Differing requirements for glycosylation in the secretion of related glycoproteins is determined neither by the producing cell nor by the relative number of oligosaccharide units.

Previous reports, using a variety of myeloma cell lines and activated normal B cells, have shown that different classes of immunoglobulins have different carbohydrate requirements for secretion. Thus, secretion of IgM and IgE was almost totally blocked by the antibiotic tunicamycin, secretion of IgA was partially inhibited, and secretion of IgG was essentially unaffected (Hickman, S., Kulczycki, A., Jr., Lynch, R. G., and Kornfeld, S. (1977) J. Biol. Chem. 252, 4402-4408; Hickman S., (1978) J. Immunol. 121, 990-996). Here, similar experiments using hybridoma cell lines secreting IgM and IgG or IgD are reported. Tunicamycin prevented the majority of IgM secretion but did not affect IgG secretion in cells producing both isotypes. This shows that the differential effects of tunicamycin on IgM and IgG secretion are due to factors intrinsic to the respective heavy chain polypeptides themselves, rather than to other properties of the producing cells. The secretion of IgD, which is as heavily glycosylated as IgM, was not inhibited by tunicamycin. Thus, the simple degree of immunoglobulin heavy chain glycosylation does not determine the extent of the requirement for glycosylation in the secretion of that isotype.