Mast cells in human lung in setting of primary graft dysfunction. (A) Hematoxylin and eosin staining in a lung biopsy taken 3 days following transplant in a patient with severe PGD. (B) Mast cells were identified by immunostaining for c-Kit (brown cells). A higher-magnification example of a degranulated mast cell is shown in the inset. (C) Toluidine blue staining shows mast cells (open arrows) in a variety of stages of degranulation as indicated by irregular borders and heterogeneously reduced staining. Scale bars: 100 μm in (A) and (B) and 50 μm in (C).