University of Wisconsin, Madison, Wisconsin USA
I. Can We Evaluate the Immune System?
A. Several common and uncommon skin diseases of companion animals are theorized to
involve host immunodeficiency as at least part of the pathogenesis. Evaluation of immunologic function of the patient seems to be a logical clinical step.
“Immunostimulatory” therapy has therefore been proposed for some of these diseases. However, is it possible to conduct a reasonable evaluation of a patient’s immune system?
1. Tests to evaluate antibody production
a) Quantitative Ig Determinations: One of the simplest methods for
initial evaluation of immunologic function is to measure the total concentrations of Ig in serum. Most commonly, this is performed with a radial immunodiffusion (RID) assay. This assay is typically available for IgG, IgM, and IgA in dogs, cats, and horses. “Normal values” of serum Ig concentration vary widely between individuals, over time in the same individual, with the presence of concurrent diseases, and substantial variation has been reported between results of kits from different manufacturers. Thus, the results are likely to be important only if they are dramatically and consistently lower than “normal.”
b) The most common skin disease in which Ig quantification has been
evaluated is canine recurrent pyoderma, where low serum IgA and/or IgM has been reported in some individuals. Selective IgA deficiency (the most common human primary immunodeficiency) has been reported in dogs, manifesting as chronic, recurrent respiratory and skin infections. These dogs have normal lymphocyte function and number, and normal concentrations of serum IgG and IgM, but persistent and very low IgA levels.
It is important to recognize that measuring serum total antibody levels is a very crude and inexact method of evaluating the overall immune system. When we measure serum antibody levels, we are measuring the end product of a very complex series of events involving everything to antigen recognition and processing to lymphocyte differentiation into plasma cells and immunoglobulin synthesis, and everything in between. There are an enormous number of immunologic lesions that might result in altered antibody synthesis. Importantly, therapy or the disease process itself may modify serum Ig levels as an incidental effect; the mere finding of a low serum Ig level does not prove cause and effect.
c) Vaccine Titers:
A normal animal, when injected with a routine
vaccine like canine distemper virus, mounts a strong, specific, and (hopefully) long-lasting antibody titer against the vaccine antigens. This principle can be used as another crude measure of immunologic function. A serum sample is obtained, and then a dose of a routine annual “booster” vaccination is given. A second serum sample is obtained 3 to 6 weeks later, and both samples are tested for specific antibody titer against distemper virus antigen. Many commercial laboratories now offer vaccine antigen titers. The expected result is a notable rise in the antibody titer; in the case of canine distemper virus, the average neutralizing antibody titer is typically at least 1:312 four weeks after vaccination. In some cases of immunodeficiency disease, the pre-vaccination titer will be low, and will not rise following the booster vaccination: the animal’s immune system is not responding appropriately to injection of a foreign antigen. This test provides compelling evidence of immunologic dysfunction, though the location of the immunologic lesion could be anywhere from the antigen-presenting cell forward. Not all animals with immunodeficiency will fail to mount vaccine antigen titers; for example, dogs with generalized demodicosis are reported to be normal in this regard.
2. Tests for Evaluating Cellular Immunity
a) Lymphocyte Numbers:
The simplest indication of a possible cell-
based immunologic defect is total lymphocyte count on a hemogram. In general, in an otherwise healthy animal, lymphocyte counts persistently less than 1000/µl have been taken as evidence for immunologic dysfunction, albeit anecdotally.
b) Lymphocyte Blastogenesis:
a crude measure of lymphocyte function,
is subject to numerous technical pitfalls, and is not generally available outside of an institutional setting. Nevertheless, its use has been reported in numerous canine skin diseases, including demodicosis and recurrent pyoderma.
c) Neutrophil Function Assays:
Exclusively research tools, various
techniques are available to measure aspects of neutrophil function such as chemotaxis, phagocytosis, and killing. Neutrophil function has been assessed in early studies of recurrent staphylococcal pyoderma in dogs, with conflicting results. These somewhat cumbersome techniques are so limited in availability, they are not at present suitable for widespread clinical use.
B. To summarize: some skin diseases where clinical observations suggest
immunodeficiency, experimental evidence supports its existence. Most of the time, only limited information is available in this regard, and our understanding is far from complete. Our ability to assess the many functional aspects of the tremendously complex immune system of our animal patients is, at present, crude and inexact. From a practical standpoint, the cost of performing an extensive immunologic evaluation must be balanced against the potential benefit to the patient. If we can document an immunologic deficiency, is there anything we can
do about it? In many, perhaps most cases the answer is “no” – we cannot with present technology identify the specific immunologic lesion, and even if we can, we do not have therapies that will correct the lesion.
II. Immunomodulatory Therapy in Clinical Practice
A. A variety of chemical and biological substances have been used in an attempt to
“nonspecifically stimulate” the immune system in several chronic diseases with suspected components of immunodeficiency. In the great majority of cases, such use has been entirely empirical. Many literature reports of use of immunomodulatory substances are case reports of one or two animals, or uncontrolled studies, such that the true benefit of the substance cannot be determined.
B. Is it REALLY what you should do for the patient?
1. There are countless examples of recurrent skin diseases, especially recurrent
infections, where it is well-established that there are important and common underlying causes for the recurrence, OTHER THAN “immunodeficiency.” One should be absolutely sure that there is not another reason for the recurrence before considering “immunomodulation.” Examples include:
a) Recurrent superficial pyoderma in dogs – may often be related to
b) Recurrent ear infections in dogs – always due to underlying disease
and/or mechanical factors in the ear; never documented to be related to immunosuppression!
has perhaps received the most attention and study. Its most
common current use is in human colon cancer, where its effect as an adjuvant
treatment is clearly documented by reduction in mortality rates. The mode of
action of levamisole is still not known at the biochemical level. Since the first
demonstration in 1971 that levamisole had immune-enhancing properties in Brucella
-infected mice, the overall conclusions of the 1000+ studies on its use are
a) it restores depress immune responses in animals and humans, but has little to no effects in immunologically competent individuals
b) its effects are related to its ability to improve deficient activities of macrophages and T-lymphocytes
c) numerous “immune functions” can be augmented by levamisole, including phagocytosis, chemotaxis, intracellular killing, delayed cutaneous hypersensitivity, and lymphocyte proliferation induced by antigens or mitogens
d) clinical effects are achieved only when it is used as an adjunct treatment, along with some other primary treatment
e) no one particular initially-measured immune parameter seems to be predictive for later responsiveness to the drug
f) some patients respond, and some don’t.
2. Many of the studies demonstrating an effect of levamisole
in animals are in
food animal species, perhaps reflecting its primary initial indication as a large
animal antiparasitic drug. In small animals:
a) Levamisole has been evaluated as adjunct treatment for neoplastic diseases such as canine mammary cancer and lymphosarcoma, without demonstrated effect.
b) In one study of 13 dogs with generalized demodicosis, treatment with amitraz alone was compared with amitraz in combination with levamisole. It was concluded that levamisole had an immunostimulatory effect, as measured by laboratory assays, but no clinical benefit was demonstrated.
c) In a study of cats with eosinophilic granuloma (most of which were resistant to corticosteroids), 18 cats were treated with oral levamisole at 5 mg/kg, 3 times weekly. Approximately 80% had partial to complete response, with about a 50% relapse rate once treatment was stopped. These response rates are impressive, especially given the number of cats that were treated, and suggest that immunotherapy should be re-evaluated for treatment of recalcitrant EGC.
d) Importantly, there is abundant documentation of adverse effects occurring from levamisole in companion animals!! Such effects include neurologic signs, skin eruptions, gastrointestinal upset, and thrombocytopenia.
(or doxycycline/niacinamide) in combination has
been reported effective for a variety of skin diseases.
a) The mechanism of action is not due to the anti-microbial properties of tetracyclines, but due to their multiple immunomodulatory properties, including
i. Inhibition of lymphocyte mitogenesis, neutrophil migration, and chemotaxis
ii. Inhibiiton of matrix metalloproteins such as collagenase
iii. Inhibition of angiogenesis or apoptosis
iii. Bullous dermatoses such as bullous pemphigoid or other diseases that involve the dermoepidermal junction and the basement membrane
iii. Idiopathic sterile granuloma and pyogranuloma of dogs
Tetracycline 500 mg TID (>10kg dog) or 250 mg TID (<10 kg dog)
Synergism with niacinamide, 250-500 mg BID to TID
If effective, gradually reduce frequency
is a phosphodiesterase (PDE) inhibitor that has multiple
immunomodulatory properties such as inhibiting pro-inflammatory cytokine
production and leukocyte adhesion and activation. Dosed in dogs at 10 mg/kg
orally, 2 to 3 times daily, it appears to be quite safe and without adverse effects.
a) Potential usefulness in atopic dermatitis: one controlled blinded study; dogs with AD treated for 4 weeks, scored for pruritus and erythema decreased slightly but significantly.
b) Potential usefulness in vasculitis. No studies, but mechanism of action (especially inhibition of TNF-alpha) would suggest it could be useful in conditions with known or suspected vasculitis.
5. Imiquimod (Aldara
is a topical immune response modifier with potent
antiviral and antitumor activity. Its use has been suggested for equine sarcoids,
squamous cell carcinomas of cats, and viral papillomas in dogs. Unfortunately,
the extremely high cost of this drug severely limits its use.
D. Immunomodulatory Bacterins and Biological Products
1. Staphage Lysate (SPL):
SPL, a preparation of Staphylococcus aureus
bacteria lysed by bacteriophage, was originally developed for human use, and later used for immunomodulation in recurrent canine superficial pyoderma. Its mechanism of action has, in rodent models, been shown to include both antigen-specific and nonspecific effects, and effects on cell-mediated immunity as well as antibody titers. The effects of SPL on the canine immune system are largely unstudied. Its efficacy in certain forms of recurrent superficial pyoderma in dogs has been demonstrated by controlled trial. The mechanism for such beneficial effects is not known, but appears unrelated to
augmentation of antistaphylococcal antibody production. In practice, it is sometimes used for other conditions, such as recurrent deep pyoderma, but efficacy in these other diseases has not been demonstrated by controlled trial.
a) The group of canine patients that seem to benefit from SPL are those
with “idiopathic recurrent superficial pyoderma.” These dogs have the following characteristics:
Superficial staphylococcal pyoderma lesions, pruritic or not.
COMPLETE clearing of all lesions and pruritus with use of antibiotic treatment ONLY. Every time the dog is treated with antibiotics only, he becomes normal.
Recurrence of lesions within 1 to 6 weeks after stopping antibiotics.
No underlying cause found with diagnostic evaluation – normal or negative to every test.
b) Protocol for use of SPL in canine idiopathic recurrent superficial
Begin treatment with an appropriate antibiotic, typically a cephalosporin.
At the same time, begin subcutaneous injections of SPL – 0.5 cc twice weekly. The owner can give these at home.
After 6 weeks, stop the antibiotics. At this point, the dog should be normal. Continue the injections only for another 4 to 6 weeks. Wait to see if dog relapses.
If dog relapses badly within a few weeks, the SPL will not work. There is no need to continue it for a longer period.
If the dog does not relapse, the SPL is working, and eventually the owner should try 0.5 cc once weekly, and if things go well after a few months even 0.5 cc every 2 weeks.
Some dogs may have a partial response, with a mild relapse that seems to cure by itself without the need for antibiotics.
c) Similar efficacy has recently been reported with use of autogenous
staphylococcal bacterins in dogs with pyoderma, though these may not be widely available.
2. Propionibacterium acnes bacterin: P. acnes
bacterin has a substantial
number of reports describing its use in human medicine, mostly under its former name, Corynebacterium parvum
. Early uses centered on possible
effects as an anticancer immunotherapeutic treatment, but numerous trials with doubtful or marginal efficacy statistics have seen its use dwindle over the years.
a) Its use in animals has centered on treatment of chronic infections. In a
double-blind, placebo-controlled study, 28 dogs with chronic or recurrent pyoderma were treated with antibiotics with or without intravenous P. acnes
bacterin (ImmunoRegulin). 80% of those treated with the combination improved, vs. 38% of those treated with antibiotics alone. However, the study length was only 12 weeks, and antibiotic treatment varied from dog to dog, making it difficult to draw firm conclusions.
™ (Pfizer Animal Health):
The product formerly known as
Baypamun. This biological product consists of inactivated ovine parapoxvirus. Its use as an immunomodulator has been suggested for everything from mammary tumors in dogs, to feline leukemia virus, to equine sarcoid, to furunculosis in rainbow trout. Its currently-approved indication is as and aid in reducing severity of herpesvirus respiratory infections in horses.
a) In one well-controlled study of equine sarcoid, 20 horses were injected
intralesionally with Baypamun or placebo; regression rates of about 40% occurred equally in both groups, suggesting that spontaneous regressions were responsible for improvement.
b) A placebo-controlled study of Baypamun in 120 cats with feline
leukemia virus infection failed to demonstrate a beneficial effect of the stimulant. One small study reported reduction in severity of calicivirus-induced respiratory infection in cats.
c) There is no current evidence that it has any usefulness in skin disease.
At one time, speculation also arose that IFN-alpha
could be used to treat recalcitrant feline eosinophilic granuloma complex, among other feline dermatoses, but such use has not been substantiated by controlled study.
E. In summary and conclusion, purported immunomodulatory actions of certain
drugs and bacterin products are at best incompletely documented for veterinary use. In some cases, immunologic effects have been demonstrated, but often this fails to translate to clinical benefit. When clinical benefit is demonstrated, it is usually in an uncontrolled study, making interpretation impossible. Variability of findings in well-controlled studies leads to the conclusion that clinical benefit of these agents varies substantially with the disease under study, the species under study, the stage of the disease, and other clinical factors. Further development and use of immunologic assays to objectively measure the immune response and its alteration by treatment may help clarify the situation in the future.
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