Two distinct lumphocyte-stimulating soluble factors (LAF) released from murine peritoneal cells. I. The cellular...

Culture fluids of murine peritoneal cells contain two distinct, non-dialysable priniciples (LAF) with thymocyte proliferation-stimulating properties. One of them is elaborated from phagocytic cells (presumably macrophages), the other is released by non-phagocytic cells (lymphocytes). cGMP added exogenously stimulates the production and/or release of LAF from phagocytic cells, but not from non-phagocytic cells. The phagocytic cells (but not the lymphocytes) require intact RNA and protein synthesis for LAF release. The action of LAF differs from those of cGMP itself by being non-dialysable, and unable to prevent the inhibitory action of cAMP on mitogen-stimulated lymphocyte proliferation.