Environmentally persistent free radicals enhance SARS-CoV-2 replication in respiratory epithelium.

Epidemiological evidence links lower air quality with increased incidence and severity of COVID-19; however, mechanistic data have yet to be published. We hypothesized air pollution-induced oxidative stress in the nasal epithelium increased viral replication and inflammation. Nasal epithelial cells (NECs), collected from healthy adults, were grown into a fully differentiated epithelium. NECs were infected with the ancestral strain of SARS-CoV-2. An oxidant combustion by-product found in air pollution, the environmentally persistent free radical (EPFR) DCB230, was used to mimic pollution exposure four hours prior to infection. Some wells were pretreated with antioxidant, astaxanthin, for 24 hours prior to EPFR-DCB230 exposure and/or SARS-CoV-2 infection. Outcomes included viral replication, epithelial integrity, surface receptor expression (ACE2, TMPRSS2), cytokine mRNA expression (TNF-α, IFN-ß), intracellular signaling pathways, and oxidative defense enzymes. SARS-CoV-2 infection induced a mild phenotype in NECs, with some cell death, upregulation of the antiviral cytokine IFN-ß, but had little effect on intracellular pathways or oxidative defense enzymes. Prior exposure to EPFR-DCB230 increased SARS-CoV-2 replication, upregulated TMPRSS2 expression, increased secretion of the proinflammatory cytokine TNF-α, inhibited expression of the mucus producing MUC5AC gene, upregulated expression of p21 (apoptosis pathway), PINK1 (mitophagy pathway), and reduced levels of antioxidant enzymes. Pretreatment with astaxanthin reduced SARS-CoV-2 replication, downregulated ACE2 expression, and prevented most, but not all EPFR-DCB230 effects. Our data suggest that oxidant damage to the respiratory epithelium may underly the link between poor air quality and increased COVID-19. The apparent protection by antioxidants warrants further research.

Deficiency in ST2 signaling ameliorates RSV-associated pulmonary hypertension.

Pulmonary hypertension (PH) observed during respiratory syncytial virus (RSV) bronchiolitis is associated with morbidity and mortality, especially in children with congenital heart disease. Yet, the pathophysiological mechanisms of RSV-associated PH remain unclear. Therefore, this study aimed to investigate the pathophysiological mechanism of RSV-associated PH. We used a translational mouse model of RSV-associated PH, in which wild-type (WT) and suppression of tumorigenicity 2 (ST2) knockout neonatal mice were infected with RSV at 5 days old and reinfected 4 wk later. The development of PH in WT mice following RSV reinfection was evidenced by elevated right ventricle systolic pressure, shortened pulmonary artery acceleration time (PAT), and decreased PAT/ejection time (ET) ratio. It coincided with the augmentation of periostin and IL-13 expression and increased arginase bioactivity by both arginase 1 and 2 as well as induction of nitric oxide synthase (NOS) uncoupling. Absence of ST2 signaling prevented RSV-reinfected mice from developing PH by suppressing NOS uncoupling. In summary, ST2 signaling was involved in the development of RSV-associated PH. ST2 signaling inhibition may be a novel therapeutic target for RSV-associated PH.NEW & NOTEWORTHY We report that the pathogenic role of ST2-mediated type 2 immunity and mechanisms contribute to RSV-associated pulmonary hypertension. Inhibiting ST2 signaling may be a novel therapeutic target for this condition.

Type I Interferon Potentiates IgA Immunity to Respiratory Syncytial Virus Infection During Infancy.

Respiratory syncytial virus (RSV) infection is the most frequent cause of hospitalization in infants and young children worldwide. Although mucosal RSV vaccines can reduce RSV disease burden, little is known about mucosal immune response capabilities in children. Neonatal or adult mice were infected with RSV; a subset of neonatal mice received interferon alpha (IFN-α) (intranasal) prior to RSV infection. B cells, B cell activating factor (BAFF) and IgA were measured by flow cytometry. RSV specific IgA was measured in nasal washes. Nasal associated lymphoid tissue (NALT) and lungs were stained for BAFF and IgA. Herein, we show in a mouse model of RSV infection that IFN-α plays a dual role as an antiviral and immune modulator and age-related differences in IgA production upon RSV infection can be overcome by IFN-α administration. IFN-α administration before RSV infection in neonatal mice increased RSV-specific IgA production in the nasal mucosa and induced expression of the B-cell activating factor BAFF in NALT. These findings are important, as mucosal antibodies at the infection site, and not serum antibodies, have been shown to protect human adults from experimental RSV infection.

Specific inhibition of NLRP3 in chikungunya disease reveals a role for inflammasomes in alphavirus-induced inflammation.

Mosquito-borne viruses can cause severe inflammatory diseases and there are limited therapeutic solutions targeted specifically at virus-induced inflammation. Chikungunya virus (CHIKV), a re-emerging alphavirus responsible for several outbreaks worldwide in the past decade, causes debilitating joint inflammation and severe pain. Here, we show that CHIKV infection activates the NLRP3 inflammasome in humans and mice. Peripheral blood mononuclear cells isolated from CHIKV-infected patients showed elevated NLRP3, caspase-1 and interleukin-18 messenger RNA expression and, using a mouse model of CHIKV infection, we found that high NLRP3 expression was associated with peak inflammatory symptoms. Inhibition of NLRP3 activation using the small-molecule inhibitor MCC950 resulted in reduced CHIKV-induced inflammation and abrogated osteoclastogenic bone loss and myositis, but did not affect in vivo viral replication. Mice treated with MCC950 displayed lower expression levels of the cytokines interleukin-6, chemokine ligand 2 and tumour necrosis factor in joint tissue. Interestingly, MCC950 treatment abrogated disease signs in mice infected with a related arthritogenic alphavirus, Ross River virus, but not in mice infected with West Nile virus-a flavivirus. Here, using mouse models of alphavirus-induced musculoskeletal disease, we demonstrate that NLRP3 inhibition in vivo can reduce inflammatory pathology and that further development of therapeutic solutions targeting inflammasome function could help treat arboviral diseases.