CX3CR1 Depletion Promotes the Formation of Platelet-Neutrophil Complexes and Aggravates Acute Peritonitis.

BACKGROUND: Peritonitis is a life-threatening condition on intensive care units. Inflammatory cytokines and their receptors drive inflammation, cause the formation of platelet-neutrophil complexes (PNCs) and therefore the migration of polymorphonuclear neutrophils (PMNs) into the inflamed tissue. CX3CL1 and its receptor CX3CR1 are expressed in various cells, and promote inflammation. The shedding of CX3CL1 is mediated by the a disintegrin and metalloprotease (ADAM) 17. The role of the CX3CL1-CX3CR1 axis in acute peritonitis remains elusive.

METHODS: In zymosan-induced peritonitis, we determined the formation of PNCs in the blood and the expression of PNC-related molecules on PNCs. PMN migration into the peritoneal lavage was evaluated in wild type (WT) and CX3CR1-/- animals by flow cytometry. CX3CL1, ADAM17, and the expression of various inflammatory cytokines were detected. Further, we determined the inflammation-associated activation of the intracellular transcription factor extracellular signal-regulated kinase 1/2 (ERK1/2) by Western blot.

RESULTS: The PMN accumulation in the peritoneal lavage and the PNC formation in the circulation were significantly raised in CX3CR1-/- compared to WT animals. The expression of PNC-related selectins on PNCs were significantly increased in the blood of CX3CR1-/- animals, as well as cytokine levels. Further, we observed an increased activation of ERK1/2 and elevated ADAM17 expression in CX3CR1-/- during acute inflammation. Selective ERK1/2 inhibition ameliorated inflammation-related increased ADAM17 expression.

CONCLUSIONS: A CX3CR1-deficiency raised the release of inflammatory cytokines and increased the PNC formation respectively PMN migration via an elevated ERK1/2 activation during acute peritonitis. Further, we observed a link between the ERK1/2 activation and an elevated ADAM17 expression on PNC-related platelets and PMNs during inflammation. Our data thus illustrate a crucial role of CX3CR1 on the formation of PNCs and regulating inflammation in acute peritonitis.