The long-term goals are to understand the mechanism of cellular hypersensitivity or immunity in man and determine the cause of defects in this immune function in certain human diseases which are associated with depressed immunity. A better understanding of the defects should lead to improved methods of therapy for such patients in particular and in certain infectious diseases in general. Cellular immunity is considered important in other biologic phenomena especially transplantation and tumor immunity. Such information should be of use in these areas as well. In this supplement it is proposed to investigate: 1) The characterization of migration inhibitory factor (MIF) produced by purified T and B cell populations and lymphocyte mitogenic factor (LMF) production by T cells. To determine whether both T and B cell mediators activate human monocytes and to further study mediator production by subpopulations of T cells and of B cells. 2) Characterization of human leukocyte inhibitory factor (LIF), determine its cell source (T or B cells) and ascertain its effect if any on polymorphonuclear (PMN) leukocyte function re phagocytosis, chemotaxis, metabolism, and bactericidal activity.