Studies on the pathogenesis of aplastic anemia

Depletion of phagocyctic cells from aplastic anemia resulted in a significant increase in colony numbers in all 10 cases studied. This depletion caused an increase in colony growth in only one case from 5 normal persons and 3 cases from 22 patients with disorders. When the positive cases were compared among 3 groups of patients, the degree of the increase of colony numbers after phagocytic cell depletion was greater in aplastic anemia patients than in normals and patients. Depletion of phacocytic cells from mononuclear cells from 8 aplastic anemia cases with proven suppressor cells resulted in a loss of the suppressive activity in all cases. Depletion of the phagocytic cells from the bone marrow of a patient caused an apparent increase in colony growth. Depletion of T cells was also effective in increasing the colony numbers, and the depletion of both phagocytic cells and T cells resulted in the most marked increase in the colony numbers. Addition of hydrocortisone to the bone marrow of this case in vitro resulted in an apparent increase in colony growth. The relationship between macrophages and stem cell differentiation in connection with T cells in the pathogenesis of aplastic anemia is discussed.