Immunologic significance of a collagen-derived culture filtrate containing proteolytic activity in Aspergillus-related diseases

Abstract

Background: Despite increasing evidence implicating fungal proteases in the virulence of pulmonary fungal diseases, routine fungal culture media do not favor protease production. Hence, filtrates that serve as the source of antigen for serologic determinations are poor in proteases, and consequently, the immunologic significance of these enzymes is unknown. Methods: A clinical isolate of Aspergillus fumigatus was cultured on collagen medium, resulting in excretion of high levels of fungal proteases in the culture filtrate. This was compared with standard culture filtrates by diverse analytic techniques including immunoblotting with sera of patients with pulmonary aspergilloma (PA) and allergic bronchopulmonary aspergillosis (ABPA). Results: Protein profiles of collagen medium filtrate showed several (glyco)proteins not found in conventional culture filtrates, including a prominent 32 kd glycoprotein, which coisolated in gel filtration and ion-exchange chromatography with elastase activity, as well as 67 kd and 94 kd (glyco)proteins. Intense IgG binding was seen with the 32 kd glycoprotein when ABPA and PA sera were used. The 94 kd protein showed intense binding with PA sera but not with ABPA sera, whereas for the 67 kd glycoprotein the reverse tended to be the case. Conclusion: Fungal culture on collagen media results in the production of filtrates with high protease activity, containing unique (glyco)proteins of which at least one (32 kd) is closely associated with fungal elastase activity. These constituents are immunologically relevant, eliciting IgG production in patients with PA and ABPA, suggesting production of these (glyco)proteins during disease in vivo. The use of collagen media filtrates may enhance our serodiagnostic capacity in patients with fungal pulmonary diseases.