Interferon-gamma (IFN-gamma) acts on a large array of different types of cell and has potent immunomodulatory activities besides cytotoxic effects on tumors. In a phase I study, some immunologic parameters of blood mononuclear cells from healthy volunteers who received intramuscular injections of natural human IFN-gamma were analyzed. The percentage of Leu-11a positive cells, natural killer (NK) activity, lymphokine (interleukin-2)-activated killer (LAK) activity and monokine production were measured either in blood mononuclear cells or in purified samples of lymphocytes or monocytes of the donors before and 24 h after IFN-gamma injection. After IFN-gamma injection, the percentage of Leu-11a positive cells and the LAK activity in the blood were significantly reduced, but NK activity and monokine production remained unchanged. These findings suggest that in vivo IFN-gamma acts directly or indirectly on Leu-11a positive cells and reduces LAK activity by changing the recruitment of LAK precursors in the blood.
