Dr. Charles Plopper of the University of California at Davis produces asthma in young monkeys by exposing them to ozone, a potentially harmful ingredient in polluted air, and dust mites. During the inflammatory process, which usually occurs within the first 6 to 12 months of life, Th2 goes on high alert and makes antibodies to anything it sees in the lungs, from viruses to inhaled particles coming from such things as dust mites, cockroaches, molds, ragweed, cigarette smoke, pollen, fungi and cat dander. Dust mites are linked to 50 to 80 percent of U.S. asthma cases, while cockroach particles are a major instigator of asthma among urban African-American children. These allergens are ubiquitous. The average mattress is home to 100,000 to 10 million mites, munching away on human skin cells, which we shed at the rate of 7 million cells per minute.
Mites are also in carpeting and furniture.
Ragweed pollen, another common allergen, is produced at the rate of one billion pollen grains per plant. Rates of allergy generally remain the same in different geographical regions even though the types of allergens change. The trouble starts when Th2 memorizes these antigens and sets up recognition receptors on immune cells. So when these antigens are again encountered, Th2 fires all of its weapons, producing allergic reactions ranging from a runny nose, itchy eyes, sneezing, itching and sometimes swelling of the lungs' airways to such an extent that breathing becomes labored and may endanger life. The Th2 system was designed to get rid of parasites, which no longer are common.