Binding parameters of the interaction between rat IgE and rat mast cell receptors.

Rat monoclonal IgE was purified by a combination of gel filtration and isoelectric focusing. The binding parameters of the IgE-target cell interaction were studied. The target cells used were normal rat peritoneal mast cells (RMC) and neoplastic rat basophilic leukocytes (RBL). BINDING assays were performed by adding different amounts of IgE to a constant cell number. A Scatchard analysis of the data indicated that both cell types have a similar affinity for rat IgE; the equilibrium constant was in the order of 10-9 M-minus 1. However, RBL have a higher number of receptor sites per cell--approximately 6 times 10-5 versus 3 times 10-5 for normal RMC. Since RMC have more than double the surface area of RBL, the data indicate a much higher receptor density on RBL.