Abstract An attempt was made to gain an established culture cell line of murine IgM myeloma cells (MOPC-104E). The growth of the tumor cells could be maintained for more than 10 months in tissue culture by adding a factor obtained from the culture medium of tissue macrophages (histiocytes) or spleen phagocytic cells of mouse. The factor is protein in nature and has a molecular weight of about 5 × 104 daltons. Without this factor the tumor cells stopped growing at G1 stage and did not continue the cell cycle; however, the synthesis of IgM and its subunit was unaffected. The factor reinitiated DNA synthesis almost synchronously with a lag of about 90 min. The factor was also found in mouse serum and its activity increased remarkably after the injection of Freund's complete adjuvant. Adenosine 3′:5′-cyclic monophosphate could substitute for the factor in a range of 0.3 µg/ml to 1.0 µg/ml. The immunologic role of the factor is discussed.
Namba et al. (Fri,) studied this question.