Precursor of mast cells fixed in the skin of mice

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Abstract
The presence and origin of mast‐cell precursors fixed in the skin tissue of mice were investigated. Giant granules of beige (C57BL/6‐bgj/bgj, Chediak‐Higashi syndrome) mice were used to distinguish different populations of mast cells. Pieces of the skin were grafted from the intact WBB6F1 (WB × C57BL/6)F1−+/+ mice onto the back of the WBB6F1−+/+ mice which had been irradiated and injected with bone marrow cells of C57BL/6‐bgj/bjj mice (bgj/bgj −+/+ chimeras). Although the number of mast cells in the skin grafts decreased after the transplantation, the mast‐cell precursors circulating in the bloodstream of bgj/bgj −+/+ chimeras (bgj/bgj 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 bgj/bgj type in skin grafted from WBB6F1‐W/Wv mice to bgj/bgj−+/+ 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.