Ontogeny of in vitro-differentiated mouse mast cells

Rat and mouse heparin-containing connective tissue mast cells (CTMC) are stained by both alcian blue and safranin, whereas the chondroitin sulfate-containing mucosal mast cells (MMC) are stained by alcian blue but not by safranin. Mouse bone marrow-derived mast cells (BMMC) (the presumptive in vitro counterpart of the in vivo-differentiated MMC) were derived by culture of progenitors in the presence of 50% WEHI-3-conditioned medium and 10% fetal calf serum and were then cultured for up to 14 days with confluent skin-derived mouse 3T3 fibroblasts in the same culture medium. Although the BMMC adhered to the fibroblast monolayer, they continued to divide, probably because of the presence of interleukin 3 in the conditioned medium. After 14 days of coculture, their cellular histamine content increased ~15-fold, and > 50% of the BMMC changed histochemically from safranin negative to safranin positive. At this time 30-50% of the glycosaminoglycans of the proteoglycans synthesized by these cocultured mast cells were heparin, whereas the initial BMMC synthesized proteoglycans containing chondroitin sulfate E. When activated immunologically, the cocultured mast cells generated approximately fivefold more prostaglandin D₂ than did the activated starting BMMC. Thus, interleukin 3-dependent mouse BMMC can be induced to undergo phenotypic changes in staining characteristics, histamine content, glycosaminoglycan structure, and metabolism of arachidonic acid to resemble heparin-containing CTMC. These findings suggest that the tissue microenvironment determines the phenotypic characteristics of mast cells. This demonstration of the functional diversity of different populations of mast cells adds an important dimension to the understanding of the role of mast cells in biological processes.