Role of macrophages in the generation of T helper cells. IV. Nature of genetically related factor derived from macrophages incubated with soluble antigens.

Macrophages incubated with soluble antigens for 1-4 days release factors capable of inducing T helper cells. The nature and some of the properties of this genetically related macrophage factor (GRF) were investigated. By use of immunoadsorbents, GRF was shown to contain I region-coded products (Ia antigens) linked to a small antigenic fragment. The genes coding for the Ia antigens detectable in GRF lie in the I region of the H-2 complex. GRF does not react with anti-immunoglobulin, anti-C3 or anti-human beta2-microglobulin antisera, and its activity cannot be removed by antigen immunoadsorbents. GRF is heat-labile, sensitive to proteolytic enzymes and has a molecular weight of about 55 000 Daltons. The relationship of GRF to other factors known to contain I region-coded products and reported to be effective in cell cooperation is discussed.