Crystalloid inclusion-containing macrophages in the bone marrow and red pulp of the mouse, with particular relation to age, sex and hydrocortisone administration: qualitative and quantitative electron microscopy.

Cytoplasmic inclusions, particularly crystalloid inclusions of macrophages in mouse bone marrow and splenic red pulp were qualitatively and quantitatively examined by electron microscopy. In mice younger than 40 days of age, macrophages in the bone marrow contain a variety of inclusions, the majority of which are spherical phagolysosomes. In mice older than 60 days, needle-like crystalloid structures occur within the phagolysosomes. The crystalloids first appear at 60 days of age, and increase in amount with age. They exhibit a remarkable increase between 90 and 120 days in females and between 60 and 90 days in males. The crystalloids are significantly more abundant in adult males than in adult females. Macrophages in the splenic red pulp have much more spherical inclusions than marrow macrophages. The crystalloid inclusions are also contained in the red pulp, but they are quite small in amount as compared with those in the marrow. After administration of hydrocortisone, the amount of crystalloids increase significantly in marrow macrophages. The crystalloids in macrophages are discussed with particular interest to their relation to erythropoietic activity in the hemopoietic tissue.