CXCL8(3-73)K11R/G31P antagonizes the neutrophil chemoattractants present in pasteurellosis and mastitis lesions and abrogates neutrophil influx into intradermal endotoxin challenge sites in vivo

The ELR+ CXC chemokines are critical for protective neutrophil responses to most bacterial infections, but nevertheless can contribute importantly to the pathogenic effects of many inflammatory responses. We recently engineered a series of high affinity CXCL8/IL-8 antagonists, one of which, CXCL8(3–73)K11R/G31P, binds very strongly to neutrophils via the CXCR1 and CXCR2. Herein we show in competitive 125I-ligand binding assays that bovine CXCL8(3–73)K11R/G31P has an affinity for neutrophils that is 2–3 orders of magnitude higher than that of CXCL8/IL-8. Furthermore, when used at ≈0.5 nM, CXCL8(3–73)K11R/G31P inhibited by 50% the chemotactic responses of neutrophils to 129 nM CXCL8/IL-8, but it also blocked chemotactic responses to the alternate ELR-CXC chemokines CXCL1/GROα and CXCL5/ENA-78. Furthermore, CXCL8(3–73)K11R/G31P could inhibit by 93–97% the spectrum of neutrophil chemotactic activities present within wash fluids from clinical bacterial pneumonia or experimental endotoxin-induced mastitis lesions. Finally, intramuscular or subcutaneous application of CXCL8(3–73)K11R/G31P (75 μg/kg) reduced by up to 97% neutrophil infiltration into intradermal endotoxin challenge sites in cattle, and prevented their circulating neutrophils from responding to CXCL8/IL-8 or ENA-78 in vitro. This data thus encourages further investigation of the potential impact of this novel antagonist on ELR-CXC chemokine-driven inflammatory disorders.