MEMBRANE IG ON HUMAN LYMPHOCYTES - RATE OF TURNOVER OF IGD AND IGM ON SURFACE OF HUMAN TONSIL CELLS

The turnover of Ig[immunoglobulin]M and IgD molecules present on the membrane of human tonsil cells was studied using immunofluorescence and peroxidase-catalyzed membrane radioiodination. With the 1st of the 2 techniques, cells were treated with pronase to remove membrane Ig, placed in culture and stained at intervals to check the reappearance of membrane IgD and IgM on the cell membrane. Membrane IgD (in contrast to membrane IgM) was extremely susceptible to proteolysis. Cells treated with a concentration of pronase found to be optimal to remove membrane IgM failed to re-express membrane IgD in vitro. The large majority of tonsil lymphocytes have membrane IgM and IgD. Due to the different behavior of reappearance of the 2 membrane molecules after treatment with pronase, it was not possible to obtain the simultaneous re-expression of membrane IgM and IgD by the cells stripped with pronase. The 2 molecules were re-expressed in vitro by the cells treated with different pronase concentrations with a similar timing, i.e., .gtoreq. 50% of the cells re-expressed membrane IgD and IgM after 8 h in culture. 131I-radioiodinated membrane IgD and IgM were released from the cell surface with a similar timing, the half-life of permanence on the cell membrane being about 4 h for both molecules. IgM and IgD molecules apparently have a similar turnover, and a cell may be capable of placing 2 different Ig molecules at a time on its surface.