Mast cell association with collagen fibres in human breast stroma

Whirl-like structures consisting of strands and bundles of collagen fibres with a central space are described in human breast stroma. Association between these structures and connective tissue mast cells is demonstrated. Mast cells in these whirls, in contrast to those in loose connective tissue, showed signs of secretory activity. On ultramicroscopy some showed electron-dense bud-like structures at the edge of the cell, and between this and adjacent collagen bundles. In the absence of cytoplasmic cover association was demonstrated between the surface of a mast cell granule and a band of collagen fibres in the stroma. In vitro production of collagen fibres was reported in 1952 on the addition of heparin powder to soluble collagen. The mechanism of that reaction was not further defined. Neither, as yet, is that underlying the present findings. The products of mast cell granules would appear to be common to both. It is suggested that these findings may represent an alternative pathway for collagen deposition in vivo, as in vitro.