Altered Fear Behavior in Aeroallergen House Dust Mite Exposed C57Bl/6 Mice: A Model of Th2-skewed Airway Inflammation.

There is a growing interest for studying the impact of chronic inflammation, particularly lung inflammation, on the brain and behavior. This includes asthma, a chronic inflammatory condition, that has been associated with psychiatric conditions such as posttraumatic stress disorder (PTSD). Although asthma is driven by elevated production of Th2 cytokines (IL-4, IL-5 and IL-13), which drive asthma symptomology, recent work demonstrates that concomitant Th1 or Th17 cytokine production can worsen asthma severity. We previously demonstrated a detrimental link between PTSD-relevant fear behavior and allergen-induced lung inflammation associated with a mixed Th2/Th17-inflammatory profile in mice. However, the behavioral effects of Th2-skewed airway inflammation, typical to mild/moderate asthma, are unknown. Therefore, we investigated fear conditioning/extinction in allergen house dust mite (HDM)-exposed C57Bl/6 mice, a model of Th2-skewed allergic asthma. Behaviors relevant to panic, anxiety, and depression were also assessed. Furthermore, we investigated the accumulation of Th2/Th17-cytokine-expressing cells in lung and brain, and the neuronal activation marker, ΔFosB, in fear regulatory brain areas. HDM-exposed mice elicited lower freezing during fear extinction with no effects on acquisition and conditioned fear. No HDM effect on panic, anxiety or depression-relevant behaviors was observed. While HDM evoked a Th2-skewed immune response in lung tissue, no significant alterations in brain Th cell subsets were observed. Significantly reduced ΔFosB+ cells in the basolateral amygdala of HDM mice were observed post extinction. Our data indicate that allergen-driven Th2-skewed responses may induce fear extinction promoting effects, highlighting beneficial interactions of Th2-associated immune mediators with fear regulatory circuits.