Clearance and re‐expression of a myeloma cell's antigenbinding receptors induced by ligands known to be immunogenic or tolerogenic for normal B lymphocytes: a model to study membrane events associated with B cell tolerance

We have previously reported that the immune response of BALB/c mice to α(1→3) linkage groups of dextran B1355 and the in vivo growth of MOPC 104E tumor cells were specifically suppressed by the administration of oxidized dextran B1355. In the present study, we report on membrane events that occur after 104E cells are incubated with either the native dextran B1355 or the oxidized dextran B1355. The 104E cells, which possess membrane‐associated receptors that are specific for the α(1→3) linkage groups of dextran, were monitored for the clearance of receptor‐antigen complexes, and the subsequent re‐expression of receptors that follow the interaction of cells with either the native ligand, dextran, or the suppressor ligand, oxidized dextran. Following incubation of 104E cells with the native ligand, complexes of dextran plus receptors aggregate and are gradually cleared (2–4 h) from the membrane. Subsequent to the receptor‐antigen clearance induced by the native ligand, a second set of dextran‐binding receptors is observed. The second set of receptors appears to be derived from a presynthesized precursor pool of receptors within the cell and not from the synthesis of new receptors. These receptors appear diffusely over the entire surface of the cell membrane as opposed to a single discrete area within the membrane. The receptors remain within the membrane for at least 48 h unless perturbed again by antigen. Re‐expression of receptors is not observed following a second perturbation with the native ligand. The membrane events which succeed the incubation of the 104E cells with the suppressor ligand differ significantly from those which are observed following incubation with the native ligand. Exposure to the suppressor ligand results in a rapid (10–30 min) and complete clearance of the complexes of oxidized dextran plus receptor from the membrane of the 104E cell, and the clearance of these complexes occurs without any detectable receptor aggregation. The most significant difference observed following the pulse with the suppressor ligand is the complete absence of a receptor re‐expression. Thus, 104E cells, following a brief pulse with oxidized dextran, fail to incorporate the presynthesized second set of receptors into the plasma membrane. This apparent suppressive signal occurs without any detectable change in cell viability. The inability of the 104E cell to express a second set of antigen‐binding receptors following a suppressor antigen‐induced clearance of the first set is presented as a possible link of a membrane event with an alteration in cell function (i.e. suppression of proliferation of the 104E cell in vivo by this antigen). The possible relationship of the 104E cell membrane events to normal B cell membrane events associated with immunity or tolerance is discussed.