Lung surfactant proteins A and D can inhibit specific IgE binding to the allergens of Aspergillus fumigatus and block allergen-induced histamine release from human basophils

Aspergillus fumigatus is an opportunistic fungal pathogen which, in the immunocompetent host, causes allergic disorders such as allergic rhinitis, allergic sinusitis, hypersensitivity pneumonitis, and allergic bronchopulmonary Aspergillosis (ABPA). In the present study, the interaction of 3-week culture filtrate (3wcf) allergens and various purified glycosylated and non-glycosylated allergens of A. fumigatus with lung surfactant proteins, SP-A and SP-D, was investigated. Purified SP-A and SP-D, isolated from human bronchoalveolar lavage fluid, bound in the 3wcf allergens and purified allergens, gp55 and gp45, in a carbohydrate-specific and calcium-dependent manner. Both SP-A and SP-D did not bind to deglycosylated allergens, suggesting that the ability of SP-A and SP-D to bind certain allergens is mediated through their carbohydrate recognition domains, interacting with the carbohydrate residues on the allergen. Both SP-A and SP-D could inhibit the ability of allergen-specific IgE from Aspergillosis patients to bind these allergens, suggesting that SP-A and SP-D may, be involved in the modulation of allergic sensitization and/or development of allergic reactions. The view that SP-A and SP-D play a protective role against airborne allergens is further supported by the demonstration of their ability to inhibit A. fumigatus allergen-induced histamine release from allergic patients' basophils.