Evidence that peptidoleukotriene is a prerequisite for antigen-dependent thromboxane synthesis in IgG1-passively sensitized guinea pig lungs.

Lungs from guinea pigs passively sensitized with an affinity-purified IgG1 antibody produce both leukotriene (LT)D4 and thromboxane (Tx)B2 upon ex vivo antigen challenge. This study was undertaken to determine the possibility of endogenously generated peptido-LTs being a prerequisite for Tx synthesis. In immunoglobulin G1-sensitized lungs, exogenous LTD4 induced TxB2 production with a median effective dose of 4.1 nM, whereas the response to LTE4, LTB4 or platelet-activating factor was relatively weak. Although LTC4 was as potent as LTD4 in stimulating TxB2 generation, LTC4's dose-response curve was shifted significantly to the right by AT-125, an irreversible gamma-glutamyl transpeptidase inhibitor, suggesting that at least a part of LTC4 sensitized lungs with antigen (0.01-30 micrograms/ml ovalbumin) for 20 min precipitated a significant amount of LTD4 production. The levels of LTD4 range from 8 to 26 nM (without taking LTD4 recovery into consideration). This level is 2- to 7-fold greater than the median effective dose value observed with exogenous LTD4. Moreover, pretreatment of sensitized lungs with ICI-198,615 a specific LTD4 antagonist, blocked equally both antigen (IC50 = 0.01 microM)- and LTD4 (IC50 = 0.017 microM)-induced TxB2 production. When sensitized lung fragments were treated with 5 mM AT-125, ICI-198,615 was effective in preventing not only antigen-but also LTC4-dependent production of TxB2 (IC50 = 0.018 and 0.021 microM, respectively). In contrast, neither WEB-2086, a platelet-activating factor antagonist, nor pyrilamine, a histamine antagonist, inhibited antigen and LTD4 responses (IC50 greater than 30 microM). Unlike its effect on antigen response, ICI-198,615 was unable to block Ca2+ ionophore-induced TxB2 production.2