nasal secretions and skin after antigen challenge, and blood after cold challenge of patients with cold-induced urticaria. Severe childhood asthma is associated ...
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Allergy and Immunology The Scientific Board of the California Medical Association presents the following inventory of items of progress in allergy and immunology. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itseff and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers, orscholars to stay abreast of these items of progress in allergy and immunology that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another. The items of progress listed below were selected by the Advisory Panel to the Section on Allergy and Immunology of the California MedicalAssociation and the summaries were prepared underits direction. Reprint requests to Division of Scientific and Educational Activities, California Medical Association, PO Box 7690, San Francisco, CA 94120-7690
Platelet-Activating Factor PLATELET-ACTIVATING FACTOR (PAF) is a potent phospholipid mediator of hypersensitivity and inflammatory reactions that may be important to the pathogenesis of allergic and inflammatory disorders. It is structurally distinct from leukotrienes and prostaglandins, but the synthesis of these lipid mediators of hypersensitivity may be linked. Platelet-activating factor is synthesized by human cells important to allergic diseases, including mast cells, neutrophils, monocytes, and endothelial cells. Increased quantities of PAF are released into the sputum of patients with asthma and chronic lung disease, nasal secretions and skin after antigen challenge, and blood after cold challenge of patients with cold-induced urticaria. Severe childhood asthma is associated with a deficiency of the specific acetylhydrolases that metabolize PAF. Platelet-activating factor has the novel capacity to induce biphasic or prolonged hypersensitivity reactions in vivo. Its inhalation by humans induces eosinophil influx and transient bronchospasm, followed by prolonged airway hypersensitivity that may persist for weeks. Airway eosinophilia and hypersensitivity are hallmarks of asthma, further suggesting that PAF contributes to the development of asthma. Intradermal PAF induces an acute wheal and flare reaction that subsides and is followed by an erythematous, indurated papule. Its capacity to induce such complex reactions may result either from the wide range of PAF target cells, including eosinophils, neutrophils, monocytes, and endothelial cells, or from complex interactions between PAF and inflammatory cytokines including interleukin- 1 and tumor necrosis factor. Potent, specific PAF antagonists are available and have revealed a critical pathophysiologic role for PAF in some animal models of allergic asthma, anaphylaxis, immune complex disease, and septic shock. Platelet-activating factor antagonists have not yet been tested systematically in human diseases, but preliminary reports suggest that they may be important agents in treating asthma and other hypersensitivity
disorders.
FRANK H. VALONE, MD
San Francisco REFERENCES
Braquet P, Touqui L, Shen TY, et al: Perspectives in platelet-activating factor research. Pharmacol Rev 1987; 39:97-145
Snyder F (Ed): Platelet-Activating Factor and Related Lipid Mediators. New York, Plenum Press, 1987 Winslow CM, Lee ML (Eds): New Horizons in Platelet-Activating Factor Research. New York, John Wiley & Sons, 1987
House Dust and Mites THE HOUSE DUST MITES Dermatophagoides farinae, Dermatophagoides pteronyssinus, and Euroglyphus maynei of the family Pyroglyphidae are major sources of multiple allergens in homes. Because mite allergens are continuously produced or linger in the home environment as seasonal breeding mite populations die, mite-induced allergic diseases are more perennial or nonseasonal than other airborne seasonal allergens such as pollen and mold. Detailed analyses of house dust from homes in the United States, Europe, and England indicate that many species of mites can be found in the dust in homes. These include plant and animal parasites and predaceous, saprophagous, and stored-product, soil, and fungal-feeding mites. Of this large array, in most homes in geographic areas where true pyroglyphid "house dust mites" are prevalent, Dfarinae, D pteronyssinus, and E maynei make up 90% to 100% of the mites found in dust samples from mattresses, carpeted floors, and fabric-covered overstuffed chairs and couches. These mites are most prevalent in high-use areas where human skin scales collect and serve as a source of food. The percentage of homes containing Dermatophagoides species and Euroglyphus species is determined by the characteristic relative humidity in a geographic area. In humid geographic areas such as Ohio and similar locations, nearly 100% of homes have mites, and mite densities may be as high as 18,000 mites per gram of dust. In drier climates, such as Denver, fewer than 10% of homes have mites and mite levels are generally well below 100 mites per gram ofdust. In temperate regions, mite density has a seasonal cycle, with high mite levels occurring in the summer or early fall during periods of high relative humidity and lowest mite levels recorded during the dry heating season. The seasonal cycle may be less pronounced or nonexistent in warmer, humid climates; in some locations several density peaks may exist. In drier climates, mattresses are the primary mite foci, where perspiration and evaporative water from the human
