Binding properties of IgE receptors on normal mouse mast cells.(1)
The number of cell-bound IgE molecules per rat mast cell or mouse mast mast cell reached a maximum at 3 ug/ml of either rat IgE or mouse IgE. Rat mast cells bound similar numbers of molecules of either rat IgE or mouse IgE. However, mouse mast cells bound much more mouse IgE than rat IgE.
Experiments with mast cells from either BALB/c or CBA/J mice confirmed that two to four times as many mouse IgE molecules as rat IgE molecules bound to mouse mast cells. Mouse IgE and rat IgE bind to the same receptors on both rat mast cells and RBL cells. Rat IgE molecules bind to only a fraction of the receptors for mouse IgE on mouse mast cells.
The k1 for the binding of mouse IgE to rat mast cell receptors was somewhat lower than k1 for rat IgE.
Both normal rat mast cells and RBL cells bound both rat IgE and mouse IgE. The values of the binding constants, k1, k-1, and KA, between rat vs mouse IgE and theIgE receptors on rat mast cells were similar to the reaction between rat IgE and RBL cells. The high affinity of the binding of mouse IgE to rat mast cell receptors explains why mouse IgE antibodies sensitize rat skin for passive cutaneous anaphylaxis reactions, and why sensitization persists for a long time.
Mast cells have two distinct types of IgE receptors. One type bound rat and mouse IgE with comparable affinity. Mast cells from CBA/ J mice consistently demonstrated more of this type of receptor (approximately one-half of their receptors) than mast cells from BALB/c mice (approximately one-third of their receptors). Thus, mast cells saturated with rat IgE retained one-half (CBA/ J) to two-thirds (BALB/c) of the original number of receptors for mouse IgE.