Question

What is wheal and flare reaction ?????
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Answer 1

The overall result of the type I reaction is an acute inflammationmarked by local seepage of fluid from and dilation of the blood vessels, followed by ingress of granulocytes into the tissues. This inflammatory reaction can be a useful local protective mechanism. If, however, it is triggered by an otherwise innocuous antigen entering the eyes and nose, it results in swelling and redness of the linings of the eyelids and nasal passages, secretion of tears and mucus, and sneezing—the typical symptoms of hay fever. If the antigen penetrates the lungs, not only do the linings of the bronchial tubes become swollen and secrete mucus, but the muscle in their walls contracts and the tubes are narrowed, making breathing particularly difficult. These are the symptoms of acute asthma. If the antigen is injected beneath the skin—for example, by the sting of an insect or in the course of some medical procedure—the local reaction may be extensive. Called a wheal-and-flare reaction, it includes swelling, produced by the release of serum into the tissues (wheal), and redness of the skin, resulting from the dilation of blood vessels (flare). If the injected antigen enters the bloodstream and interacts with basophils in the blood as well as with mast cells deep within the tissues, the release of active agents can cause hives, characterized by severe itching. If the antigen enters through the gut, the consequences can include painful intestinal spasms and vomiting. Local reaction with mast cells increases the permeability of the mucosa of the gut, and in many cases the antigen enters the bloodstream and also produces hives. Regardless of whether the allergen is injected or ingested, if it ends up in the bloodstream, it can induce anaphylaxis, a syndrome that in its most severe form is characterized by a profound and prolonged drop in blood pressureaccompanied by difficulty in breathing. Death can occur within minutes unless an injection of epinephrine is administered immediately. This type of severe allergic reaction can occur in response to foods, drugs such as penicillin, and insect venom.
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