Evidence that tissue mast cells derive from mononuclear phagocytes.

A new method has been developed that allows in vitro differentiation of rat mast cells from precursor cells in the absence of feeder layers. In the present investigation, the precursor cells are further characterized as to their nature, state of activation and distribution in different organs of the rat. The data support our previously published evidence, based on morphology and enzyme-cytochemical reaction patterns that the precursor cells are mononuclear phagocytes. Peritoneal macrophages elicited by mineral oil, thioglycollate or proteose-peptone have lost the ability to differentiate into mast cells. Single cell suspensions of spleen and bone marrow contain mast cell precursors, while cells from mesenteric lymph nodes and thymus or purified lymphocytes never yield mast cells in this culture system.