Immunoproliferation and cancer: a common macrophage-derived promoter substance.

It is suggested that a common proliferative factor is required for the growth of clones of both antigen-triggered B lymphocytes and carcinogen-triggered epithelial cells, and that the common growth-promoting substance is secreted by macrophages which have originally differentiated in support of the immune response. This macrophage-derived factor seems to be antigenically distinct from granulocyte colony-stimulating factor. Identification of the macrophage-derived clonal proliferative factor could provide new understanding of the proliferation of clones of immunocytes and neoplastic cells.