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Hypersensitivity due to peanuts is the most common allergic reaction existing in todays world. It is characterised by uncontrolled production of IgE in the body. The exact cause of this allergic reaction till recent times remains to be unknown. Peanuts contain allergen proteins such as Ara h 1, 2, 3 which are the most potent allergens in hypersensitivity due to peanuts. The target population of this disease mainly is children below the age of 5. To diagnose this disease tests such as skin prick test, immune cap or RAST test which includes detection of specific IgE in the serum can be done. Symptoms include abdominal pain, itching, swelling, vomiting. Symptoms can be seen within minutes of accidental consumption of peanuts or any peanut product. Treatment of this allergy mainly is avoidance of peanuts. But certain allergen specific and allergen non specific therapies prove to be beneficial which include Oral immunotherapy, recombinant vaccines, Chinese herbs.
Hypersensitivity due to peanuts -A hard nut to crack.
Type 1Hypersensitivity is defined as an allergic reaction which occurs after an exposure to a substance called an allergen. The exposure may be in any form like Inhalation, ingestion, injection or direct contact. Food allergy is included under type 1 hypersensitivity which is a immunoglobulin E (IgE)-mediated hypersensitivity response. Foods such as peanut ,tree nut , fruits such as apple , peach are the most comman fruits that provoke a severe reaction and which has affected almost 2.4 - 3.7% of adults. These reactions are so severe that they may sometimes even result in death. This review article focuses on causes and allergens that causes hypersensitivity due to peanuts , symptoms , diagnosis methods and its treatment and management of peanut allergy.
Peanut and tree nut allergy are the most comman foods allergies that are caused in children and adults.
According to a study carried out on 784 children it was proved that the allergic reaction to peanuts goes on increasing with age. also 68% of these children showed worst reactions to peanuts when compared to any other nut like brazil nut or hazel nut. This same study also found out that as the age of the child increases he/she is multisensitized (develops an allergic reaction to many nuts) and is no longer monosensitized like in his/her childhood, this was found using the skin prick test (SPT).
In another study which was carried out on the serum IgE samples of 731 pateints suffering from nut allergy, it was found that acute allergy to nuts is predominant in younger males and older females. It was also found that The frequency of multiple-nutspecificity is suficiently high.
A study also showed that there exits a cross reactivity between peanut and tree nut. Peanut-allergic subjects often have serum IgE antibodies that cross-react with other legumes such as soybean.
CAUSES OF HYPERSENSITIVITY DUE TO PEANUTS:
Hypersensitivity due to peanuts has become the most increasing and commonest cause of anaphylaxis. Peanut allergy is an unsolved issue that is spreading its wings in the whole world.  Almost 5 % of the infants of US are allergic to nuts which include peanuts, brazil nuts, hazel nuts and cashew nuts. Cashew nuts may cause more severe reactions compared to peanuts. But unfortunately the main cause of any nut allergy continues to stay unknown.
A slight ray of hope can be seen when a study conducted in 2010 showed that maternal ingestion of peanuts during pregnancy had a dose-dependent association with peanut sensitization which may lead to peanut allergy in the new born baby. This does not mean that consumption of peanuts during pregnancy is a risk factor for peanut allergy. But it is advised that pregnant women who suffer from atopy (a genetic predisposition toward the development of immediate hypersensitivity reactions) should abstain from the consumption of peanuts because this may further lead to the infants being sensitized to peanuts. There is a high frequency of sensitivity to tree nuts in peanut allergic patients. This occurs because of the cross reactivity of tree nut and peanut allergens.[6,12]
Allergens bind to IgE in the serum of allergic individuals and activate mast cells and/or basophils that have been sensitized with IgE containing serum. There are 11 peanut allergens of which Ara h 2 and Ara h 6 allergens are considerably more potent than Ara h 1 and Ara h 3.  Ara h 1,2 and 6 belong to the prolamins family of allergens while Ara h 3 belongs to the cupin family. The most immunodominant allergens with primary peanut allergy, are Ara h 2, Ara h 6 and Ara h 1. Reactivity to Ara h 2 and Ara h 6 has the major risk factor for significant clinical reactivity.
Symptoms of a peanut allergy can range from mild to severe. A mild reaction may cause itching, swelling, hives and a runny nose. Another common symptom is abdominal pain and vomiting immediately after consumption of peanuts or any peanut product. Extra sensitive patients may undergo difficulty in breathing and excessive coughing. If the reaction is worse additional symptoms like tight throat, wheezing and diarrhoea may occur. The symptoms are seen within minutes to hours after consumption of peanuts or any peanut product.
Some people who are allergic to peanuts may have a life threatening reaction called anaphylaxis. The symptoms of anaphylaxis include dizziness, unconsciousness, dangerously low blood pressure.
DIAGONOSTIC TESTING FOR DETECTION OF PEANUT HYPERSENSITIVITY:
The two tests which are widely used to detect any food allergy are skin prick test (SPT) and serum specific IgE testing (sIgE). these tests are used to detect IgE antibodies.
Skin prick testing: This is the first test that is recommended when an allergy is suspected. In this test a small amount of allergen is introduced in the skin (usually forearm) by pricking the skin through the drop of allergen, allowing the allergen to penetrate in the body. 
A positive result can be noted by the presence of itchy skin. This is followed by redness and swelling which will form a 'wheal' of >3mm near the prick. This indicates that the patient is allergic to the particular allergen.[16,17] Precaution should be taken to stop the intake of antihistamine medicines at least 72 hours prior to the test. Failing in doing so, the test will show negative results.
Advantages: This test is quick (prviding results within 20 minutes), simple and inexpensive. This test is more reliable than any other test to detect peanut hypersensitivity.[16,17]
Serum specific IgE testing (previously known as RAST- Radioallergosorbent test): this test measures the amount of IgE in the serum when provoked by a particular allergen. In the US currently there are three commercial assays that measure specific IgE levels.
Both the above tests are successfull to an extent but they lack precision. A major disadvantage of the above test is that they cannot predict the severity of allergic reactions.  Keeping this in mind a new test was introduced.
Double blind placebo controlled oral food challenge (DBPCFC).
This test proved to be of a golden standard to dectect food allergies. This test involves feeding of a particular allergen in increasing doses under strict supervision. The allergen is mixed in a food vehicle which may be apple sauce , pudding , ice cream or yoghurt and hence this test is named in such a way. The dose of the allergen is increased every 30 minutes till the final dose reaches 2500 mg in the same day. If any allergic symptoms arise the test will be terminated and the highest tolerated dose was considered to be the thresh hold limit. Based on this the results of the test could be mild, moderate or severe. If the subject completes the test without any reaction, he/she is considered to be non reactive to the particular allergen. This test proved to be beneficial for testing hypersensitivity reactions in infants.
For treating any food allergy it is important to identify the food allergen and to educate the patient on how to avoid its consumption unknowingly. It is also important to treat the early signs which occur due to accidental ingestion of a particular allergen. A strict elimination diet and to treat any Reactions from accidental ingestions with epinephrine and antihistamines is the standard treatment for peanut allergy. For treating hypersensitivity due to peanuts there are two types of therapies:
Allergen specific therapy.
Allergen non-specific therapy.
Both these therapies are under investigational study.
Allergen specific therapy:
Oral immunotherapy (OIT): This involves gradually increasing the exposure to allergens which results in providing desensitization (temporary loss of responsiveness due to continuous exposure) or in inducing tolerance (permanent immunologic nonresponse). OIT may cause some adverse side effects which are unpredictable.[15,16] Sublingual immunotherapy (SLIT) was investigated for treatment of hazelnut allergy. Both the therapies may offer permanent tolerance after 5-6 months of treatment. OIT thus offers a promising therapy for allergic patients.
Modified recombinant vaccines: To avoid the harmful side effects of OIT, modified peanut allergens (Ara h 1, 2, 3) were altered using site directed mutagenesis. This stimulates T cells to proliferate thus reducing IgE production.
Peptide immunotherapy: In this therapy, the peptides fragments contain T cell epitopes. But since they are not of sufficient length, they are not allowed to cross-link with IgE antibodies, thus reducing mast cell and basophil activation. This therapy is in its clinical phase and has proved to provide protection against peanut anaphylaxis in mice. Further investigation is needed.
Immunostimulatory sequence conjugated protein immunotherapy: The ISS bound to protein act as adjuvants to promote switching to a TH1 response. This therapy has proved to provide protection for peanut anaphylaxis in mice.[15,16]
Allergen non specific therapy:
Anti IgE: By introducing anti-IgE in the body free circulatin IgE is reduced in the body. This inhibits early and late phase allergic response. It also suppresses inflammation which is caused due to the allergic reaction. Anti IgE is combined with oral immunotherapy for better results.
Chinese herbal medicine: Chinese herbal extracts such as Rubia Cordifoila (Quincao) and Dianthus superbus (Qumai) are found to be effective in suppressing the production of IgE during a hypersensitivity reaction. these Chinese herbal extracts inhibit the TH-2 response and provide a long term protection from peanut anaphylaxis in a murine model.[16,22] the phase 1 study of these extracts are completed and further research is on. along with peanut allergens, these herbal extracts can be useful in treating any food allergen.
TLR-9: A new therapy which promotes TH1 immune response during an allergic reaction is in study. This provides protection during peanut anaphylaxis in a murine model.[16,20
Management of peanut allergy is possible by the following methods:
The patient and the patient's family need to instructed to avoid peanuts and peanut products.
The patient should be aware about early signs and symptoms that may occur after an accidental exposure to peanut allergens.
The patient should be given proper education to use the self injectable epinephrine injections (Epipen)
Since small children are more susceptible to peanut allergies, they should be properly instructed by their parents and doctors to avoid peanuts in their diet completely. The family members should check the ingredient label properly before feeding anything to the child suffering from peanut allergy. If possible the patient should be kept away from all types of nuts since multisensitization of nuts is highly dangerous.[4,14]
Hypersensitivity due to peanut presents many challenges in the present world scenario. These challenges are increasing daily. Peanut allergy has now become the most common form of allergy. It targets mainly children below the age of 5. Adults are also prone to this allergy. A perfect cause is unknown to us. But research to find the cause of peanut allergy continues. Diagnosis of this allergy in the early stages is better. Skin prick test is the most reliable test done to find out the level of severity. After diagnosis with peanut allergy it is advised to abstain from consumption of any type of nut. Avoidance is the best treatment. OIT has proved beneficial in the treatment of peanut allergy. For treating an allergic reaction more research needs to be done and the clinical trials of the discovered vaccines and drugs should be completed as soon as possible. In case of anaphylaxis, epinephrine self injectables should be kept handy. Lastly, future studies should make use of the existing knowledge of therapeutics and prophylactics to find out a safer and more convenient treatment for hypersensitivity due to peanuts rather than avoidance of peanuts.