The production of membrane or secretory forms immunoglobulins is regulated by C-gene-specific signals.

Selective patterns of antibody isotypes are produced in response to thymus-dependent and thymus-independent antigens and mitogens. Together with information on the organization of immunoglobulin CH genes in myelomas, various models on the control of C-gene expression and switch in normal B cells have been proposed but only secreted products or secretory cells have been considered. We report here a dissociation between expression of membrane-bound immunoglobulins and secretion of the same isotype, and in this case describe C-gene specific signals which regulate the production of membrane versus secretory forms of immunoglobulin. These results indicate that regulation of isotypic patterns operate at levels other than immunoglobulin gene structure, and suggest that the secretory phenotype alone is inadequate as the measure of C-gene expression.