ANW Apprenticeship Guide # 2
Dog and Cat Immunology Basics
In this Guide, you will learn the basics of your pet's Immune System, and how nutrition plays a significant role in keeping it healthy and efficient. The immune system is an incredibly complex network within our bodies that is made up of many different kinds of specialized cells, tissues, and organs that keep us safe from disease and illness. Certain foods help to make this system stronger, while others can hinder the immune system over time.
Ready to learn more about the link between your pet's immune system and its diet? Then let's begin the second lesson of the Apprenticeship!
When you think about nutrition, the immune system isn't often the first connection that comes to mind. You most likely think about fitness, food, or diet. But nutrition is so much more than that. Good nutrition is the foundation and fuel of a healthy, functioning body - and that includes our immune systems.
Dogs and cats both have very similar immune systems, though there are some distinct differences. Some of these innate immunological differences appear to be the result of different levels of domestication. Most of us are aware that dogs have been domesticated for much longer - in fact, there is evidence that dogs were domesticated around 30,000 years ago, while cats were only domesticated around ten to twelve thousand years ago.
This also accounts for the difference in communication styles between dogs and humans and cats and humans. As shown by the brilliant Patricia McConnell, Ph.D., in her book 'For the Love of a Dog’, dogs even use the same facial expressions as we do for different moods!
So, unsurprisingly, a dog's immune system is also very similar to ours Unfortunately, this is why dogs are often used in toxicology studies for human drugs, however. That being said, it means that we can learn a lot about the immune systems of both our pets and ourselves at the same time.
Critical to survival, a well-functioning immune system can mean the difference between contracting an illness or remaining healthy or recovering from an illness or not. I believe it was the Greek physician Hippocrates that was quoted as saying, "All disease begins in the gut".
Since we've already looked at the digestive part of the gut, let's take a look at some of the complex interactions that occur between different cells here that contribute to our immune defenses - and throughout the rest of the body, too.
I'll break up the Immune System, which is mind-bogglingly complex, into a few 'digestible' parts to just get you acquainted with it:
The External Defenses
Inflammation and Fever
The 'Ground Troops'
The Microbiome
The External Defenses
This is the first line of defense against parasites, bacteria, viruses, fungi, and other dangerous invaders trying to make you sick. The chemical and physical barriers on the outside of an animal - humans included - are mainly the skin, mucus, tears, saliva, and the cilia in the upper respiratory tract.
Skin is the largest organ of our bodies, and it's the barrier between pathogens and our insides. Once broken, pathogens have a pathway inside. Intact skin, even at its densest parts, is only a few millimeters thick.
Wizard's Note: The thinnest part of the skin is usually the eyelids, at about 0.05 mm thick - or roughly the thickness of a piece of copy paper.
Injured skin receives additional blood supply to increase protection and speed up healing, meaning new cells are formed to create new skin in that area.
There are three layers of skin. These are the epidermis, the dermis, and the hypodermis.
The epidermis is the layer we can see, as it's the outermost, and thinnest, layer of skin. Epi means 'outer' and Derma means skin'. The epidermis actually consists of five layers (strata) itself. These strata each perform different services for the body, such as keeping water from easily entering and leaving your body, providing flexibility and strength, providing pigmentation (color) of the skin, producing hair, new cells, and protecting your body from UV rays and pathogens.
The dermis is the next layer of skin and the thickest. It supports the overall structure of the skin with collagen and elastin - a protein that helps the tissues and organs in your body stretch, allowing movement of parts of the body such as the lungs, which inflate and deflate as you breathe, and the ligaments which connect bones and joints.
The last layer is the hypodermis, which also contains nerve endings, sweat glands, and oil glands.
Your skin is somewhat acidic, around a pH of 5 - 7, which inhibits the growth of certain bacteria. This is due to the Hydrolipid Barrier, more commonly known as the Acid Mantle. This Acid Mantle is made up of a mixture of sebum, hair, and dirt, and while it sounds gross, this protective film is what locks moisture in, and keeps bacteria and parasites out. It's also what you're removing when you bathe your dog, which is why overbathing can actually exacerbate some skin problems.
Unless recommended otherwise by a veterinarian who is familiar with your pet's special circumstances, a dog should be bathed no more than once every two weeks. A cat should only be bathed if they absolutely need it - like if they accidentally rolled around in some unpleasant organic matter...
Wizard’s Note: Exceptions make the rule - some breeds of dog or cat, like the Sphinx, for example, require more or less bathing than others!
In fact, the Acid Mantle is one of the parts of the skin that benefit from the supplementation of Omega 3 Essential Fatty Acids (or EFAs) - particularly eicosapentaenoic acid (or EPA) and docosahexaenoic acid (or DHA). Disruption of the Acid Mantle is usually the result of overbathing, using harsh chemicals on the skin, using unbalanced pH products on the skin, and - most importantly - an imbalance in the microbiomes. Altering or destroying the beneficial bacteria on our skin and in our guts affects our health in a myriad of ways. One of the most common results, for humans, of disturbing the delicate balance of acids, oils, and beneficial bacteria on the skin, is acne.
For dogs and cats, it's usually dry, flaky skin, itchy skin, redness, bumps, and dull coats. Again, dietary intervention can help tremendously in this area - and it is why we will often see shinier coats, and more supple, healthy skin when we supplement our pets' diets with a good source of EFAs.
Now, mucus, tears, and saliva protect the mouth, nose, and eyes - which are open pathways into the body. All of these bodily liquids contain enzymes called Lysozymes which catalyze the destruction of the cell wall in some bacteria (mainly gram-positive). Think of it as a microscopic cleaver - slashing through nasty little pathogenic invaders to protect your inner body from harm.
Mucociliary clearance (MCC) is the primary, innate defense mechanism of the lung and upper air pathways. The functional components of which are the Cilia, and the Mucus Membrane. Cilia (which is plural for Cilium) which line the bronchus in the lungs and the upper respiratory tract are organelles resembling little, hair-like projections that beat in what is called Metachronal Waves (MCWs). They move microbes and other debris trapped in the mucus out of your airways.
The mucus is created by goblet cells among the Cilia which secret Mucin, creating a mucous membrane that acts as a protective layer. The mucus traps smaller particles like pollen, dust, or smoke.
It is worth mentioning that other defenses the body has against pathogens include urination, defecation, vomiting, and the strong acidic juices within the stomach.
Inflammation and Fever
Inflammation, which often presents as localized swelling, hot, and often painful, is a response to damage to tissue, pathogens, or irradiation. The purpose of this is to bring more white blood cells to the area and initiate the healing process. Now, inflammation is a natural biological response and is vital to health. But prolonged inflammation has the opposite effect.
Uncontrolled, acute inflammation has the potential to become chronic and is involved in a whole host of conditions, including heart disease, diabetes, and cancer. This is because, to put it simply, inflammation over a prolonged period of time can lead to damage to the DNA and death of tissue.
In fact, it is thought that inflammation initially meant to heal is the origin of most cancer.
And fever generally develops for more serious infections, where inflammation alone is not enough. A fever essentially makes the environment (your body) too hot for the invading organism to reproduce.
Coming back around to the nutrition side of things, chronic inflammation is a major factor in why the decision to reduce the carbohydrates in your pet's diet is so important. As mentioned in my previous guide, carbohydrates = sugar. Sugar causes inflammation. A high sugar diet is absolutely a risk factor for disease up to and including cancer. And for an animal that is not meant to be ingesting carbohydrates at levels beyond 2%-15%, such as cats, the effects of a dry, high sugar diet can be detrimental in a myriad of ways that don't manifest outwardly until the damage has been building for years.
The Ground Troops
Cells are the smallest parts of the body that are capable of life, and they are constantly working to keep you alive. In the Guide Description, I mentioned specialized cells. This is because cells can specialize in the work that they do. For example, certain cells lining the intestinal tract absorb nutrients. Red Blood Cells carry oxygen. Nerve cells send electrical impulses throughout the body for intercellular communication. And adipocytes store fats.
All in all, cells can be very specialized in how they look, and in how they function. Each performs one or more tasks, and all come together in an intricate dance of life - moving our bodies along like a well-oiled machine.
And, like a well-maintained machine, if one part begins to have trouble functioning, it can increase the workload in all the other systems, eventually leading to more major issues. Similar to the game of war; first you have the battlefield. In this case, your body (or your pet's body). When faced with the threat of a foreign invasion, a healthy immune system responds very much like well-trained troops, and their job is to neutralize the invaders. The host of this body needs to supply the troops with proper nutrients to function well.
Some of these troops include neutrophils, macrophages, B cells, and T cells.
Neutrophils, a type of white blood cell, are the first line of defense once a pathogen has entered the body, and are considered the suicide squad. They make up approximately more than half of the white blood cells in our bodies and are the first cells to respond when experiencing a bacterial infection. Once there, they engulf and neutralize the invader in a process called Phagocytosis - resulting in both the destruction of the Neutrophil itself and the invader.
Wizard's Note: Neutrophils also help with the regulation of the immune response in general. They have a very short lifespan of only about 8 hours, which is why our bodies produce roughly 100 billion of these cells each day. But a specific range of neutrophils is needed to remain in your body to prevent conditions such as Neutropenia (a lack of neutrophils), or Neutrophilia (an overabundance of neutrophils). Neutrophilia can be one of the results of chronic inflammation.
Macrophages are sort of like a cleanup crew, removing the leftover bits of these invaders. They also act similarly to field medics and burial personnel.
B Cells and T Cells, put simply, are chemical warfare and identification squads. B Cells identify the bits of invaders and process the information using plasma cells to form Antibodies which will then use that information to neutralize that invader. And when Macrophages attack a pathogen the host body has seen before, they cause special immune cells called T Cells to become activated. This is what's known as Cell-Mediated Immunity (CMI). These memory T cells will become rapidly activated if they re-encounter virally infected cells. As a result, they function to protect against secondary exposures to the original viral pathogen.
All of these cells (and many, many more not mentioned here) communicate through a series of coded chemical receptors. A group of signaling proteins called Interferons, for example, are made and released by the host's cells in response to the presence of several viruses. Usually, a virus-infected cell will release these interferons, which cause nearby cells to heighten their anti-viral defenses.
Think of these coded chemicals being sent through the immune system as a sort of communication headquarters for the ground troops; relaying information as to who is invading and where they're located.
Now, the vast majority of these battles are minor, and they are pretty much continuously taking place. But, sometimes, a pathogen overcomes a host's defenses and sets up camp in their body. If our defense mechanisms are compromised by poor nutrition, stress, or even other diseases, then it becomes much easier for invaders to establish themselves.
Once established, the invader tries to alter the host's response for its own benefit. For example, instead of nourishing the immune system, amino acids (protein) are taken from the host's diet to be used by the invader. If these amino acids aren't readily available in the diet (such as a host on a plant-based diet), then the invader will take them from the muscles of the host instead, causing muscle wasting. This is also known as muscle atrophy.
These amino acids will also be used for the growth of the invader instead of the weakened host. This leaves the host to rely on fat tissue as an alternate supply of energy and is why a host may begin to waste away.
In addition, iron becomes tightly packed in storage cells by the host in an attempt to prevent the invader from using it. But if this occurs over a long period of time, the host can develop chronic anemia.
Appetite can also be affected, which of course complicates things. Valuable minerals are lost while fighting invaders and we can't win the fight if nutrients aren't absorbed to replace them. We can intervene with medicine, and/or nutrition, to shift the battle in favor of the host - but sometimes that shift is only temporary and eventually the host might lose the battle.
It's better that the host and its immune system are already in a superior position to battle, through a nutritious, digestible diet. It's clear that nutrition plays a critical role in maintaining the health of the barriers against pathogens, both internally and externally. And even when pathogens manage to get through our defenses, nutrition still helps our bodies win the fight by strengthening the immune system.
As for the Microbiome, well, that is going to need a guide all on its own.
This is why Guide # 3 will be focused on the last, but not least, part of the Immune System.
Nutritional gaps, large and small, can have major ramifications over time. One of my favorite quotes in regard to this is by Sherry A. Rogers, who states,
"The road to health is paved with good intestines!”
Now, immunology is a broad, biological field of study, dealing mainly with the immune system, and to become an Immunologist requires extensive training and education. One must obtain a BS and become very familiar with biology, chemistry, biochemistry, toxicology, and mathematics. If an Immunologist wishes to teach at University or perform scientific research, they also need to obtain a Ph.D. And even with years of higher education and study focusing on our body’s defenses and biological processes, one still won't know all there is to know about the Immune System.
As someone who has largely learned from self-study and pet nutrition programs, I am by no means an expert on Immunology, and this guide is not comprehensive. What this guide does provide is the introductory data needed solely for building your foundation in pet nutrition, and to gain an understanding of the essential and critical role of nutrition in your pet's health.
Congratulations! You’ve just completed my guide on the basics of your pet's immune system.
You should now be able to -
Explain why good nutrition is imperative for a functioning, healthy immune system.
Demystify some of the complexity involved in all of our moving parts
Feel confident in the decision to improve your pet's diet where needed
Thank you for reading, and remember - Nutrition is magic!