Control of IFN-I responses by the aminopeptidase IRAP in neonatal C57BL/6 alveolar macrophages during RSV infection

Sex- and time-dependent role of insulin regulated aminopeptidase in lipopolysaccharide-induced inflammation

The enzyme, insulin regulated aminopeptidase (IRAP), is expressed in multiple immune cells such as macrophages, dendritic cells and T cells, where it plays a role in regulating the innate and adaptive immune response. There is a genetic association between IRAP and survival outcomes in patients with septic shock where a variant of its gene was found to be associated with increased 28-day mortality. This study investigated the role for IRAP in a lipopolysaccharide (LPS)-induced inflammatory response which is thought to model facets of the systemic inflammation observed in the early stages of human gram-negative sepsis. The frequencies and activation of splenic immune cell populations were investigated in the IRAP knockout (KO) mice compared to the wildtype controls over a period of 4-, 24-, or 48-hours following LPS stimulation. Dendritic cells isolated from the spleen of female IRAP KO mice, displayed significant increases in the activation markers CD40, CD86 and MHCII at 24 hours after LPS induction. A modest heightened pro-inflammatory response to LPS was observed with increased expression of activation marker CD40 in M1 macrophages from male IRAP knockout mice. Observations in vitro in bone marrow-derived macrophages (BMDM) revealed a heightened pro-inflammatory response to LPS with significant increases in the expression of CD40 in IRAP deficient cells compared with BMDM from WT mice. The heightened LPS-induced response was associated with increased pro-inflammatory cytokine secretion in these BMDM cells. A genotype difference was also detected in the BMDM from female mice displaying suppression of the LPS-induced increases in the activation markers CD40, CD86, CD80 and MHCII in IRAP deficient cells. Thus, this study suggests that IRAP plays specific time- and sex-dependent roles in the LPS-induced inflammatory response in dendritic cells and macrophages.

Diverging patterns in innate immunity against respiratory viruses during a lifetime: lessons from the young and the old

Respiratory viral infections frequently lead to severe respiratory disease, particularly in vulnerable populations such as young children, individuals with chronic lung conditions and older adults, resulting in hospitalisation and, in some cases, fatalities. The innate immune system plays a crucial role in monitoring for, and initiating responses to, viruses, maintaining a state of preparedness through the constant expression of antimicrobial defence molecules. Throughout the course of infection, innate immunity remains actively involved, contributing to viral clearance and damage control, with pivotal contributions from airway epithelial cells and resident and newly recruited immune cells. In instances where viral infections persist or are not effectively eliminated, innate immune components prominently contribute to the resulting pathophysiological consequences. Even though both young children and older adults are susceptible to severe respiratory disease caused by various respiratory viruses, the underlying mechanisms may differ significantly. Children face the challenge of developing and maturing their immunity, while older adults contend with issues such as immune senescence and inflammaging. This review aims to compare the innate immune responses in respiratory viral infections across both age groups, identifying common central hubs that could serve as promising targets for innovative therapeutic and preventive strategies, despite the apparent differences in underlying mechanisms.

Severity of neonatal influenza infection is driven by type I interferon and oxidative stress

Neonates exhibit increased susceptibility to respiratory viral infections, attributed to inflammation at the developing pulmonary air-blood interface. IFN I are antiviral cytokines critical to control viral replication, but also promote inflammation. Previously, we established a neonatal murine influenza virus (IV) model, which demonstrates increased mortality. Here, we sought to determine the role of IFN I in this increased mortality. We found that three-day-old IFNAR-deficient mice are highly protected from IV-induced mortality. In addition, exposure to IFNβ 24 h post IV infection accelerated death in WT neonatal animals but did not impact adult mortality. In contrast, IFN IIIs are protective to neonatal mice. IFNβ induced an oxidative stress imbalance specifically in primary neonatal IV-infected pulmonary type II epithelial cells (TIIEC), not in adult TIIECs. Moreover, neonates did not have an infection-induced increase in antioxidants, including a key antioxidant, superoxide dismutase 3, as compared to adults. Importantly, antioxidant treatment rescued IV-infected neonatal mice, but had no impact on adult morbidity. We propose that IFN I exacerbate an oxidative stress imbalance in the neonate because of IFN I-induced pulmonary TIIEC ROS production coupled with developmentally regulated, defective antioxidant production in response to IV infection. This age-specific imbalance contributes to mortality after respiratory infections in this vulnerable population.