Deficiency of ROR$${\rm{\gamma }}$$t promotes inflammation and compromises bacterial clearance in a mouse model of cystic fibrosis-like lung disease

Cystic fibrosis (CF) leads to dehydration of the airway surface liquid layer, resulting in hyperconcentrated mucus, airway obstruction, chronic lung inflammation, bronchiectasis, alveolar space enlargement, compromised mucociliary clearance, and increased susceptibility to bacterial infection. Retinoic acid receptor-related orphan receptor gamma (RORγt) is a transcription factor influencing type 3 immunity, which is associated with immune cell recruitment, lung inflammation, and bacterial clearance. However, the role of RORγt in the pathogenesis of CF has not been determined. Therefore, we hypothesized that the ablation of RORγt modulates the mucoinflammatory phenotype in sodium channel non-voltage-gated 1, β subunit ( Scnn1b )-transgenic (Tg+) mice, a mouse model for human cystic fibrosis-like lung disease. To test this hypothesis, we examined the effect of RORγt deletion on the manifestation of mucoinflammatory lung disease in juvenile Tg+ mice. RORγt deletion did not alter the immune cell composition in lung airspace of wild-type (WT) mice. However, RORγt deletion in Tg+ mice resulted in increased immune cell counts in lung airspaces attributable to an increased number of macrophages, neutrophils, and lymphocytes. Also, RORγt deletion in Tg+ mice increased levels of inflammatory mediators, including IL-2, IL-6, IP-10, KC, MIP-1 \({\rm{\beta }}\) , and IL-4 in lung homogenates. Further, the RORγt deficiency resulted in sustained bacterial load in the Tg+ juveniles. The RORγt deletion in both WT and Tg+ mice resulted in increased numbers of tertiary lymphoid structures (TLS), which were characterized by CD3+ T-cells polarized to one side of the structure and CD20+ B-cells organized into distinct follicular aggregates. However, RORγt deletion did not alter mucous cell metaplasia, muco-obstruction, and alveolar space enlargement. Overall, our findings indicate that RORγt deletion exacerbates inflammatory responses and impairs bacterial clearance in CF-like lung disease, thus providing new insights into the roles of RORγt in mucoinflammatory lung diseases.