Protein Kinase C-θ Is Required for Murine Neutrophil Recruitment and Adhesion Strengthening under Flow

<jats:title>Abstract</jats:title> <jats:p>Protein kinase C (PKC)-θ is involved in T cell activation via regulating the avidity of the β2 integrin LFA-1 in the immunological synapse. LFA-1 also mediates leukocyte adhesion. To investigate the role of PKC-θ in neutrophil adhesion, we performed intravital microscopy in cremaster venules of mice reconstituted with bone marrow from LysM-GFP+ (wild-type [WT]) and PKC-θ gene-deficient (Prkcq−/−) mice. Following stimulation with CXCL1, both WT and Prkcq−/− cells became adherent. Although most WT neutrophils remained adherent for at least 180 s, 50% of Prkcq−/− neutrophils were detached after 105 s and most by 180 s. Upon CXCL1 injection, rolling of all WT neutrophils stopped for 90 s, but rolling of Prkcq−/− neutrophils started 30 s after CXCL1 stimulation. A similar neutrophil adhesion defect was seen in vitro, and spreading of Prkcq−/− neutrophils was delayed. Prkcq−/− neutrophil recruitment was impaired in fMLP-induced transmigration into the cremaster muscle, thioglycollate-induced peritonitis, and LPS-induced lung injury. We conclude that PKC-θ mediates integrin-dependent neutrophil functions and is required to sustain neutrophil adhesion in postcapillary venules in vivo. These findings suggest that the role of PKC-θ in outside–in signaling following engagement of neutrophil integrins is relevant for inflammation in vivo.</jats:p>