Spinal Cord Compression in a Horse due to a Granular Cell Variant of Neurofibroma.

A neurofibroma of granular cell subtype is described in a 7-year-old horse. The horse had a 3-month history of ataxia affecting the forelimbs and hindlimbs, suggesting a C1-C6 neuroanatomical localization. Post-mortem examination revealed an intradural mass arising from the right sixth cervical spinal nerve and compressing the spinal cord. Histologically, the mass was composed largely of wavy spindle cells (a mixture of Schwann cells, perineurial cells and fibroblasts) intimately associated with ropy collagen fibres. Approximately 25% of the spindle cells were swollen and contained densely-packed, eosinophilic and periodic acid-Schiff-positive cytoplasmic granules. Immunohistochemistry for S100 and glial fibrillary acidic protein antigens labelled a proportion of neoplastic cells, while the cytoplasmic granules were positive for S100 and neuron specific enolase. This is the first report of a neurofibroma with granular cell differentiation in an animal. Granular cell differentiation in other peripheral nerve sheath tumours of animals is briefly discussed.

The Use of Recombinant Tissue Plasminogen Activator (rTPA) in The Treatment of Fibrinous Pleuropneumonia in Horses: 25 Cases (2007-2012).

BACKGROUND: Information about treatment protocols, adverse effects and outcomes with intrapleural recombinant tissue plasminogen activator (rTPA) use in horses with fibrinous pleuropneumonia is limited. HYPOTHESIS/OBJECTIVES: Describe factors that contribute to clinical response and survival of horses treated with rTPA intrapleurally. ANIMALS: Horses with bacterial pneumonia and fibrinous pleural effusion diagnosed by ultrasonography, that were treated with rTPA intrapleurally. METHODS: Retrospective multicenter case series from 2007-2012. Signalment, history, clinical and laboratory evaluation, treatment, and outcome obtained from medical records. Regression analysis used to identify associations between treatments and outcomes. RESULTS: Thirty three hemithoraces were treated in 25 horses, with 55 separate treatments. Recombinant tissue plasminogen activator (375-20,000 µg/hemithorax) was administered 1-4 times. Sonographically visible reduction in fibrin mat thickness, loculations, fluid depth, or some combination of these was seen in 32/49 (65%) treatments. Response to at least 1 treatment was seen in 17/20 (85%) horses with sonographic follow-up evaluation after every treatment. Earlier onset of rTPA treatment associated with increased survival odds. No association was found between cumulative rTPA dose or number of rTPA doses and survival, development of complications, duration of hospitalization or total charges. Clinical evidence of hypocoagulability or bleeding was not observed. Eighteen horses (72%) survived to discharge. CONCLUSIONS AND CLINICAL IMPORTANCE: Treatment with rTPA appeared safe and resulted in variable changes in fibrin quantity and organization within the pleural space. Recombinant tissue plasminogen activator could be a useful adjunct to standard treatment of fibrinous pleuropneumonia, but optimal case selection and dosing regimen remain to be elucidated.

Serum bile acid concentrations, histopathological features, and short-, and long-term survival in horses with hepatic disease.

BACKGROUND: Serum bile acid concentrations (SBA) and a histopathological biopsy score [Equine Vet J 35 (2003) 534] are used prognostically in equine hepatic disease. HYPOTHESIS: Histopathologic features and scores, but not SBA, differ between survivors and nonsurvivors and correlate with histopathologic evidence of hepatic inflammation and fibrosis. ANIMALS: Retrospective study. Records (1999-2011) of horses with hepatic disease diagnosed by biopsy and with concurrent measurements of SBA. METHODS: Retrospective cohort study. Biopsies were examined for inflammatory cell infiltration including type and distribution, fibrosis, irreversible cytopathology affecting hepatocytes, hemosiderin, or other pigment deposition and bile duct proliferation. SBA, histopathological findings and a histological score [Equine Vet J 35 (2003) 534] were compared between short- (survival to discharge) and long-term (>6 months) survivors and correlations between SBA and histopathological findings investigated. RESULTS: Of 81 cases 90% survived short-term and 83% long-term. Short-term and long-term nonsurvival were associated with SBA (P = .009; P = .006), overall (P = .001; P = .002) and parenchymal (short-term only; P = .01) inflammation, portal and bridging fibrosis (all P < .001), apoptosis or single cell necrosis (P < .001; P = .008), hemosiderin deposition in hepatocytes (P = .011; P = .028), biliary (both P < .001), vascular (P = .003; P = .045) and endothelial (P < .001; P = .02) hyperplasia, nucleic changes (P = .004; P < .001) and the histopathological score (both P < .001). SBA were significantly and positively correlated with overall (P = .001), parenchymal (P < .001) and portal (P = .004) inflammation and portal (P = .036) and bridging (P = .002) fibrosis. CONCLUSIONS AND CLINICAL IMPORTANCE: SBA, histopathological findings and scores differ between survivors and nonsurvivors. SBA concentrations are associated with inflammation and fibrosis suggesting interference with hepatic function. A histopathological score >2 and, less so, SBA >20 µmol/L are specific but not sensitive indicators of nonsurvival.

Suspected acorn toxicity in nine horses.

REASONS FOR PERFORMING STUDY: Acorn toxicity has been anecdotally reported to cause fatal colitis and colic in horses but reports in the scientific literature are sparse. OBJECTIVES: This study reports the diagnosis, treatment, prognosis and outcome of 9 cases with suspected acorn toxicity admitted to 2 referral hospitals. STUDY DESIGN: Retrospective case series. METHODS: Case records from 2004 to 2013 were reviewed. Horses were included in the study if they met 3 of 4 criteria: exposure to acorns; clinical and laboratory data suggesting alimentary or renal dysfunction; acorn husks in the faeces or gastrointestinal tract; and necropsy and histopathological findings consistent with acorn toxicity. Data collected included case history, clinical presentation, clinicopathological data, ultrasonographic findings, case progression, and necropsy and histopathological findings. RESULTS: Nine horses met the inclusion criteria. Five cases presenting with haemorrhagic diarrhoea deteriorated rapidly and were subjected to euthanasia or died. Four cases showed signs of colic with gas distension, displacement of the large colon and diarrhoea. Three of these (33%) survived with medical management, the fourth was subjected to euthanasia. Post mortem examination of 6 cases demonstrated submucosal oedema of the large intestine and caecum (n = 6), acute tubular nephrosis (n = 6), diffuse necrohaemorrhagic and ulcerative typhlocolitis and enteritis (n = 4), and small intestinal oedema (n = 3). CONCLUSIONS: Acorn ingestion may be associated with typhylocolitis leading to diarrhoea, colic and acute renal tubular nephrosis. Recovery is possible in mildly affected cases; more severe cases show hypovolaemia, intractable pain, renal dysfunction and cardiovascular failure, and often succumb to the disease process. Disease is only seen in a small proportion of the population exposed to acorns and there seems to be an increased occurrence in certain years. Further investigation into factors predisposing to disease is required, but limiting exposure to acorns in the autumn seems prudent.

Rater agreement on gait assessment during neurologic examination of horses.

BACKGROUND: Reproducible and accurate recognition of presence and severity of ataxia in horses with neurologic disease is important when establishing a diagnosis, assessing response to treatment, and making recommendations that might influence rider safety or a decision for euthanasia. OBJECTIVES: To determine the reproducibility and validity of the gait assessment component in the neurologic examination of horses. ANIMALS: Twenty-five horses referred to the Royal Veterinary College Equine Referral Hospital for neurological assessment (n = 15), purchased (without a history of gait abnormalities) for an unrelated study (n = 5), or donated because of perceived ataxia (n = 5). METHODS: Utilizing a prospective study design; a group of board-certified medicine (n = 2) and surgery (n = 2) clinicians and residents (n = 2) assessed components of the equine neurologic examination (live and video recorded) and assigned individual and overall neurologic gait deficit grades (0-4). Inter-rater agreement and assessment-reassessment reliability were quantified using intraclass correlation coefficients (ICC). RESULTS: The ICCs of the selected components of the neurologic examination ranged from 0 to 0.69. "Backing up" and "recognition of mistakes over obstacle" were the only components with an ICC > 0.6. Assessment-reassessment agreement was poor to fair. The agreement on gait grading was good overall (ICC = 0.74), but poor for grades ≤ 1 (ICC = 0.08) and fair for ataxia grades ≥ 2 (ICC = 0.43). Clinicians with prior knowledge of a possible gait abnormality were more likely to assign a grade higher than the median grade. CONCLUSION AND CLINICAL IMPORTANCE: Clinicians should be aware of poor agreement even between skilled observers of equine gait abnormalities, especially when the clinical signs are subtle.

Severe hypertriglyceridaemia in horses and ponies with endocrine disorders.

REASONS FOR PERFORMING THE STUDY: Severe hypertriglyceridaemia in horses and ponies with endocrine disorders has been reported anecdotally but has not been documented in the literature. OBJECTIVES: To describe historical and clinicopathological findings as well as progression and outcome in horses and ponies with severe hypertriglyceridaemia (serum triglyceride concentration >5.65 mmol/l) secondary to an endocrine disorder that were otherwise apparently healthy. METHODS: Cases from 6 participating institutions were identified and case details extracted from the medical records. RESULTS: Case details of 3 horses and 4 ponies were available. Presenting complaints included weight loss despite good appetite in 4 animals, while in 3 hypertriglyceridaemia was identified incidentally. All animals were bright and alert and showed a normal or increased appetite. Serum triglyceride concentrations ranged from 10.5 to 60.3 mmol/l. Other abnormalities included hyperglycaemia in 6 animals, suspected insulin resistance and mild to severe increases in hepatic enzyme activities. In 2 animals, moderate hepatic lipidosis was confirmed histologically. Three horses and 3 ponies were diagnosed with pituitary pars intermedia dysfunction based on clinical signs and basal adrenocorticotropic hormone (ACTH) concentrations or dexamethasone suppression test results. In 5 of these, type 2 diabetes mellitus was also confirmed, while one pony suffered from type 2 diabetes mellitus without concurrent pituitary pars intermedia dysfunction. Laboratory abnormalities improved in 4 animals with treatment (pergolide and/or insulin), in one horse specific treatment was not attempted, and in 2 ponies treatment was impaired by the owner or only partly effective. In one of the latter cases, biochemical abnormalities persisted for 7 years without apparent ill effects. CONCLUSIONS AND POTENTIAL RELEVANCE: Horses and ponies may develop severe hypertriglyceridaemia secondary to endocrine disorders that are associated with insulin resistance. Hypertriglyceridaemia can resolve with treatment of the endocrinopathy. Although biochemical evidence of hepatic compromise was present, clinical abnormalities were not noted in these animals.

Blood lactate concentrations in ponies and miniature horses with gastrointestinal disease.

REASONS FOR PERFORMING STUDY: Clinical impression suggested that pony and miniature breeds (collectively referred to as ponies) presenting to a referral hospital for investigation of gastrointestinal disease had higher blood lactate concentrations on admission than large breed horses. OBJECTIVES: The study tested the hypothesis that ponies with gastrointestinal disease had higher blood lactate concentrations on admission than large breed horses with similar disease severity. STUDY DESIGN: Retrospective case-control study. METHODS: Medical records from September 2006 to July 2011 were reviewed for ponies with a primary presenting complaint of gastrointestinal disease. Two larger breed horses with gastrointestinal disease were selected as controls for each case. Data collected included case details, historical and clinicopathological findings, diagnosis and outcome. RESULTS: Information was collected on 50 ponies and 100 horses. Ponies had higher mean ± s.d. respiratory rates (27 ± 13 vs. 21 ± 13 beats/min; P = 0.01) and rectal temperatures (37.9 ± 0.6 vs. 37.4 ± 0.6°C; P = 0.006) and a longer median duration of clinical signs prior to presentation (10 h [1-72 h] vs. 6 h [1-120]; P<0.001). Median blood lactate concentrations on admission were higher in ponies than in horses (2.8 mmol/l [0.7-18.0] vs. 1.6 mmol/l [0.4-8.1]; P = 0.001). All other parameters relating to colic severity were not significantly different between groups, although more horses underwent exploratory laparotomy (19/50 ponies and 55/100 horses; P = 0.05). Median blood lactate concentrations in ponies with large intestinal disease, nonstrangulating lesions, undergoing medical treatment and surviving ponies were significantly higher than in horses in the same category. In contrast to horses, no differences in blood lactate concentrations exist between ponies with medical vs. surgical treatment, strangulating and nonstrangulating lesions and surviving and nonsurviving ponies. CONCLUSION AND POTENTIAL RELEVANCE: Ponies might present with higher blood lactate concentrations than horses and might falsely be suspected of having a surgical lesion or a poorer prognosis if veterinarians are not aware of breed differences.

Equine platelets inhibit E. coli growth and can be activated by bacterial lipopolysaccharide and lipoteichoic acid although superoxide anion production does not occur and platelet activation is not associated with enhanced production by neutrophils.

Activated platelets can contribute to host defense through release of products with bactericidal actions such as antimicrobial peptides and reactive oxygen species (ROS), as well as by forming heterotypic aggregates with neutrophils and enhancing their antimicrobial properties. Whilst release of vasoactive mediators from equine platelets in response to stimuli including bacterial lipopolysaccharide (LPS) has been documented, neither ROS production, nor the effects of activated platelets on equine neutrophil ROS production, have been reported. This study first sought evidence that activated equine platelets inhibit bacterial growth. Platelet superoxide production in response to stimuli including Escherichia coli-derived LPS and lipoteichoic acid (LTA) from Staphylococcus aureus was then determined. The ability of LPS and LTA to up-regulate platelet P-selectin expression and induce platelet-neutrophil aggregate formation was investigated and the effect of co-incubating activated platelets with neutrophils on superoxide production measured. Growth of E. coli was inhibited in a time-dependent manner, and to a similar extent, by addition of platelet rich plasma (PRP) or platelet poor plasma (PPP) obtained by centrifugation of PRP. Activation of platelets in PRP by addition of thrombin led to a significant increase in the inhibitory action between 0.5 and 2h. Although phorbol myristate acetate (PMA) caused superoxide production by equine platelets in a protein kinase C-dependent manner, thrombin, platelet activating factor (PAF), LPS, LTA and formyl-methionyl-leucyl phenylalanine (FMLP) were without effect. LPS and LTA did induce platelet activation, measured as an increase in P-selectin expression (% positive cells: 17±3 (un-stimulated); 63±6 (1µg/ml LPS); 64±6 (1µg/ml LTA); n=5) but not platelet superoxide production or heterotypic aggregate formation. Co-incubation of activated platelets with neutrophils did not increase neutrophil superoxide production. This study has demonstrated for the first time that when activated, equine platelets, like those of other species, are capable of releasing ROS that could assist in bacterial killing. However, the findings suggest that neither superoxide production by platelets nor enhancement of production by neutrophils is likely to play a significant role. Nevertheless, as has been reported in man, equine PPP and PRP did inhibit E. coli growth in vitro, and addition of thrombin significantly increased the inhibitory effect of PRP. This suggests that products released from activated platelets could contribute to antimicrobial activity in the horse. The factors in equine plasma and released by activated platelets that are responsible for inhibiting bacterial growth have yet to be determined.

Comparison of two antimicrobial regimens on the prevalence of incisional infections after colic surgery.

Appropriate durations of perioperative antimicrobial therapy following exploratory coeliotomy in horses are controversial, and with the rising prevalence of multiresistant bacteria there is a strong incentive to use antimicrobials for the shortest time possible. Following exploratory coeliotomies, incisional infections are an important cause of morbidity in horses and could be influenced by the duration of systemic antimicrobial therapy. The aim of this study was to investigate whether 72 hours of perioperative antimicrobial therapy is as effective as 120 hours at preventing the development of postoperative incisional infections. Horses undergoing exploratory coeliotomy at two referral hospitals were assigned randomly into Group 1 (receiving 72 hours of perioperative antimicrobial therapy) and Group 2 (receiving 120 hours of perioperative antimicrobial therapy). Only horses recovering from surgery and surviving for >120 hours were included in the study. Ninety-two horses met the criteria for inclusion in the study, 42 in Group 1 and 50 in Group 2. The overall incisional complication rate was 42.2 per cent, and no significant difference in the number of incisional complications in the two groups was identified. Results of the study suggest that there is no benefit in using 120 hours over 72 hours of perioperative antimicrobial therapy to prevent incisional infections.

Pneumocephalus in five horses.

Pneumocephalus is occasionally encountered in horses but poorly described in the literature. The study aimed to describe historical, clinical and diagnostic imaging findings and outcome in horses to increase the awareness and recognition of the condition amongst equine practitioners, allowing appropriate management of these cases. Cases of pneumocephalus from 4 participating institutions were identified and case details extracted from the medical records. Five cases of pneumocephalus were identified. Head trauma with suspected or confirmed fractures of the sinuses was the underlying cause in 4 cases, while the remaining horse was thought to have developed pneumocephalus secondary to sinusitis or trauma. Diagnosis was established radiographically in 4 cases and by computed tomography in a fifth. Gas was noted between the cranial vault and the brain, in the lateral ventricles, in the brain parenchyma and within the cranial cervical canal. The gas accumulation resolved gradually in all horses and did not appear independently to result in neurological compromise. Long-term outcome was available for 3 cases, 2 of which were ultimately subjected to euthanasia due to neurological deficits. Pneumocephalus is a possible consequence of head trauma or sinusitis in horses; although the finding is frequently incidental, it has the potential to develop into a life-threatening complication. Imaging the complete skull and cranial cervical spine is important to allow identification and appropriate management of these cases. The use of computed tomography enables easier identification and localisation of the gas accumulation within the central nervous system.

Stimulus-dependent release of tissue-regenerating factors by equine platelets.

REASONS FOR PERFORMING THE STUDY: Platelet-rich plasma (PRP) is increasingly used for treatment of orthopaedic injuries. However, the effects of different stimuli on the release pattern of regenerative and proinflammatory factors from equine platelets are largely unknown and an optimal treatment protocol remains to be established. OBJECTIVES: The aim of this study was to identify a stimulus that enhanced release of histopromotive factors (platelet-derived growth factor BB [PDGF] and transforming growth factor 1ß[TGF]) without causing concurrent release of a proinflammatory mediator (CCL5). METHODS: Washed platelets were prepared from 6 healthy ponies and release of growth factors and CCL5 measured using commercially available ELISAs for human proteins following incubation with or without thrombin, chitosan or equine recombinant tumour necrosis factor (erTNF) over 24 h and subsequently over 96 h. Additionally, noncoagulated samples were analysed. RESULTS: Regardless of whether a stimulus was present or what stimulus was used, PDGF and TGF release was maximal by 0.5-1 h when clot formation took place and very little release was observed after 24 h. Growth factor release was minimal in noncoagulated samples. In contrast, CCL5 release was not associated with coagulation and appeared to persist for much longer. High concentrations of erTNF caused significantly greater release of CCL5 at 6 h than any other stimulus tested. CONCLUSIONS: Growth factor release from equine platelets is dependent on coagulation but independent of the initiating stimulus, and is accompanied by more sustained release of proinflammatory mediators. POTENTIAL RELEVANCE: Supernatants collected from coagulated platelets could be an alternative treatment to PRP.

Putative intestinal hyperammonaemia in horses: 36 cases.

REASONS FOR PERFORMING THE STUDY: Intestinal hyperammonaemia (HA) has been infrequently reported in individual horses; however, there have been no studies describing clinical and laboratory data as well as short- and long-term outcome in a larger number of cases. OBJECTIVES: To describe clinical and laboratory data and short- and long-term outcome in a large group of horses with intestinal HA. METHODS: Multi-centred, retrospective study; case records of horses with HA were reviewed and any horse with a clinical or post mortem diagnosis of intestinal HA was included. Hyperammonaemia was defined as a blood ammonium (NH(4) (+)) concentration ≥60 µmol/l and horses with a diagnosis of primary hepatic disease were excluded. Relevant data were recorded and, if appropriate, data from survivors were compared to nonsurvivors to identify potential prognostic indicators. RESULTS: Thirty-six cases, 26 mature horses and 10 foals with intestinal HA were identified. Case histories included diarrhoea, colic and neurological signs and the most common clinical diagnosis was colitis and/or enteritis. The most common clinical and laboratory abnormalities included tachycardia, increased packed cell volume, hyperlactataemia and hyperglycaemia. Fourteen horses (39%) survived to discharge; NH(4) (+) concentration on admission was the only parameter significantly associated with survival. All surviving horses and foals for which follow-up information was available recovered completely and returned to their intended use without further complications. CONCLUSIONS AND POTENTIAL RELEVANCE: Intestinal HA occurs in mature horses and foals and can be associated with severe clinical and laboratory abnormalities; further studies are required to investigate predisposing factors and delineate possible differences in aetiologies.

PKC isoenzymes in equine platelets and stimulus induced activation.

Protein kinase C (PKC) is an important regulator of platelet activation and different isoenzymes can play positive and negative regulatory roles. The PKC isoenzymes expressed in equine platelets have not been documented but pharmacological inhibition has suggested a role for PKC delta (δ) in modulating responsiveness to platelet activating factor (PAF) (Brooks et al., 2009). Here the PKC isoenzyme profile in equine platelets has been characterised and PKCδ activation by PAF investigated. Platelet lysates were probed by Western blotting using a panel of antibodies against individual PKC isoenzymes. PKCδ and eight other isoenzymes were identified, namely classical PKCs alpha (α), beta (ß), (both ßI and ßII) and gamma (γ), the novel PKCs epsilon (ɛ), eta (η) and theta (θ) and atypical PKC zeta (ζ). Having shown PKCδ to be present, a method was developed to measure PAF-induced isoenzyme translocation by preparing cytosolic and membrane fractions from digitonin permeabilised platelets. Phorbol 12-myristate 13-acetate (PMA) was shown to cause translocation of PKCδ to the membrane within 5s. PAF also caused PKCδ translocation although the response occurred more slowly; a significant, 7.6 ± 1.2 fold, increase in band density compared to unstimulated platelets was observed at 15 min; p=0.036, n=3. These data support a role for PKCδ in regulating PAF-induced functional responses in equine platelets.

Association between hypercoagulability and decreased survival in horses with ischemic or inflammatory gastrointestinal disease.

BACKGROUND: Coagulopathies are common in horses with ischemic or inflammatory gastrointestinal (GI) disturbances. There is indirect evidence suggesting that early stages of these diseases are characterized by hypercoagulability (HC). HYPOTHESIS/OBJECTIVES: HC, assessed via thromboelastography (TEG), is common in horses with ischemic or inflammatory GI diseases. The degree of HC is correlated with nonsurvival and thrombotic complications. ANIMALS: Thirty client-owned horses with ischemic or inflammatory GI disease, 30 client-owned horses with nonischemic or inflammatory GI disease, and 30 healthy horses (control group). METHODS: Prospective, observational clinical study. TEG profiles of 30 horses with ischemic or inflammatory GI disease were obtained on admission and 48 hours after admission, and these were compared with profiles from 30 horses with nonischemic or inflammatory GI disease and 30 healthy controls. Prothrombin time (PT), activated partial thromboplastin time (aPTT), antithrombin activity (AT), and D-Dimer concentrations were also determined in horses with GI disease. RESULTS: Horses with ischemic or inflammatory GI disease had shorter R times compared with healthy horses (14.8±8.3 versus 22.8±12 minute; P=.011). However, changes were subtle and TEG profiles did not resembled those obtained from animals or humans presumed to be hypercoagulable. Although conventional coagulation testing supported the presence of HC (decreased AT and increased D-Dimer concentrations), TEG and coagulation abnormalities were rarely found in the same horses and the methods were not statistically related. CONCLUSIONS AND CLINICAL IMPORTANCE: There is evidence of HC in horses with GI disease but techniques for diagnoses require refinement.

Neutrophil and platelet activation in equine recurrent airway obstruction is associated with increased neutrophil CD13 expression, but not platelet CD41/61 and CD62P or neutrophil-platelet aggregate formation.

Recurrent airway obstruction (RAO) in mature horses is characterized by reversible airway obstruction and neutrophilic inflammation; there is also functional activation of circulating platelets and neutrophils. This study was undertaken to determine if changes in activation marker expression and heterotypic aggregate formation can be used as an indicator of this increased functional responsiveness. In vitro conditions for flow cytometric measurement of CD13, CD41/61 and CD62P expression on activated cells and heterotypic aggregate formation were established. Values were then compared before and after antigen challenge of RAO and healthy horses. Platelet adhesion to serum-coated plastic was measured as a functional marker of platelet activation. In vitro activation resulted in increased expression of neutrophil CD13 and platelet CD41/61 and CD62P. Activation of both cell types caused a significant increase in neutrophil-platelet aggregates. In horses with RAO, but not controls, there was a significant increase in the percentage of CD13 positive neutrophils at 10h and 24h and in the mean fluorescence intensity at 10h. This was accompanied at 24h by an increased mean platelet side scatter and thrombin-stimulated platelet adhesion. In conclusion, CD13 expression can be used as an indicator of equine neutrophil activation both in vitro and in vivo. Equine platelet activation in vitro can be detected by measuring CD41/61 or CD62P expression, and PAF-activated platelets and neutrophils form aggregates. However, despite evidence of circulating platelet activation, neither a change in expression of platelet activation markers, nor heterotypic aggregate aggregate formation could be detected.

Platelet activation in ponies with airway inflammation.

REASON FOR PERFORMING STUDY: Platelet activation occurs in human obstructive airway diseases and in laboratory animal models. However, there is limited evidence that platelets may be involved in equine recurrent airway obstruction (RAO) and other inflammatory diseases. This study investigated whether platelet activation also occurred in RAO. HYPOTHESIS: Platelet function is altered in ponies with active RAO. This alteration can be detected ex vivo by measuring platelet adhesion. METHODS: An in vitro platelet adhesion assay measuring acid phosphatase (AcP) activity colorimetrically was adapted for use with equine platelets and responses to selected agonists were established. Platelet adhesion and aggregation was evaluated in vitro on platelets isolated from 6 ponies with RAO before, during and after a 7 h natural antigen challenge. Three ponies with no history of airway disease were also studied. RESULTS: Adhesion of equine platelets to serum coated plastic was detected at concentrations of 10-100 radicaló 10(9)/l. Adhesion increased in response to stimulation with platelet activating factor and thrombin, but not equine interleukin 8. Prior to the antigen challenge, adhesion of nonstimulated platelets was low and increased significantly (P<0.05) 24 h after initiation of the challenge in RAOs, but not in the normal animals. No changes in platelet aggregation were noted in either group. CONCLUSIONS: The described assay offers an alternative method to evaluate platelet function in healthy and diseased horses and can detect changes not observed using a classic aggregation assay. Circulating platelets are activated 24 h after antigen challenge of ponies with RAO and may play a role in pulmonary inflammation and/or the pathophysiology of RAO. POTENTIAL RELEVANCE: Investigating platelet function in RAO and airway inflammation may reveal new aspects of the pathogenesis of inflammatory lung disease in the horse.