Exocytosis of toxic primary granules by human neutrophils is associated with high surface TRPM2 expression and pinocytosis (INC6P.401)

Abstract Polymorphonuclear neutrophils (PMNs) play a key role in host defense against microbial infection. PMN responses culminate in the mobilization of highly toxic intracellular primary granules toward either the phagosome (during phagocytosis), nucleus (during NETosis), or plasma membrane (exocytosis). Mechanisms regulating the fate of PMN primary granules remain unclear. Here, we studied the dynamics of PMN primary granule exocytosis in two relevant sets of conditions: 1- in vivo migration of blood PMNs into chronically infected airways of patients with cystic fibrosis; 2- in vitro treatment of blood PMNs with latrunculin B and fMLF. Using flow and image cytometry, we show a striking resemblance between these two sets of conditions, with a close association between primary granule exocytosis (based on surface CD63 expression) and increased surface expression of the inflammatory calcium channel TRPM2. In addition, high primary granule exocytosis associates with major membrane rearrangements, as evidenced by the loss of surface phagocytic receptors (e.g., CD16 and CD35) and high pinocytosis (based on Lucifer Yellow uptake), a process previously linked to TRPM2 activation. All the while, exocytosing PMNs maintain their nuclear integrity. Thus, high primary granule exocytosis, surface TRPM2 upregulation and high pinocytosis are a concerted set of events indicative of a functional program in activated PMNs that is distinct from phagocytosis and NETosis.