Hypersensitivity reactions - Type I: Nursing

A hypersensitivity reaction is an overreaction to a foreign antigen which then causes serious damage to the body’s tissues. There are four types of hypersensitivity reactions: type I is immunoglobulin E, or IgE mediated; type II is mediated by antibodies that activate cellular cytotoxicity, type III is mediated by immune-complexes, and type IV is a delayed T cell mediated hypersensitivity reaction. Type 1 hypersensitivity reactions, or IgE-mediated reactions, are an immediate immune response where the IgE antibody responds to an antigen, causing acute inflammation.

Let’s start by looking at the physiology of the immune response. A food allergen or pathogen enters the body and runs into antigen-presenting cells, or APCs. APCs like macrophages or dendritic cells, then engulf and digest the allergen and the fragments are then presented on the APC’s surface via proteins called major histocompatibility complex class II, or MHC II. Now these fragments serve as antigens which are any thing that could trigger an immune response. So the APCs present these antigens to T helper cells which have T-cell receptors, or TCRs, that recognize the antigen. In response, the T helper cells will signal B Cells to transform into plasma cells that will start producing antigen specific IgE antibodies.