Mast cells that have bound to an IgE can now recognize the bad stuff, the allergens. You might have picked up that in a lot of these illos, it's the Ige that's bound to a receptor on the surface of the mast cell that will do the future binding to whatever allergen it's been "sensitized" to. SO, like a lock to a key, that mast cell can now recognize that allergen.
And then that mysterious cross-linking between two IgEs on the mast cell has to occur (see middle image in pic) before the mast cell has the "go-ahead" to release its histamines!
According to the bottom-most diagram, as well as previous posts on this topic, what are two things that histamines will do, AND, how do these actions help the body to rid itself of the allergen?
We'll conclude the topic of allergic reactions with a brief discussion on macrophages.