Daley, Henry

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Bridgewater ReviewVolume 13 | Issue 1 Article 5Jan-1994The Chemistry of AllergiesHenry DaleyBridgewater State CollegeThis item is available as part of Virtual Commons, the open-access institutional repository of Bridgewater State University, Bridgewater, Massachusetts.Recommended CitationDaley, Henry (1994). The Chemistry of Allergies. Bridgewater Review, 13(1), 7-9.Available at: http://vc.bridgew.edu/br_rev/vol13/iss1/5B Y H E N R Y D A L E YtheCHEMISTRYof Illustration by Miriam Walshach year in the United States, over 5000 people die frombronchial asthma, 40 from insect stings, and around 300 from ordi-nary doses of penicillin. The reason: allergies. Allergies are the fourthmost commQn activity-limiting chronic disorder and may constitute the most preva-lent disease found in the United States. It is estimated that over 20% of Americans sufferfrom allergic reactions sometime in their lives. The extent of this reaction can be very mild to life-threatening. In fact some reactions are so mild that the person having the reaction may not be aware that heor she is experiencing one.Bridgtwaur RtlIitw 7.Illustration by huret bwsonThe tail of an IgE molecule (which is Y shaped)attaches itself to certain cells in the body known as mast cells. Asingle mast cell can bind more than 100,000 IgE molecules.Within the mast cells are granules that contain chemicals~wn as mediators. When an allergen combines with an IgEmolecule on the mast cell, the mediators are released. Althoughnumerous different chemicals are present as mediators, only twoof them appear to playa role in human allergies. These areknown as histamine and slow reacting substance (SRA-A). Ofthese two, histamine is the chemical responsible for the sidereactions we associate with allergies such as itching, swelling,and runny-nose.Basic Types ofI~ Allergiesfl{i'I, There are four waysin which allergensinvade our bodies. They can be(a) inhaled, (b) ingested (eatenor drunk), (c) touched (skincontact), and (d) injected (stingor bite). Once the allergen ispresent in the body, there aretwo different types of allergicreactions. They are classified asimmediate or delayed, depend-ing upon the time it takes forthe allergic reaction to appear.An immediate reac-tion is one in which symptomsappear within minutes afterexposure to the allergen. Whereas in a delayed reaction it takesat least four hours or some-times even days after exposurefor the symptoms to appear.Typical of delayed reactions arecontact allergies such as perfumes in soaps, poison ivy, andorgan rejections.Different mechanisms are at work in the two types ofallergic reactions. The mechanism described above applies toimmediate allergic reactions. However in delayed reactions, noantibodies are found in the blood; instead delayed reactions arebelieved to be mediated by cells. Many of the delayed reactionsinvolve the other types of immunoglobins. IgG is involved inthe Rh factor associated with newborns and with allergic pneu-monia. IgA and IgM have been associated with allergic reac-tions involving blood vessels and the kidneys. Both IgA and IgEare involved with food allergies which usually occur in peoplewho lack IgA. IgA blocks food allergies by combining with theallergen associated with these allergies.Although it is often assumed that certain types ofallergic reactions can be triggered by stress and emotional reac-tions, this is not true. Stress and emotions can intensifY a reac-tion, especially in bronchial asthma and hay fever but cannotinitiate a reaction. However, there is a correlation betweenheredity and allergies. If one of your parents has allergies, thereis a better than normal chance that you will have an allergy. Ifboth your parents have allergies your chance of having similarallergies is about 80%, although it may not necessarily be thesame allergy as your parents.What is an allergy?The answer to the question, exactly what an allergy is, isnot known. What is known is that some peoples' bodiesoverreact to the presence of certain substances. Thesesubstances produce no ill effect in most humans.The chemical basis of the human body's ability to over-come diseases is the production of antibodies. These are complexprotein structures known as globulins. There are three basic typesof globulins alpha, beta, and gamma. Most antibody molecules aregamma globulins. Because of their relationship to the immunesystem, they are also known as immunoglobulins and are given thesymbol Ig. There are five differenttypes of immunoglobulins: IgA,IgD, IgE, IgG, and IgM. Those Nassociated with allergic reactions ~ Iare mainly of the type IgE.Substances that stimulatethe production of antibodies are N1called antigens. Antigens are usu-ally proteins or complex protein Hcarbohydrate structures. In allergicreactions, these antigens are asmall part of the substance thathas entered the body and causedthe reaction. Examples of thesesubstances (which are called aller-gens,) include dust, pollen, andinsect venom. The term allergen isalso sometimes used in place ofantigen. In ragweed, the chiefantigen represents about 0.5% ofthe total mass of the solid in thepollen. It is known as antigen E.An injection of 1 x 10-12 grams ofan tigen E is enough to cause aresponse in allergic people.Cells in the body analyz.e these an tigens and transferinformation about them to other cells that produce the antibodies.These antibodies attack a specific antigen and have little or noeffect on other antigens. The antibodies remain in the blood-stream after the antigen is removed. The IgE antibodies areresponsible for many of the most common allergic reactions suchas hay fever, asthma, anaphylaxis, hives and eczema.No one is born with IgE antibodies in their body. Whenfirst exposed to an allergen, it takes about 10 days before the IgE isdeveloped. By this time the allergen is gone so no allergic reactionoccurs. A second or later exposure to the allergen causes the aller-gic reaction. It takes repeated exposures to allergens for people todevelop an allergy.The Role of IgE~ IgE is not a single protein structure (molecule), but a," class of molecules each having a slightly different struc-ture. Each molecule reacts with a specific antigen. This iswhy people have specific allergies. The IgE that reacts with rag-weed is not the same form ofIgE that reacts with the antigen froma bee sting.IgE is present in the body in extremely small amounts,about 1 part per million in blood plasma. People who have allergicreactions have more IgE present than normal. For example, a per-son with allergic asthma has six times as much IgE as one withnon-allergic asthma and those who suffer from hay fever have 14times as much IgE as non-allergic people.8. Bridg~waur Rtvi=To learn more about allergies and the drugs that are available to combat allergies thefollowing research guides are invaluable: The Complete Drug Reference. ConsumerReports Books. United States Pharmacopoeia. 1992 and Allergy: Its MysteriousCauses and Modern Treatment. The Allergy Foundation of America. Grosset andDunlap. also see Chemical & Engineering News "Allergy. A Protective MechanismOut of Control:' May 1,. 1970 pp 84-132. For those of you who suffer from allergies.remember. significant stndes have been made and will continue to be made to helpyou face up to the watery eyes. the sneezing. the general discomfort and in somecases the danger associated with allergic reactions.The Role of HistamineHistamine, formed by the breakdownof a common amino acid known ashistidine, is found in high concen tra-tions in the granules in mast cells, and isreleased as the granules move to the outer edgeof the mast cell. They discharge the histaminethrough a temporary gap in the cell membrane.In immediate reactions, histamine canaccount for many, if not all, of the symptomsassociated with an allergic reaction. Histaminecauses dilation of the blood vessels and increas-es the ability of blood fluids to leak out of cap-illaries. These fluids are responsible for theswelling of tissues. Histamine also causes con-traction and swelling of the smooth muscles,stimulates the production of saliva, tears andsecretes mucus. It can also cause a large drop inblood pressure and produce a condition knownas anaphylactic shock, leading to death.Treatment ofAllergiesI*~ Three procedures are used in the treat-~ ment of allergies: (a) avoidance, (b)desensitization, and (c) chemicals.Once a person knows what material he/she isallergic to, the best treatment is to avoid theallergen as much as possible. In some cases itwould seem that moving to a different part ofthe country might help, especially with pollenallergies, but in general this does not work.People with hay fever who move from a part ofthe country high in pollen to one low in pollenoften develop an allergy to the different pollensfound in their new home.Desensitization therapy involves theinjection of an increasing amount of allergen ifthe person has a high IgE concentration. Themodern term for desensitization is hyposensiti-zation, which means reduced sensitivity. Smallamounts of allergen are injected over a periodof weeks. Benefits are not apparent until six totwelve months of treatment. Injections shouldbe given in a doctor's office because of the pos-sibility of a severe reaction (anaphylaxis) to theinjection. It may seem strange to inject a personwith the same allergen that is causing the prob-lem, but the procedure appears to work byincreasing the amount of IgG antibodies in thebody. These antibodies block the combinationof the allergen with IgE, preventing the releaseof the chemical mediators. This procedure isparticularly useful for allergies to bee, hornet,and wasp stings, and is effective for pollen aller-gIes.Chemical trea tmen t involves th reedifferent classes of drugs: Epinephrine(adrenaline), steroids, and antihistamines,AntihistaminesD Antihistamines are probably the bestknown and most widely distributedclass of chemicals used to relieve thesymptoms of allergies. Over 50 different anti-histamines are available in the United States,often combined with decongestants or analgesics incough medicines.Antihistamines do not cure allergies. Theywork by competing with histamine for sites on cells.By blocking the histamine from these sites they pre-vent the swelling, itching and other symptoms associ-ated with the reaction of histamine with the cells. Theearly histamines can pass through the brain membraneand cause drowsiness, which has led to their use assleeping medications. Two of the newer antihis-tamines, astemiwle and terfenadine, cannot cross thisbarrier, and thus do not cause drowsiness. Other seri-ous side effects have recently been associated withthese antihistamines.The reason there are so many antihistaminesis that each affects different people in various ways.Only by working with your doctor can you determinewhich is the best for you to take.Ep.inephrine~ Epinephrine (adrenaline) was the first strong'f!D> drug sold for the treatment of allergies. Itrelaxes the muscles in the bronchi and thus iseffective in bronchial asthma. When people are rushedto the hospital with a severe allergic reaction,epinephrine is injected. This has saved the lives ofmany people who have suffered anaphylactic shockdue to a reaction to an allergen. Epinephrine is knownas a sympathomimetic drug, as it stimulates the sym-pathetic nervous system along with relaxing thesmooth muscles.Numerous other compounds are also used assympathomimetic chemicals: better known are norad-renaline (norepinephrine), ephedrine and isoproterenol.The xanthines and theophylline are similar. Theophyl-line is often used in inhalants as a bronchial dilator. It isalso used to determine lung capacity. Some patients withbronchial problems feel they can breathe better afterdrinking a cup ofcoffee. This happens because theophyl-line is one of the hundreds of chemicals found in thevapor of coffee.SteroidsI~ ~drenocort~coids (~orticoster?ids) are also veryV Important In treating allergIes. Some of themore common steroid drugs used are hydrocor-tisone, prednisone, betamethasone, triamcinolone, andfluocinolone. They help relieve the redness, swelling anditching associated with allergic reactions and are espe-cially useful for bronchial asthma, hives, eye disorders,and eczema. Steroids reduce the swelling and fluid build-up associated with the allergic reactions and are sopowerful they may be used in severe cases of bronchialasthma.Henry Daley is Professorof ChemistryBridgtwaur Rtvitw 9.

The Chemistry of Allergies

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The Chemistry of Allergies

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