Immobilized Immune Complexes Induce Neutrophil Extracellular Trap Release by Human Neutrophil Granulocytes via FcγRIIIB and Mac-1

Abstract

Canonical neutrophil antimicrobial effector mechanisms, such as degranulation, production of reactive oxygen species, and release of neutrophil extracellular traps (NETs), can result in severe pathology. Activation of neutrophils through immune complexes (ICs) plays a central role in the pathogenesis of many autoimmune inflammatory diseases. In this study, we report that immobilized ICs (iICs), which are hallmarks of several autoimmune diseases, induce the release of NETs from primary human neutrophils. The iIC-induced NET formation was found to require production of reactive oxygen species by NADPH oxidase and myeloperoxidase and to be mediated by FcγRIIIb. Blocking of the β2 integrin macrophage-1 Ag but not lymphocyte function–associated Ag-1 abolished iIC-induced NET formation. This suggests that FcγRIIIb signals in association with macrophage-1 Ag. As intracellular signaling pathways involved in iIC-induced NET formation we identified the tyrosine kinase Src/Syk pathway, which downstream regulates the PI3K/Akt, p38 MAPK, and ERK1/2 pathways. To our knowledge, the present study shows for the first time that iICs induce NET formation. Thus, we conclude that NETs contribute to pathology in autoimmune inflammatory disorders associated with surface-bound ICs.

Plasmacytoid Dendritic Cell Activation and IFN-α Production Are Prominent Features of Murine Autoimmune Pancreatitis and Human IgG4-Related Autoimmune Pancreatitis

“…6D, 6E). Presumably the latter can occur because, as shown previously, the neutrophils are capable of producing LF that can then react with anti-LF Ab to form NET-stimulating immune complexes (46,47). It should be noted, however, that IgG4 subclass isolated from patient serum did not have the capacity to induce NETs in vitro, probably because the concentration of anti-LF Ab in this preparation was too low (data not shown).…”

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“…Baxter) antigen and rabbit polyclonal anti-HSA-IgG (Sigma Aldrich) as described previously (Behnen et al, 2014).…”

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“…This may explain some variability in early genetic knock out studies when defining which receptor is critical in mediating NET release. It would seem molecular pattern‐related NET release is mediated predominantly through TLRs 2, 4 and 9,31, 46, 47 immune complex‐related NET release is mediated via Fc receptors and MAC‐a48 and larger pathogens or inorganic matter lead to NETosis though size. The inability to phagocytose large particles within a given time appears to drive neutrophils to autodigest and release NETs in a process dependent on dectin‐1 49.…”