Hay fever is the common name for seasonal allergic rhinitis. Rhinitis is an inflammation of the mucous membrane that lines the nose and sinus. Millions of patients spend billions of dollars per year treating this disease. In most cases rhinitis is caused by an allergic response and can be triggered by any airborne allergen. Allergic reactions are caused by the immune system identifying an allergen as a pathogen and trying to kill it.
An allergic response is not triggered the first time one is exposed to an allergen. It can take as little as two or as many as a thousand exposures before symptoms appear. The reasons are not understood. It is also true that greater exposure to a particular allergen increases the likelihood of developing an allergy to it.
Allergies develop when helper T-cells identify an allergen as an invading organism. There is no allergic response with first time exposure because the allergen is flushed from the system by normal nasal flow, digestion, or is washed from the skin before the immune system can develop a response. When T-cells detect the allergen they release Immunoglobulin E (IgE). Cells that synthesize IgE can be found throughout the body but are found predominantly in association with mucosal tissues like the nasal passage and lungs. When IgE binds to IgE receptors on mast cells, histamine and other chemicals are released. Mast cells are a type of leukocyte (white blood cell), which contain metachromatic granules that store several inflammatory mediators. These mediators include histamine, leukotrienes, serotonin, proteolytic enzymes, heparin, and chondroitin sulfate; these mediators cause the symptoms associated with the allergic response (1). Histamine causes inflammation in the region where the allergen is present.
The current recommended treatment for allergies is avoiding allergens that trigger a response. For most people with allergic rhinitis that means never going outside or owning any pets which may trigger a response. The easier treatment is antihistamines. Antihistamines work by blocking histamine, preventing the inflammation and other symptoms from occurring (1). Older antihistamines, like Benadryl, have more side effects than newer antihistamines. Benadryl can cause drowsiness, of varying degrees, and in rare cases hallucinations. Newer antihistamines, like Claritin and Tavist-D, no longer cause drowsiness in most people because these drugs do not cross the brain blood barrier.
Another treatment is allergy shots. Allergy shots work by injecting small amounts of the allergen under the skin and, over the course of one to three years, gradually increasing the dose. The body is stimulated to neutralize IgE as a result (1). Extremely severe side effects such as, anaphylactic reactions, heart attacks, and death, have been reported with this treatment (2). Because none of the current treatments are one hundred percent effective, new treatments are always being researched.
One of the more promising treatments currently being researched involves inhibiting the IgE receptor on mast cells (3). Inhibiting the IgE receptor would prevent histamine and leukotrienes from being released, stopping the allergic response. Various compounds of indoyl, napthyl, and phenylethyl substituted halopyridyl, thiazolyl, and benzothiazolyl thioureas have been tested. Two of the most promising compounds are seen in figure 1 below (3).
In one experiment, ninety-five of these compounds were synthesized in an oxygen-deprived system. An oxygen-deprived system is necessary because oxygen is a highly reactive molecule, when it is activated by iron(II) in the body, and may react to form unexpected compounds. The structures of each of the compounds was determined using HNMR, CNMR, UV spectra, IR spectra, mass spectroscopy, and the optical rotation was determined for chiral naphthyl derivatives (3).
IgE-sensitized mast cells are used to test the candidate drugs. A significant amount of leukotriene C4 was released when IgE-sensitized mast cells were incubated for thirty minutes with the antigen DNP-BSA. IgE-sensitized mast cells were then incubated under the same conditions with one of the synthesized compounds. Some of the tested compounds showed a significant decrease in the release of leukotrienes by the mast cells. Twenty-two of the compounds demonstrated an inhibitory effect by significantly lowering the amount of leukotriene C4 released by the mast cells.
A correlation between lipophilicity and biological activity was sought for the compounds that showed an inhibitory effect. The theory was that more lipophilic (nonpolar) compounds would be able to enter the mast cells and thus raise their intercellular concentrations. The lipophilicity was determined by dissolving a known amount of the thiourea compounds, in a solution containing octanol and water. The mixture was shaken for 4 hours. The two phases were separated and filtered through a Millipore filter. The solutions are filtered to prevent clogging of the HPLC.
HPLC is used to analyze the partition coefficient, which is a measure of the lipophilicity. Methanol is used as the eluent with a flow rate of 1 ml per minute. The wavelength of detection is kept at 254 nm. The partition coefficient is calculated from the amount of compound dissolved in octanol, (area under the curve), divided by the amount of compound dissolved in water. No correlation was found between lipophilicity and leukotriene release in the 22 candidates that showed inhibitory effects on the IgE receptor (3).
Hospitals have switched to non-latex gloves because many hospital workers develop latex allergies. Latex dust from gloves, like any other allergen, can be a trigger for allergic rhinitis. There have been many studies concerning the relationship between, exposure to latex, and the development of allergies. Skin prick tests, where a needle containing a trace amount of latex is inserted under the skin, are used to detect the presence of latex allergies in humans for most studies. Research shows that on average 5% to 17% of health care workers have an allergy to latex (4).
Many studies try to correlate the percentage of allergy sufferers to the number of years spent working in the medical field. Data shows that allergies are most likely to develop within the first few years of exposure. Most studies show a small increase or no correlation when looking at medical professionals who have been working for more than a few years. The studies that have concentrated on dental and medical students show an increase from near 0% in first year students to above 10% in fourth year students (4). Allergies are less likely to develop after the first several years of exposure.
Not only are new drugs for treating allergies being tested but new methods for testing drugs are also being developed. RBL SX-38 cells are rat cells that express a, b, and g chains of the human receptor for IgE. The chains allow the rat cell to behave like a human mast cell by binding to IgE from sera of allergic individuals. RBL cells have the advantage of being easier to culture than human mast cells.
To test RBL cells as an alternative to mast cells, sera was collected from patients with allergies to peanuts and to at least two of the following: walnuts, soybean, timothy grass, ragweed, and cats (5). RBL cells are put in 48-well plates with 5-hydroxytryptamine and are incubated overnight. Human serum from the donors is added. The cultures are allowed to incubate for an additional 24 hours. After a series of washings, allergen extracts are added. After 30 – 45 minutes, at 37oC, the samples were cooled on ice. Percentage of radio-labeled serotonin is calculated because serotonin is released as part of the allergic response.
The results from the experiment show that RBL cells behave like human mast cells. RBL cells that were exposed to serum from patients with peanut allergies and grass allergies showed similar sensitivities to both allergens. RBL cells exposed to serum from patients with peanut allergies and no grass allergies showed a much greater sensitivity to the peanut allergen. Human mast cells behave in a similar fashion making RBL cells a possible alternative.
Allergic rhinitis effects millions of people. A lot of time and money are spent annually to make better treatments for this disease. Better drugs are always in development. Alternative products like non-latex gloves are being used to avoid exposure to allergens. New research methods are being developed to make research into allergies easier and faster.
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Copyright 2003 Matt Page and Koni Stone