An overview of allergens.

Most allergens are proteins or glycoproteins that range in molecular weight from 5000 to 100,000 Da, although polysaccharides and low-molecular-weight substances may also be allergenic. Common allergens include pollens, fungal spores, house-dust mites, and animal epithelial materials but can also include drugs, biologic products, and insect venoms. The allergic response is dependent on the route of exposure. If the exposure is to an inhaled aeroallergen, then the allergic response will be respiratory in nature. Ingested or injected exposure gives rise to gastrointestinal, cutaneous, or anaphylactic reactions. The size of the pollen determines the clinical manifestation of allergy. For example, particles between 20 and 60 µm in diameter can be carried by the wind and cause nasal and ocular symptoms (allergic rhinoconjunctivitis). Particles of <7 µm can deposit in the airways and cause symptoms of asthma. Animals produce allergens in forms unique to each species. Cat allergen, most importantly Fel d 1, is buoyant and "sticky," which means it easily remains airborne and may last in a home for up to 6 to 9 months after the source is removed. Cat allergen adheres to clothes and can be found in public places, e.g., schools. Dog allergen, particularly Can f 1, is present in dander, saliva, urine, and serum. All dog breeds produce allergenic proteins (even poodles and "hairless" dogs).

Allergen immunotherapy: definition, indications, and reactions.

Specific allergen immunotherapy is the administration of increasing amounts of specific allergens to which the patient has type I immediate hypersensitivity. It is a disease-modifying therapy, indicated for the treatment of allergic rhinitis, allergic conjunctivitis, allergic asthma, and Hymenoptera hypersensitivity. Specific immunoglobulin E (IgE) antibodies for appropriate allergens for immunotherapy must be documented. Indications for allergen immunotherapy include (1) inadequate symptom control despite pharmacotherapy and avoidance measures; (2) a desire to reduce the morbidity from allergic rhinitis and/or asthma, or reduce the risk of anaphylaxis from a future insect sting; (3) when the patient experiences undesirable adverse effects from pharmacotherapy; and (4) when avoidance is not possible. Several studies reported that immunotherapy in allergic rhinitis seems to prevent the development of new allergic sensitizations and/or new onset asthma. Humoral-, cellular-, and tissue-level changes occur with allergen immunotherapy, including induction of allergen-specific regulatory T and B cells, interleukin 10, and transforming growth factor ß production; suppression of T-helper type 2 cell proliferation; large increases in anti-allergen IgG4 antibodies; and reduction in basophil, mast cell, and eosinophil mediator release. Allergen immunotherapy can be administered either subcutaneously in the physician's office or sublingually by the patient at home. The use of immunotherapy in food allergy is still under investigation.

Occupational immunologic lung disease.

Occupational immunologic lung disease is characterized by an immunologic response in the lung to an airborne agent inhaled in the work environment and can be subdivided into immunologically mediated occupational asthma (OA) and hypersensitivity pneumonitis (HP). Irritant-induced OA, a separate nonimmunologic entity, can be due to chronic exposure to inhaled irritants or reactive airways dysfunction syndrome (RADS). RADS is defined as an asthma-like syndrome that persists for >3 months and occurs within minutes to hours after a single exposure to a high concentration of a respiratory irritant. Workers in high-risk fields for OA include farmers, printers, wood workers, painters, plastics workers, cleaners, spray painters, electrical workers, and health-care workers. OA can be triggered by high-molecular-weight (HMW) proteins that act as complete allergens or by low-molecular-weight (LMW) sensitizers that act as haptens. HMW proteins (>10 kDa) are generally derived from microorganisms (such as molds and bacteria, including thermophilic actinomycetes), plants (such as latex antigens and flour proteins), or animals (such as animal dander, avian proteins, and insect scales) and are not specifically regulated by the Occupational Safety and Health Administration. LMW haptens that bind to proteins in the respiratory mucosa include some Occupational Safety and Health Administration regulated substances, such as isocyanates, anhydrides, and platinum. HP can present in an acute, chronic, or subacute form. The acute, subacute, and early chronic form is characterized by a CD4+ T-helper type 1 and CD8+ lymphocyte alveolitis. Classically, the bronchoalveolar lavage in HP will show a CD4/CD8 ratio of <1.

Managing Younger Siblings of Food Allergic Children.

Current guidelines state that there is insufficient evidence to recommend testing siblings of food allergic children before introduction of potential allergic foods, but the topic continues to remain controversial. Although the proportion of siblings who are sensitized to a food without clinical reactivity is high in comparison to those with a true food allergy, there is still a known increased risk amongst siblings of children with food allergies that has led to much apprehension about management. The appropriateness of testing and further steps for management of sensitization in the absence of history of clinical reactivity should be discussed with parents.