Clinical Review ABC of allergies

Pathogenic mechanisms: a rational basis for treatment

BMJ 1998; 316 doi: http://dx.doi.org/10.1136/bmj.316.7133.758 (Published 07 March 1998) Cite this as: BMJ 1998;316:758
  1. Peter H Howarth

    Allergic diseases such as asthma, rhinitis, eczema, and anaphylaxis are increasingly common and, in addition to being associated with morbidity and potential mortality, constitute a considerable burden on health resources, with both direct and indirect costs. This article discusses the pathogenic mechanism underlying the clinical signs and symptoms of these diseases and explains the basis for the choice of differing treatments.

    Immunohistology of nasal mucosa in allergic rhinitis using alkaline phosphatase/anti-alkaline phosphatase technique showing individual cells stained red: mast cells (top), eosinophils (bottom left), and CD4 T lymphocytes (bottom right)

    Relation of atopy and allergy to disease

    About 40% of the population is atopic as evidenced by a positive response to a skin prick test with an allergen, but not all show signs and symptoms of clinical disease. There may be a latency period, as students who have positive skin prick tests with grass pollen but who do not experience hay fever have been shown to go on to develop seasonal allergic rhinitis. A threshold response may also be required for signs and symptoms of clinical disease to develop, as allergic airway inflammation is present in the lower airways of patients with perennial allergic rhinitis sensitive to house dust mite who do not have clinical asthma. This inflammatory response falls between the response in patients with clinical asthma and that in non-atopic healthy controls.

    Regulation of B lymphocyte IgE synthesis by T lymphocytes. T cells with the Th2 cytokine profile increase interleukin 4 and interleukin 13 synthesis, which promotes IgE isotype switching, whereas the development of T cells with a Th1 cytokine profile, which generate the interferon gamma, inhibits B cell isotype switching for IgE synthesis. This process also involves antigen uptake and processing by mucosal dendritic cells (commonly Langerhans' cells in the airways) and the presentation of antigen in a modified format to T lymphocytes, typically …

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