Ibrutinib Abrogates TREM-1 Mediated Neutrophil Activation

Triggering receptor expressed on myeloid cells 1 (TREM-1) is an activating receptor on neutrophils (PMN) and important in the innate host defence against microbial pathogens. Here we examined the influence of the Bruton tyrosine kinase (BTK) inhibitor ibrutinib on TREM-1 dependent activation of human PMNs. Firstly, ibrutinib specifically inhibited TREM-1 mediated PMN activation of the oxidative burst and CD62L shedding, whereas TLR mediated activation remained unaffected. Correspondingly, ibrutinib suppressed ERK phosphorylation after TREM-1, but not after TLR ligation. To clarify whether this TREM-1 specific effect of ibrutinib was also relevant in vivo, we treated mice with ibrutinib, and analyzed fungal clearance in vivo upon pulmonary challenge with A. fumigatus and PMN activation ex vivo upon TREM-1 or TLR ligation, again finding that TREM-1, but not TLR induced activation was suppressed. Equivalent results were obtained in PMNs of six lymphoma patients under treatment with ibrutinib. In summary, BTK plays an important role in TREM-1 mediated PMN activation, providing a potential mechanism for the frequently observed infectious complications in patients treated with ibrutinib, and fosters studies using this drug as a novel tool to modulate TREM-1 activity for therapeutic purposes, i. e. in sepsis or autoimmune diseases.