Mast cell granule formation in the beige mouse.

The formation of mast cell granules was studied in the beige mouse utilizing histochemistry and electron microscopy. The time and sequence of appearance of heparin, histamine and the chymotrypsin-like protease were normal. By electron microscopy, the initial formation of progranules and subsequent aggregation was normal, but the granules from early stages were abnormally large. Reorganization of intermediate granule forms to homogeneous mature granules was delayed. Late fusions of intermediate and/or mature granules were not observed. Our findings indicate that the defect lies in the excessive initial fusion of progranules rather than in continued formation of new progranules or in fusion of mature granules with one another.