Determinants of host susceptibility to murine respiratory syncytial virus (RSV) disease identify a role for the innate immunity scavenger receptor MARCO gene in human infants

AbstractBackgroundRespiratory syncytial virus (RSV) is the global leading cause of lower respiratory tract infection in infants. Nearly 30% of all infected infants develop severe disease including bronchiolitis, but susceptibility mechanisms remain unclear.MethodsWe infected a panel of 30 inbred strains of mice with RSV and measured changes in lung disease parameters 1 and 5days post-infection and they were used in genome-wide association (GWA) studies to identify quantitative trait loci (QTL) and susceptibility gene candidates.FindingsGWA identified QTLs for RSV disease phenotypes, and the innate immunity scavenger receptor Marco was a candidate susceptibility gene; targeted deletion of Marco worsened murine RSV disease. We characterized a human MARCO promoter SNP that caused loss of gene expression, increased in vitro cellular response to RSV infection, and associated with increased risk of disease severity in two independent populations of children infected with RSV.InterpretationTranslational integration of a genetic animal model and in vitro human studies identified a role for MARCO in human RSV disease severity. Because no RSV vaccines are approved for clinical use, genetic studies have implications for diagnosing individuals who are at risk for severe RSV disease, and disease prevention strategies (e.g. RSV antibodies)

IL-1 Receptors Mediate Persistent, but Not Acute, Airway Hyperreactivity to Ozone in Guinea Pigs

Ozone exposure in the lab and environment causes airway hyperreactivity lasting at least 3 days in humans and animals. In guinea pigs 1 day after ozone exposure, airway hyperreactivity is mediated by eosinophils that block neuronal M2 muscarinic receptor function, thus increasing acetylcholine release from airway parasympathetic nerves. However, mechanisms of ozone-induced airway hyperreactivity change over time, so that depleting eosinophils 3 days after ozone makes airway hyperreactivity worse rather than better. Ozone exposure increases IL-1β in bone marrow, which may contribute to acute and chronic airway hyperreactivity. To test whether IL-1β mediates ozone-induced airway hyperreactivity 1 and 3 days after ozone exposure, guinea pigs were pretreated with an IL-1 receptor antagonist (anakinra, 30 mg/kg, intraperitoneally) 30 minutes before exposure to filtered air or to ozone (2 ppm, 4 h). One or three days after exposure, airway reactivity was measured in anesthetized guinea pigs. The IL-1 receptor antagonist prevented ozone-induced airway hyperreactivity 3 days, but not 1 day, after ozone exposure. Ozone-induced airway hyperreactivity was vagally mediated, since bronchoconstriction induced by intravenous acetylcholine was not changed by ozone. The IL-1 receptor antagonist selectively prevented ozone-induced reduction of eosinophils around nerves and prevented ozone-induced deposition of extracellular eosinophil major basic protein in airways. These data demonstrate that IL-1 mediates ozone-induced airway hyperreactivity at 3 days, but not 1 day, after ozone exposure. Furthermore, preventing hyperreactivity was accompanied by decreased eosinophil major basic protein deposition within the lung, suggesting that IL-1 affects eosinophil activation 3 days after ozone exposure

In control (air exposed) guinea pigs electrical stimulation of the vagus nerves (3–30V, 0.2 ms pulse width, 15 Hz, 5 sec duration at 1 minute intervals) resulted in vagally induced bronchoconstriction (measured as an increase in pulmonary inflation pressure; 16±1 mmH₂O).

<p>An M₂ receptor antagonist, gallamine, potentiated vagally induced bronchoconstriction up to 6-fold in air exposed animals (open circles) demonstrating that functional M₂ receptors were limiting acetylcholine release. The potentiation by gallamine was decreased in ozone-exposed animals, demonstrating M₂ receptors were dysfunctional after ozone exposure (closed circles). V-05-013 partially prevented M₂ receptor dysfunction (C closed squares), while V-05-014 (B closed triangles) and V-05-015 (C closed inverted triangles) completely protected M₂ receptor function. Vagally induced bronchoconstriction in the absence of gallamine was not different from control among all groups. Ozone and air exposed controls are the same in A–C. *p<0.05, **p<0.01 Significantly different from air exposed controls. Data are mean ± SEM. n = 4–7.</p

Blocking p38 and JNK MAPK completely prevented ozone-induced airway hyperreactivity mediated by the vagus nerves.

<p>In anesthetized and vagotomized guinea pigs, stimulation of the vagus nerves (10V, 0.2 ms pulse width, 1–25 Hz, 5 sec duration at 1 minute intervals) caused frequency dependent bronchoconstriction (A open circles; measured as an increase in inflation pressure in mmH₂O) that is significantly potentiated one day post-ozone exposure (A closed circles). Pretreatment with dual MAPK inhibitors V-05-013 (A closed squares), V-05-014 (B closed triangles), or V-05-015 (C closed inverted triangles) completely prevented ozone-induced airway hyperreactivity. All three dual MAPK inhibitors suppressed parasympathetic nerve activity (A open squares, B open triangles, C open inverted triangles). Ozone and air exposed control data are the same in A-C. *p<0.05, **p<0.01 Significantly different from air exposed controls. Data are mean ± SEM. n = 4–7.</p

Ki values for dual p38 and JNK MAPK inhibitors.

<p>All compounds have a Ki greater than 1 µM for all other kinases tested.</p>*<p>This one value is an IC50, not a Ki.</p

Chemical structures of dual p38 and JNK MAPK inhibitors.

<p>Chemical structures of dual p38 and JNK MAPK inhibitors.</p

Ozone exposure increased neutrophils in bronchoalveolar lavage (D closed bar).

<p>No other inflammatory cell type number was affected by either ozone or the dual p38/JNK MAPK inhibitors. *p<0.05 Significantly different from air exposed controls. Data are mean ± SEM. n = 3–6.</p