The immune system is a complex and intricate collection of cells, tissues and organs that work together with one basic goal in mind: to defend the body from foreign invaders. How this system functions is far beyond the scope of this program and it would be fair to say that despite all we know of the immune system, we still understand very little. As this program is concerned more with abnormal conditions and their treatment, it will be sufficient to say that, at times, this complex system does not perfectly perform its functions and disease results.

For this discussion, there are four basic types of immune-mediated diseases: Hypersensitivity disorders which include allergic type reactions; Autoimmune Disease wherein the immune system attacks the normal tissues of the individual; Immune Complex Disease which occurs most commonly as antibodies in clumps become deposited in friendly tissues and cause an inflammatory response; and Immunodeficiency Disease where the body fails to produce needed levels of protection. Some veterinarians will classify Immune Complex Disease as a Hypersensitivity disorder, but for clarity, we have separated these in this work.

Hypersensitivity disorders can best be thought of as an exaggerated or excessive response by the body to foreign stimuli. In other words, the system is trying to do its job in defending the body, but goes a bit too far. The common hypersensitivity disorders include Angioedema and Urticaria, Atopic Dermatitis, Contact Hypersensitivity, Food Allergy, Flea Allergic Dermatitis and Miscellaneous Allergic Reactions.

Angioedema is most often characterized by sudden swelling of an area, often the face, when fluid leaks out of the blood vessels into the surrounding tissues. (edema) The cat may or may not seem itchy, but many times will scratch at the area or rub the face on the floor. The swelling may come on quickly and progress rather rapidly. ((Swollen Face))

Urticaria can best be thought of as "hives", more properly called wheals, or little bumps or swellings that occur in various locations on the skin. These too will appear suddenly and may persist for some time, or seem to disappear and reappear again. These hives may or may not be itchy for the cat.

Sudden reactions to insect bites and inhaled pollens are considered the usual initiating factors, but reactions to foods, bacteria, chemicals, drugs, vaccinations and parasites among others can set these reactions into full swing. Both conditions may be very irritating to your pet and angioedema can be life threatening if swelling of the throat or fluid leakage into the lungs occurs. Diagnosis is based on history and obvious clinical signs. This condition is quite rare in the cat as compared to the dog.

Rapid attention in all cases of angioedema is advised, as it is difficult to determine which reactions will become life threatening and which will not. All cases should be treated to comfort the cat. The use of injectable cortisone, epinephrine and antihistamines will quickly reverse the reaction, with a few days of cortisone and/or an antihistamine often used to prevent immediate recurrence. If a cat has had a reaction to a bite or vaccination, this does not mean that this reaction will occur again, as these tend to be sporadic and unpredictable reactions.

Atopy is the second most common form of allergic reaction, producing the usual symptoms of "allergies" in the cat. Some cat breeds seem to be more prone to Atopy but all breeds can be affected. Cats with allergies will usually start showing symptoms between 1-3 years of age, but symptoms can begin any time, at any age and without prior history of such.

Allergic Dermatitis is caused when an allergen is inhaled or otherwise absorbed into the body and an allergic reaction begins. The most outstanding clinical sign will be that of pruritus, which is the medical term for itching! Cats with allergic dermatitis, however, can have very different skin lesions. Some will lick away hair in areas, others will develop lesions consistent with eosinophilic granuloma complex; some will have miliary dermatitis and some will have itching of the face, neck and ears without skin lesions. While this pruritus is the main clinical sign, as the cat scratches, rubs or licks the areas involved, hair loss, skin infections, redness or seborrhea may occur as secondary problems. This type of allergy may also be seasonal or nonseasonal, depending upon what the cat is allergic to.

Some cats will exhibit non-dermatologic symptoms including sneezing, trouble breathing, coughing, conjunctivitis and ceruminous otitis, but these are less common and will more likely be in conjunction with obvious skin disease. It is important to note that not all cats will have all the symptoms or areas affected, there may be combinations of the above described lesions and often itching is passed off by the owner until secondary problems due to self trauma, such as a skin infection, become more apparent. Diagnosis is based on the clinical signs, history, the use of intradermal skin testing, RAST testing and skin biopsy. Other conditions causing itching should be carefully ruled out.

Ideally, avoiding whatever the cat is allergic to would solve the problem. Practically, unless your veterinarian does the more extensive testing, you will only be able to guess at the cause, making avoidance very difficult. Also, with the allergens most often being airborne and inhaled, the practicality of such a plan is poor.

The use of prednisolone or triamcinolone, steroidal drugs, is most often employed. The doctor will often give an injection first, then follow up with oral medication. These drugs work best because they not only stop the allergic reaction, but they relieve the skin inflammation and thusly, the itching. For long term use, however, these drugs should be avoided or restricted to avoid side effects.

Antihistamines can be used, but their effect is minimal in feline allergies and should be considered helper drugs. Fatty acid supplements such as Derm Caps and EFA Cap and special non-allergenic diets are also useful. These can sometimes provide moderate relief without all the effects of cortisone. Your veterinarian will provide several suggestions for these and you should expect to have a trial period of 60-120 days to be able to determine how useful this type of therapy can be.

Medicated shampoos, antibiotics and other treatments may be needed if secondary skin disease and self-trauma have occurred. If your cat has been allergy tested and the offending substances identified, hyposensitization therapy can be undertaken. This involves giving injections from a series of treatment solutions designed to meet your cat's allergy profile for a period of several months, then on a regular basis to maintain the effect. This treatment often works well, but is not without possible complications including total failure or an exacerbation of the allergic symptoms.

Contact allergy is very rare. People often think their cat became itchy from touching the grass or carpet, when in reality, if an allergic reaction is occurring, it is most probably atopic. Contact allergy has been reported after contact with certain plants, topical medications, chemicals, chlorine and materials found in the home such as food bowls and fabrics.

Clinical signs include skin irritation between the toes, on the chest and abdomen, chin, groin and genital areas. The amount of itching will vary greatly and secondary redness, small bumps forming in the area, changes in pigmentation and crusting of the skin may also all be present. Careful history, physical exam and testing to rule out other skin diseases are essential for diagnosis. A "patch" test is the only reliable and definitive test, but is rarely undertaken due to difficulty with the actual procedure. Histopathology may also be useful in these cases.

Injectable and oral prednisolone or triamcinolone is often very effective. Most cats will respond well and quickly return to normal. Antibiotics and shampoos may be needed if secondary problems are present. Avoidance of the allergen(s) in question, if identified, is the best form of therapy.

Food allergy is uncommon, but it can cause significant pruritic (itchy) dermatitis in the cat, most often of the face, head, ears and neck. Allergens in food also seem to enhance cases of atopic dermatitis. Any cat can be affected, even from food they have eaten for long periods of time, with the problem usually being nonseasonal. Food allergy may also be confused with other skin problems and some veterinarians may be slow to consider it in making a diagnosis.

Clinical signs will include itching, but hives, redness, crusting and scaling may also occur to variable degrees. There is, however, no classical case of food allergic dermatitis. As for cats with atopy, food allergic cats may show one or combinations of the following patterns of skin disease: hair loss due to licking, miliary dermatitis and eosinophilic granuloma complex. If the itching is treated with cortisone, though, most cats will not respond as well as if they had simple atopic dermatitis and this may be a clue in diagnosis. Often pruritus of the ears, seborrhea and diarrhea and/or vomiting will concurrently be present. Some cats will develop lymphocytic/plasmacytic enteritis.

Diagnosis is based on history, clinical signs, ruling out other diseases, evaluation of the response to prednisolone therapy and allergy testing. Most often, diagnosis will be based on a therapeutic trial with a special diet over a period of time. Several special diets are now available through your veterinarian, but the process may indeed be one of trial and error. A cat needs to be on the special food for at least ninety days to determine if the desired response will be had.

After a determination has been made that your cat has food allergy and by trial and error, a diet has been selected, long-term use of the special food and avoidance of other treats and table foods can be very effective. The use of prednisolone or antihistamines may help in more difficult cases. Some owners and veterinarians prefer to improvise homemade diets and if so, special care needs to be given to formulation to insure essential nutrients are not omitted.

Fleas in and of themselves cause a very itchy bite. When they bite, a small amount of flea saliva is secreted under the skin and in some cats, will cause a very intense allergic reaction. Any cat can be affected and in some cases where multiple cats are in an area and have fleas, only one will develop an allergic reaction to the flea saliva. Flea allergic dermatitis is the most common allergic-type skin disease in the cat.

Clinical signs include the presence of fleas, extreme and intense itching, redness of the skin, loss of hair often on the back, rump, neck and flank areas and secondary infections of the skin. Most often, cats exhibit the miliary dermatitis pattern, but may also develop self-induced hair loss or the eosinophilic granuloma complex lesions. A crusty, scaly dermatitis with a fetid odor can occur later in the course of the disease. ((FAD))

Diagnosis is based on these clinical signs and finding the fleas or evidence of their presence (flea dirt etc.). A specific flea allergen test is available and may be advised in some circumstances. Most of the time, with these signs and finding the flea, the diagnosis will be flea allergic dermatitis until proven otherwise. Cats with FAD may also have atopy and food allergies which all the more so makes diagnosis difficult.

Control of the Flea, like any other form of avoidance therapy, is paramount to solving this condition. As only one fleabite can trigger major clinical signs in the allergic cat, even the smallest infestation can cause the biggest of problems for the cat. This means that environmental extermination should take top priority in the treatment program.

The use of prednisolone or triamcinolone, first as an injection and then orally, is very effective in curbing the allergic reaction, but oral medication must be used until all fleabites have stopped. Antihistamines, medicated shampoos and fatty acid supplements can all be used to speed healing and antibiotics may be needed of secondary infections have occurred.

Cases where cats bitten by mosquitoes and a few other flying/stinging insects develop allergic skin disease have been seen. Usually the head and neck are bitten and affected. Clinical signs include itching of the head, face, nose, footpads and ears; red raw areas, crusting and in some cases loss of hair, pigment and frank ulceration of the skin. Diagnosis is based on history of exposure and clinical signs. (skin lesions)

Most cats respond well to cortisone type drugs and avoidance of insects if possible. Do not use DEET or other insect repellents, as these can be toxic to cats.

Hypersensitivities to drugs, a cat's own hormones, sarcoptic mange, ticks, internal parasites, ear mites, heartworms, bacteria and fungi have all been reported. While most of these conditions are rare, it is important to note that allergic reactions can happen against a wide variety of causes. Although these are rare conditions and not a typical diagnosis, they may be suspect in cases where drug administration is present or parasitic disease has been diagnosed. Clinical signs will always include some degree of itching, with secondary areas of infection, crusting and hair loss. Diagnosis depends highly on historical information and related diagnosis.

Diagnosis of the primary problem and treatment of that will do the most to relieve the clinical signs. Antibiotics, removal of drug therapy and parasitic dips are appropriate for their specific conditions. Prednisolone or triamcinolone, antihistamines and medicated shampoos are commonly employed to soothe and heal the skin.

Autoimmune disease can literally be thought of as the body attacking itself. This is a rare occurrence which may be due to a loss of "self-tolerance", for reasons poorly understood, or it may occur secondarily as the body is trying to attack a foreign invader but mistakenly starts producing immunity to normal body cells. This type of reaction is seen commonly in cats with autoimmune hemolytic anemia, a destruction of blood cells by antibodies in the system. These processes are still poorly understood as science is just now beginning to explore and understand the immune system.

Pemphigus involves a set of diseases whereby antibodies have been formed against skin cells. These conditions are rare and are characterized by cracks, blisters and ulcers of the skin.

PEMPHIGUS FOLIACEUS is the most common form of the disease seen in cats. It is highly variable on how it will appear, how severe it will become and how uncomfortable the patient will be. Most cats will develop the disease before the age of 5, having had several years' history of pruritic skin disease. The skin on the nose, face, ears, feet, abdomen and groin is most commonly involved, but in a few cases may progress to cover larger areas of the body. The disease begins as small red spots that turn into pustules, (swellings that contain pus) and then rupture and turn crusty. Cats usually have a decreased appetite and enlarged lymph nodes. The degree of itching is variable.

Several other variations exist:

PEMPHIGUS ERYTHEMATOSUS is considered a mild or more benign form of pemphigus foliaceus seen as red, raw pustules on the face and ears and is quite rare.

PEMPHIGUS VULGARIS is very rare. Clinical signs include blisters and ulcers of the lips, eyelids, ears, nose, genital areas and anus. Most cats will have lesions on the mouth and lips and may have a foul oral odor and salivation. These cases are difficult to treat.

Diagnosis of this complex of diseases is based on history, clinical signs, cytology of exudates, cultures and blood testing. The most important diagnostic test is performing a skin biopsy followed by special pathologic testing.

Early and aggressive treatment with prednisolone is considered the mainstay of therapy, but therapy should be based and extended in correlation with the severity of the lesions and the discomfort of the feline. Other treatments include the use of aurothioglucose, a gold salt, azathioprine and cytoxan. All these medications including prednisolone can have side effects so careful patient monitoring by your veterinarian is very important. Antibiotics and medicated shampoos are also used to treat secondary infections and soothe and cleanse the skin.

This disease is characterized by a sudden and often devastating destruction of red blood cells within the circulatory system. It is caused when antibodies attach to the surface of red blood cells and trigger their destruction. AIHA can occur in any cat but feline leukemia, hemobartonellosis, FIP and chronic fight abscesses may all play some role in initiating the disease. Rarely will cat owners recognize their cat as having blood destruction occurring. Symptoms include fever, weakness, lethargy and poor appetite. Some cats will vomit and/or have diarrhea; icterus (yellow gums/sclera) may be noted and/or the gums may seem quite pale. Rarely will cats bleed outwardly.

It is possible to have a hemolytic anemia that is not immune-mediated. Drugs, chemicals, plant poisons, cancers, hemobartonellosis and metabolic disease can all lead to blood destruction and the symptoms previously described. Other than the initiating cause being different, the clinical signs, diagnosis and treatment will all be the same as for cats with actual immune-mediated blood destruction.

Diagnosis will be based on history, physical exam where the doctor may also detect an enlarged spleen or liver, rapid heart and respiration rates, as well as blood tests including blood counts, serum chemistry, urinalysis and special testing to detect the enemy antibodies, known as a Coombs test. The disease may be seen concurrently with immune-mediated thrombocytopenia and SLE or secondary to parasitic blood disorders such as hemobartonellosis, so diagnosis should be thorough as to not miss these other problems.

The first goal of treatment is to stop further red cell destruction and stabilize the patient. Most cats will need hospitalization with intravenous fluid administration. Intravenous steroids will be injected, then oral steroids thereafter. Cimetidine is also given to help prevent gastric ulceration due to the steroids. Danazol can also be used but the cost is somewhat high. Cyclophosphamide, an immunosuppressive drug, is employed in some cases. Blood transfusions are given to some cats, but these should be reserved for cases where blood counts have dropped to dangerous levels. Removal of the spleen is also performed on occasion, but this too should be approached with caution.

If treatment is started early and there are few systemic side effects, the prognosis can be quite good, even in the long term. If organ damage or other immune mediated disease is present, the prognosis is then somewhat poor. Some cats can be put into complete remission and live a very normal life.

This disease is very similar to autoimmune hemolytic anemia, except those antibodies attack the platelets, the blood clotting cells in the circulation. It is most commonly seen in cats with AIHA, SLE or early neoplastic diseases. (cancers) Clinical signs of this disease are generally vague and include lethargy, loss of appetite and weight loss. Black, tarry stools, small hemorrhagic spots on the gums or skin and possibly spitting up blood or passing blood in the urine can occur in rare cases. Diagnosis is made from physical findings, blood counts, serum chemistries, urinalysis, special tests to measure how the blood clots and taking a biopsy the bone marrow.

Treatment initially is similar to that of autoimmune hemolytic anemia: hospitalization with intravenous fluid administration, intravenous steroids, then oral steroids thereafter and administration of cimetidine and danazol. The use of a drug called vincristine with or without a platelet transfusion may also be helpful. Splenectomy may be performed but should be reserved for refractory cases.

Neonatal isoerythrolysis literally defines blood destruction in very young kittens. It occurs when newborn kittens with type A blood are born to queens with type B blood. (there are only these two blood types known in cats) As these kittens drink the mother's milk, which can contain antibodies against type A blood, the antibodies cause hemolytic anemia once they are within the kittens' circulation. Clinical signs include kitten deaths 1-2 days after birth, dark colored urine, weakness and a failure to nurse. Diagnosis is based on history, clinical signs, urinalysis and blood typing.

Affected kittens should be removed from the mother immediately and bottle-fed or nursed by another queen. They could, however, be put back on their true mother 3-4 days after birth as no further antibody absorption can occur after this time. Blood transfusions may also be needed despite the obvious difficulty in doing so. Unfortunately most kittens with this condition will die.

Several other diseases have been described where the immune system attacks specific organs and often produces disorders specific to malfunction of that organ and not specific for immune disease. These include immune-mediated hypothyroidism, diabetes mellitus, polymyositis, myasthenia gravis causing weakness as the immune system attacks the nervous system and conjunctivitis, meningitis and orchitis among others.

Immune complex diseases are caused as groups or clumps of antibodies are deposited in certain tissues and inflammation occurs in those tissues or organs.

SLE is a rare, difficult disease to diagnose because so many differing and variable clinical symptoms can occur, often resembling some other disease condition. Antibody-antigen complexes (large protein clumps) are formed in these cats and deposited in certain tissues causing inflammation and dysfunction. The joints, kidneys, skin and blood cells are most commonly affected. Clinical signs include arthritis in multiple joints, manifested as lameness; sore muscles, itching, redness and ulcers of the skin and mouth, fever, weight loss, lymph node enlargement, seizures and symptoms related to glomerulonephritis, hemolytic anemia and immune-mediated thrombocytopenia. To reiterate, there is no specific or single group of symptoms that characterize this disease.

Diagnosis is challenging to say the least. Besides history and clinical signs, blood counts, serum chemistries, urinalysis and special tests for immune mediated diseases, including SLE should be performed. Skin biopsy may be useful if lesions of the skin are present. Hopefully the veterinarian will have an instinctive feel that SLE may be the primary condition and search accordingly.

Treatment success for SLE is also variable and unpredictable and will most often depend on the severity of the disease at the time of diagnosis. Otherwise, treatment is similar to that of other immune mediated diseases: oral prednisolone in high doses to start with the use of azathioprine or chlorambucil if that proves unsatisfactory. Management of secondary infections or hemolytic anemia will also be needed if these are present concurrently. The response to therapy will vary, some cats living long term in remission, others dead or euthanised due to complications and relapses in less than a year.

Discoid lupus seems to be a benign localized form of SLE. Most cats exhibit loss of pigment from the nose, localized inflammation followed by crusting and scaling. The area may appear quite red and raw. Later, erosions and ulceration of the nose and nearby skin will be noted. Involvement of other body systems does not occur. The condition will occur more often in outdoor cats secondary to exposure to UV light. A few new cases discovered may indicate that this condition also occurs on the trunk of cats but there are too few cases to form a good database.

All cases will benefit by keeping the cat out of the sun. Sunscreens applied to the nose and/or cortisone creams also seem to be of benefit. Oral vitamin E (only as directed by a veterinarian) and prednisolone will in most cases be effective over the long term.

Glomerulonephritis occurs when the body produces antibodies that attack the glomerulus, or when complexes (large clumps) of antibodies get deposited in and damage the glomerulus. This alters the functional ability of the nephron leading to loss of protein in the urine, a decrease in protein in the blood, an increase in blood cholesterol and fluid collecting in areas of the body (edema). Progressive kidney damage usually occurs leading to renal failure.

While some cases occur for no apparent reason, other cats will be found to have glomerulonephritis secondary to feline leukemia virus, feline infectious peritonitis, FIV, mycoplasma infections, SLE, pancreatitis, chronic progressive polyarthritis, tumors of the blood system, lymphosarcoma, mercury toxicity and inherited disease.

Clinical signs most often occur in cats under four years of age and include a poor appetite, loss of weight, swelling of the limbs and fluid collection in the abdomen, legs and possibly the lungs. If renal failure occurs, those clinical signs also occur and most cats will die. Diagnosis is based on these signs, blood and urine tests and a biopsy of the kidney.

Amyloid is a protein-sugar mixture that has a long, fibrous appearance, often produced secondary to other bodily infections. This amyloid is deposited in the glomerulus just as the immune complexes are in glomerulonephritis. This alters the functional ability of the nephron leading to loss of protein in the urine, a decrease of protein in the blood, an increase in blood cholesterol and fluid collecting in areas of the body (edema). Progressive kidney damage usually occurs leading to renal failure. This condition is quite rare in cats excepting the Abyssinian breed, which seems to have a genetic defect causing the condition.

The condition is rare in cats. Clinical signs include loss of weight, increased thirst, lethargy, swelling of the limbs, a poor haircoat and fluid collection in the abdomen, legs and lungs. If renal failure occurs, those clinical signs also occur and most cats will die. Diagnosis is based on these signs, blood and urine tests and a biopsy of the kidney.

There is no known cure for these conditions. An attempt to find any underlying cause is very important. Certain strong immunosuppressive drugs and cortisone are used but the success rate is not high. Management of renal failure, control of the protein in the diet, the use of diuretics to help remove fluid from the extremities and abdomen and identification and control of any other diseases present will be supportive for these cats.

Some cats with these problems will do quite well; others will quickly progress and die despite treatment.

VASCULITIS, inflammation of the blood vessels, can occur when immune complexes are deposited on the walls of veins and arteries. Clinical signs can be similar to SLE, or can also include small hemorrhagic spots on the skin, ulcers and symptoms similar to urticaria. The condition is rare and diagnosis is based on physical examination, blood and urine tests, biopsy of affected areas and special serological tests. Treatment is similar to that for pemphigus.

There are two basic classifications of immunodeficiency disease: primary or congenital, meaning belonging to the cat, often genetic; secondary or acquired, meaning caused by something else. In general, immunodeficiency disease makes a cat more susceptible to infections.

The most common primary immunodeficiencies are the Pelger-Huët anomaly which causes a defect in certain white blood cells and the Chédiak-Higashi syndrome of Persian cats which includes white blood cell changes, increased susceptibility to infection, bleeding problems and haircoat paleness. Symptomatic treatment is all that can be done for any of these two syndromes.

Secondary immunodeficiency or immunosuppression has been well documented to be caused by infectious organisms including feline leukemia, FIV and feline panleukopenia. Kittens which fail to receive adequate colostrum, antibodies transferred from mother to kittens in the milk, will be more susceptible to disease for their first 2-3 months of life until their own immune system begins working. Drugs and endocrine diseases can also lead to immunodeficiency problems.

Progressive polyarthritis is a disease characterized by joint damage in young or older cats. While this is considered an immune mediated disease, there may be a link to feline leukemia virus and its relative, Feline Syncytia-Forming Virus. (FeSFV) All cats with the disease have been found to be positive for FeSFV and over 60% are positive for FeLV. Immune complexes (clumps of antibodies and antigens) related to these viruses seem to be involved with causing the damage related to the disease.

There are two classifications of the disease; a surface inflammation of the bones and joints most common in young male cats and severe joint deformity most often seen in older cats. Besides damage and inflammation of multiple joints which gets worse over time (hence the name), clinical signs include fever, weight loss, loss of appetite, muscle wasting, lameness and joint swelling. Diagnosis is based on history, clinical signs, physical examination, X-rays, joint fluid cytology, blood counts and serum chemistries. Most cats get worse with time but can be maintained with early and aggressive therapy.

Cats positive for feline leukemia will often respond poorly to treatment. FeLV negative cats can do well on prednisolone therapy alone or combined with azathioprine and cyclophosphamide. Adequan, Cosequin or Synovi-Cre may also be helpful but little research has been done as to their effectiveness.

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