| Abstract: | The growth of mouse and rat T and B lymphocytes, activated by concanavalin A or lipopolysaccharide, is increased over growth in protein-free medium 5–20-fold by human or bovine serum albumin. The growth is dependent on the concentration of albumin. At a concentration of 2–4 mg/ml the growth rate is the same as in the presence of 10% fetal bovine serum. Of the other serum proteins (Cohn fractions) only human fraction VI supports growth somewhat while human fractions II–IV and bovine fraction VI do not support growth. The growth of mouse and rat lymphocytes is greatly suppressed if lymphocytes are cultured at high cell concentrations, and the growth-promoting ability of serum albumin cannot be detected under such conditions. The growth rate can be improved by daily adjustment of the pH, by daily refeeding, and by daily change of medium. The growth inhibitory activity can be removed largely by dialysis. It is concluded that the suppression of growth at high cell concentrations is caused by a combination of effects, i.e., a shift of pH, lack of nutrients, and accumulation of cellular metabolites. |
