Neutrophil activation netosis pathway
The neutrophil is the first responder of innate immunity — and its most destructive effector. Tissue injury and infection release CXCL1, CXCL2, CXCL8/IL-8, bacterial fMLP, LTB₄, C5a and PAF, which are read by the Gαi-coupled receptors CXCR1, CXCR2, FPR1, FPR2/ALX, BLT1, C5aR1 and PAFR. Free Gβγ activates PI3Kγ to build PIP₃ at the leading edge, where DOCK2 and P-Rex1 load Rac1/Rac2 and Cdc42 onto the WAVE2–WASP–Arp2/3 actin machinery while PTEN and RhoA–ROCK1–myosin‑IIA hold the uropod — the molecular compass of chemotaxis. In parallel, TNF, IL-1β, GM-CSF, G-CSF, IL-17A, LPS and S100A8/A9 prime the cell through TNFR1, IL-1R1, TLR4–CD14, G-CSFR and TREM-1, converging on Src-family kinases, Syk, Btk, PLCβ2, STIM1–ORAI1 store-operated Ca²⁺ entry, PKCδ, ERK1/2 and p38–MK2. Primed neutrophils release four granule subsets (MPO, elastase, PR3, cathepsin G, α-defensins, lactoferrin, NGAL, LL-37, MMP-8, MMP-9, arginase-1) via Rab27a, assemble the NOX2 holoenzyme (p22/p47/p67/p40‑phox) for the oxidative burst, and — when PAD4 citrullinates histone H3 and GSDMD perforates the nuclear envelope — extrude neutrophil extracellular traps. Click any protein for the matching Assay Genie In Vivo antibody or ELISA kit.
Recruitment and the chemotactic compass. Neutrophils leave the marrow when G-CSF acting on G-CSFR (CSF3R) collapses the CXCL12–CXCR4 retention axis, then follow an ascending gradient of CXCL1, CXCL2 and CXCL8 (via CXCR1/CXCR2) and of the “end-target” attractants fMLP (FPR1), LTB₄ (BLT1), C5a (C5aR1) and PAF (PAFR). All are Gαi-coupled: released Gβγ activates PI3Kγ, whose product PIP₃ nucleates a leading edge where DOCK2, P-Rex1 and Vav1 load Rac1 and the neutrophil-restricted Rac2, and Cdc42 sets direction. WAVE2, WASP, Arp2/3 and cofilin then build branched F-actin. Polarity is enforced by mutual antagonism: PTEN degrades PIP₃ at the sides and rear, while RhoA–ROCK1 drives myosin‑IIA contraction to form the uropod. Adhesion runs in parallel — L-selectin (CD62L) and PSGL-1 mediate rolling on endothelial P-selectin, LFA-1 (CD11a) and Mac-1 (CD11b) with the common CD18 (β2) chain mediate firm arrest on ICAM-1, and ADAM17 sheds CD62L as the cell transmigrates.
Priming, calcium and granule release. TNF, IL-1β, GM-CSF, IL-17A, LPS (through TLR4 and CD14) and the alarmin S100A8/A9 convert a resting neutrophil into a primed one, signalling through TNFR1, IL-1R1, TREM-1 and FcγRIIIb to the Src-family kinases Hck/Fgr/Lyn, then Syk, Btk and PLCβ2. PLCβ2 generates DAG and IP₃; store depletion is sensed by STIM1, which gates ORAI1 for sustained Ca²⁺ influx. Ca²⁺ plus DAG activate PKCδ, and the TAK1–p38–MK2, ERK1/2 and NF-κB modules complete the primed state. Rab27a then docks the four granule subsets for exocytosis: azurophilic (MPO, neutrophil elastase, proteinase 3, cathepsin G, α-defensins), specific (lactoferrin, NGAL, LL-37, arginase-1), gelatinase (MMP-8, MMP-9) and secretory vesicles, which deliver fresh receptor to the surface. Simultaneously the cytosolic p47‑phox, p67‑phox and p40‑phox subunits translocate onto membrane NOX2 (gp91‑phox) and p22‑phox, generating O₂•⁻, then H₂O₂ and MPO-derived HOCl; SOD and arginase-1 restrain the burst.
NETosis, damage and resolution — the In Vivo opportunity. When activation is intense, ROS and Ca²⁺ activate PAD4, which citrullinates histone H3 to citH3; chromatin decondenses, neutrophil elastase and MPO enter the nucleus, and caspase-4/11-cleaved GSDMD perforates the nuclear and plasma membranes so that DNA studded with histones, MPO and elastase is extruded as a neutrophil extracellular trap. NETs trap bacteria, but they also drive endothelial injury, tissue factor- and vWF-dependent immunothrombosis and autoantigen exposure. Resolution is equally programmed: loss of Mcl-1 and activation of caspase-3 drive apoptosis, phosphatidylserine exposure invites macrophage efferocytosis, and annexin A1 with FPR2/ALX, IL-10 and TGF-β close the episode. Because so many entry points are surface receptors and secreted cytokines, this map is directly addressable in vivo: anti-Ly-6G, anti-Gr-1, anti-Ly-6C, anti-CD11b, anti-CD18, anti-CD62L, anti-ICAM-1, anti-CD44, anti-TNF, anti-IL-1β, anti-IL-1R, anti-TNFR1, anti-GM-CSF, anti-IL-17A, anti-CXCR4 and anti-TREM-1 all perturb it, while ELISA kits quantify every intracellular node and secreted product. For research use only; not for diagnostic or therapeutic procedures.
Every protein node links to a product — In Vivo antibody, ELISA kit or research antibody.