Inhibition of protein synthesis by monoclonal anti-idiotypic antibody-ricin A chain conjugates in MOPC 315 myeloma cells.

Three monoclonal antiidiotypic antibodies (AIA) to MOPC 315 IgA, G3 (IgG2b), A2 (IgG1) and D10 (a hybrid molecule consisting of gamma 1 and gamma 2a heavy chains), were characterized with respect to their binding constants (Ka) to MOPC 315 mouse myeloma cells. The Ka of G3 and A2 was 10(8)/mole; and that of D10 was 3 X 10(7)/mole. The AIA did not bind to a non-immunoglobulin (Ig) producing subclone of MOPC 315 cells (MOPC 315.36). Immunotoxins derived by conjugating ricin A chain (RTA) to G3 and A2 but not to D10 preferentially inhibited protein synthesis in MOPC 315 over MOPC 315.36 cells. These results suggest that the effectiveness of these immunotoxins assessed on the basis of their targeted cytotoxicity against MOPC 315 cells was dependent on the Ka but not on the Ig subclass of the AIA component of the immunotoxin.