DEOXYSPERGUALIN INHIBITS KAPPA-LIGHT-CHAIN EXPRESSION IN 70Z 3 PRE-B CELLS BY BLOCKING LIPOPOLYSACCHARIDE-INDUCED NF-KAPPA-B ACTIVATION/

Deoxyspergualin (DSC) is a potent immunosuppressive agent that is curr ently undergoing clinical trials for treatment of transplant rejection , prevention of human anti-mouse Ab response, and blocking autoimmune disease progression. The mechanism of action of DSG appears to be nove l, with in vivo activity attributable to the suppression of both humor al and cell-mediated immunity. In this study we investigated the effec t of DSG on the induction of Ig expression in the 70Z/3 murine pre-B c ell line. Treatment of 70Z/3 cells with DSG for 24, 48, or 72 h before LPS or IFN-gamma induction resulted in a time-dependent inhibition of surface IgM expression, with greater than 80% inhibition observed aft er 72 h of pretreatment. Inhibition of surface expression was specific for IgM, as neither MHC class I nor CD45 (B220) surface expression wa s affected by DSC pretreatment. Cyclosporin A was ineffective at suppr essing surface IgM induction. DSG pretreatment resulted in a 10-fold r eduction in LPS- or IFN-gamma-induced kappa L chain protein and mRNA e xpression. No change was observed in either mu or beta-actin mRNA leve ls. Analysis of nuclear and cytoplasmic NF-kappa B expression using el ectrophoretic mobility shift analysis and Western analysis, revealed t hat DSG blocked LPS-induced NF-kappa B nuclear translocation, but had no effect on cytoplasmic NF-kappa B levels. We conclude that DSG may a ct to suppress humoral immune responses by blocking the transcriptiona l activation of kappa L chain expression during certain stages of B ce ll development.