The role of pro- and anti-inflammatory cytokines in the pathogenesis of spontaneous canine CNS diseases

Dogs are comparatively frequently affected by various spontaneously occurring inflammatory and degenerative central nervous system (CNS) conditions, and immunopathological processes are a hallmark of the associated neuropathology. Due to the low regenerative capacity of the CNS a sophisticated understanding of the underlying molecular basis for disease initiation, progression and remission in canine CNS diseases represents a prerequisite for the development of novel therapeutical approaches. In addition, as many spontaneous canine CNS diseases share striking similarities with their human counterpart, knowledge about the immune pathogenesis may in part be translated for a better understanding of certain human diseases. In addition to cytokine-driven differentiation of peripheral leukocytes including different subsets of T cells recent research suggests a pivotal role of these mediators also in phenotype polarization of resident glial cells. Cytokines thus represent the key mediators of the local and systemic immune response in CNS diseases and their orchestration significantly decides on either lesion progression or remission. The aim of the present review is to summarize the growing number of data focusing on the molecular basis of the immune response during spontaneous canine CNS diseases and to detail the effect of cytokines on the immune pathogenesis of selected idiopathic, infectious, and traumatic canine CNS diseases. Steroid-responsive meningitis arteritis (SRMA) represents a unique idiopathic disease of leptomeningeal blood vessels characterized by excessive IgA secretion into the cerebrospinal fluid. Recent reports have given sophisticated insights into the cytokine-driven, immune-mediated pathogenesis of SRMA that is characterized by a biased T helper 2 cell response. Canine distemper associated leukoencephalitis represents an important spontaneously occurring disease that allows investigations on the basic pathogenesis of immune-mediated myelin loss. It is characterized by an early virus-induced up-regulation of pro-inflammatory cytokines with chronic bystander immune-mediated demyelinating processes. Lastly, canine spinal cord injury (SCI) shares many similarities with the human counterpart and most commonly results from intervertebral disk disease. The knowledge of its pathogenesis is largely restricted to experimental studies in rodents, and the impact of immune processes that accompany secondary injury is discussed controversially. Recent investigations on canine SCI highlight the pivotal role of pro-inflammatory cytokine expression that is paralleled by a dominating reaction of microglia/macrophages potentially indicating a polarization of these immune cells into a neurotoxic and harmful phenotype. This report will review the role of cytokines in the immune processes of the mentioned representative canine CNS diseases and highlight the importance of cytokine/cytokine interaction as a useful therapeutic target in canine CNS diseases.

Marked MMP-2 transcriptional up-regulation in mononuclear leukocytes invading the subarachnoidal space in aseptic suppurative steroid-responsive meningitis-arteritis in dogs

Canine Steroid-Responsive Meningitis-Arteritis (SRMA) is a suitable animal model for studies on the development of neutrophilic pleocytosis in aseptic meningitis. Samples of dogs in the acute phase of SRMA (n=16) were examined for gene expression of matrix metalloproteinases (MMP)-2 and -9 and tissue inhibitors of metalloproteinases (TIMP)-1 and -2. Results were compared to those of dogs under glucocorticosteroid treatment for SRMA (n=16) and dogs with other inflammatory and neoplastic diseases of the central nervous system (CNS) (n=19). Samples included mononuclear (PBMCs) and polymorphonuclear cells (PBPMNs) of peripheral blood and cerebrospinal fluid white blood cells (CSF WBCs). In the acute phase of SRMA CSF WBCs showed mRNA expression for MMP-2 and -9 and TIMP-1 and -2, highlighting a contribution of these cells to the overall content of MMPs and TIMPs in CSF. MMP-2 mRNA levels in CSF WBCs were significantly up-regulated in comparison to PBMC expression levels, suggesting that MMP-2 is relevant for PBMC invasion into the subarachnoidal space and that the expression is influenced by migratory activity through the blood-CSF-barrier.

Disproportionally strong increase of B cells in inflammatory cerebrospinal fluid of dogs with Steroid-responsive Meningitis-Arteritis

Steroid-responsive Meningitis-Arteritis (SRMA) is a systemic inflammatory disease of juvenile to young adult dogs with a relapsing course and most prominent manifestation in the cervical meninges. Immunophenotyping and flow cytometric measurement of lymphocytes in peripheral blood (PB) and CSF was performed in the acute phase of SRMA (n=12) and during glucocorticosteroid treatment (n=10). Values were compared to those from dogs with other neurologic diseases (n=63) and healthy individuals (n=7). Dogs with SRMA had high CD4:CD8alpha ratios in PB and low T:B cell ratios in PB and CSF suggesting that a T(H)2-mediated immune response occurs. The T:B cell ratio in CSF was markedly lower than that in PB indicating that either a selective recruitment of B cells or, alternatively, their strong intrathecal proliferation takes place. SRMA appears to be a valuable animal model for the investigation of compartmentalization of immune responses and for studies on differences in local central nervous system and systemic immune responses.

Differentiating spontaneous from drug-induced vascular injury in the dog

When vascular injury is observed in dogs used in preclinical toxicology studies, careful evaluation of the lesions is warranted, especially when differentiating drug-induced vascular changes from spontaneous findings, such as idiopathic canine polyarteritis. The clinical signs as well as the nature and distribution of lesions can often be distinguishing, as is the case with vasoactive drugs, including vasodilators and/or positive inotropes (hydralazine, minoxidil, endothelin receptor antagonists, and phosphodiesterase III inhibitors). For most types of vasodilator-induced vascular injury, the lesion is often restricted to coronary arteries, whereas in idiopathic canine polyarteritis, arterial lesions not only involve coronary arteries, but also medium to small arteries of other organs. In addition, the nature of the changes in vessels yields important clues. Medial and adventitial hemorrhage is generally associated with vasodilator-induced arterial lesion, whereas hemorrhage is generally absent in idiopathic polyarteritis. Although idiopathic canine polyarteritis can generally be differentiated from vasoactive-induced vascular injury in dogs, there are increasing incidences of this type of polyarteritis in dogs receiving any 1 of a number of unrelated classes of compounds, suggestive of an exacerbation of the spontaneous disease. Therefore, in order to differentiate drug-induced injury from idiopathic canine polyarteritis, it is critical that examination of the vascular pathology be conducted with good understanding of clinical, pharmacological, and mechanistic data associated with the drug.

Detrusor myopathy in young beagle dogs

Hematoxylin and eosin-stained sections of urinary bladder were examined microscopically from 449 male and female beagle dogs after 2- to 4-week toxicology studies. Degenerative lesions (detrusor myopathy) of the urinary bladder muscular tunic were present in 59 of 449 (13%) dogs. Myopathic lesions consisted of focal to multifocal areas of smooth muscle fiber atrophy with cytoplasmic basophilia and vacuolation, individual cell necrosis, enlarged smooth muscle nuclei and nucleoli, and occasional mitotic figures. Adjacent areas of arteritis and periarteritis were present in 10 of 59 (17%) beagles with detrusor myopathy suggesting a possible ischemic pathogenesis of the smooth muscle lesions. There was no significant difference in prevalence of myopathy in beagles administered vehicle or various test compounds. Prior urinary catheterization procedures appeared to augment the prevalence of myopathy; some lesions were adjacent to minor, iatrogenically traumatized urinary bladder mucosa. Muscle lesions were not observed in urinary bladders from mongrel dogs, monkeys, cats, rats, or microswine. When compared to crossbred dogs and other laboratory species, the beagle dog thus appears to be sensitive to development of detrusor myopathy.

Interleukin-6 activity in dogs with juvenile polyarteritis syndrome: effect of corticosteroids

Juvenile polyarteritis syndrome (JPS) is an idiopathic febrile disease in dogs. Elevated serum levels of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) have been reported in human patients with vasculitis. We investigated whether these cytokines are also elevated in serum of dogs with JPS using sensitive bioassays. Increased levels of IL-6 activity were detected in the serum of 12 acutely ill dogs, whereas the IL-6 activity decreased to low or undetectable levels during convalescence. Treatment of 5 acute JPS dogs with prednisone resulted in a rapid clinical improvement accompanied by a decrease of IL-6 activity. Withdrawal of prednisone treatment caused reappearance of clinical symptoms and high serum IL-6 activity within a few days. TNF activity could not be detected in the samples of normal dogs, convalescent JPS, or acute JPS dogs. These studies support a role for IL-6 in the pathogenesis of JPS.

Pathologic features of naturally occurring juvenile polyarteritis in beagle dogs

Eighteen young Beagle dogs (eight males and 10 females), ages 6-40 months, with canine juvenile polyarteritis syndrome (CJPS), a naturally occurring vasculitis and perivasculitis of unknown etiology, were necropsied, and their tissues were examined by histopathologic and histochemical methods. The condition is characterized by recurring episodes of an acute onset of fever (> 40 C) and neck pain that persist for 3-7 days. The major histopathologic alterations were a systemic vasculitis and perivasculitis. During the febrile, painful period of CJPS, the vascular lesions ranged from a histiocytic-lymphocytic periarterial infiltration to transmural arterial inflammation with concomitant fibrinoid necrosis and vascular thrombosis. Massive periarterial accumulations of inflammatory cells were common and often extended into adjacent tissues. The small- to medium-sized muscular arteries of the heart, cranial mediastinum, and cervical spinal meninges were consistently involved. Vasculitis occasionally occurred in other organ systems. The vascular lesions in dogs examined during clinically normal periods consisted of intimal and medial fibrosis, ruptured elastic laminae, and mild perivasculitis; these lesions were probably related to previous episodes of vasculitis. Eight dogs that had experienced repeated acute episodes also developed splenic, hepatic, and renal amyloidosis. The clinical signs, laboratory abnormalities, and the vascular lesions suggest that the condition may be immune-system mediated. CJPS may serve as a naturally occurring animal model of human immune-system-mediated vasculitides such as polyarteritis nodosa, infantile polyarteritis, and Kawasaki disease.

Neuroimmunological studies in steroid-responsive meningitis-arteritis in dogs

The clinical and pathological expression of steroid-responsive meningitis-arteritis (SRMA) is predominantly neurological and the present study was therefore mostly concerned with the intrathecal humoral immune responses of 13 dogs suffering from the disease. All the dogs synthesised IgG intrathecally, indicating that the immune response in SRMA is in part specifically directed towards the central nervous system (CNS). Half of the dogs also had high levels of IgM only in the cerebrospinal fluid (CSF) and nearly all of them had high levels of IgA in the CSF as well as in the serum. Six of the dogs had circulating immune complexes in the serum, but not in the CSF. Neither IgM nor IgA rheumatoid factors were found. A chemotaxis assay revealed enhanced migration of neutrophils into the CSF in three cases. All the dogs had marked meningeal inflammation and arterial lesions of the meningeal blood vessels. Only one dog had arterial involvement outside the CNS. The acute vascular lesions consisted mostly of degenerative changes of the media and periarterial inflammation, and there was no evidence of immune complex deposition. Chronic lesions were mostly characterised by stenosis, adventitial thickening and periarteritis. Focal deposits of IgA were found in the vascular wall of one chronic case. It was concluded that the meningeal lesions in SRMA are a primary event, rather than the result of a generalised immune complex disease. These lesions are associated with an intrathecal humoral immune response, in which IgA appears to play a central role.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunologic abnormalities in canine juvenile polyarteritis syndrome: a naturally occurring animal model of Kawasaki disease

This study describes the immunologic abnormalities during the acute phase of juvenile polyarteritis syndrome (JPS), a multisystem necrotizing vasculitis of young dogs with a predilection for the coronary arteries. JPS has striking clinical, laboratory, and pathologic similarities to Kawasaki disease (KD), the most common cause of acquired heart disease in children in the United States. The immunologic abnormalities include an increase in serum IgA, an increase in the percentage of peripheral B cells and a decrease in the percentage of total peripheral T cells, a marked suppression of the blastogenic response to mitogenic stimulation, an inability to generate immunoglobulin-secreting plasma cells following polyclonal activation, the presence of antineutrophil cytoplasmic antibodies, and evidence of monocyte/macrophage activation. These immunoregulatory abnormalities are similar to those observed in children during the acute phase of KD. This unique, naturally occurring animal model of necrotizing vasculitis may prove useful for investigating novel therapeutic interventions in the treatment of necrotizing vasculitis and may yield insight into the immunopathology and etiology of KD.

Vascular toxicity in dogs associated with overdoses of a novel benzodiazepine receptor partial agonist

Necrotizing arteritis and periarteritis were found in Beagle and German Shepherd dogs treated for 13 or 52 weeks with the novel benzodiazepine receptor (BZR) partial agonist Ro 16-6028 (generic name bretazenil). Eight male and one female out of a total of 20 dogs treated with 40-60 mg/kg/day Ro 16-6028 developed the arteritis, predominantly in the heart or the epididymis. Two of these animals died prematurely following treatment at the initial dosing levels of 80 and 55 mg/kg/day; one of these two dogs was asymptomatic and in good general condition until death. Clinically, all but one of the dogs showed sedation, ataxia, stiff gait, body weight-loss and a deterioration of the general condition as well as changes of some laboratory parameters. No signs of arteritis and untoward clinical or laboratory findings were seen at lower doses. Possible aetiologies, as well as the mechanisms involved in arteritis in general and the genetic disposition of beagles in particular for this type of effect, are discussed. Reflections on the potential risk to man of this so far unknown finding after oral treatment with 1,4-benzodiazepines (BZs) are presented.

Spontaneous and induced arterial disease in the dog: pathology and pathogenesis

The spontaneous arterial diseases of the dog relevant to safety assessment studies of drugs are the extramural coronary arteritis of Hartman, intramural coronary arteriosclerosis (with amyloid deposition) occurring in older dogs with cardiac disability, intramural arteriosclerosis without amyloid deposition in the left ventricle of dogs with congenital subaortic stenosis or in the right ventricle in dogs with severe pulmonic stenosis, and necrotizing polyarteritis (nodosa). Experimentally induced lesions include right atrial necrosis and arteritis produced by minoxidil and theobromine, extramural coronary arteritis produced by positive inotropic/vasodilator drugs, intramural coronary arteriosclerosis associated with decreased peripheral resistance and tachycardia induced by hypotensive drugs (including antihypertensive and positive inotropic/vasodilator agents), and intramural arteriosclerosis associated with rapid ventricular pacing. The pathogenesis of none of these lesions is known. The left ventricular subendocardial and papillary muscle intramural coronary arterial lesions are associated with hyperdynamic activity and, in the case of drugs and subaortic stenosis, the possibility of lowered perfusion pressure and tachycardia. This has led to the supposition that these are ischemic lesions, but the evidence available either does not support or refutes that conclusion since subendocardial coronary flow and perfusion pressure are adequate with pacing tachycardia and in toxicity trials. Necrotizing polyarteritis appears to be an immune mediated disease that may appear in genetically prone beagles when they are placed under the stresses of experimental manipulation and/or a new environment. Since the right atrial minoxidil lesion can also be produced by theobromine in dogs and minoxidil can cause a left atrial lesion in swine, it is neither species nor drug specific. Its cause, however, escapes us. There appears to be little in common between the extramural coronary artery Hartman lesion and that caused by positive inotropic/vasodilator drugs. Left ventricular subendocardial and papillary muscle intramural coronary arterial lesions induced by ventricular pacing at 250 beats/min for 2 months are generally similar to those seen in toxicity trials with peripheral vasodilator drugs that induce tachycardia in electrocardiograms exceeding 200 beats/min, although in acute pacing experiments subendocardial perfusion is adequate at these heart rates. Coronary artery autoregulation may be compromised or so destabilized by the drugs that episodes of underperfusion can account for these lesions.(ABSTRACT TRUNCATED AT 400 WORDS)

Classification of naturally occurring arterial disease in the dog

Evaluation of induced arterial toxicity in safety assessment of drugs involves recognition of morphologic differences between groups of animals. In this organ system, as in all others, it is necessary to be familiar with the background pathology that can occur in control animals of the test species, since such lesion "noise" may complicate the evaluation of drug-related effects if naturally occurring diseases have morphologic features in common with those that can be produced by drugs. Background arterial lesions have been regarded as relatively unimportant in both the laboratory-maintained beagle and in the larger range of domesticated breeds of dog and few of these vascular lesions lead, per se, to functional organ compromise. At least this appears to be the case in young and middle-aged subjects, within the epidemiologic limits of data from veterinary medical centers where systematic and thorough necropsies are done and recorded. Arterial lesions are, however, not uncommon naturally occurring incidental necropsy findings in dogs; however, in most cases they are of uncertain functional significance. This presentation summarizes the main pathologic patterns of lesions that can affect arteries in dogs that are not used in safety evaluation studies. The main patterns can be classified as degenerative, proliferative, and inflammatory, although there is some overlap between these partly arbitrary designations. In some cases, etiopathogenesis of the arterial lesion is unclear; in others, there are clear associations with disease processes in other organ systems. Congenital vascular lesions and vascular components of congenital cardiac defects are excluded from consideration since such lesions are unlikely to occur in dog populations used in the safety assessment of drugs.

Spontaneous extramural coronary arteritis in dogs

Control and treated beagle and random-source dog hearts obtained from 119 toxicological experiments were evaluated histologically to study the incidence and characteristics of a microscopic inflammatory lesion specific to the extramural coronary arteries. The lesion occurred in 23% of the experiments. The incidence was 2.3% of the control and treated beagle hearts examined. In the control beagles, it was present in 3.1% of males and 1.3% of females and in the treated beagles, in 1.8% males and 2.8% females. It occurred in 4.7% of the random-source animals. While not visible grossly, histologically, the solitary lesions were characterized by adventitial infiltrates of mononuclear cells, occasional areas of necrosis with inflammatory cell infiltrates occurring in the mural and subendothelial regions. The latter resulted in prominent separation of the intima from the media. The lesions occurred in the right and left coronary arteries and in the dorsal, circumflex and ventral descending branches of the left coronary artery. Similar vascular lesions were not found in the intramural coronary vessels or in other organs in the affected animals. Expanded sampling of the extramural coronary arteries revealed an incidence of 5-9%. This lesion of focal extramural coronary arteritis was considered idiopathic, and not a manifestation of recently reported polyarteritis syndromes in dogs.

An idiopathic febrile necrotizing arteritis syndrome in the dog: beagle pain syndrome

The clinical, laboratory, and pathologic features of a syndrome in dogs characterized by intermittent pain, fever, neutrophilia, and necrotizing arteritis are described to alert others involved in toxicity testing to the existence of this disorder. It is considered that this idiopathic syndrome is a latent condition, the expression of which can be precipitated in predisposed dogs by experimental treatment, and thus, its occurrence could complicate interpretation of toxicity studies. We have observed the disorder in 14 beagle dogs. The syndrome is rare and most cases for study were supplied by the breeder. Typical clinical signs observed included evidence of pain when the mouth was opened, grunting when lifted, and standing with an arched back and lowered head. Appetite was usually reduced. Body temperature was elevated (e.g., 104-106 degrees F). There was progressive, bilateral atrophy of temporal and cervical musculature. Such signs have been observed to persist unremittingly or, more commonly, with periods of expression and remission. Neutrophilic leukocytosis and thrombocytosis were present. Hemoglobin and hematocrit were usually slightly decreased. Serum total protein was usually normal but albumin was reduced and alpha-2 globulins were markedly increased. Rheumatoid factor was elevated in several dogs. Arteritis was observed histologically and was characterized by necrosis, intimal proliferation, neutrophil and mononuclear cell infiltration in the media and periarterial tissues, and hemorrhage. Amyloidosis was observed in several dogs. The cause of this disorder is unknown. Knowledge of the distinct features of this syndrome should obviate complication of interpretation of results in toxicity studies and hopefully will lead to studies of this syndrome to provide an understanding of its etiopathogenesis.

Spontaneous disseminated panarteritis in laboratory beagle dogs in a toxicity study: a possible genetic predilection

Disseminated panarteritis was found in 16 (9 males and 7 females) of 49 laboratory beagle dogs (25 males and 24 females) from one breeding kennel. The dogs had been used in a 6-month oral toxicity study. Panarteritis was not associated with clinical or gross abnormalities. The incidence was similar in the control and test article-treated groups. Mainly medium-sized arteries throughout the body, particularly intercostal arteries (at their aortic origin), and coronary, epididymal and thymic vessels were affected. Chronic mononuclear-cell periarteritis was the predominant feature. Mixed cellular inflammation of the wall, proliferation or degeneration of muscle cells, focal "fibrinoid" material in the tunica media, fragmented internal elastic lamina and intimal thickening associated with myointimal cellular proliferation also occurred. These histologic changes are compatible with those of immune arteritis. Round worm intestinal infestation and granulomas of visceral larva migrans were common in several organs. Statistical analyses suggested that the pedigree of dogs is related to panarteritis, but the presence or absence of parasitization alone is not. The possible roles of genetic predilection and/or parasites in the pathogenesis are discussed. This panarteritis is spontaneous and may complicate the interpretation of lesions in toxicity studies.

Idiopathic extramural coronary arteritis in beagle and mongrel dogs

Hearts obtained from 119 toxicological experiments on dogs during a 21-year period (1965-1986) were evaluated histologically to determine the incidence and characteristics of focal microscopic inflammatory lesions of the extramural coronary arteries. Lesions were encountered in 23% of 119 experiments. The average overall incidence was 2.3% of 1,905 control and chemically treated male and female beagle hearts (3.1% of male and 1.3% of female control beagles, and 1.8% of male and 2.8% of female treated beagles). Lesions were seen in 4.7% of 127 random-source mongrel dogs. Histologically, lesions were characterized by adventitial infiltrates of mononuclear cells, areas of mural necrosis, and inflammatory cell infiltrates in both mural and subendothelial regions. In the latter region, fibrosis developed separating the intima from the internal elastic membrane. Lesions occurred in the right and left coronary arteries and in the dorsal, circumflex, and ventral descending branches of the left coronary artery. Vascular lesions were not present in the intramural coronary vessels or in vessels of other organs in affected animals. More extensive sampling of the extramural coronary arteries revealed an incidence of 5-9%. The lesion of focal extramural coronary arteritis was idiopathic, and not a manifestation of the polyarteritis syndrome of dogs.

Periarteritis in a beagle colony

Primary periarteritis, an uncommon necrotizing vasculitis in the dog, was found to affect, almost exclusively, the major branches of the coronary arteries in a number of young beagle dogs. The arteritis was mainly distributed in the proximal segment of the right coronary artery. Immunocytochemical studies failed to identify immunoglobulin deposits in the lesions and the cause of the arteritis remains unknown. It is important to be aware of this spontaneous condition and its regional distribution since certain cardiovascular drugs may also produce necrotizing arteritis at similar sites.