Epithelial modulation of thromboxane A2 and PAF involvement in IgE- and IgG-mediated guinea pig anaphylaxis.

The role of prostanoids and platelet-activating factor (PAF) was studied in the in vitro response of guinea pig trachea to immunochallenge according to the presence or the absence of the epithelial layer and to the sensitization procedure leading to the preferential synthesis of immunoglobulin E (IgE) or immunoglobulin G (IgG) antibodies. Indomethacin, a cyclooxygenase inhibitor, potentiated the antigen-induced contractions both in IgE and IgG models, suggesting the involvement of relaxant prostaglandins (PGs), independently of the presence of the airway epithelium. UK-38485, a thromboxane synthetase inhibitor, did not modify the tracheal response to antigen in the IgE model. However, this compound enhanced the maximum contractile response to antigen of the intact tracheal strips of IgG-sensitized guinea pig, but reduced the contractile response of the epithelium-free tracheal strips. Two potent non-structurally related PAF antagonists, Ro 19-3704 and BN 52021, reduced antigen-induced contraction of the epithelium-free tracheal strips in the IgE model. In contrast, these compounds did not affect the contractile responses of the preparations in the IgG model. These results suggest the selective implication of thromboxane A2 and PAF, in IgG- and IgE-mediated guinea pig anaphylaxis respectively. Finally, these results indicate that thromboxane A2 (TXA2) and PAF are potent inducers of epithelium-derived mediators.