Previous studies have demonstrated that highly multivalent DNP conjugates of γ-globulins, but not of KLH or BSA, inhibit the production of anti-DNP IgA antibody by the mouse plasmacytoma line, MOPC 315, in vitro. The present experiments were designed to compare the fate of various DNP antigens, trace-labeled with 125I, in MOPC 315 cells. After continuous exposure of MOPC 315 cells to various antigens for up to 20 hr, suppressive DNP-globulin conjugates are extensively internalized by the cells

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... hereas nonsuppressive DNP-KLH and DNP-BSA remain largely bound to the surface. These differences are not attributable to cooperative binding of DNP-globulins to Fc receptors, and, at least with DNP-KLH, are not due to major differences in the molecular charge of the antigens. Moreover, all internalized antigens persist within cells and are not extensively hydrolyzed for up to 18 hr of antigen-free culture. Electron microscopic studies show that internalized antigens are not enclosed within pinocytotic vesicles, and are often found close to the endoplasmic reticulum or Golgi complex. It is proposed that prolonged intracellular persistence of antigens may be a central mechanism in the inactivation of antibody-secreting cells as well as in B lymphocyte tolerance.