IgG vs IgE: Mediators of antigen-induced guinea pig lung parenchymal contraction

The present studies were conducted to determine whether different mediators are responsible for antigen-induced contraction of guinea pig lung parenchymal strips sensitized with either IgG or IgE. Passive sensitization was employed using IgG- or IgE-type antibody to ovalbumin which had been separated using Protein A-Sepharose as previously described (Regal, 1984a). Such a system ensures the presence of only one type of cytophilic antibody to mediate antigen-induced contraction of the isolated lung parenchymal strip. Pyrilamine, an H₁ antagonist, caused a very slight delay in the onset of the antigen-induced contractions in both IgG- and IgE-sensitized strips, suggesting a very minor role for endogenous histamine in both systems. A combination of the leukotriene antagonists, FPL 55712, and pyrilamine caused a significant reduction in the antigen-induced contraction in IgE- but not IgE-sensitized lung parenchymal strips. Histamine release was detected on antigen challenge of both IgG- and IgE-sensitized lung. Using bioassay techniques leukotriene release was primarily detected from IgG-sensitized lung and only minimally from IgE-sensitized lung. Thus, our studies have demonstrated a differential antagonism of IgG- and IgE-mediated airway contraction and suggest that leukotrienes are important mediators of antigen-induced lung parenchymal contraction in IgG- but not IgE-sensitized tissues.