SERPINB6 is expressed by mast cells in different tissues. Tissue sections were stained for SERPINB6 expression (mAb PI6-18; A-F) and mast cell tryptase (mAb AA1; G-H), as described in “Patients, materials, and methods.” Slides were stained with AEC and counterstained with hematoxylin. Arrow indicates mast cell showing strong SERPINB6 staining (E-F); arrowhead, neutrophil (E) or starry sky macrophage (F) with weak SERPINB6 staining. Original magnifications, × 400 (B), × 630 (A, F), and × 1000 (C-E). (G) Fluorescent double staining of SERPINB6 (green) with tryptase (red) in skin. (H) Fluorescent double staining of SERPINB6 (green) with CD117 (red) in tonsil. In the latter a clear membranous staining of CD117 is seen. Original magnifications, × 1000 (G-H).