ANTIBODY-STIMULATING FACTOR SECRETED BY SPLEEN-CELLS INVITRO

The intensity of antibody formation in irradiated syngeneic recipients was studied in relation to its restoration by various cell suspensions. A lymphocyte suspension free of macrophages restored the ability of the irradiated recipients to respond to sheep's red blood cells only weakly. Addition of peritoneal or splenic macrophages to the lymphocytes led to a sharp increase in plaque formation. The same response was produced by injecting a suspension of spleen cells incubated beforehand in vitro for 3 h at 37°C into the recipients. After incubation of the spleen cell suspension in this way in the absence of antigen, a factor capable of sharply increasing antibody formation in irradiated recipients on restoration of their immune response by injection of donors' lymphocytes was secreted into the medium. The antibody-stimulating factor was not produced after incubation of lymphocytes for the same times. It is suggested that the antibody-stimulating factor appearing in the medium during culture of spleen cells in vitro in the absence of antigen is formed by cells of the mononuclear phagocytic system. © 1980 Plenum Publishing Corporation.