Airway mucus is essential for lung defense, but excessive mucus in asthma obstructs airflow, leading to severe and potentially fatal outcomes. Current asthma treatments have minimal effects on mucus, and the lack of therapeutic options stems from a poor understanding of mucus function and dysfunction at a molecular level and in vivo. Biophysical properties of mucus are controlled by mucin glycoproteins that polymerize covalently via disulfide bonds. Once secreted, mucin glycopolymers can aggregate, form plugs, and block airflow. Here we show that reducing mucin disulfide bonds disrupts mucus in human asthmatics and reverses pathological effects of mucus hypersecretion in a mouse allergic asthma model. In mice, inhaled mucolytic treatment loosens mucus mesh, enhances mucociliary clearance, and abolishes airway hyperreactivity (AHR) to the bronchoprovocative agent methacholine. AHR reversal is directly related to reduced mucus plugging. These findings establish grounds for developing treatments to inhibit effects of mucus hypersecretion in asthma.

Dendritic cells (DCs) are required for the induction of cytotoxic T cells (CTL). In most tissues, including the lung, the resident DCs fall into two types expressing the integrin markers CD103 and CD11b. The current supposition is that DC function is predetermined by lineage, designating the CD103(+) DC as the major cross-presenting DC able to induce CTL. Here we show that Poly I:C (TLR3 agonist) or R848 (TLR7 agonist) do not activate all endogenous DCs. CD11b(+) DCs can orchestrate a CTL response in vivo in the presence of a TLR7 agonist but not a TLR3 agonist, whereas CD103(+) DCs require ligation of TLR3 for this purpose. This selectivity does not extend to antigen cross-presentation for T-cell proliferation but is required for induction of cytotoxicity. Thus, we demonstrate that the ability of DCs to induce functional CTLs is specific to the nature of the pathogen-associated molecular pattern (PAMP) encountered by endogenous DC.

In asthma, airflow obstruction is thought to result primarily from inflammation-triggered airway smooth muscle (ASM) contraction. However, anti-inflammatory and smooth muscle-relaxing treatments are often temporary or ineffective. Overproduction of the mucin MUC5AC is an additional disease feature that, while strongly associated pathologically, is poorly understood functionally. Here we show that Muc5ac is a central effector of allergic inflammation that is required for airway hyperreactivity (AHR) to methacholine (MCh). In mice bred on two well-characterized strain backgrounds (C57BL/6 and BALB/c) and exposed to two separate allergic stimuli (ovalbumin and Aspergillus extract), genetic removal of Muc5ac abolishes AHR. Residual MCh responses are identical to unchallenged controls, and although inflammation remains intact, heterogeneous mucous occlusion decreases by 74%. Thus, whereas inflammatory effects on ASM alone are insufficient for AHR, Muc5ac-mediated plugging is an essential mechanism. Inhibiting MUC5AC may be effective for treating asthma and other lung diseases where it is also overproduced.

Pulmonary arterial hypertension (PAH) is an obstructive disease of the precapillary pulmonary arteries. Schistosomiasis-associated PAH shares altered vascular TGF-β signalling with idiopathic, heritable and autoimmune-associated etiologies; moreover, TGF-β blockade can prevent experimental pulmonary hypertension (PH) in pre-clinical models. TGF-β is regulated at the level of activation, but how TGF-β is activated in this disease is unknown. Here we show TGF-β activation by thrombospondin-1 (TSP-1) is both required and sufficient for the development of PH in Schistosoma-exposed mice. Following Schistosoma exposure, TSP-1 levels in the lung increase, via recruitment of circulating monocytes, while TSP-1 inhibition or knockout bone marrow prevents TGF-β activation and protects against PH development. TSP-1 blockade also prevents the PH in a second model, chronic hypoxia. Lastly, the plasma concentration of TSP-1 is significantly increased in subjects with scleroderma following PAH development. Targeting TSP-1-dependent activation of TGF-β could thus be a therapeutic approach in TGF-β-dependent vascular diseases.