BTK and aspergillosis: However, we found a similar temporal accumulation of neutrophils in the lungs and BAL fluid of WT and Btk–/– mice during aspergillosis and observed no difference in the frequency of extravasated neutrophils in WT and Btk–/– lungs, as assessed using an intravascular staining approach (43) followed by flow cytometry–based immunophenotyping (Supplemental Figure 2, A–C).