Pharmacological Modulation of the Antigen-Induced Expression of the Low-Affinity IgE Receptor (FcεRII/CD23) on Rat Alveolar Macrophages

Brown-Norway (BN) rats were sensitized by 3 aerosol exposures to ovalbumin (OA; 10 mg/ml) at days 1, 3 and 14. At day 21, the rats were challenged with the antigen or vehicle by aerosol. Alveolar macrophages (AM) were obtained by bronchoalveolar lavage and the expression of FceRII/CD23 was assessed by flow cytometry after staining with the BB10 monoclonal antibody. A maximum of 74% of the AM from sensitized and challenged BN rats expressed FCeRII/CD23 24 h after OA exposure, compared to 12% of the cells from rats exposed to vehicle. Sprague-Dawley rats were passively sensitized by intravenous injection of 0.1 or 0.05 ml/kg mouse ascitic fluid containing dinitrophenyl (DNP)-specific monoclonal IgE (2682–1) and after 24 h exposed to an aerosol of 5 mg/ml of DNP-bovine serum albumin for 30 min. In this case also, antigen exposure induced the expression of FceRII/CD23 on 75% AM, compared to 17% AM from saline-challenged rats. Such an induction of FceRII/CD23 on AM was, however, not observed when the animals were challenged with either histamine, serotonin or acetylcholine by aerosol. The antigen-induced expression of Fce-RII/CD23 on AM was inhibited upon treatment of the rats with ketotifen or beclomethasone. In addition, oral or aerosol administration of respectively BN 50730 or BN 52021 (two structurally unrelated platelet-activating factor antagonists), inhibited the antigen-induced FceRII/CD23 expression on AM, indicating the participation of this lipid mediator in this process.