Cross-Linking of Surface Immunoglobulins and Endocytosis of Antigen are not Sufficient to Suppress Antibody Production of two Hybridoma Cell Lines

Abstract

The two cell lines Lev 1–3 and AS3, which secrete monoclonal anti-levan antibody and express surface membrane immunoglobulins that are capable of binding the levan, were cultured for 24 h or 48 h with levan of various molecular weights (5 × 10⁴, 2 × 10⁵ or 2 × 10⁷ daltons). The production of antibody was measured by a plaque-forming cell assay for AS3 cells and by biosynthetic labelling for Lev 1–3 cells. Surface immunoglobulins were detected by a rosette-forming cell assay. By using immunoenzymatic procedures, we observed that levan of 5 × 10⁴ and 2 × 10⁵ daltons was intensely endocytosed by the cells and localized mainly in the cellular center, whereas levan of 2 × 10⁷ daltons remained mostly associated with the plasma membrane and formed surface aggregates. After transfer of cells in levan-free medium, it was shown that internalized levan could persist several days inside the cells without being degraded. Viability, growth, antibody synthesis and secretion were not modified in cells cultured with levan, whatever the molecular weight of the antigen used. Our results show that cross-linking of surface immunoglobulins by multivalent antigen or endo-cytosis of antigen do not appear t o be sufficient to induce a suppression of antibody production or membrane immunoglobulin expression.