PR3 and NB1 colocalize on and coimmunoprecipitate from the neutrophil plasma membrane. Confocal microscopy of live neutrophils showed colocalization of PR3- and NB1-stained spots on the plasma membrane in comparison to CD66b and CD16b (A). Line scans of fluorescence intensity indicate colocalization of peak color intensities. Immunoprecipitation and Western blot analysis of PR3 and NB1 was performed from the supernatant of TNF-α–primed, phospholipase C–treated neutrophils. This procedure resulted in specific coimmunoprecipitation of PR3 after NB1 precipitation and vice versa (B).