Cell surface immunoglobulin. VI. Dynamics on a human lymphoma line

Release of cell surface Ig and secretion of Ig has been studied in Daudi cells, a human lymphoma cell line synthesizing IgM that appears to be a neoplastic counterpart of B lymphocytes. In contrast to murine splenocytes, virtually no internally labeled Ig and only a small proportion of cell surface Ig are released during 8 hours of in vitro incubation. Released cell surface Ig can be recovered in the medium predominantly as 8 S IgM monomer probably attached noncovalently to a fragment of plasma membrane. This shedding of cell surface Ig appears to be dependent on the prior culture phase of the cells. Thus, in cells from cultures kept at high density, there was greater release of cell surface Ig apparently associated with cell death.