What is the late-phase reaction, and how is it caused?

It's when a severe inflammatory response and tissue injury that occurs. A) Kinetics of the immediate and late-phase reactions. The immediate vascular and smooth muscle reaction to allergen develops within minutes after challenge (allergen exposure in a previously sensitized individual), and the late-phase reaction develops 2 to 24 hours later.  B) Morphology of the immediate reaction is characterized by vasodilation, congestion, and edema.  C) The late-phase reaction is characterized by an inflammatory infiltrate rich in eosinophils, neutrophils, and T cells.  This inflammatory component is called the late-phase reaction, and it is mainly responsible for the tissue injury that results from repeated bouts of immediate hypersensitivity.