Phytohemagglutinin committed lymphocytes: the mitotic activity of the phytohemagglutinin stimulated lymphocytes.

The purpose of these experiments was to find out why there was a decrease in the mitotic activity in the prolonged PHA stimulated lymphocyte cultures. The present observations suggested that the decrease in the mitotic rate in the prolonged PHA-stimulated lymphocytes was not due to a deficiency in the essential material in the culture medium to sustain a maximum mitotic response, nor was it due to an accumulation of the metabolites that might inhibit the lymphocytes to undergo further division. However, the results obtained suggest that there may be a limitation in the number of generation cycles in which the T lymphocytes can be stimulated with the PHA. They also suggest that a second dose of PHA may stimulate some of the original noncommitted lymphocytes to undergo mitosis thus attempting to maintain the in vitro lymphocyte population.