Figure 7. Detection of extracellular DNA by propidium iodide-staining after co-incubation of neutrophils with Aspergillus morphotypes.

The different morphotypes of A. fumigatus were co-incubated for 180 min with neutrophils and the release of extracellular DNA was determined by measuring the fluorescence intensity of propidium iodide. Hyphae (black bars), swollen conidia (grey bars) and resting conidia (white bars) of A. fumigatus were used. (A) A. fumigatus ATTC 46445 wild type strain after co-incubation with human neutrophils. DNase I or DPI were added from the beginning of the co-incubation. Asterisks indicate significant differences (*p<0.05 or **p<0.01) based on Student's t-test. (^*1) Indicates comparison of each morphotype of the wild type (ATCC 46645) strain with the DNase I treated wild type strain; and (^*2) with the DPI treated wild type strain. (B) Analysis of different A. fumigatus wild type and mutant strains. In some experiments, 0.07 µg RodA protein was added to the A. fumigatus mutant strain ΔrodA just 15 min prior to the co-incubation with neutrophils. Asterisks indicate significant difference (*p<0.05 or **p<0.01) in the formation of extracellular DNA by neutrophils during (*¹) co-incubation of HF treated resting conidia of the DAL wild type strain in comparison to untreated resting conidia as a control, during (*²) co-incubation with the DAL wild type strain in comparison to the mutant strain ΔrodA, and (*³) during co-incubation with the mutant strain ΔrodA in comparison to ΔrodA supplemented with the spore surface protein RodA. Only the single morphotypes were compared with each other.