Inhibition of secondary IgG responses by N-acetyl-D-galactosamine

A range of monosaccharides were tested for their ability to inhibit a variety of in vitro immune response. The most striking specific inhibition was produced by N-acetyl-D-galactosamine (GalNAc). This sugar strongly inhibited the secondary IgG antibody response to two different hapten-carrier systems, but had no effect on primary and secondary IgM responses, generation of cytotoxic T cells to alloantigens and mixed lymphocyte reactions. By exposing secondary antibody cultures to GalNAc for varying periods of time, it was observed that GalNAc only exerted its inhibitory effect on day 4 of the culture, the day when IgG plaque-forming cells first appeared. Furthermore, GalNAc could override the action of T helper factor in T cell-depleted cultures. Collectively, these data indicate that GalNAc inhibits the initiation of IgG synthesis probably by blocking the interaction of a helper factor for IgG synthesis with its target cell.