Explanation of IgE (immediate) vs. IgG (delayed) allergic reactions

[Guest guest]

Here's a good explanation of the difference between IgE and IgG

allergic reactions. It's from the website of a well-repected lab -

Great Smokies Diagnostic Laboratory - that does allergy testing for

both types of reactions. There's alot more info about this topic

here:

http://www.gsdl.com/assessments/allergy/appguide/index4.html

Role of IgE and IgG

IgE antibodies are believed to trigger allergic reactions when they

crosslink on the surface of gastrointestinal mast cells, stimulating

the release and production of chemical mediators such as histamine,

proteoglycans, and leukotrienes. These potent reactors instigate a

barrage of effects on surrounding intestinal tissue and, by inducing

intestinal permeability, may also allow passage of food antigens into

the bloodstream. When this happens, other organs in the body then

become targets for the allergic reaction; further involvement with

other cell types in the body may result in the creation of a chronic,

perpetual immune response.

Since most severe, immediate allergy symptoms are IgE-mediated, many

doctors have limited their testing to this class of immunoglobulins.

Certainly, an abundance of medical literature supports using the IgE

assay as a means of diagnosing Type I allergic reactions.31-35 There

is also considerable evidence, however, underscoring the significance

of IgG as a marker in allergy testing as well. In fact, it is

estimated that IgG and IgG complex mediators are involved in 80% of

all food allergy reactions.36

Repeated exposure to an antigen can eventually produce allergy-like

responses, or hypersensitivities. These reactions are usually

delayed, with symptoms that may not surface until hours, or even

days, after the initial exposure. One study found that nearly 60% of

patients with food intolerance exhibited late (delayed), rather than

early or immediate reactions to provoking foods.37

Although IgE may be involved, it is theorized that these delayed

reactions are primarily mediated by IgG. Specific IgE has a half-life

in circulation of one to two days, and a half-life on the mast cell

of about 14 days. IgG, on the other hand, appears to have a

circulating half-life of 21 days, with a residual time on the mast

cells that can last as long as 2-3 months.38 Thus an IgG assay is an

essential tool for diagnosing the possible causes of delayed, non-

anaphylactic responses, the so-called " hidden " allergies,

which

cannot be detected with conventional IgE tests such as

radioallergosorbent test (RAST) or skin testing.

Numerous studies indicate a role for IgG in non-IgE, mast-cell

mediated diseases as well as various food allergies.39-43 IgG can

induce basophil degranulation, triggering the release of histamine

and other potent chemical mediators upon exposure to specific

antigens—a common mechanism of allergic reactions.

In one study, individuals with hypersensitivity to shrimp were

determined by double-blind, placebo controlled challenges. Shrimp-

specific IgE and IgG, but not IgM and IgA, were significantly higher

in the group with shrimp hypersensitivity as compared to controls.44

Another group of researchers verified that children with atopic

eczema showed much higher levels of IgG antibodies to casein and

ovalbumin subclasses than did controls.