Asthma presents as a heterogeneous syndrome characterized by airway obstruction, inflammation and hyper‐reactivity (AHR). Spleen tyrosine kinase (Syk) mediates allergen‐induced mast cell degranulation, a central component of allergen‐induced inflammation and AHR. However, the role of Syk in IgE‐mediated constriction of human small airways remains unknown. In this study, we addressed whether selective inhibition of Syk attenuates IgE‐mediated constriction and mast cell mediator release in human small airways.

Human precision cut lung slices (hPCLS) ex vivo derived from non‐asthmatic donors were incubated overnight with human IgE, dexamethasone, montelukast, antihistamines or a selective Syk inhibitor (SYKi). High‐affinity IgE receptor (FcεRI) activation by anti‐IgE cross‐linking was performed, and constriction and mediator release measured. Airway constriction was normalized to that induced by maximal carbachol stimulation. Syk expression (determined by qPCR and immunoblot) was also evaluated in human primary airway smooth muscle (HASM) cells to determine whether Syk directly modulates HASM function.

While dexamethasone had little effect on FcεR‐mediated contraction, montelukast or antihistamines partially attenuated the response. SYKi abolished anti‐IgE‐mediated contraction and suppressed the release of mast cell or basophil mediators from the IgE‐treated hPCLS. In contrast, SYKi had little effect on the non‐allergic contraction induced by carbachol. Syk mRNA and protein were undetectable in HASM cells.

A selective Syk inhibitor, but not corticosteroids, abolished FcεR‐mediated contraction in human small airways ex vivo. The mechanism involved FcεRI receptor activation on mast cells or basophils that degranulate causing airway constriction, rather than direct actions on HASM.