Inhibition of IgE production in vitro by intact and fragmented intravenous immunoglobulin.

BACKGROUND

Intravenous immunoglobulin (IVIG) has been shown to suppress Ig production both in vivo and in vitro. We have previously found that IVIG inhibits IgE synthesis in human tonsillar B cells stimulated with IL-4 and anti-CD40 antibody.

OBJECTIVE

The purpose of this study was to further clarify the mechanism behind the inhibition of IgE production by IVIG through comparing the effects of intact whole molecular IVIG and the F(ab')(2) or Fc fragments of IVIG.

METHODS

Human B lymphocytes were purified from tonsils. Cell proliferation was measured by means of tritiated thymidine incorporation. IgE was determined by means of ELISA. Cell-cycle analysis was performed by using flow cytometry.

RESULTS

Both intact and fractionated IVIG inhibited anti-CD40- and IL-4--stimulated IgE production in a dose-dependent manner. The maximal inhibition was achieved at 67 micromol/L (eg, 10, 6, and 4 mg/mL for intact IVIG, Fab', and Fc, respectively). The effect of F(ab')(2) was more pronounced than that of Fc at equimolar concentrations. Similarly, both intact and fragmented IVIG dose-dependently decreased tritiated thymidine incorporation. F(ab')(2) was also more potent than Fc in this effect. Heat-aggregated IVIG exhibited similar potency to regular IVIG in inhibiting B-cell proliferation. The inhibitory effects of IVIG were unlikely to have been caused by the induction of apoptosis because neither intact nor fractionated IVIG had a significant effect on cell-cycle parameters at the concentrations used.

CONCLUSION

These data suggest that both F(ab')(2) and Fc portions contribute to the inhibition of in vitro IgE production by IVIG. The role of the F(ab')(2) portion is more important than that of the Fc portion.