The role of macrophages in the generation of T helper cells. III. Influence of macrophage-derived factors in helper cell induction.

Helper cell induction to soluble or particulate antigens in vitro requires the cooperation of T cells and macrophages. A direct contact between macrophages and T cells is not obligatory for this cooperation and factors released from macrophages are as effective in activating T cells as the cells themselves. Two different types of macrophage-derived factors where found. The supernatant obtained from purified macrophages incubated with antigen for several days generates helper cells in absence of macrophages or additional antigen, but only if obtained from macrophages which were identical at the I-A subregion of the H-2 complex as the T cells. This factor was called genetically related macrophages factor (GRF). The other factor(s), which is present in the supernatant obtained from macrophages incubated for several days without antigen, replaces macrophages only if the antigen is particulate. This factor(s), called nonspecific macrophage factor (NMF) is not restricted genetically and is also obtained from allogeneic macrophages. The importance of both these factors in helper cell induction is discussed.