRAK-4-deficient neutrophils were tested for their responsiveness to various TLR ligands. Essentially all TLR responses in neutrophils, including the induction of reactive oxygen species generation, adhesion, chemotaxis and IL-8 secretion, were found to be dependent on IRAK-4. Surprisingly, the reactivity towards certain established TLR ligands, imiquimod and ODN-CpG, was unaffected by IRAK-4 deficiency, demonstrating their activity is independent of TLR. TLR-4-dependent signaling in neutrophils was totally dependent on IRAK-4 without any major TRIF-mediated contribution. We did not observe any defects in killing capacity of IRAK-4-deficient neutrophils for Staphylococcus aureus, Escherichia coli and Candida albicans, suggesting that microbial killing is primarily TLR independent.