Dictionary of Allergies .. Atopens

Atopens are nonspecific activators of physiological enzyme systems in man and are indicators of the atopic status. Allergens are considered to be those substances, not necessarily immunogenic by themselves, capable of deliberately directing the immune response into IgE production. Ongoing IgE synthesis may eventually produce IgE antibodies reacting with nonallergenic antigens[1]. Sensitization to atopens is an early phenomenon that overlaps with the onset of atopic dermatitis (AD) in infancy. Early epidermal barrier impairment may facilitate the epicutaneous penetration of atopens[2].

Atopens are water-soluble proteins that induce in sensitized individuals upon inhalation or ingestion immediate hypersensitivity reactions mediated by atopen-specific IgE and late phase reactions characterized by tissue infiltrations of CD4+ T lymphocytes, basophils and eosinophils. Sensitization is associated with development of disorders such as allergic rhinitis, allergic asthma and atopic dermatitis (AD). AD lesions are characterized by accumulation of atopen-specific CD4+ T lymphocytes, because in panels of CD4+ T lymphocyte clones (TLC), obtained by random cloning from biopsies of lesional AD tissue, the frequency of TLC reacting to house dust mite Dermatophagoides pteronyssinus (Dp) was higher than in TLC panels randomly cloned from peripheral blood. Activation of Dp-specific CD4+ TLC from both AD patients and nonatopic controls seemed to be normal. It required atopen processing and was restricted by HLA-DR molecules.

Development of AD to Dp was strongly associated with aberrant production of the lymphokines by atopen-specific CD4+ T cells. In contrast to Dp-specific TLC from a nonallergic control, Dp-specific TLC from atopic patients were Th2 cells that secreted (apart from IL-6, GM-CSF and TNF-Ëœ) IL-4, IL-5 but little IL-2 and IFN-Å¡. These TLC appeared to be efficient helper cells for IgE secretion because of  1) their high IL-4 and low IFN-Å¡ secretion,  2) their ability to provide an accessory contact-mediated signal,  3) their lack of cytolysis [3].

References

1. Berrens L. The atopen: a rehabilitation. Ann Allergy. 1976 May;36(5):351-61.

Boralevi F, Hubiche T, Léauté-Labrèze C, Saubusse E, Fayon M, Roul S, Maurice-Tison S, Taïeb A. Epicutaneous aeroallergen sensitization in atopic dermatitis infants - determining the role of epidermal barrier impairment. Allergy. 2008 Feb;63(2):205-10.

3. Kapsenberg, M.L., et al: Allergen-specific CD4+ T lymphocytes in contact and atopic dermatitis: In the Skin as an Immune Organ. Annual meeting of EAACI, Zűrich, Switzerland, May 25-29, 1991.