The Neutrophil Btk Signalosome Regulates Integrin Activation during Sterile Inflammation

• Btk is required for neutrophil recruitment during sterile inflammation
• Btk is required for selective fMLF-triggered Mac-1, but not LFA-1, activation
• Hck, WASp, and PLCγ2 are key signaling molecules in the fMLF-triggered pathway
• Btk is required for integrin-mediated outside-in signaling and FcRγ-mediated functions

SummaryNeutrophils are recruited from the blood to sites of sterile inflammation, where they are involved in wound healing but can also cause tissue damage. During sterile inflammation, necrotic cells release pro-inflammatory molecules including formylated peptides. However, the signaling pathway triggered by formylated peptides to integrin activation and leukocyte recruitment is unknown. By using spinning-disk confocal intravital microscopy, we examined the molecular mechanisms of leukocyte recruitment to sites of focal hepatic necrosis in vivo. We demonstrated that the Bruton’s tyrosine kinase (Btk) was required for multiple Mac-1 activation events involved in neutrophil recruitment and functions during sterile inflammation triggered by fMLF. The Src family kinase Hck, Wiskott-Aldrich-syndrome protein, and phospholipase Cγ2 were also involved in this pathway required for fMLF-triggered Mac-1 activation and neutrophil recruitment. Thus, we have identified a neutrophil Btk signalosome that is involved in a signaling pathway triggered by formylated peptides leading to the selective activation of Mac-1 and neutrophil recruitment during sterile inflammation.