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Plant biologist Daphne Preuss and immunologist Albert Bendelac study why pollen triggers allergies.
"Lipids are a major component of pollens," Bendelac says, "and when immune cells encounter lipids, they release hormone-like factors that orchestrate inflammation and immune responses." Bendelac has devised sensitive assay techniques that detect these immune responses to lipids—techniques that have proved integral to Preuss's research.
In addition to surface lipids, Preuss is exploring the allergenic properties of pollen surface proteins. HHMI investigator Arthur Weiss, a clinical immunologist based at the University of California, San Francisco, notes that "a vital aspect of Daphne Preuss's work is understanding the properties of pollen's surface antigens that make them so immunogenic. Knowing that might lead to a better understanding of why allergies develop in the first place, and why they develop in response to specific stimulants."
Preuss is indeed moving in this direction in the search for human genes associated with immune responses and the identification of plant cell fractions that contain allergens. As an alternative to current allergy testing, which screens for pollen allergies but doesn't usually tease out which species elicits allergic reactions in genetically predisposed individuals, she and her colleagues have designed a diagnostic chip that carries extracts of pollen material. "These extracts are primarily protein from 22 different species. We probe the chip with patient sera and can detect specific antibodies," Preuss says. "In the process of working out methods for purifying surface materials from many different [unwashed] pollen species, we've been able to demonstrate that humans create antibodies to pollen's outer coat. This is an exciting proof of concept."
Preuss presented her work at the annual meeting of the American Academy of Allergy, Asthma, and Immunology on March 3. "By discovering the specific antigens that elicit allergic responses," adds Weiss, "it may be possible to alter or prevent those responses." And at that point, adds Preuss, "We will be looking at new therapeutic opportunities." 
Photos: Lisa Predko
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GESUNDHEIT!
Ragweed is one of the most prolific producers of allergy-causing pollen. A single ragweed plant can generate a million grains of pollen a day. And, no doubt about it, those light, dry grains can travel. Scientists have collected samples of ragweed pollen 400 miles out at sea and 2 miles high in the air, according to the National Institutes of Health.
Flamboyant flowers usually aren't the culprits in seasonal allergies. The types of pollen that most commonly cause allergies are produced by the more unassuming—and abundant—plain-looking plants, such as trees, grasses, and weeds. When allergy-causing pollen lands on the mucous membranes of the nose, local mast cells release a chemical called histamine. As a result, small blood vessels in the nose dilate, nasal passages swell, and congestion results. Histamine also causes itching, irritation, and excess mucous production. Prostaglandins and leukotrienes play a role in allergy symptoms as well.
Current allergy treatments work to block histamines, constrict blood vessels to reduce swelling, or inhibit mucous production. Most of those products have annoying side effects, such as drowsiness, while others take several days or weeks to work. Allergy shots—injected diluted extracts of pollen under the skin—are expensive and time-consuming (they have to be given many times with gradually increasing doses), and don't work for everyone.
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