Germinal centre proliferation in response to mitogenic lymphokines.
Lymphokines which were mitogenic for cultured lymphocytes caused germinal centre enlargement within the regional lymph node following their intralymphatic injection. It was found that 17 μg of a lymphokine preparation, produced by 2·5 × 104 peritoneal exudate lymphocytes, resulted in a 14-fold increase in germinal centre area and a 7-fold increase in the labelled cell content of these centres on the 3rd day after injection. 
 
Since the daily rate of lymphocyte recirculation through the regional node would supply sufficient numbers of antigen-sensitive lymphocytes to generate this amount of mitogenic lymphokine following antigenic stimulation, it is argued that lymphokine-induced germinal centre enlargement plays a physiological role in immunoregulation.