IgG anti-hapten antibody secretion in vitro commences after extensive precursor proliferation

We have investigated whether the intermediate cells that arise in primed mice after boosting require further cycles of division in culture before maturation into IgG antibody secreting cells. Killing of dividing cells between days 1--4 in culture, by exposure to BUdR-uv irradiation ablated the high IgG response observed on day 5 in control cultures. After T cell removal and replacement by a soluble factor (TRF) similar results were obtained. Thus B cell division over an extended period occurs prior to the appearance of IgG secreting cells. Furthermore, autoradiography of plaques from cultures briefly exposed to [3H]thymidine before harvest showed that some antibody secreting cells were synthesizing DNA at the time of assay.