Mite be trouble
|Cleanliness is not only next to godliness; it might also be a salve against allergies.
Exposure to household allergens is a major cause of chronic inflammatory disease worldwide, including asthma, rhinitis, and atopic dermatitis. Allergens are typically soluble, low-molecular-weight proteins that are released from their sources (house dust mites, pollen, domestic animals, etc.) and recognized by components of the immune system. More specifically, an allergic reaction is an immune response called immediate hypersensitivity. Upon exposure to an antigen, B cells are induced to produce the IgE class of antibodies. The IgE is secreted and binds a high-affinity receptor on the surface of mast cells and basophils. The introduction of the allergen and subsequent production of IgE constitute sensitization to the allergen. Reintroduction of the foreign antigen results in cross-linking of the IgE antibody to the cell surface and subsequent activation of mast cells and basophils, causing a rapid release of mediators that leads to local inflammation. The response to the second exposure to an allergen can occur within minutes.
Sensitization to allergens of the house dust mite Dermatophagoides pteronyssinus is common in asthmatic patients. There are two major allergens from house dust mites: Der p 1, a glycoprotein in dust-mite fecal particles, and Der p 2, a protein thought to be involved in mite reproduction. Approximately 85% of individuals with asthma have IgE antibodies to house dust mite allergens. Identification of these inhalant allergens and of those from cats (Fel d 1) and dogs (Can f 1) is an important advance in the management and treatment of allergic disease, both for allergen avoidance and in therapy development. Although complete avoidance of inhalant allergens is impossible, several protocols have been established to decrease exposure of individuals to house hold allergens, and in some cases these protocols have led to a decrease in clinical symptoms.
Various vapor- and air-permeable coverings are now on the market, including sheets and pillowcases made from the same tightly woven cotton fabric used for typewriter ribbons. These fabrics, which are more comfortable than plastic and nonwoven synthetic coverings, can be produced with varying pore sizes (220 µm), allowing different degrees of airflow. A 6-µm pore size allows little or no leakage of mite allergens and prevents the leakage of allergens from cat dander.
A recent study in Thailand, where the warm and humid climate favors growth of dust mites, provides support for covering mattresses to avoid dust-mite allergens. The study demonstrated that partial encasing of mattresses with a nylon sheet (fashioned like a fitted bedsheet) and covering pillows significantly reduced dust-mite allergen levels on the surface of the bed and kept the levels lower than those in the control group for up to six months.
A study in Australia, where house dust-mite allergens are also prevalent, showed that encasing mattresses and pillows in occlusive coverings as well as washing other bedding with Acaril, which contains the acricidal benzyl benzoate, reduced Der p 1 levels to 10% of control beds after four days. Repeatedly washing bedding with Acaril bimonthly for six months lowered Der p 1 levels to less than 30% of preintervention levels. In addition, the amount of Der p 1 found in dust that settled adjacent to the beds decreased from 24 ng/m2/d at baseline to 10.0 ng/m2/d. If Acaril use is not possible, bedding should be washed in very hot water (130 °F) without detergents and tumble-dried for at least 20 min to kill dust mites.
Although vacuuming cannot significantly reduce the load of dust mites in carpets, removal of other inhalant allergens can significantly improve clinical symptoms in allergic people. A recent study investigated the effects of high-efficiency vacuum cleaners (those with S-class filtration systems) and standard vacuum cleaners in reducing allergen levels at four separate household locations. Der p 1 reduction was not achieved with either vacuum cleaner over the period of the study, but the high-efficiency vacuum cleaner significantly reduced Fel d 1 levels at all locations, and the patients allergy symptoms decreased. Similarly, another study compared the effects of weekly and monthly vacuuming and found a decrease in the house dust-mite allergens Der p 1 and Der p 2 in only a few homes. Weekly vacuuming was effective in most of the homes, but allergen levels in other homes in the same study either did not change or increased with weekly and monthly vacuuming.
Because the effects of vacuuming on dust-mite allergen levels have been variable, it is clear that other approaches are necessary for removing these allergens from upholstery and carpets. One approach is to kill the dust mites and thus remove the source of the allergen. But it must be remembered that dust mites are not insects, and so insecticides that are safe for household use do not kill them. Chemicals, including benzyl benzoate and tannic acid, have been recommended for use on upholstery and carpets, although achieving effective concentrations of these agents for cleaning heavily mite-loaded carpets has proven difficult.
Instead of using chemical agents, a recent study demonstrated a decrease in dust-mite allergen levels in homes where carpets, upholstery, mattresses, and blankets were treated with heat, steam, and then heat again. Allergic patients in these homes also showed a fourfold decrease in bronchial hyperreactivity up to nine months after the treatment.
Peptides-based immunotherapy. T-cell-reactive overlapping peptides of Fel d 1 are being used in immunotherapy in the belief that they would bind major histocompatability II molecules in vivo and be presented to T cells in a manner that would alter the T cell response. Furthermore, because the epitopes recognized by B cells rely on conformation, linear peptides should not be able to trigger IgE-mediated responses. Unfortunately, trials with Fel d 1 elicited only a limited response. It is possible that the peptides do not cover enough T cell epitopes or are unstable in sera and thus are quickly degraded.
Recombinant allergens. Commercial quantities of allergens can be produced as modified recombinants that are less likely to result in anaphylaxis. The recombinant could be an isoform of an allergen that is less reactive with IgE. Alternatively, the epitopes that bind to IgE might be altered to reduce binding without necessarily decreasing its efficacy.
Other immune system components. By better understanding the components of the immune system involved in the allergic response, it may become possible to target other cell types and mechanisms with immunotherapy.
Voula Kanelis is a freelance writer living in Toronto, ON. Send your comments or questions regarding this article to email@example.com or the Editorial Office by fax at 202-776-8166 or by post at 1155 16th Street, NW; Washington, DC 20036.