Serum albumin is essential for in vitro growth of activated human lymphocytes

The effect of human plasma, the plasma protein fractions of Cohn, and crystallized serum albumin on the in vitro growth of human lymphocytes activated by concanavalin A (Con A) or bacterial lipopolysaccharide was compared. It was found that fraction V or serum albumin (SA) is essential for growth of activated T and B lymphocytes. The other plasma proteins have no effect. The growth response of Con A-activated T lymphocytes to increasing concentrations of SA is similar to the response to increasing equivalent concentrations of plasma suggesting but not proving that SA is the only growth-stimulating factor in plasma when added to a protein-free culture medium. The growth-promoting effect of SA is not due to the fatty acids or hormones bound to SA but is attributed to the albumin molecule itself or to a factor tightly bound to it. SA can also effectively replace plasma to stimulate proliferation of lymphocytes activated by allogeneic lymphocytes or purified protein derivative of tuberculin.