Quick Immunology Lesson
The immune system is an amazingly complicated defense system that our body uses to keep us healthy. It uses several strategies to locate and destroy harmful substances such as bacteria and germs. One way that it does this is to create immunoglobulins (Ig) that locate these substances. One type of immunoglobulin, IgE, can actually attach itself to other immune cells (called mast cells and basophils), which allows those cells to detect proteins in harmful substances and then release chemicals (histamines) to attack it. IgE antibodies hang out all over the body, always on the look out for dangerous proteins. Food is made of various components (sugars, fats, etc), including proteins. Sometimes the IgE molecules will get confused and start to recognize the proteins in food as possibly harmful. Once the mast cells are told that there is a problem, they start to attack, no questions asked. This type of reaction to food is called an IgE-mediated allergy.
As I mentioned above, immunoglobulins are only one of the tools that the immune system uses to keep us healthy. T-cells are also helpful in identifying dangerous proteins and initiating a response. When T-cells detect a problem they may send out pro-inflammatory cytokines, which cause eosinophils to start an inflammatory response, releasing chemicals to destroy the dangerous protein and resulting in swelling, itching, and irritation. The inflammatory response can occur wherever the proteins are discovered in the body – on the skin, nose, lungs, GI tract, etc. These are referred to as non-IgE-mediated responses. T-cells, by the way, can also initiate an increase in production of IgE antibodies, causing an IgE-mediated response instead of, or in addition to, the non-IgE-mediated response.
Most of the time when people talk about food allergies they are referring to IgE-mediated allergies. These are the allergies that usually have a fast onset and can be severe and systemic, dramatically affecting the whole body. IgE allergies can lead to anaphylaxis (hives, difficulty breathing, etc.) and sometimes require the use of epinephrine (i.e., an epipen). About 90% of IgE food allergies are attributed to “The Top 8” Allergens: cow’s milk, egg, peanut, tree nut, soy, wheat, fish, and shellfish. Diagnosis is fairly straightforward and can usually be determined with a scratch test or blood test.
Food Protein-Induced Enterocolitis Syndrome (FPIES)
Food Protein-Induced Enterocolitis Syndrome (FPIES) is a rare type of non-IgE-mediated food allergy that primarily affects the GI tract. The onset is usually much slower, occurring about 2.5 hours after ingesting a food protein. The symptoms include vomiting, diarrhea, weakness, poor circulation and can lead to dehydration and shock. Sometimes IV fluids and steroids are necessary to treat the reaction. The most common FPIES triggers are milk, soy, rice, and oat. Symptoms can be chronic (lasting for several days) or acute (short-term). Diagnosis is very difficult because there are no tests that accurately and reliably diagnose. The only way to know for sure is to conduct an oral food challenge, during which the child is given the food and then observed for a reaction. The good news is that many children outgrow FPIES by age 3.
*Most of this information was from “Understanding and Managing Your Child’s Food Allergies” By Scott H. Sicherer, MD. You can also find great information and resources from the FPIES Foundation and International Association for Food Protein Enterocolitis.