The effect of antibody valency and lysosomotropic amines on the synergy between ricin A chain- and ricin B chain-containing immunotoxins

R. J. Fulton, J. W. Uhr, E. S. Vitetta

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34 Scopus citations

Abstract

The cytotoxicity of A chain immunotoxins containing IgG or Fab fragments specific for the surface immunoglobulin of the Daudi cell line was assessed in the presence of B chain immunotoxins (IgG or Fab) or lysosomotropic amines, or both. The concentration required for 50% inhibition of protein synthesis (IC50) in Daudi cells was 1.3 x 10-8 M for IgG-A and 5 x 10-8 M for Fab-A. The toxicity of both A chain immunotoxins was enhanced twofold by ammonium chloride. In the presence of A chain immunotoxins and ammonium chloride, a maximum of 99 and 90% reduction of clonal precursors was obtained with IgG and Fab-A chain immunotoxins respectively. Immunotoxins containing ricin B chain and IgG or Fab fragments specific for the antibody portion of A chain immunotoxins were used as secondary 'piggyback' immunotoxins to treat cells that were pretreated with A chain immunotoxins. Both B chain immunotoxins were non-toxic at 1 x 10-6 M. When added to target cells pretreated with specific A chain immunotoxins, the IC50 of the A chain immunotoxins was decreased up to 16-fold in the absence of ammonium chloride. In contrast to the results obtained with A chain immunotoxins alone, ammonium chloride significantly increased the toxicity of the complete piggy-back system, resulting in the killing of 99.999% or five logs of target cells in the clonal assay. This decreased the IC50 of A chain immunotoxins up to 116-fold when compared with A chain immunotoxin alone. This enhanced toxicity was independent of the valency of either immunotoxin.

Original languageEnglish (US)
Pages (from-to)3103-3109
Number of pages7
JournalJournal of Immunology
Volume136
Issue number8
StatePublished - 1986

ASJC Scopus subject areas

  • Immunology and Allergy
  • Immunology

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