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LATE PHASE ALLERGY CULPRIT
By Sean Henahan, Access Excellence
NEW YORK- A protein isolated from bronchial fluids appears to play an important role in triggering the "late-phase" allergic response, reported researchers from the Johns Hopkins University School of Medicine at the annual meeting of the American Academy of Allergy and Immunology. In the acute phase of an allergic reaction, a protein called an IgE antibody binds to the surface of a basophil, a component of the immune system. The job of the IgE antibody is to recognize an allergen, such as cat dander or ragweed pollen. When this IgE antibody encounters the allergen while bound to a basophil, the basophil releases histamine, a chemical that causes typical allergy symptoms such as itching and swelling. However, about half of all allergy sufferers experience "late phase" allergic reactions, so called because symptoms do not occur for several hours after exposure to allergens. While researchers have long suspected that the late phase reaction is triggered by some element in the immune system, until now no such trigger has been identified. Johns Hopkins' immunologist Susan MacDonald, M.D. reported the identification of such as trigger, called IgE-dependent histamine releasing factor (HRF). The protein was obtained from fluids washed from the lungs of patients experiencing late-phase asthma attacks. MacDonald and colleagues were able to isolate and copy a gene for the HRF protein from the lung fluids. The gene for HRF protein had been identified and reproduced earlier, but MacDonald was the first to identify one of the protein's functions. The researchers also determined that histamine is sometimes released when HRF reacts with the basophil-IgE combination. Further experiments showed that the reaction only occurs in the presence of IgE antibodies from late-phase patients, especially those with asthma. "Based on this discovery, we refer to IgE protein in late-phase allergy sufferers as IgE+," says MacDonald. "We'd like to know what the molecular differences are in this form of IgE." The next step will be to try and determine whether HRF binds chemically to the basophil or to IgE+. The researchers will also be studying the factors that affect production of HRF, which is made in immune system cells. The ultimate hope is that this research will help clarify the biological differences that leave half of all allergy patients suffering late-phase attacks, eventually leading to preventive and therapeutic interventions. Transmitted: 95-03-07 19:04:34 EST
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