The Canine Immune System In Relation To Allergies
If the immune system fails (with an overactive, underactive, or inappropriate response), your dog is left vulnerable to disease.
In the December issue of WDJ, we discussed the dog’s complex immune system. We described what body parts and functions actually comprise the dog’s “system of immunity” and explained how this system acts to protect the dog from foreign agents including viruses, bacteria, fungi, and parasites.
The immune system helps the dog when it responds appropriately, identifying and eliminating invaders before they threaten or inhibit the dog’s health. But we also hinted that the immune system can fail to do its job, responding to invaders in three negative ways:
Hyperactively: as with allergies
Inappropriately: as when the immune system treats its own cells as invaders, causing what are called auto-immune disorders
Inadequately: as in cancers or other immune deficiency disorders
In this article, we will discuss the wide range of immune disorders, from minor to life-threatening, from common to extremely rare. While immune imbalance can often be corrected with no more effort than a change in diet, other immune disorders are far more difficult to treat.
In next month’s issue, we will discuss treatments – from both traditional and alternative medicine – that are intended to help the immune respond appropriately.
What follows are some of the more common immune ailments. Keep in mind that they are described in a general way; many disorders have numerous sub-groups, with more specific symptoms.
Humans tend to manifest allergies in our nose, throat, or eyes. With some notable exceptions, dogs generally manifest allergies in the skin. While allergies are not often as “sudden” as we sometimes believe (resulting, as they do, from a sensitivity which has escalated over time), they certainly seem sudden when our dogs begin displaying signs of distress. Common allergies most often result from immune overreaction to airborne agents which most dogs (and most people) take in biochemical stride. The most common offending agents include dust, chemicals, fleas, mites, seasonal pollens, fungi, and numerous others.
While the sources capable of stimulating these reactions are almost endless, the clinical signs in dogs are often similar: skin eruptions of varying severity and duration, and, less often, eye and ear discharges, or nasal and bronchial inflammation. Why individual dogs respond differently to the presence of allergens is not yet fully understood. What is well understood is the role of genetic transference. When both parents exhibit an allergy, there is a 75 percent chance that the offspring will exhibit that same allergy; if one parent is allergic, the likelihood drops to 50 percent.
The most dramatic – or hypersensitive – allergic reactions occur when dogs harbor elevated levels of specific IgE antibodies fixed to the white blood cells called stem cells. A dog with antibodies specific to a certain pollen, say, will exhibit an immediate response to that stimuli, while other dogs will not respond at all to that particular pollen. When that pollen enters the nasal passages of a dog with elevated IgE antibodies, white blood cells called basophils rush to the site, releasing chemicals called histamines in enormous quantities. While these histamines would be useful – even instrumental – in an immune system battle against an invader that could cause harm to the host, they are also the immediate cause of allergic inflammation. Hence, the operative nature of the over-the-counter “allergy relief” drugs you can buy at the corner store: “Anti-histamines” chemically block the release of the histamines.
When a dog is allergic to that pollen in question, the allergy almost invariably becomes permanent. For once exposed, and reactive, a dog will quickly deploy its higher caliber immune “guns.” While the classic allergic reaction involves IgE antibodies, many other complex processes are involved: Often, IgM antibodies are produced following initial exposure. A second exposure elicits IgG production, whose presence, in a broader immune context, signals the arming of a long-term immune response, as if to some infectious disease. Rabies vaccines, for example, cause the production of IgG antibodies, antibodies capable of remembering the “enemy” for years. All of which helps explain why allergic reactions tend to increase in severity over time.
Unfortunately, in the real world, few canine allergies are specifically identified. While antibody types can be identified with blood tests, the true causative agent usually remains obscure. It can take a long time, but owners can try to determine the putative allergen, sequentially eliminating dietary or other environmental factors until the culprit is circumstantially revealed. Food accounts for many allergic syndromes. Allergy-prone dogs transitioned to diets that are free of offending agents often magically transform their overall health.
More and more veterinarians are accepting the notion that “immune load” plays an integral role in a dog’s health, and many are finding that the simple reduction of stress in a dog’s life can produce amazing results. The more stresses in the “immune load” that are minimized – through improved diet, exercise, and environmental changes – the better our dogs will be able to withstand what for many becomes a lifelong scourge.
Briefly, the three main areas where a dog will manifest an allergy are the respiratory and nasal tracts, the skin, and the digestive system.
Following are some of the common canine allergies, and the signs that those allergies frequently cause.
• Allergic Rhinitis is an often-persistent inflammation of the nasal passages, caused according to the reactive tendencies of individual dogs – by any number of irritants, including pollen, mold spores, cigarette smoke, cosmetics, and many others. The symptoms are typically sneezing and/or reverse sneezing; diagnosis is based upon nasal cultures, which – in the absence of any suspect bacteria – show elevated levels of the non-specific immune soldiers known as eosinophils and neutrophils.
• Allergic bronchitis is generally associated with the same, rarely identified irritants as rhinitis. The symptoms, however, involve persistent coughing. Again, diagnosis follows the elimination of bacteria as a cause and the elevated presence of eosonophils.
• Allergic Pneumonitis is rare in healthy dogs but frequent in immune-compromised dogs. The clinical signs of the disorder include fatigue, disinterest, and labored breathing. While the disease is identified by the abnormal presence of immune cells found in culture, it is interesting to note that there seems to be a genetic connection to where these and other allergies manifest in a dog’s body. Given the same allergen, one dog might develop a rash, while another will get allergic bronchitis.
• Flea Allergy Dermatitis afflicts more dogs than any other allergy-mediated skin disorder. It is also safe to say that the flea is the catalyst for more canine skin complaints than any other single factor. While there are some 2000 flea species worldwide, only a few of those species regularly inhabit dogs. The average dog, meanwhile, would be less than overjoyed to hear that his most frequent oppressor, Ctenocephalides Felis, is also known as the cat flea.
The bite of a flea injects its saliva into the dog’s skin; the saliva contains enzymes and proteins that trigger often-escalating symptoms for susceptible dogs. When fleas bite, dogs begin to itch and scratch. In allergic dogs, that scratching can lead to secondary bacterial infections, as well as elevated lesions and localized hair loss. For allergic dogs, of course, fleas can bring a lifetime of seasonal misery.
• Pyotraumatic Dermatitis, or “hot spot,” is a malady closely associated with flea allergy, but is actually a secondary bacterial infection caused by the classic itch/scratch flea syndrome. Symptoms include red, often discharging areas of thickened skin, which, if left untreated, can become a harrowing obsession for the afflicted dog.
• Demodicosis, or mange, is caused by an overpopulation of the mites which normally live in canine hair follicles (not to mention human hair follicles). Mange develops when skin-dwelling immune cells fail to keep the mite population in check. While a number of breeds are genetically unresistent to the mange mite (and therefore, prone to the disease known as mange), it is also typically seen in immune-suppressed dogs.
• Allergies that manifest in the digestive system include Allergic Gastritis and Allergic Enteritis. Both are caused by allergies to foods or other ingested substances. The difficulty in diagnosing these syndromes accurately lies in the fact that digestive problems can be the result of a true allergy (involving IgE-mediated hypersensitivities or non-IgE-mediated immune mechanisms) OR other abnormal physiological responses, often called “food intolerences.” This latter term is often confused with “food allergies,” but is actually meant to convey metabolic, pharmacological, or toxic responses – not allergies.
To further confuse matters, it should be noted that true food allergies can manifest themselves in the digestive tract OR the skin, respiratory tract, central nervous system, or any combination of these systems. In the end, it’s really not necessary to distinguish between food allergies and food intolerences; the important thing is to identify and eliminate the food that causes the problem.
This, the second major category of ways that the immune system can fail, include all the syndromes in which the immune system “attacks” some element of the dog’s own body.
For the most part, the immune system does not react to the body tissues it is meant to protect; the various immune cells recognize and eliminate only “non-self” cells. Disease arises, however, when the immune system fails to maintain this equilibrium. It is generally thought that this crucial self-tolerance develops early in fetal development, but that, for unknown reasons, certain normal cells sometimes remain hidden during the fetal stage, in what are called immunologically privileged sites. The result can be, under certain circumstances, that those normal cells are later seen as invaders by the cells of the immune system.
However, predisposed individuals do not always acquire the autoimmune disease to which they are genetically prone. There is much evidence that a number of other factors are also in play, and that only chance combinations of these factors trigger disease. While the precise cause of disease in an individual dog cannot yet be decisively established, it is known that genetics play an important role.
Yet genetic proclivities can be weak or strong. In mildly predisposed dogs, stress can play an important role. Stress and trauma release hormones and other neuro-messengers which can play a dramatic role in disease onset. Also, there is no longer any doubt about the association between auto-immune disease and exposure to chemicals and drugs. (We’ll discuss this further in next month’s article about ways to optimize your dog’s immune function.) Some of the common canine auto-immune diseases are described below:
• Autoimmune Hemolytic Anemia. In this common (and sometimes fatal) canine disease, auto-antibodies (antibodies reacting against the dog itself) cause the destruction of red blood cells, resulting in anemia. In simplest terms, a cellular miscommunication causes healthy red blood cells to be marked for destruction by the normally protective cells of the immune system. Left untreated, this leads to lethargy, labored breathing (since red blood cells that carry oxygen are in short supply) and ultimately signs of dementia such as loss of balance, personality changes, etc.
• Arthritis. There are a number of auto-immune arthritic conditions that beset dogs, too numerous to detail here. In general, arthritis is caused when antigens and antibodies, failing to react in the normal way, join in a cellular structure which migrates into various joints. These immune complexes, in turn, chemically summon other immune cells, which together cause long-term and often debilitating inflammation. The various arthritic conditions – as is true of auto-immunity in general – tend to afflict certain breeds more than others.
• Systemic Lupus Erythematosus. In its most severe form in humans, lupus can launch an attack on seemingly every body system, thus explaining its reputation as the “classic” immune disorder. For most dogs, however, especially with early intervention, the results are less serious than in humans. It is thought that viruses might play a triggering role in the disease, particularly for genetically susceptible dogs. In addition, sunlight tends to aggravate symptoms.
The disease is characterized by the fact that many immune players cease normal functioning, compromising even the DNA in cell nuclei. Somehow, regulatory T-cells induce the sustained overreaction of B-cell antibodies in a dog’s kidneys, joints, or skin. The disease tends to wax and wane, but the first onset of the disease is often the most severe.
Clinical signs often include skin lesions and ulcers on the face and legs, and swollen lymph nodes. In Discoid Lupus Erythematosus, the symptoms are generally limited to the face, and often just the nose, accounting for its common name: Collie Nose. Suspected lupus cases are conclusively diagnosed with a test isolating the hyperactive antibodies in cell nuclei.
Immune deficient disorders
As the term implies, with immune deficient disorders, the immune system fails to work as aggressively as it needs to, or fails to respond to invading pathogens at all. Some of the most common immune deficient disorders include:
• Cancer. Cancers are not generally listed with immune deficiency disorders, but they, too, are caused when the immune system fails to recognize and control abnormal cell growth. Cancer tumor cells often closely mimic the healthy cells from which they mutated. The relentless and often unstoppable disease called cancer occurs when, presented with this recognition challenge, the immune system fails to identify and “kill” the abnormal cells.
While dogs are subject to more than 100 types of cancer, it is far more common in older dogs. Some 50 percent of all dogs over 10 years of age will die of cancer, directly or indirectly, and there is little doubt that geriatric cancer results from the fact that the immune system becomes less and less vigilant with advancing age.
• Canine Granulocytopathy Syndrome. With cancer, immune deficiency is, in a sense, the disease itself. In classic immune deficiency disorders, immune dysfunction is the catalyst, rendering the host defenseless against routine microbial attacks that a healthy dog would easily defeat. One of these rare diseases, which is known to attack only Irish Setters, is called Canine Granulocytopathy Syndrome. In this disorder, neutrophils (the all-purpose infantry of the non-specific immune system) cease to function effectively, for unknown reasons. As a result, any bacterial invasion becomes life-threatening.
• Selective IgA Deficiency. In this syndrome, the antibodies which defend the “mucosal immune system” die out, for unknown reasons, and are not replaced in quantities sufficient to protect the dog against respiratory infection.
• Cyclic Hematopoiesis of Gray Collies. This is another incredibly specific failure of the immune system. Here, the bone marrow’s blood cell-production shuts down at irregular, and perhaps stress-related intervals. This creates cyclic deficiencies of the white blood cells that are critical to immune system function. The dog is left completely vulnerable to infection until the immune system somehow “reboots” itself.
This has been a highly abbreviated account of the immune dysfunctions that can befall a dog. Needless to say, owners are well advised to educate themselves about immune disorders in general, and breed-favoring disorders in particular. Breed clubs and web sites are an excellent place to start. Such knowledge encourages proactive care, as your veterinarian may not be familiar with the specific immune disorder afflicting your dog.
In next month’s issue, we will look at the wide world of treatment. In the traditional Western medical world, steroids are the drugs of choice for a wide range of immune disorders. In holistic medicine, treatments strive toward immune empowerment, enabling the immune system to function as intended, controlling immune disorders at the source, even when that source is not clearly understood. As always, it is critically important to understand what you are fighting, and then avail yourself of the widest range of safe and effective treatments possible in order to do the most good for your canine companion.
-By Roger Govier
Roger Govier is a freelance writer from San Francisco. A dedicated owner of two shelter “mutts,” Govier has prepared articles on many of WDJ’s toughest topics, from cancer to vaccinations.