PAD4-deficiency does not affect bacteremia in polymicrobial sepsis and ameliorates endotoxemic shock

Neutrophil extracellular traps (NETs), consisting of nuclear DNA with histones and microbicidal proteins, are expelled from activated neutrophils during sepsis. NETs were shown to trap microbes, but they also fuel cardiovascular, thrombotic, and autoimmune disease. The role of NETs in sepsis, particularly the balance between their antimicrobial and cytotoxic actions, remains unclear. Neutrophils from peptidylarginine deiminase 4-(PAD4^-/-) deficient mice, which lack the enzyme allowing for chromatin decondensation and NET formation, were evaluated. We found that neutrophil functions involved in bacterial killing, other than NETosis, remained intact. Therefore, we hypothesized that prevention of NET formation might not have devastating consequences in sepsis. To test this, we subjected the PAD4^-/- mice to mild and severe polymicrobial sepsis produced by cecal ligation and puncture. Surprisingly, under septic conditions, PAD4^-/- mice did not fare worse than wild-type mice and had comparable survival. In the presence of antibiotics, PAD4-deficiency resulted in slightly accelerated mortality but bacteremia was unaffected. PAD4^-/- mice were partially protected from lipopolysaccharide-induced shock, suggesting that PAD4/NETs may contribute to the toxic inflammatory and procoagulant host response to endotoxin. We propose that preventing NET formation by PAD4 inhibition in inflammatory or thrombotic diseases is not likely to increase host vulnerability to bacterial infections.