A role for IgE in extrinsic allergic alveolitis?

Receptors for the Fc portion of immunoglobulin E (IgE; CD23) can be detected on the surface of alveolar macrophages (AM) in extrinsic allergic alveolitis (EAA), using monoclonal antibodies in immunocytology. More than 50% of AM were positive in 16 of the 20 patients reported here, while the remaining 4 had 11-47% positive cells. Staining with anti-IgE antibody can, in addition, demonstrate endogenous IgE bound to the AM. This suggests that IgE might be involved in the process. Since IgE-mediated asthma is associated with bronchoconstriction, we asked whether EAA patients do in fact exhibit an obstructive component. In 3 out of 10 patients we did indeed find clearly increased airway resistance (greater than 30 kPa x s x l-1). These findings are consistent with the observation of immediate bronchoconstriction observed in some patients upon allergen challenge. Since only 1 of the 20 patients studied was a smoker, and since in the literature the majority of reported cases of EAA are in nonsmokers, we speculate that smoking may interfere with immunological processes leading to EAA.