Lecture 22 Food Allergies

Delayed Hypersensitivity reactions (>8hours after ingestion):

cellular immunity involving T-lymphocytes and macrophages

cross reaction

the reaction of one antigen with antibodies developed against another antigen.

Allergy Diagnosis

- Determine if the symptoms are mediated by the immune system - Complete physical - Detailed case history - Food diary - Positive identification of the allergen

Most Common sites for allergic reactuons

- Mouth: swelling of the lips or tongue, itching lips - Airways: wheezing or breathing problems - Digestive Tract: stomach cramps, vomiting, diarrhea - Skin: hives, rashes or eczema

Human Body has two categories of defense system:

- Non specific defenses - Specific defenses or specific Immunity

Immediate hypersensitivity with IgE occurs within minutes to a few hours after ingestion of offending foods.

- Systemic: Itching, urticaria (hives), Vomiting, Abdominal cramps, diarrhea and respiratory distress, and in severe cases anaphylactic shock - Localized: hives and eczema or atopy (an umbrella term covering clinical presentations of food allergy etc)

Types of Food Allergies

- immediate hypersensitivity - delayed hypersensitivity

Lymphocytes

1. B lymphocytes - mature in Bone marrow and lymphatic tissue (spleen and lymph nodes) 2. T lymphocytes - mature in the Thymus

Common cross reaction foods

1. Cows milk: goats milk,ewes milk 2. Hens eggs: eggs from other birds 3. Peanuts: soybeans, green beans, green peas 4. Soybeans: Peanuts, green beans, green peas 5. Cod: Mackerel, Herring 6. Shrimp: Other Crustaceans 7. Wheat: Other grains, mostly rye

Food aversion vs Intolerance

1. Food aversion - a strong desire to avoid a particular food 2. Food Intolerance - adverse reaction to food that does not involve the immune system

Acquired Immunity

1. Passive (ready made antibodies) - Natural Maternal Antibodies - Artificial (antibodies from other sources) 2. Active (our own body makes antibodies) - natural (exposure to foreign agents) - artificial (immunization)

Anaphylaxis

1. Potential fatal reaction to a food allergen causing reduced oxygen supply to the heart and other body tissues. 2. Symptoms include: difficult breathing, low blood pressure, pale skin, a weak rapid pulse, loss of consciousness, death.

Primary and Secondary responses to an antigen

1. Primary response: first response when host 's B-cell recognize the antigen 2. Secondary response: upon second exposure to the antigen, the memory cells will divide, thus make more of the total antibody

stages of hypersensitivity

1. Sensitization: initial meeting of an allergen and the immune system that results in IgE production! 2. Activation of mast cells - IgE - Non-IgE substances (eg. Drugs)

Nature of IgE Allergic Reactions

Antigen + IgE + Mast cells = Mediator release Mediators= histamine and others

Histamine release

Induced by very many substances, including IgE

Antibody structure

Variable domain allows for antigen-binding specificity. the constant domains are for common biological function.

Antibody

a protein produced in response to an antigen that is capable of binding specifically to the antigen!

Allergic Reactions are...?

antigen-antibody reactions

Antigen

foreign substance

Wheat Allergy

• 4 major proteins in wheat - albumin, globulin, gliadin and glutenin (gluten) -vary in proportion according to the type of wheat. • The majority of IgE-mediated reactions to wheat involve the albumin and globulin fractions. • Caused by ingestion of wheat-containing foods or by inhalation of flour containing wheat • Ale, beer, bourbon, and whiskey contain wheat -- and so does wine. • Another manifestation of allergic reaction to wheat is really intolerance to gluten -- the protein found in wheat, rye, barley, and oats. • Gluten intolerance is associated with the disease called "gluten-sensitive enteropathy" or "celiac disease." Genetic causes may play a role.

Celiac Disease

• A digestive disorder that occurs in reaction to gluten • Gluten: - elastic, rubbery protein in wheat, rye, barley and oats. - binds the dough in foods such as bread. - contributes to spongy consistency. - Rice and maize do not contain gluten. • The body's immune system reacts to the gluten and causes damage to the intestine. • Celiac disease, also known as celiac sprue or gluten-sensitive enteropathy, is fairly common. • One in 133 Americans has the disorder and needs to follow a gluten-free diet. • Often misdiagnosed as irritable bowel syndrome, Crohn's Disease or gastric ulcers.

When does a food allergy occur?

• A food allergy occurs when the immune allergic response can occur. system responds to a harmless food as if it were a threat. • The first time a person with food allergy is exposed to the food, no symptoms occur; but the first exposure primes the body to respond the next time. • When the person eats the food again, an allergic response can occur

Milk allergies

• A milk allergy is a reaction to milk protein, casein. • Some people cannot drink cow's milk but are fine with sheep's or goat's milk. • Common symptoms are severe stomach pain, diarrhea, skin hives, or difficulty breathing.

Celiac Disease Symptoms

• Abdominal bloating and pain • Diarrhea • Vomiting • Constipation • Pale, foul-smelling stool

Restaurants and food allergies

• African, Chinese, Indonesian, Mexican, Thai, and Vietnamese dishes often contain peanuts. It is recommended that peanut-allergic individuals avoid these types of foods and restaurants. • For traditional food restaurants, cross-contamination of allergens to other foods can also be a problem.

Failure to absorb nutrients may lead to other problems, including weight loss and malnutrition. Signs and symptoms related to weight loss or malnutrition can include:

• Anemia • Fatigue • Osteoporosis • Infertility or miscarriage • Mouth ulcers • Tingling, numbness in the hands and feet

Specific defenses or specific immunity

• Antibodies (many kinds of antibodies for many kinds of • Food allergies are related to specific defenses or specific immunity. • Immune literary means "free of burden". • Actions of the immune system are triggered by antigens (foreign substances). • Most antigens are large protein molecules; Some antigens are polysaccharides and few are glycoproteins (carbohydrate and protein) or nucleo-proteins.

Celiac vs Wheat allergy

• Celiac disease and wheat allergy both involve the immune system but the reaction within the body is different. • Celiac disease is the result of IgA and IgG antibody responses to gluten. • Wheat allergy is mediated by IgE antibodies. • Celiac disease is an autoimmune disease that causes damage to the lining of the intestine. It is a lifelong disorder.

Celiac vs Lactose Intolerance

• Celiac disease damages the inner lining of the small intestine, and that may lead to difficulty digesting lactose, a sugar found in milk and milk products. • Following a gluten-free diet allows the intestine to recover, and people with celiac disease may discover that they are able to digest lactose once again.

food intolerance

• Direct effect of food • Enzyme deficiency (e.g., lactase, sucrase etc) • Symptoms of food intolerance: bloating, cramping, gas and diarrhea • Main cause of food intolerance: carbohydrates (lactose, fructose, sorbitol)

Prick skin Test (PST)

• Drop of the substance under test on the forearm • Allow a tiny amount to enter the skin (doctor pricks it with a needle) • After 15min, verify presence of "bump"

The Big 8: Most common allergenic foods

• EGGS • MILK • PEANUTS • TREE NUTS • SOY • WHEAT • FISH • SHELLFISH

Prevalence of Food Allergies

• Experts agree that allergies in developed countries are becoming more common. • In the U.S., food allergies afflict 2-2.5% adults and 6-8% children. • 100-175 people in the U.S. die each year. • Death generally result from anaphylactic shock, often to peanuts or tree nuts. • More than 160 foods have been associated with allergic reactions.

Resources for food allergies

• Food Allergy and Anaphylaxis network (FAAN) • American Academy of Allergy, Asthma and Immunology • American Dietetic Association • Asthma and Allergy Foundation

What is a food allergy?

• Food allergy is an inappropriate immune response to an otherwise harmless food. • True food allergy involves several types of immunological responses. • Food allergens are usually proteins.

Histamine

• Formed by decarboxylation of the amino acid histidine. • Stored preformed in mast cells and basophils. • Mast cells are found in blood and lymph vessels around nerves. • more abundant in the skin, upper and lower respiratory tract, gastrointestinal tract and reproductive mucosa.

Children and Food Allergy

• High prevalence in the first few years of life • Immature immune system and immature digestive system • Cow's milk and soy, most common allergens • Breast feeding is recommended • Delay introduction of common allergenic foods • Sensitivity to most of the allergenic foods is usually lost by young children as they grow up

Immunological Concepts

• Human body has many defense mechanisms to fight off infectious diseases and other toxic foreign substances. • Strong healthy adult human can fight off most of infectious diseases. • Ability to fight off disease can be modulated by genetics, age, race and lifestyles (diets, exercise and amount of sleep etc.)

Non-IgE mediated food allergy

• Immune Complex-mediated - Symptoms usually gastrointestinal • Delayed type hypersensitivity - Symptoms usually gastrointestinal

Egg Allergies

• In most cases, egg allergies are mild but are caused by even tiny amounts of egg. • Sometimes, it's the egg white (albumen) that's the problem • For other people, it's the egg yolk. • In rare cases, an egg allergy can trigger anaphylaxis.

Celiac Disease Damage the Intestinee

• In people with celiac, the body's immune response is triggered by gluten in food. • Antibodies attack the intestinal lining, damage the villi in the small intestine. • Damaged villi can't effectively absorb nutrients through the intestinal wall. As a result, fats, proteins, vitamins, and minerals get passed through the stool.

Tree Nut Allergies

• Likely to be coupled with peanut allergy • What are included in tree nuts? - cashews, almonds, pecans, walnuts, hazelnuts, pine nuts, Brazil nuts, and macadamia nuts. - Coconut, chestnut, ginkgo nuts, and lychee nuts are also considered tree nuts. • Even added in nonfood products like lotions and shampoos.

Other causes of allergy-like food problems

• Microbial products- e.g. histamine - Some food products have high levels of histamine (eg fermented foods) • Pharmacological reaction-tyramine, phenylethylamine, caffeine - dose dependent • Idiosyncratic reactions - (adverse reactions of drugs etc - dose dependent) • Psychological disorders

Hidden Food Ingredients in "ready made" food products

• Milk and milk product derivatives • Egg and egg derivatives • Peanuts, tree nuts and derivatives • Fish derivatives (surimi, fish sauce, fish paste etc) • Soy and its derivatives

Shellfish Allergies

• More likely to develop in adulthood than childhood; tend to be severe and lifelong • Symptoms usually appear within minutes to two hours of eating shellfish. - Skin reactions such as hives or eczema. - Allergic conjunctivitis: Itchy, red, watery eyes. - GI reactions such as nausea, abdominal pain, vomiting, or diarrhea. - Airways symptoms such as wheezing or coughing or runny nose. - Angioedema: Swelling of lips, tongue, or face - Anaphylaxis.

symptoms of food allergies

• Nausea • Diarrhea • Abdominal cramps • Pruritic rashes • Angioedema • Asthma/rhinitis • Vomiting • Hives • Laryngeal edema • Anaphylaxis • Exercise may exacerbates symptoms: Also, food-associated exercise-induced anaphylaxis (FAEIA)

Peanut allergies

• One of the most common food allergies • Leading cause of deadly food allergy reactions. • Shaking hands with someone who has handled peanuts, or even smelling peanuts, can produce an allergic reaction in some people. • For some people, the reaction is so severe that it causes fatal anaphylaxis.

Solutions to food allergy

• People who have food allergy need a total avoidance of the offending foods. • Read food ingredient list. • Eliminate cross-contamination during cooking and preparation!!!!

non-specific defenses

• Physical barriers (skin and mucous membrane) • Chemical barriers (saliva, mucus, gastric juices, etc) • Cellular defenses (certain cells can eat invaders-phagocytes) • Inflammation (reddening, swelling and temperature increase of the affected sites) • Fever (elevated body temperature) • Molecular defenses (interferons or complementary system etc.)

Antibodies (immunoglobulins)

• Produced by B-linfocytes (bone marrow) • Five classes of Immunoglobulins 1) IgG: Main class of antibodies in blood-also from mother-to-child (20%) 2) IgA: Small amount in blood, but larger amount in tears, milk, saliva, mucus and the lining tissues 3) IgM: First Antibody secreted during the primary response 4) IgE: Found mainly in body fluids and skin --- Associated with allergy reactions! 5) IgD: Found in B-Cell membrane

Fish Allergies

• Relatively easiest allergy to avoid!!! • Linked with the oral allergy syndrome (in which the mouth itches or tingles after eating an allergen) in people with occupational contact with fish. • The greatest risk from fish allergies is anaphylaxis: life-threatening breathing, cardiac, and gastrointestinal symptoms

Radioallergosorbent test (RAST)

• Requires blood samples • Laboratory test are performed to look if the patients has IgE against specific types of food

Soy allergies

• Soy and its derivatives are widely used in processed foods; very difficult to avoid. • Ingredients/ terms like "hydrolyzed protein," "lecithin," "texturizer," "emulsifier," "protein filler," or "extender " are soy-based.

What happens in a food allergy situation?

• The body produces a specific type of antibody called immunoglobulin E (IgE) • The binding of IgE to specific molecules present in a food triggers the immune response. • The response may be mild or in rare cases it can be associated with the severe and life-threatening reaction called anaphylaxis

allergy vs intolerance

• True Allergy-Total avoidance necessary! • Intolerance- Small amount may be tolerated

Medications for food allergy

• epinephrine (relaxes smooth muscle, constricts blood vessels, and stimulates the heart; used for severe systemic reactions-anaphylaxis); • antihistamines (block the binding of histamine to histamine receptors on target cells); • sodium cromolyn (prevents mast cells from releasing histamines).

Effects of Histamine

• smooth muscle contraction of airways; airflow to lungs restricted • increased vascular permeability: blood and immune cells cause swelling • Pruritus - itching • gastric acid secretion • increased airway mucus secretion • esophageal contraction