The proposed project is to study factors controlling the proliferation and maturation of granulocytes in vivo and in vitro. The major emphasis is directed toward the study of in vitro proliferation of colonies of granulocyte and mononuclear cells from marrow and blood of animals and man. Colonies are cultured in a soft gel system (agar or methylcellulose) in the presence of a colony stimulating activity (CSA). Human and animal cells will also be cultured in liquid suspension. Studies will include the following: 1) to determine the effect of immuno-suppressant agents on release of colony stimulating activity (CSA) from lymphocytes, 2) to determine the mechanisms for leukopenia in viral disease and to determine the cellular distribution of viruses in hematopoietic cells, 3) to determine the role of the spleen in granulopoiesis following cytotoxic treatment, 4) to determine the role of complement in production and release of CSA, 5) to determine the effect of prolonged chemotherapy on granulopoiesis, 6) to attempt to isolate and purify granulocyte progenitor cells (CFU-C) in order to study the mechanism of action of CSA in inducing cell proliferation and maturation, 7) to study the pattern of in vitro colony formation and response to therapy in leukemia. BIBLIOGRAPHIC REFERENCES: Kolitsky, M.A., and Chervenick, P.A. Dissimilarity of In Vitro Colony-forming Cells and Erythrocyte Enhanced Colony-forming Cells from Mouse Marrow. J. Lab. Clin. Med. In press, 1977. Boggs, D.R., Malloy, E., Boggs, S.S., Chervenick, P.A., and Lee, R.E. Kinetic Studies of a Tumor Induced Leukemoid Reaction in Mice. J. Lab. Clin. Med. 89: 80, 1977.