A brief, light-triggered pulse of chemokine secretion rapidly enhances cell interactions in vitro. (A) Representative images of cocultured HEK293T cells and mouse neutrophils before and after activation. White arrows indicate contacts. Scale bar = 25 µm. (B) Percentage of neutrophils forming contacts with transfected HEK239T cells (out of the number of neutrophils present in the same area). Repeated measures ANOVA with Bonferroni posttest was applied. n = 3 values representing independent experiments. Error bars represent standard error of the mean. (C) Examples of contact formation after photoactivation of Cxcl2 secretion. Scale bar = 10 µm.