Suppressor T Cell Action Inhibits the Expression of an Excluded Immunoglobulin Gene

Cells of the murine plasmacytoid line MOPC-315 synthesize two distinct immunoglobulin light chains: a normal $\lambda _{II}$ protein, which is incorporated into secretory and surface-bound immunoglobulin, and a truncated, nonfunctional $\lambda _{I}$ protein found only in the cytoplasm. Idiotype-specific suppressor T lymphocytes selectively inhibit the expression of both $\lambda _{II}$- and $\lambda _{I}$-specific messenger RNA by MOPC-315 cells. This finding demonstrates that phenotypically excluded light chain genes can be subject to immunoregulatory control and suggests that the expression of divergent $\lambda $ isotypes may be coordinately regulated in immunoglobulin-secreting cells.