Uptake of vitamin B 12 by phytohaemagglutinin-transformed lymphocytes.

Abstract

Summary.Phytohaemagglutinin (PHA)‐transformed lymphocytes have been used as a model cell system to study the uptake of radioactive vitamin B12 by haemopoietic cells. Both mature granulocytes and PHA‐transformed lymphocytes took up more vitamin B12 than mature, non‐transformed lymphocytes. Uptake of vitamin B12 by PHA‐stimulated lymphocytes was greatest at 48–72 hr of culture, i.e. at about the time or just before the time of peak DNA synthesis.Vitamin B12 deficient lymphocytes took up significantly less vitamin B12 than normal lymphocytes. Folate deficient lymphocytes took up an average of about 50% more vitamin B12 than normal but the difference was not statistically significant for the numbers tested. Vitamin B12 uptake by PHA‐stimulated lymphocytes was related to their rate of RNA synthesis (measured by 3H‐uridine uptake) and was closely related to active cytoplasmic protein synthesis since it was rapidly inhibited by puromycin and cycloheximide.