The presence of mast cell precursors in rat peripheral blood.

Soft agar culture of mononuclear cell fractions prepared from rat peripheral blood yielded numerous colonies consisting of mast cells. The mast cell nature of the cells was established by ultrastructural and histochemical analyses as well as by the demonstration the the colonies contained histamine and that the cells possessed receptors for the Fc component of IgE. Stringent criteria for the distinction of mast cells from monocytes/macrophages that could have metachromatic inclusions were applied. The alcian-blue-safranin technique delineated the maturation of mast cell granules by showing the loss of alcian-blue and increase in safranin-positive organelles presumed to reflect the increase in N-sulfated polysaccharides representing heparin. The mast cells exhibited low or absent reactions for peroxidase, alpha-naphthyl butyrate, periodic acid Schiff, and Sudan black reacting lipid, whereas macrophages stained in parallel were positive for these substances. Since it is known that extracellular conditions may cause variations in phenotypic expression, the observations have led to the hypothesis that mast cells and macrophages may have a common precursor.