Proliferation of antibody-forming cells within the lymphoid system

Mice were given subcutaneous priming injections of horse radish peroxidase (HRP) in the hind leg foot pads, and ten weeks later intravenous booster injections. Cell suspensions of popliteal lymph nodes, spleen and bone marrow were obtained at various time intervals after boosting and incubated in vitro for 1 h in the presence of 3H-thymidine (3H-TdR). In each suspension the number of cells showing simultaneously anti-HRP antibody and incorporation of 3H-TdR was determined. Whereas in spleen and bone marrow only very few 3H-TdR labelled antibody-forming cells were observed, a clear proliferative response was noticed in the popliteal lymph nodes. Already on the first day after booster injection proliferation of cells showing incipient antibody synthesis was demonstrable in lymph nodes. It is strongly suggested that most - if not all - antibody-forming cells in these animals are derived from proliferating cells in the local draining lymph nodes. A relationship between the route of primary immunization and nature and location of the secondary proliferative response is discussed.