Asthma and PTSD association: relevant models and a role of IL17AA

Strong genetic and epidemiological evidence supports an asthma-PTSD association, however, contributory immune mediators/mechanisms are unclear. Here, we examined a direct role of severe asthma associated Th17/ IL-17A in regulating PTSD-relevant behaviors using mouse aeroallergen house dust mite (HDM) models. 3 strategies were used: 1) BALBc-C5a receptor treatment that shifts Th2 mild asthma phenotype to Th17/IL17a expansion; 2) IL-17a receptor knockout mice and 3) sufficiency testing with intracerebroventricular (ICV) administration of recombinant IL17a effects on behavior. Fear conditioning and extinction, maze exploration and social behaviors were assessed. Absence of IL-17 signaling attenuated HDM effects on fear extinction while induction of Th17/IL-17 in the BALBc/anti-C5aR1 treated mice resulted in compromised fear extinction. ICV IL-17a promoted an anxiogenic phenotype and impaired social behaviors. Preliminary evidence suggests a role of cortical mechanisms (under investigation). Overall, our work highlights severe asthma inflammatory mediator IL17a in regulating PTSD-relevant behaviors. Beyond asthma-PTSD, our findings have relevant implications for other pulmonary (e.g. COVID-19) and autoimmune inflammatory conditions and PTSD risk.