Larger oligomers of IgE are more effective than dimers in stimulating rat basophilic leukemia cells.

The relative activity of rat IgE oligomers in eliciting secretion from mast cells and tumor basophils was examined using stable oligomers prepared by cross-linking IgE with dimethyl suberimidate. Oligomers were tested in vivo using passive cutaneous anaphylaxis (PCA) and in vitro by measuring their capacity to induce histamine release from normal rat mast cells and [3H]-5-hydroxytryptamine release from rat basophilic leukemia (RBL) cells. The PCA results confirmed previous work that showed no large differences in the activity of dimers, trimers, and higher oligomers of IgE. The same was also true with normal rat mast cells; however, the RBL cells sharply discriminated between the variously sized oligomers. The stimulatory activity of all oligomers on the RBL cells was enhanced by D2O. The findings imply that the manner by which the clustering of the receptors for IgE leads to generation of signals in RBL cells involves a mechanism capable of discriminating between a variety of polymeric states of the receptors. In addition, our results suggest that no more than a few hundred trimers or an even smaller number of higher oligomers are capable of inducing a considerable amount of secretion from these cells.