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Background Secreted phospholipases A2 (sPLA2s) are released in plasma and other biologic fluids of patients with inflammatory, autoimmune, and allergic diseases. Objective We sought to evaluate sPLA2 activity in the bronchoalveolar lavage fluid (BALF) of asthmatic patients and to examine the expression and release of sPLA2s from primary human lung mast cells (HLMCs). Methods sPLA2 activity was measured in BALF and supernatants of either unstimulated or anti-IgE–activated HLMCs as hydrolysis of oleic acid from radiolabeled Escherichia coli membranes. Expression of sPLA2s was examined by using RT-PCR. The release of cysteinyl leukotriene (LT) C4 was measured by means of enzyme immunoassay. Results Phospholipase A2 (PLA2) activity was higher in the BALF of asthmatic patients than in the control group. BALF PLA2 activity was blocked by the sPLA2 inhibitors dithiothreitol and Me-Indoxam but not by the cytosolic PLA2 inhibitor AZ-1. HLMCs spontaneously released a PLA2 activity that was increased on stimulation with anti-IgE. This PLA2 activity was blocked by dithiothreitol and Me-Indoxam but not by AZ-1. HLMCs constitutively express mRNA for group IB, IIA, IID, IIE, IIF, III, V, X, XIIA, and XIIB sPLA2s. Anti-IgE did not modify the expression of sPLA2s. The cell-impermeable inhibitor Me-Indoxam significantly reduced (up to 40%) the production of LTC4 from anti-IgE–stimulated HLMCs. Conclusions sPLA2 activity is increased in the airways of asthmatic patients. HLMCs express multiple sPLA2s and release 1 or more of them when activated by anti-IgE. The sPLA2s released by mast cells contribute to LTC4 production by acting in an autocrine fashion. Mast cells can be a source of sPLA2s in the airways of asthmatic patients.

We show that the P2Y6 receptor, a G-protein-coupled receptor with high affinity for the nucleotide uridine diphosphate, is an important endogenous inhibitor of T cell function in allergic pulmonary inflammation. Mice conditionally deficient in P2Y6 receptors [p2ry6 (flox/flox);cre/+ mice] exhibited severe airway and tissue pathology relative to P2Y6-sufficient [p2ry6 (flox/flox)] littermates (+/+ mice) when treated intranasally with an extract (Df) of the dust mite Dermatophagoides farinae. P2Y6 receptors were inducibly expressed by lung, lymph node and splenic CD4+ and CD8+ T cells of Df-treated +/+ mice. Df-restimulated P2Y6-deficient lymph node cells produced higher levels of Th1 and Th2 cytokines, and polyclonally-stimulated P2Y6-deficient CD4+ T cells proliferated faster than comparably stimulated P2Y6-sufficient cells. The absence of P2Y6 receptors on CD4+ cells, but not antigen presenting cells, was sufficient to amplify cytokine generation. Thus, P2Y6 receptors protect the lung against exuberant allergen-induced pulmonary inflammation by inhibiting the activation of effector T cells.