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Type I immediate hypersensitivity

Created: 23/11/2004
Updated: 14/10/2008
 

Immediate Type I hypersensitivity (immediate allergic reaction)

An immediate allergic reaction (or IgE-mediated hypersensitivity reaction) is caused by latex proteins, which directly sensitise the patient and subsequently cause allergic symptoms, including rhinitis, conjunctivitis, urticaria, angioedema, asthma, anaphylaxis and death.

Type I hypersensitivity represents one of the most powerful immune responses in the body. It results from the activation of mast cells by IgE antibodies, with a rapid release of chemical mediators of inflammation. This reaction is called immediate hypersensitivity because it develops within minutes of antigenic stimulation. Only certain antigens are capable of stimulating immediate hypersensitivity reactions. Additionally, atopic individuals tend to produce higher levels of IgE antibodies in response to antigenic stimulation, as compared with normal, non-atopic individuals, and are therefore at greater risk for immediate hypersensitivity.

The development of immediate hypersensitivity is a two-step process


(Click Phase 1/Phase 2 on the image below)



Phase 1: Sensitisation phase - When the immune system of atopic individuals is first exposed to an allergen, B lymphocytes produce an excess of IgE antibodies. These antibodies have a strong affinity for mast cells (and basophils) and coat the surface of these cells by binding to receptors for the heavy chain portion of the IgE molecule (IgE Fc receptors). 

Phase 2: Activation phase - Subsequently, when sensitised mast cells, coated with IgE antibodies, are re-exposed to the specific allergen, they rapidly release vasoactive mediators such as histamine and serotonin from cytoplasmic granules. A requirement for activation of mast cells appears to be the cross-linking of surface IgE molecules by the inciting allergen. Later, prostaglandins and leukotrienes are also synthesised in, and released from, the mast cell plasma membrane. Among other things, this leads to an accumulation of neutrophils and eosinophils at the site of antigenic stimulation. This stage of the immediate hypersensitivity reaction is sometimes referred to as a late phase response.

The clinical manifestations of immediate sensitivity reactions depend on whether the antigen is introduced into the skin, lungs or bloodstream.

Direct contact with the medical product is not needed for sensitisation to latex. Allergenic latex proteins are also adsorbed on the glove powder; when latex gloves are snapped on and off, these become airborne and can be directly inhaled. Direct latex exposure at mucosal or serosal surfaces also occurs by repeated use of rubber catheters or gloves used intraoperatively during abdominal or urological surgery.


ArticleDate:20041123
SiteSection: Article
 
   
    
                                            
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