EVIDENCE FOR IN-VIVO MITOSIS BY GRANULE-CONTAINING MAST-CELLS FROM CANINE MASTOCYTOMAS

Mast cell accumulations are generally considered to arise almost exclu sively from the recruitment of non-granulated, bone-marrow-derived, pr ecursor cells, with the stem cell factor (SCF) reported to play a cruc ial role in the growth, development and maturation of granulated mast cells within specific tissue sites. In this study dog mastocytoma spec imens have been examined by both immunohistochemical and ultrastructur al techniques, to demonstrate that fully granulated mast cells are cap able of mitotic activity. Observations showing the formation of mitoti c spindles, chromosome separation and cytokinesis all support the conc ept that granulated mast cells are capable of proliferative activity. The ability of mature granulated mast cells to replicate provides an a lternative process for local increases in mast cell numbers, at least in canine mast cell tumours. Such observations suggest the possibility that normal or neoplastic human mast cells, fully granulated, have th e potential to proliferate in specific tissue sites.