Immunoglobulin produced by guinea-pig leukaemic B lymphocytes: its source and use as a monitor of tumour load.

The cells of the B lymphocytic leukaemia (L2C) of strain 2 guinea-pigs have IgM on their surfaces but produce insufficient monoclonal IgM in vivo to be detectable by conventional serum electrophoresis. A radioimmunoassay, using anti-idiotypic antibody raised against the surface IgM of these cells, has been used to estimate levels of extracellular IgM produced both in vitro and in vivo. Analyses of the contributions to such IgM from the cell surface and from an export pathway have been made by examining the effect of prior removal of surface Fab mu by papain, and by following the fate of radio-iodinated surface IgM. Results suggest that the extracellular IgM arises predominantly from an export pathway, being exported in both pentameric and monomeric forms. Only a minute contribution, possibly in the form of vesicle-bound monomeric IgM, appears to derive from the cell surface. Radioimmunoassay was used to monitor the increasing levels of this leukaemic cell product during the course of the disease. Idiotypic IgM was detectable when the body load of neoplastic cells was approximately 4% of that detectable by an increased white cell count in the blood.