IL33 and inflammation: Here, we show that induction of an acute exacerbation is associated with marked upregulation of the expression by AM of markers of alternative activation, as well as of proinflammatory cytokines and of cell surface proteins associated with antigen presentation to T cells; that expression of IL-33 in the airway wall is enhanced; and that IL-33 plays a key role both in the activation of AM and the development of airway inflammation.