Several Methods Are Used to Detect Type I Hypersensitivity Reactions

Type I hypersensitivity is commonly identified and assessed by skin testing. Small amounts of potential allergens are introduced at specific skin sites either by intradermal injection or by superficial scratching. A number of tests can be applied to sites on the forearm or back of an individual at one time. If a person is allergic to the allergen, local mast cells degranulate and the release of histamine and other mediators produces a wheal and flare within 30 min (Figure 16-10). The advantage of skin testing is that it is relatively inexpensive and allows screening of a large number of allergens at one time. The disadvantage of skin testing is that it sometimes sensitizes the allergic individual to new allergens and in some rare cases may induce systemic anaphylactic shock. A few individuals also manifest a late-phase reaction, which comes 4-6 h after testing and sometimes lasts for up to 24 h. As noted already, eosinophils accumulate during a late-phase reaction, and release of eosinophil-granule contents contributes to the tissue damage in a late-phase reaction site.

Another method of assessing type I hypersensitivity is to determine the serum level of total IgE antibody by the radioimmunosorbent test (RIST). This highly sensitive technique, based on the radioimmunoassay, can detect nanomolar levels of total IgE. The patient's serum is reacted with agarose beads or paper disks coated with rabbit anti-IgE. After the beads or disks are washed, 125I-labeled rabbit anti-IgE is added. The radioactivity of the beads or disks, mea sured with a gamma counter, is proportional to the level of IgE in the patient's serum (Figure 16-11a).

The similar radioallergosorbent test (RAST) detects the serum level of IgE specific for a given allergen. The allergen is coupled to beads or disks, the patient's serum is added, and

Weal Intradermal Test Forearm

Skin testing by intradermal injection of allergens into the forearm. In this individual, a weal and flare response developed within a few minutes at the site where grass was injected, indicating that the individual is allergic to grass. [From L. M. Lichtenstein, 1993, Sci. Am. 269(2):117. Used with permission]

FIGURE 16-10

Skin testing by intradermal injection of allergens into the forearm. In this individual, a weal and flare response developed within a few minutes at the site where grass was injected, indicating that the individual is allergic to grass. [From L. M. Lichtenstein, 1993, Sci. Am. 269(2):117. Used with permission]

Radiolabeled

Paper disk or agarose bead

Paper disk or agarose bead

Anti-IgE coupled to solid phase

Radiolabeled

Radioimmunosorbent Test Method Image

Patient IgE

Count bound label

Patient IgE

Count bound label

Allergen coupled to solid phase

Allergen coupled to solid phase

Patient IgE

Bound allergen specific IgE

Patient IgE

Bound allergen specific IgE

Radioimmunosorbent Test

Nonspecific IgE is washed away

Radiolabeled anti-IgE

Count bound label

Nonspecific IgE is washed away

Radiolabeled anti-IgE

Count bound label

FIGURE 16-11

Procedures for assessing type I hypersensitivity. (a) Radioimmunosorbent test (RIST) can quantify nanogram amounts of total serum IgE. (b) Radioallergosorbent test (RAST) can quantify nanogram amounts of serum IgE specific for a particular allergen.

unbound antibody is washed away. The amount of specific IgE bound to the solid-phase allergen is then measured by adding 125I-labeled rabbit anti-IgE, washing the beads, and counting the bound radioactivity (Figure 16-11b).

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Responses

  • demsas negassi
    What method is used to detect ige?
    8 years ago
  • mitchell
    What method is used for detecting IgE?
    8 years ago
  • KEIREN
    How RADIOimmunosorbent technique is performed to detect TOTAL IgE IN SERUM?
    8 years ago

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