Differentiation of Lymphoid Cells: The in Vitro Emergence of Immunoglobulin M-Secreting Cells

Abstract

Abstract Freshly isolated rabbit popliteal lymph node cells synthesize and secrete principally immunoglobulin G (IgG) together with a relatively small amount of immunoglobulin M (IgM). After incubation of such cells in tissue culture for 48 hr, [3H]IgG production decreased markedly and approached zero, in most experiments. On the other hand, [3H]IgM production increased 5- to 10-fold. Thus, at 48 hr and thereafter τ;90% of the [3H]Ig was accounted for as [3H]IgM. In contrast, lymphoid cells derived from rabbit appendix do not show enhanced [3H]IgM production although such cells predominantly secrete [3H]IgM when freshly isolated and in decreasing amounts during tissue culture incubation. The enhanced [3H]IgM production observed with popliteal lymph node cells is dependent on the presence of fetal calf serum during tissue culture incubation. This requirement cannot be replaced by serum from the same rabbit that was the source of the cells and, indeed, such autologous serum in the presence of fetal calf serum inhibited enhanced [3H]IgM production. Serologic techniques, DEAE-cellulose chromatography, Bio-Gel chromatography, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis were used to distinguish IgM from the other classes of Ig. Fluorodeoxyuridine, an inhibitor of DNA synthesis, abolished the emergence of enhanced [3H]IgM production when added to cells during the latent period, but the inhibitor was without effect on Ig secretion when incubated with cells after enhanced [3H]IgM production had already emerged. The results indicate that the cellular source for the enhanced IgM secretion cannot be the original IgG-secreting cells but may be derived from some of the original IgM secreting cells or, alternatively, may be derived from cells that are quiescent in the freshly isolated population.