Secretion of idiotypic IgM by the mouse B-cell leukaemia (BCL1) occurs spontaneously in vitro and in vivo.

An analysis has been carried out to investigate the ability of neoplastic cells from the mouse B-cell leukaemia (BCL1) to secrete idiotypic IgM. Tumour cells taken from the spleen and placed in short-term culture without stimulation secreted quite large amounts of idiotypic IgM with a mean value for six animals +/- SD of 11,5000 +/- 6800 molecules of pentamer/cell/hr, with levels increasing steadily over a 7-hr period. Tumour cells from the blood of matched animals also secreted idiotypic IgM in amounts generally less than the spleen cells (4100 +/- 2000 molecules/cell/hr. The IgM produced was found to be mainly pentameric, with some material of lower molecular weight. This idiotypic IgM could also be detected in the serum of leukaemic animals as pentameric IgM, and amounts increased during tumour development to 1-2 mg/ml in the terminal phase of disease. Since binding of anti-idiotypic antibody to tumour cells is inhibited by this material, it should be taken into account in immunotherapeutic schedules involving such antibody. However, it also presents a useful marker of disease, and perhaps of response to therapy.