Allergies: Body Defenses Gone Haywire
Your dog’s body protects itself from unwelcome invaders using a fascinating, highly complex defense network of cells, tissues, organs, chemical signals and chemical reactions — otherwise known as the immune system. But as amazing as the immune system is, it sometimes makes mistakes.
Allergies are one result of an immune system that’s gone wrong. Here’s a simplified overview of what happens inside a dog’s body during an allergic reaction that results in skin issues, such as itching and hives.
What is an allergy?
An allergy occurs when the immune system misidentifies a typically harmless substance as one that’s a threat to the body and then produces an unnecessary response to that substance. Things that trigger allergic reactions — such as certain foods, dust, plant pollens or medicines — are called allergens.
Priming the immune system
White blood cells, which are part of a dog’s (and our) immune systems, make large numbers of small, Y-shaped proteins called antibodies to help protect the body from disease-causing invaders, such as viruses, bacteria and even some parasites. This process is known as sensitization, and it’s a normal immune system response to potentially harmful substances.
Veterinarians take advantage of the sensitization process when they vaccinate your dog against diseases such as parvovirus or rabies. By priming your dog’s immune system to recognize a potential health threat, his body can use those antibodies to fight potential disease-causing viruses and bacteria if exposure occurs.
Unfortunately, and for reasons we still don’t understand, the system sometimes goes a little haywire. White blood cells mistakenly make specific antibodies called immunoglobulin E (IgE) to an allergen such as plant pollen or dust, which is the first step in allergy development.
IgE antibodies bind to the surface of other white blood cells called mast cells and basophils. Mast cells are found in connective tissues, including the skin and linings of the stomach, intestines, nose, airways and lungs. Because of where they’re located in tissues, mast cells play a critical role in helping to defend the body from potential disease-causing threats. Basophils, one of the less-common types of white blood cells, are found circulating in blood. These cells can contribute to allergic reactions like mast cells and to the body’s immune response to internal parasites. Both mast cells and basophils are filled with packets, called granules, of histamine, heparin, chemical messengers and other substances that are associated with inflammation.
Remembering prior exposure
Once a dog’s immune system (by way of mast cells and basophils) has been sensitized to a particular allergen, their body “remembers” that allergen as a threat when the dog encounters it again. Mast cells with that allergen’s specific antibodies bind to the allergen, triggering the mast cells to release the contents of their granules into whatever tissue they happen to be in. Granule contents, whose normal role is to fight infection, cause the symptoms of an allergic reaction.
Histamine and other substances released by mast cells and basophils have different effects in various tissues. In skin, histamine can produce itching, redness, hives and swelling in the deep skin layers. If the reaction is prolonged, atopic dermatitis — a very itchy, chronic skin disease — may occur.
What you can do if you suspect your dog has an allergy
Talk with your veterinarian if your dog is constantly scratching, licking, chewing and biting at his skin. Because there are many possible causes for your dog’s symptoms, it’s important to have him evaluated to determine the underlying trigger. Nutrition can also help manage some allergies, so be sure to check out this post: The Right Food Can Help a Dog With Sensitive Skin.