See Arachidonic Acid.

This type of reaction resembles eczema, except that the inflamed skin has sharper borders, does not commonly affect the crease areas, nor does it last as long. Blisters are more likely. Removal and avoidance of the chemical responsible for the blisters will, in most cases, provide relief within two weeks. Hay Fever Itching within the nasal passages, a prominent symptom of hay fever, causes nose-rubbing and facial contortions as a person attempts to relieve the misery. The inner corners of the eyes, and even their entire surface, may itch, resulting in tears. Also, itching of the roof of the mouth can be extremely annoying.

Complement is a group of proteins, many of which are enzymes that interact sequentially after activation by an antigen-antibody reaction. Complement plays an important mediatory role in immune reactions by helping attract cells to the area, by increasing the permeability of the blood vessels, and by causing lysis (destruc­tion) of the attacking microorganisms. Under certain conditions, however, the complement system may also play a part in hyper­sensitivity reactions such as serum sickness.

. An aerosolized bronchodilator such as isoetharine (Bronkosol) or metaproterenol (Alupent or Meta-prel) can be used fairly often if the patient has not previously overused them. Intravenous corticosteroids. Although physicians do not fully understand the function of corticosteroids, they do know that in­travenous corticosteroids enhance the effect of certain broncho-dilators.

Allergic disease occurs when the body mounts a specific response to foreign substances in the environment. A vast amount of research has been devoted to understanding the foreign substances, or antigens, that initiate these responses and the many ways in which the body reacts to the antigens. Most antigens are complex molecules. Because of their dissimilarity to the body’s natural proteins, the body can recognize them as foreign. These antigens are usually made up of specific, recognizable de­terminants bound to a carrier substance. Specific determinants stimu­late certain cells (B lymphocytes) of the immune system, producing antibodies directed against the determinants. The carrier molecules stimulate T lymphocytes, which may be helpers or suppressors of the В lymphocytes’ productivity. Both В and T cells cooperate in producing an antibody response to foreign proteins. During the 1970s, an extensive study was made of the immune response mechanism. The two major classes of lymphocytes— В and T—were distinguished and separated on the basis of different surface characteristics. Modulation of the cells that produce antibodies is of major importance. В lymphocytes differentiate into plasma cells that produce antibodies, proteins with determinants capable of recognizing antigens and that result from immune mechanisms. The classes of immunoglobulin are IgA, IgD, IgE, IgG, and IgM. Im­munoglobulins are composed of molecules held together in a specific array. Portions of these molecules recognize and react with foreign proteins (antigens), whereas other portions attach to and react with cells and biologically active molecules of the body. The interaction of antigen and immunoglobulin then results in immune responses and/or allergic manifestations in an individual. Immunoglobulin E is the antibody most frequently associated with allergic disease. It is bound to cells in the respiratory tract, gastro­intestinal tract, and skin. After it has been formed by initial exposure and response to an antigen, a subsequent antigen challenge produces an interaction that results in the release of mediators capable of causing such allergic manifestations as wheezing or runny nose, de­pending on the level of exposure and the individual’s reaction pattern. Research in the future will likely be aimed at refining knowledge of antigen molecules, identifying those that can be used in allergy testing and the study of immune response mechanisms. The recognition and description of T lymphocytes has recently advanced to a sophisticated level. These cells serve at least four distinct functions. First, "helper" T cells appear to energize В cells and make it easier for them to produce immunoglobulins. They are stimulated when antigens are processed by macrophages, a type of cell. The macrophage-processed antigen stimulates T helper cells, which stimulate the production of В cells. Second, T cells kill other cells in a process called cytolysis. In addition to their ability to kill, cytotoxic T cells play a major role in rejecting such foreign cells as transplanted tissues, tumors, and viruses. The third function of the T cell is production of lymphokines, chemicals that regulate immune events, for example, the migration of cells to sites of im­mune reactivity. Fourth, suppressor T cells prevent В cells from pro­ducing antibody. Current research suggests that allergic immuno­therapy helps suppress allergic symptoms by stimulating suppressor T cells, which, in turn, prevent allergic antibody IgE from being produced in the usual amounts. Investigato rs in basic research have begun to isolate some of the factors involved in the inheritance of allergic tendencies. Largely through experiments in which animals with known genetic makeups were inbred and their immune responses were evaluated, it has been observed that certain genes control the function of T cells and thereby determine an individual’s immune response to a particular stimulus. Thus immune reactivity is programmed as part of an individual’s genetic structure. The amount of IgE a person has may be controlled by a single IgE regulator gene, which depends on T cells to carry out its instructions. Research has shown that, in addition to antigen recognition and antibody production, numerous other biological systems contribute to the versatility and complexity of the immune response. Consider­able research effort continues to be devoted to characterizing the numerous interactions.

Statistics compiled by the National Institute of Allergy and Infec­tious Diseases show that thirty-five million people suffer from allergy and that nine million of this group have asthma.

Pericarditis is an inflammation of the membrane covi ing the heart.

Of the plantain family (Plantaginaceae), English plantain is the best-known species. It is wind-pollinated and may cause hay fever during the summer. Pollination occurs from June to August.

A scratch test is an allergy skin test in which the allergen is applied directly to small scratches or needle pricks made in the skin. See also Prick Test.

In immunotherapy, also known as hyposensitization or desensiti-zation, a person is injected with antigens to which he or she is allergic, in hopes that he or she will be protected from adverse reactions in the future. Initially, injections are given at frequent intervals, but eventually they are given at longer intervals. The amount of antigen injected increases as treatment progresses. Clinical studies have verified the effectiveness of immunotherapy in reducing the symptoms of allergic rhinitis. In addition, recent evidence suggests that bron­chial irritability present in asthma is reduced by immunotherapy. As we saw above, venom immunotherapy appears to diminish the risk of serious reactions to stinging insects. The mechanism by which immunotherapy relieves symptoms is not yet well understood. Allergy shots appear to stimulate the production of blocking antibodies and to decrease production of allergic anti­body. They also appear to change mast-cell sensitivity, so that histamine and other mediators of allergic reactions cannot be released as easily. Much remains to be learned. The interaction of T and В cells seems to be altered by immunotherapy, thus making it possible for suppressor cells to prevent the production of certain immunoglob­ulins. This interaction also stimulates helper cells to produce blocking antibodies. Whether this actually occurs remains to be learned. The antigens used in injection therapy need to be standardized, and studies must be made of their effectiveness. Does immunotherapy for rhinitis indeed affect the progression from allergic rhinitis to asthma? Investigators are currently working on "allergoids" for immunotherapy, molecules that, it is hoped, will resemble environ­mental allergens closely enough to stimulate symptomatic improve- ment but without the risk of an allergic reaction. Scientists are also studying compounds that have a sustained action and that have a symptomatic benefit with fewer injections. The goal is to create com­pounds that require infrequent administration, yet which confer a significant, long-lasting benefit.