Are hypersensitivity reactions are caused by the cross linking of antibodies?

On the cell surface.: Ige mediated allergic reactions involve 2 ige antibodies directed against the same allergens in close proximetry on the surface of mast cells or basophils. The antibody then fits in between the 2 ige antibodies. That activates the cell to release mediators (chemicals) that directly or indirectly by activating other cells resulting in allergy symptoms. The ige antibodies themselves do'nt cross link.