Reduced C epsilon transcription by stabilization of CD23 in B cells (HYP7P.320)

The low affinity receptor for IgE (CD23, FcepsilonRII) is part of the broad regulatory network controlling IgE synthesis. It occurs as membrane and as soluble receptor generated in vivo by specific proteolysis. Targeting membrane CD23 with either IgE or anti-CD23 antibodies is believed to inhibit IgE synthesis. However, the mechanism behind this negative feedback remains unclear. This mechanism was investigated by examining the effect of anti-CD23 molecules in form of designed-ankyrin-repeat-proteins (DARPins) specific for CD23. Previous experiments using anti-CD23 antibodies were difficult to interpret as their Fc portion also mediate feedback mechanisms. The DARPins were produced as monovalent and bivalent molecules that were able to compete with the binding of IgE to CD23. The effects of anti-CD23 DARPins were assessed in an in vitro system using anti-CD40/IL-4 stimulated B cells. Treatment of B cells with anti-CD23 DARPins resulted in stabilization of membrane CD23. The released amount of soluble CD23 was reduced while CD23 mRNA expression was unchanged suggesting that the anti-CD23 DARPins stabilize CD23 and prevent its proteolysis. IgE secretion was significantly reduced by anti-CD23 DARPins. In addition, analysis of the epsilon transcript confirmed the reduction of IgE synthesis whereas IgG secretion was not influenced by the anti-CD23 DARPins. Further experiments will be performed to assess signalling pathways triggered by CD23 cross-linking.