The life cycle of antibody-forming cells. II. Evidence for steady state proliferation of direct haemolytic plaque-forming cells during the primary and secondary responses.

The nature of the proliferation kinetics of direct plaque-forming cells (PFC) was studied with an double isotope labelling method. The method measures and compares the cell fluxes crossing two different points in the cell-generation cycle. It could be shown with mathematical models that, in steady state proliferation, equal fluxes should be observed at all points of the cycle, and that, in exponential proliferation, unequal fluxes should be observed at all points. The technique and the models were tested on mouse leukaemia ascites cells and were shown to be valid for cell populations known to be proliferating with exponential kinetics. By contrast, the data obtained from the PFC indicated that these cells proliferated with steady state kinetics; the data were not consistent with the exponential model. A hypothesis is presented to account for the steady state proliferation of PFC in the economy of the immune system.