CXCL1-mediated leukocyte adhesion was almost absent in HPK1-deficient mice. (A) Leukocyte rolling flux fraction and (B) leukocyte adhesion efficiency in postcapillary venules of mouse cremaster muscle as assessed by intravital microscopy. Leukocyte rolling and adhesion were measured at different time points in each vessel: before CXCL1 injection as well as 3, 6, and 9 minutes after systemic administration of CXCL1 (600 ng) via the carotid artery. n = 10 venules from 5 HPK1^+/+ mice and 15 venules from 6 HPK1^−/− mice. Diagrams show mean ± standard error of the mean (SEM); *P < .05; n.s. = not significant.