Functional symmetry amongst daughter cells arising in vitro from single antibody-forming cells.

The open carboxymethylcellulose (CMC) haemolytic plaque technique was used to study the antibody-forming capacity of daughter cells arising from single plaque-forming cells (PFC) after mitosis. Spleen cells from mice immunized 2–5 days previously with sheep red blood cells (SRBC) were used. The number of mitoses was increased by giving mice colcemid 2 hours before killing. The experimental protocol involved allowing cells to form haemolytic plaques in a liquid medium; selecting the largest available PFC; transferring them to wash droplets to await colcemid-escape and completion of mitosis; separating the two daughter cells from each other by micromanipulation; transfer of each daughter cell pair to a CMC plaque-revealing monolayer; and continuous assessment of plaque formation rate by daughter cell pair members. The whole procedure was carried out with the micromanipulation set up at 37°. Altogether, seventeen experiments on IgM (direct)-PFC and two on IgG (enhanced)-PFC were performed. Of eighty-seven daughter cell pairs transferred, eighty-six behaved symmetrically with both daughter cells forming antibody (seventy-four cases) or not forming antibody (twelve cases). Arguments are presented to suggest that this failure rate of 14 per cent is due to technical factors inherent in the micromanipulation steps. In the great majority of cases, daughter cells were symmetrical in size and plaque formation rate. Plaques from daughter cells were always of similar morphology, and when mixed sheep and goat RBC monolayers were used to reveal plaques, both cells of a pair always behaved similarly in that either both formed a clear plaque or both formed a turbid plaque. The results are discussed in the light of the hypothesis of Tannenberg and Malaviya (1968) for asymmetric divisions amongst PFC, which they do not favour. It is stressed, however, that the possibility of asymmetric divisions amongst antibody-forming cell precursors is not eliminated.