Proliferation of Peritoneal

Peritoneal mast cells and macrophages are commonly used to study functions of these two types of cells (1-3). Although many investigators have studied the production of peritoneal macrophages both in vivo (4-6) and in vitro (7, 8), only a few investigators have taken an interest in production of peritoneal mast cells (9-11). Both mast cells and macrophages are the progeny of the multipotential hematopoietic stem cell (CFU-S) ~ (12, 13). Although most of the progeny of CFU-S (such as erythrocytes, neutrophils, and platelets) differentiate within hematopoietic tissues, undifferent iated precursors of mast cells leave the hematopoietic tissues, migrate in the peripheral blood (14-16), and enter connective tissues, where they proliferate, and differentiate into mast cells (17-19). Such a mode of differentiation bears some resemblance to that of macrophages, because monocytes, the precursors of macrophages, often undergo final differentiation in nonhematopoiet ic tissues (20). Since Lin and his co-workers (7, 8) have demonstra ted the presence of macrophage precursors in the peritoneal cavity of mice and have characterized such precursors, we examined the presence of mast cell precursors in the peritoneal cavity. For this purpose, we used mice of W / W v genotype as recipients of cells, because these mutant mice genetically lack tissue mast cells (21, 22). When a cell suspension, containing mast cell precursor(s), was injected directly into the skin of W / W v mice, a cluster of mast cells appeared at the injection site (16). By determining the proport ion of injection sites at which mast cells appeared, the concentration of mast cell precursors can be calculated with the limiting dilution analysis. Unexpectedly, the concentration of mast cell precursors in the peritoneal cavity was about five times as great as the value observed in the bone marrow. Physical characterization revealed that mast cell precursors in the peritoneal cavity differed from mast cell precursors in the bone marrow. When a single peritoneal mast cell was picked by the micromanipulator and injected into the skin of W / W v mice, a mast cell cluster containing ~2,000