Precursor of mast cells fixed in the skin of mice.

The presence and origin of mast-cell precursors fixed in the skin tissue of mice were investigated. Giant granules of beige (C57BL/6-bh'/bg', Chediak-Higashi syndrome) mice were used to distinguish different populations of mast cells. Pieces of the skin were grafted from the intact WBB6F1 (WB X C57BL/6)F1-+/+ mice into the back of the WBB6F1-+/+ mice which had been irradiated and injected with bone marrow cells of C57BL/6-bg'/bg'leads to +/+ chimeras). Although the number of mast cells in the skin grafts decreased after the transplantation, the mast-cell precursors circulating in the bloodstream of bg'/bg' leads to +/+ chimeras (bg'/bg' type) did not seem to enter into the skin grafts, because most of mast cells were of +/+ type after the recovery of mast-cell number to pregrafting levels. As a considerable proportion of +/+-type mast cells was labeled with 3H-thymidine, the recovery of mast-cell number in the grafts was attributed to the proliferation and differentiation of +/+-type precursor cells fixed in the skin tissue of the donor. On the other hand, the skin of WBB6F1-W/Wv mice seemed to be depleted of fixed precursors, because most of mast cells were of bg'/bg'-type in skin grafted from WBB6F1-W/Wv mice to bgJ/bgJ leads to +/+ chimeras. Since the fixed precursor cells which proliferate and differentiate into mast cells after skin grafting may be transferred to WBB6F1-W/Wv mice by bone marrow transplantation, such precursor cells seem to have been derived from the bone marrow.