AUTORADIOGRAPHIC STUDIES ON THE IMMUNE RESPONSE

SUMMARY The primary immune response in rat popliteal lymph nodes to Salmonella flagella was studied by a combination of autoradiographic and single‐cell micromanipulatory techniques from the following three points of view: the cellular proliferative changes in the nodes; the kinetics of appearance of serum antibody; and the functional potential of small lymphocytes. It was shown that changes in cellular proliferation in the node occurred virtually without lag. Blast cells divided exponentially, giving rise to the exponential appearance of plasma cells and of cells forming antibody detectable by single cell techniques. Mature plasma cells, active single cells and the first trace of detectable scrum antibody all made their appearance simultaneously shortly after three days. The results suggested that antigen has the dual function of causing certain cells to proliferate and simultaneously to differentiate into massive protein producers, capable of accelerated antibody synthesis. Considerable net immigration of cells into the nodes during the first days was also suggested. The rise in serum antibody titres was exponential for two days or so following its first appearance. The lower the dose of antigen given, the earlier did the first traces of detectable antibody appear in the serum. The pattern of labelling of the first‐appearing plasmablasts did not favour the view that they were derived by dedifferentiation of small lymphocytes, as has been suggested in homograft situations. Rather, they suggested derivation from primitive lymphocytes, as in our previous studies on the secondary response. However, in view of the problems of reutilization discussed in the previous paper of this series, formal proof of a lack of participation of small lymphocytes could not be obtained.