Uptake of Vitamin B12 by Phytohaemagglutinin-Transformed Lymphocytes

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.