IgE cross-linking

[Phloston]

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In type-I hypersensitivity reactions, which part of the adjacent IgEs are actually undergoing cross-linking? What's actually happening?

 

[withrye]

The Fc portion is attached to an Fc receptor on the mast cell or basophil. This leaves the Fab portions open to crosslinking by antigen.

 

[Phloston]

I just encountered this in UWorld.

The Fab do not cross-link. Instead, the antigen binds one of the Fab arms on two separate IgE, thereby forming a bridge between adjacent Fabs. This brings the IgE Fc-receptors closer together. It is the aggregation of IgE Fc-receptors that induces mast cell degranulation.

 

[withrye]

I just encountered this in UWorld.

The Fab do not cross-link. Instead, the antigen binds one of the Fab arms on two separate IgE, thereby forming a bridge between adjacent Fabs. This brings the IgE Fc-receptors closer together. It is the aggregation of IgE Fc-receptors that induces mast cell degranulation.

That's what cross-linking means. Two or more different molecules are linked together, not that one molecule is doubly-stimulated.

EDIT: I say this to clarify the point that when you hear "cross-linking" you should always think of two or more molecules bridged by an intermediate.