In Vitro Release by Aspergillus fumigatus of Galactofuranose Antigens, 1,3-β- d -Glucan, and DNA, Surrogate Markers Used for Diagnosis of Invasive Aspergillosis

Aspergillus markers are becoming increasingly important for the early diagnosis of invasive aspergillosis. The kinetics of release of these surrogate markers, however, is largely unknown. We investigated the release of β-(1-5)-galactofuranosyl (gal f ) antigens (Platelia Aspergillus ), 1,3-β- d -glucan (BG) (Fungitell), and DNA (PCR) in an in vitro model of Aspergillus fumigatus . The results showed that release is correlated to the growth phase of the fungus, which depends on available nutrients. Whereas gal f antigens and BG are released during logarithmic growth, DNA is released only after mycelium breakdown. During early logarithmic growth, gal f antigens seem to be released somewhat earlier than BG. Furthermore, gal f antigen concentrations of more than 120,000 times the serum cutoff value (0.5 ng/ml) can be measured, while BG concentrations reach a value only 978 times the serum cutoff value (60 pg/ml). During lytical growth, release of gal f antigens further increased to a maximum level, which depended on pH. After that, the concentration of gal f antigens stayed high (pH 7.4) or decreased to zero within 4 days (pH 5.0). In contrast to gal f antigens, BG concentration decreased after 1 day of growth. The decrease of gal f components seems to be due to the enzyme β-galactofuranosidase, which is able to destroy gal f epitopes and whose activity fluctuates in the culture filtrates in parallel with gal f antigen concentration. Fungal DNA seems to be released only due to autolysis caused by nutrient limitation. In conclusion, several factors clearly influence the release of surrogate markers in vitro. These same factors might also play a role at the infection site of Aspergillus disease in humans.