Ligand‐Induced Redistribution and Augmentation of Surface‐Bound Myeloma Protein on MOPC315 Plasmacytoma Cells

The dinitrophenyl (DNP)‐ and trinitrophenyl (TNP)‐binding IgA(λ2) myeloma protein M315, bound on the surface of MOPC315 mouse plasmacytoma cells, was redistributed into spots, patches, and, more rarely, into caps by TNP 14 ‐BSA and by divalent but not monovalent anti‐M315 antibodies. Antiserum to the L‐chain of M315 (L 315 ) induced similar redistribution of L 315 bound on the surface of variant cells that only produced L 315 . The spots were much larger and more brilliant when the cells were incubated with the ligands at 37°C than at 4°C. Redistribution of M315 also occurred on M315‐producing cells in peritoneal diffusion chambers incubated in BALB/c mice producing antibodies against the M315 idiotype. The clearance of immune aggregates and the regeneration of new surface‐bound M315 in diffusion chambers were much slower for MOPC315 cells than that reported for B lymphocytes. The total pool of M315 was 1.9 pg per cell (about 8 × 10 6 7S molecules), but only an average of 6 × 10 3 [ 125 I]TNP‐BSA molecules were bound on the surface of each MOPC cell at 4°C. The amount of surface‐bound TNP‐BSA increased eightfold when the cells were preincubated at 37°C with rabbit anti‐mouse IgA; at 4°C the increase was only twofold. The data indicate that multivalent ligands specific for M315 induce an accumulation of M315 on the cell surface that correlates with secretion; the immediate precursors of secreted myeloma protein may be arrested in their transit through the membrane by the ligands.