A small study in adults with mild or moderate persistent asthma demonstrated that lower serum vitamin D concentrations were associated with impaired lung function, increased airway hyperresponsiveness, and decreased in vitro corticosteroid response, with higher serum vitamin D concentrations associated with enhanced dexamethasone-induced expression of mitogen activated protein kinase phosphatase-1 by PBMCs in an apparently IL-10–independent fashion [11]. Here, IL10 is linked to airway hyperresponsiveness.