Fig 1: Granulocytes, including eosinophils, are the main source of SLPI among circulating leukocytes in healthy individuals. Granulocytes (A) and PBMCs (B) from healthy donors were subjected to flow cytometry analysis for SLPI expression using anti-SLPI mAbs (clone: 31, Abcam) (shaded histograms) or isotype control (empty histograms). Eosinophils (Eos) and neutrophils (Neu) were identified in granulocyte fraction on the basis of the gating strategy indicated (dot plots, A), whereas LDGs, monocytes (Mo), NK cells, T cells, and B cells in the PBMC fraction were identified on the basis of gating on singlets, cell w/o debris, and staining for CD14, CD3, CD15, CD19, CD56, and/or CD16. Representative histograms for these cells are shown in (A, B) Data from all donors are shown as mean fluorescence intensity (MFI), (C). Data from donors stained with alternative anti-SLPI mAbs [Creative Diagnostics (CDg) and R&D] or isotype control are shown for Eos and Neu as MFI (D). Lines indicate the median value for each data set. n = 29 or n = 10 for granulocytes and PBMCs, respectively (C) or n = 8 (D). **p < 0.01; ***p < 0.001; Mann–Whitney test.