IFN-κ Diminishes the Severity of Viral Bronchiolitis in Neonatal Mice by Limiting NADPH Oxidase-Induced PAD4-Independent NETosis

Infants with attenuated type III IFN (IFN-κ) responses are at increased risk of severe lower respiratory tract infection (sLRI). The IL-28Rα-chain and IL-10Rβ-chain form a heterodimeric receptor complex, necessary for IFN-κ signaling. Therefore, to better understand the immunopathogenic mechanisms through which an IFN-κlo microenvironment predisposes to a sLRI, we inoculated neonatal wild-type and IL-28R-deficient (IL-28R-/-) mice with pneumonia virus of mice, a rodent-specific pneumovirus. Infected IL-28R2/2 neonates displayed an early, pronounced, and persistent neutrophilia that was associated with enhanced reactive oxygen species (ROS) production, NETosis, and mucus hypersecretion. Targeted deletion of the IL-28R in neutrophils was sufficient to increase neutrophil activation, ROS production, NET formation, and mucus production in the airways. Inhibition of proteinarginine deiminase type 4 (PAD4), a regulator of NETosis, had no effect on myeloperoxidase expression, citrullinated histones, and the magnitude of the inflammatory response in the lungs of infected IL-28R-/- mice. In contrast, inhibition of ROS production decreased NET formation, cellular inflammation, and mucus hypersecretion. These data suggest that IFN-κ signaling in neutrophils dampens ROS-induced NETosis, limiting the magnitude of the inflammatory response and mucus production. Therapeutics that promote IFN-κ signaling may confer protection against sLRI.