Mycobacterium avium subsp. paratuberculosis is the causative agent of Johne's disease, a chronic granulomatous enteritis of wild and domestic ruminants. During a long subclinical period, the organism persists in the intestine despite systemic cellular and humoral immune responses. To explore the mucosal immune response in Johne's disease, we isolated mononuclear leukocytes from the ileum of cows naturally infected with M. avium subsp. paratuberculosis and from cows that were not infected. We evaluated the immunophenotype of these cells and the proliferative responses after the addition of M. avium subsp. paratuberculosis sonicate or B-cell or T-cell mitogens. Although the percentage of T cells was increased in infected cows, these cells consisted mostly of memory (CD2+CD62L−) and regulatory (CD4+CD25+) T cells. Further evidence of immune hyporesponsiveness included a decrease in the percentage of T cells with an activated phenotype and a decrease in cells expressing major histocompatibility factor class II (MHC class II). Unlike the spleen, ileal lymphocytes from infected cows failed to proliferate in response to M. avium subsp. paratuberculosis sonicate. Additionally, ileal lymphocytes from infected cows proliferated poorly in response to concanavalin A and pokeweed mitogen, suggesting generalized T cell and B cell hyporesponsiveness. These results indicate that a state of tolerance may exist in the intestine of cows subclinically infected with M. avium subsp. paratuberculosis organisms in subclinically infected cows. This effect may be induced, at least in part, by proliferation of regulatory T cells that nonspecifically suppress mucosal immune responsiveness.

OBJECTIVE:To determine functional characteristics of monocytes obtained from cows with subclinical infection with Mycobacterium avium subsp paratuberculosis (MAP) that may have predisposed those cows to becoming infected with MAP SAMPLE POPULATION: Monocytes obtained from 5 uninfected cows and 5 cows subclinically infected with MAP in a herd with a high prevalence of paratuberculosis (ie, Johne's disease).PROCEDURES:Monocytes from uninfected and subclinically infected cows were incubated with MAP for 2, 6, 24, 72, or 96 hours. Variables measured included expression of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-10, IL-12, transforming growth factor-beta, and suppressor of cytokine signaling-3 (SOCS-3); apoptosis of monocytes; acidification of phagosomes; and killing of MAP.RESULTS:Monocytes from infected cows had greater expression of IL-10 and SOCS-3 at 2 hours of coincubation with MAP and lower expression of TNF-alpha and IL-12 when results for all incubation times were combined. Monocytes from infected cows had a greater capacity to acidify phagosomes. No differences were observed in the rate of apoptosis or capacity of monocytes to kill MAP organisms.CONCLUSIONS AND CLINICAL RELEVANCE:Monocytes obtained from cows with subclinical infection with MAP had upregulated expression of IL-10 and SOCS-3 within the first 2 hours after exposure to MAP organisms. Although this did not inhibit acidification of phagosomes, apoptosis of monocytes, or attenuation of the capacity to kill MAP organisms, it may have attenuated the capacity of mononuclear phagocytes to initiate inflammatory and adaptive immune responses.

OBJECTIVESTo evaluate the role of interleukin (IL)-10 in the inability of monocyte-derived bovine macrophages to kill Mycobacterium avium subsp paratuberculosis organisms in vitro.SAMPLE POPULATIONMonocytes were obtained from healthy adult Holstein dairy cows that had negative results when tested for infection with M avium subsp paratuberculosis.PROCEDUREMonocyte-derived macrophages were incubated with M avium subsp paratuberculosis for 2, 6, 24, 72, or 96 hours with or without addition of saturating concentrations of a goat anti-human IL-10 that has been documented to neutralize bovine IL-10 activity. Variables assessed included ingestion and killing of M avium subsp paratuberculosis; expression of tumor necrosis factor (TNF)-alpha, IL-12, IL-8, major histocompatability (MHC) class II, vacuolar H+ ATPase, and B cell CLL/lymphoma 2 (BCL-2); production of nitric oxide; acidification of phagosomes; and apoptosis of macrophages.RESULTSNeutralization of IL-10 enabled macrophages to kill 57% of M avium subsp paratuberculosis organisms within 96 hours. It also resulted in an increase in expression of TNF-alpha, IL-12, IL-8, MHC class II, and vacuolar H+ ATPase; decrease in expression of BCL-2; increase in acidification of phagosomes; apoptosis of macrophages; and production of nitric oxide.CONCLUSIONS AND CLINICAL RELEVANCEThe capacity of M avium subsp paratuberculosis to induce IL-10 expression may be a major determinant of virulence for this organism.

We investigated mechanisms involved in killing of mycobacterial organisms by comparing the response of bovine monocyte-derived macrophages to ingestion of Mycobacterium avium subsp. paratuberculosis or M. avium subsp. avium organisms. Previous studies have shown that bovine macrophages have the capacity to kill M. avium subsp. avium organisms in vitro but cannot kill M. avium subsp. paratuberculosis organisms. We used bovine cDNA microarray technology to investigate sequential gene expression by bovine monocyte-derived macrophages and function assays to correlate gene expression with biological activity. Results of the gene expression studies indicated substantial differences between macrophages phagocytizing the two organisms. At 2, 6, and 24h after infection, 12, 53, and 19 genes, respectively, were differentially expressed. Over all time periods, approximately twice as many genes had lower expression in M. avium subsp. paratuberculosis-infected macrophages than had greater expression. Differentially regulated genes of most interest to antimicrobial responses included inflammatory molecules (transforming growth factor-β, thrombospondin 1, monocyte chemokine, and cathepsin K), phagosome–lysosome-related genes (H+ ATPases, lysosomal-associated membrane protein 2, vesicle trafficking protein, and solute carrier protein), and apoptosis-related genes (tumor necrosis factor receptor-associated factor 2, and tumor protein p53 binding protein). Function assays indicated that M. avium subsp. avium-infected macrophages had a greater capacity to acidify phagosomes and a greater percentage of apoptotic cells. In conclusion, these results suggest that a complex interaction between macrophages and mycobacterial organisms is involved in determining the fate of the organism. Although multiple genes and metabolic pathways are involved, the capacity of cells to acidify phagosomes and induce apoptosis appears to play a prominent role.

Journal of Veterinary Pharmacology and TherapeuticsVolume 27, Issue 5 p. 377-379 Comparison of three arginine-glycine-aspartate-containing peptides as inhibitors of equine platelet aggregation D. J. Weiss, D. J. Weiss Department of Veterinary PathoBiology, College of Veterinary Medicine, University of Minnesota, St Paul, MN, USASearch for more papers by this authorO. A. Evanson, O. A. Evanson Department of Veterinary PathoBiology, College of Veterinary Medicine, University of Minnesota, St Paul, MN, USASearch for more papers by this author D. J. Weiss, D. J. Weiss Department of Veterinary PathoBiology, College of Veterinary Medicine, University of Minnesota, St Paul, MN, USASearch for more papers by this authorO. A. Evanson, O. A. Evanson Department of Veterinary PathoBiology, College of Veterinary Medicine, University of Minnesota, St Paul, MN, USASearch for more papers by this author First published: 20 October 2004 https://doi.org/10.1111/j.1365-2885.2004.00592.xCitations: 3 Douglas J. Weiss, University of Minnesota, 1971 Commonwealth Ave, St Paul, MN 55108, USA. E-mail: weiss005@umn.edu Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume27, Issue5October 2004Pages 377-379 RelatedInformation

Ten healthy 2 to 4-week-old Holstein calves were randomly allotted into control and infected groups. Control calves (n=5) were inoculated intrabronchially with 5ml of Dulbecco's phosphate-buffered saline solution (DPBSS). Infected calves (n=5) were inoculated intrabronchially with 5x10(9) log-phase Mannheimia haemolytica organisms suspended in 5ml of DPBSS. Blood samples were obtained 15 minutes before and one, two, four and six hours after inoculation. Serum protein concentrations were determined by means of sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Serum concentrations of proteins with molecular weights of 125,000 D (ceruloplasmin), 60,000 D (a 1-antitrypsin), 45,000 D (haptoglobin), and 40,000 D (acid glycoprotein) were significantly increased in calves with pneumonic pasteurellosis, compared with concentrations in control calves. Results indicate that acute phase proteins increase more rapidly after the onset of inflammation than previously thought. Measurement of serum protein concentrations may be useful in monitoring the progression of the induced pneumonic pasteurellosis in calves.

OBJECTIVE:To evaluate the activation status of neutrophils in blood samples obtained from horses with naturally occurring colic associated with strangulating obstruction, nonstrangulating obstruction, or inflammatory bowel disease. ANIMALS:30 horses with naturally occurring colic and 30 healthy control horses. PROCEDURE:Activation status of neutrophils was determined by assessing the number of neutrophils that could pass through filters with 5-microm pores, cell-surface CD11-CD18 expression, and alterations in size and granularity of neutrophils. RESULTS:Horses with impaction or gas colic did not have evidence of activated neutrophils. Horses with inflammatory bowel disease consistently had evidence of activated neutrophils, including decreased leukocyte deformability, increased CD11-CD18 expression, increased neutrophil size, and decreased neutrophil granularity. Horses with strangulating colic had variable results. Of horses with strangulating colic, 7 of 14 had marked changes in filtration pressures, 5 of 14 had increased CD11-CD18 expression, 6 of 14 had changes in neutrophil size, and 5 of 14 had changes in neutrophil granularity. Among horses with strangulating colic, changes in deformability, size, and granularity of neutrophils correlated with an adverse outcome. CONCLUSIONS AND CLINICAL RELEVANCE:Activated neutrophils were detected in all horses with inflammatory bowel disease and a few horses with strangulating colic. Correlation of activated neutrophils with horses that had strangulating colic that died or were euthanatized indicates that activated neutrophils are a negative prognostic indicator. Additional studies are needed to determine whether activated neutrophils contribute directly to the adverse outcome in horses with strangulating colic.

OBJECTIVE:To evaluate lipopolysaccharide (LPS)-induced activation of equine neutrophils in blood.SAMPLE POPULATION:Blood samples from 5 healthy adult Thoroughbreds.PROCEDURES:Neutrophil integrin (CD11/CD18) expression, size variation, degranulation, and deformability were measured with and without incubation with LPS. Time and concentration studies were done. The mechanism of endotoxin-induced neutrophil activation was investigated by inactivating complement or preincubating neutrophils with inhibitors of tumor necrosis factor-alpha (TNF-alpha) synthesis, prostaglandin-leukotriene synthesis, or platelet-activating factor.RESULTS:Incubation of equine neutrophils with LPS increased cell surface expression of CD11/CD18, decreased neutrophil deformability, increased and decreased neutrophil size, and induced neutrophil degranulation. The LPS-induced neutrophil activation was attenuated by addition of inhibitors of TNF-alpha and prostaglandin-leukotriene synthesis.CONCLUSIONS AND CLINICAL RELEVANCE:Equine neutrophils are readily activated in vitro by LPS, resulting in increased expression of integrin adhesion molecules, decreased deformability, variation in neutrophil size, and degranulation. The tests used to detect activated neutrophils in this study may be useful in detecting in vivo neutrophil activation in horses with sepsis and endotoxemia.

ABSTRACT Mycobacterium avium subsp. paratuberculosis and Mycobacterium avium subsp. avium are antigenically and genetically similar organisms; however, they differ in their virulence for cattle. M. avium subsp. paratuberculosis causes a chronic intestinal infection leading to a chronic wasting disease termed paratuberculosis or Johne's disease, whereas M. avium subsp. avium causes only a transient infection. We compared the response of bovine monocyte-derived macrophages to ingestion of M. avium subsp. paratuberculosis and M. avium subsp. avium organisms by determining organism survival, superoxide and nitric oxide production, and expression of the cytokines tumor necrosis factor alpha (TNF-α), gamma interferon (IFN-γ), interleukin-8 (IL-8), IL-10, IL-12, and granulocyte-monocyte colony-stimulating factor (GM-CSF). Unlike M. avium subsp. paratuberculosis , macrophages were able to kill approximately half of the M. avium subsp. avium organisms after 96 h of incubation. This difference in killing efficiency was not related to differences in nitric oxide or superoxide production. Compared to macrophages activated with IFN-γ and lipopolysaccharide, macrophages incubated with M. avium subsp. paratuberculosis showed greater expression of IL-10 and GM-CSF (all time points) and IL-8 (72 h) and less expression of IL-12 (72 h), IFN-γ (6 h), and TNF-α (6 h). When cytokine expression by macrophages incubated with M. avium subsp. paratuberculosis was compared to those of macrophages incubated with M. avium subsp. avium , M. avium subsp. paratuberculosis -infected cells showed greater expression of IL-10 (6 and 24 h) and less expression of TNF-α (6 h). Therefore, the combination of inherent resistance to intracellular degradation and suppression of macrophage activation through oversecretion of IL-10 may contribute to the virulence of M. avium subsp. paratuberculosis in cattle.

OBJECTIVE:To develop an in vitro model of the bovine alveolar-capillary interface and to evaluate the roles of interleukin-8 (IL-8) and platelet-activating factor (PAF) in neutrophil-mediated endothelial injury induced by infection with Mannheimia haemolytica.SAMPLE POPULATION:Cultured bovine pulmonary microvascular endothelial cells, freshly isolated bovine neutrophils, and monocyte-derived bovine macrophages.PROCEDURE:A coculture system was developed in which endothelial cells were grown to confluence in tissue culture inserts, neutrophils were added to the inserts, and macrophages were added to tissue culture wells. Mannheimia haemolytica-derived lipopolysaccharide (LPS) or supernatant was added to activate macrophages, and inhibitors of PAF or IL-8 were added to the insert. Endothelial cell cytotoxicity and permeability (ie, albumin leakage) and neutrophil activation (ie, adhesion, degranulation [lactoferrin expression], and superoxide production) were assessed.RESULTS:The addition of M haemolytica-derived LPS to bovine macrophages in the coculture system resulted in significant increases in endothelial cell cytotoxicity and permeability and neutrophil degranulation and adhesion. Inhibition of IL-8 reduced endothelial cell permeability and neutrophil degranulation induced by exposure to M haemolytica-derived supernatant, whereas inhibition of PAF decreased superoxide release by neutrophils.CONCLUSIONS AND CLINICAL RELEVANCE:In vitro activation of bovine macrophages by M haemolytica-derived LPS resulted in neutrophil activation and neutrophil-mediated endothelial damage. Neutrophil-mediated endothelial injury and neutrophil degranulation were, at least in part, mediated by IL8, whereas PAF promoted superoxide release by neutrophils in this in vitro system designed to mimic the in vivo events that occur during the early stages of bovine pneumonic pasteurellosis.

Mycobacterium avium subsp. paratuberculosis and Mycobacterium avium subsp. avium are antigenically and genetically very similar organisms; however, they differ markedly in their virulence for cattle. We evaluated the capacity of bovine macrophages infected with M. avium subsp. paratuberculosis or M. avium subsp. avium to express major histocompatibility complex (MHC) class I and class II antigens on their surface and to interact with primed autologous lymphocytes. Our results indicate that infection of bovine macrophages with M. avium subsp. paratuberculosis promoted the downregulation of MHC class I and class II molecules on the macrophage surface within 24 and 12 h, respectively. Alternatively, MHC class II expression by M. avium subsp. avium-infected macrophages was not detected until 24 h after infection, and the magnitude of the decrease was smaller. Decreased MHC class I expression by M. avium subsp. avium-infected macrophages was not detected. Unlike M. avium subsp. paratuberculosis-infected macrophages, M. avium subsp. avium-infected macrophages upregulated MHC class I and class II expression after activation by gamma interferon or tumor necrosis factor alpha. Further, M. avium subsp. avium-infected macrophages were lysed by primed autologous lymphocytes, whereas M. avium subsp. paratuberculosis-infected macrophages were not. Overall, the results support the hypothesis that the difference in the virulence of M. avium subsp. paratuberculosis and M. avium subsp. avium for cattle is dependent on a difference in the capacity of the organisms to suppress mycobacterial antigen presentation to T lymphocytes.

Platelet glycoprotein IIb/IIIa (GPIIb/IIIa) receptor antagonists have been highly effective inhibitors of platelet aggregation in preclinical studies and in clinical trials. However, decreased platelet counts have been documented in preclinical studies and in some patients receiving GPIIb/IIIa antagonists. We evaluated changes in platelet kinetics and fate in dogs receiving the GPIIb/IIIa receptor antagonist RPR 109891 orally for 4 days. Dogs receiving RPR 109891 had a 22-52% decrease in platelet count with the nadirs at 3-5 days after initiation of treatment. Platelet survival time was reduced by 19%, and platelet half-life was reduced by 63%. Indium-111-labeled platelets were rapidly cleared from the blood within 1 hour after administration of RPR 109891 on treatment days 1 and 2. This clearing was associated with a sharp increase in radioactivity in spleen but not in liver or lung. Platelet clearance was markedly attenuated on treatment days 3 and 4. Platelet counts returned to baseline within 1 week after discontinuation of treatment. These data indicate that RPR 109891 causes rapid and selective sequestration of platelets in the spleen.

OBJECTIVES:To study the in vitro effects of cecal contents incubated with corn starch on colonic permeability in horses.ANIMALS:4 healthy adult ponies.PROCEDURE:Mucosal specimens were obtained from the right ventral colon and mounted in Ussing chambers. Changes in short circuit current, conductance, and large-molecule permeability in response to addition of cecal contents and cecal contents incubated with corn starch were evaluated for 120 minutes.RESULTS:Incubation of cecal contents with corn starch for 8 hours resulted in a decrease in cecal content pH and an increase in lactic acid concentration. These changes were similar to those reported in vivo for ponies given corn starch. Exposure of colonic mucosa to cecal contents incubated with corn starch resulted in an increase in tissue conductance and permeability of technetium Tc 99m pentetate, compared with mucosa exposed to cecal contents alone.CONCLUSIONS AND CLINICAL RELEVANCE:In vitro exposure of colonic mucosa to cecal contents incubated with starch resulted in increased paracellular permeability. Fermentation of excessive amounts of carbohydrate in the intestinal lumen of horses may directly induce increased intestinal permeability associated with carbohydrate-induced laminitis.

To better define the incidence and causes of canine pancytopenia, we retrospectively evaluated the results of complete blood counts submitted to the University of Minnesota Veterinary Teaching Hospital during a 1-year period. Pancytopenia was defined as packed cell volume < 36%, total leukocyte count < 6,000/microliter or total segmented neutrophil count < 3,000/microliter, and platelet count < 200,000/microliter. Of 4,560 complete blood counts, 110 (2.4%) samples from 51 dogs met the criteria for pancytopenia. Eleven different disease processes were identified. These included chemotherapy-associated pancytopenia (n=22), parvovirus infection (n=5), malignant histiocytosis (n=5), idiopathic aplastic anemia (n=3), sepsis (n=3), myelodysplastic syndrome (n=3), immune-mediated hematologic disease (n=3), lymphoblastic leukemia (n=2), ehrlichiosis (n=2), estrogen toxicity (n=2), and multiple myeloma (n=1). Malignant histiocytosis and idiopathic aplastic anemia occurred more frequently than was expected. Doxoruicin was the chemotherapeutic agent associated with pancytopenia. Hematologic recovery and patient survival time varied with the cause of pancytopenia; therefore, a specific diagnosis was essential for establishing prognosis. Differentiation among causes of pancytopenia requires a systemic approach that includes elimination of infectious and drug-induced causes, and examination of bone marrow aspiration and core biopsy specimens.

OBJECTIVETo determine whether platelet-activating factor (PAF) is involved in acute lung microvascular injury associated with pneumonic pasteurellosis in calves.ANIMALS15 healthy 2- to 4-week-old male Holstein calves.PROCEDURECalves were anesthetized and inoculated intrabronchially with saline (0.9% NaCl) solution (n = 5) or 1x10(9) Pasteurella haemolytica organisms (n = 10). Of the 10 calves inoculated with P haemolytica, 5 also were treated with WEB 2086, a potent inhibitor of PAF, and 5 were treated with vehicle. Blood and bronchoalveolar lavage samples were collected before and 1, 2, 4, and 6 hours after inoculation of P. haemolytica. Blood samples were analyzed to evaluate total number and differential counts of leukocytes, dilute whole-blood leukocyte deformability, size of neutrophils, and neutrophil CD11b expression. Bronchoalveolar lavage samples were analyzed for total number and differential counts of nucleated cells, total protein concentration, and hemoglobin concentration. Size and gross and histologic appearance of lung lesions also was determined.RESULTSTreatment of calves with WEB 2086 reduced size of lung lesions, attenuated the increase in microvascular permeability, and reduced neutrophil infiltration in the first 4 hours after inoculation. Treatment with WEB 2086 also attenuated a decrease in leukocyte deformability, increase in size of neutrophils, and CD11b expression by circulating neutrophils.CONCLUSIONS AND CLINICAL RELEVANCEIt appears that PAF is a major mediator for altered lung microvascular permeability and activation of circulating neutrophils in the first 4 hours after onset of pneumonic pasteurellosis in calves.

OBJECTIVETo investigate rheologic properties of bovine neutrophils that may result in adhesion molecule-independent sequestration of neutrophils in inflamed lungs of cattle.ANIMALSHealthy 2- to 4-week-old male Holstein calves.PROCEDURESNeutrophil deformability, filamentous actin (F-actin) content, and CD11b expression was determined for unstimulated bovine neutrophils and bovine neutrophils incubated with the inflammatory mediators tumor necrosis factor-alpha (TNF), platelet-activating factor (PAF), interleukin-8 (IL-8), zymosan-activated plasma (ZAP), Pasteurella haemolytica-derived lipopolysaccharide (LPS), and P haemolytica leukotoxin. Neutrophils were separated into 3 subpopulations on the basis of size. The Factin content and CD11 b expression were evaluated by use of flow cytometry. Leukocyte deformability was evaluated by filtration of dilute whole blood.RESULTSThe subpopulation of the smallest-sized neutrophils (>90% of neutrophils) contained little F-actin. A subpopulation of slightly larger neutrophils had a profound increase in F-actin content and CD11 b expression. The subpopulation of the largest neutrophils had increased F-actin content and CD11b expression, compared with those for both subpopulations of smaller neutrophils. Incubation of neutrophils with PAF and ZAP but not TNF, IL-8, LPS, or leukotoxin, resulted in decreased neutrophil deformability and increased F-actin content. Incubation with PAF and TNF induced an increase in size of neutrophils.CONCLUSIONS AND CLINICAL RELEVANCESize can be used to identify subpopulations of large and rigid neutrophils in blood samples from healthy calves. Platelet-activating factor and activated complement fragments are potent inducers of F-actin formation and neutrophil rigidity. Physical changes in neutrophils may impede their transit through lung microvasculature and result in leukocyte trapping independent of adhesion molecule interactions with endothelial cells.

The filterability of platelet-neutrophil aggregates through filters containing 5 μm pores was determined to evaluate the potential of plateletneutrophil aggregates to alter blood flow in the microvasculature. Incubation of platelet-neutrophil mixture with platelet-activating factor (PAF) and with 0.5 μM adenosine diphosphate (ADP) resulted in large platelet-neutrophil aggregates which rapidly plugged filter pores. Incubation of platelet-neutrophil mixtures with lower concentrations of ADP resulted in small platelet-neutrophil aggregates that contained only one neutrophil. Filtration of these samples resulted in a 1.3-, 3.2- and 3.7-fold increase in initial filtration pressure at ADP concentrations of 0.05, 0.15 and 0.25 μM, respectively. We conclude that platelet-neutrophil aggregates have reduced deformability and may alter blood flow in the microvasculature.

OBJECTIVES:To determine the structural and functional alterations in circulating neutrophils that may lead to sequestration in lung microvasculature and endothelial injury in calves with experimentally induced pneumonic pasteurellosis.ANIMALS:10 healthy, 2- to 4-week-old male Holstein calves.PROCEDURES:Holstein calves were anesthetized and inoculated intrabronchially with Dulbecco phosphate buffered saline (0.9% NaCl) solution (DPBSS; 5 control calves) or 1 x 10(9) Pasteurella haemolytica organisms (5 infected calves). Blood samples were collected before and 1, 2, 4, and 6 hours after inoculation. Total and differential WBC count, dilute whole blood leukocyte deformability, neutrophil size distribution, and neutrophil surface CD11b expression were measured in blood samples.RESULTS:A progressive decrease in leukocyte deformability and increase in neutrophil size was detected 1, 2, 4, and 6 hours after inoculation of P haemolytica. Neutrophil surface CD11b expression was greater than baseline values at 6 hours after inoculation of P haemolytica. Two populations of neutrophils with an increase in size were detected in P haemolytica-infected calves. Both subpopulations had increased CD11b expression, compared with neutrophils that were typical in size.CONCLUSIONS AND CLINICAL RELEVANCE:Neutrophils circulate in an activated and nondeformable state in calves with experimentally induced pneumonic pasteurellosis. A decrease in neutrophil deformability and neutrophil aggregation may contribute to neutrophil trapping in the lung microvasculature during pneumonic pasteurellosis in calves.

Objectives-To determining whether inhibition of platelet aggregation prevents development of carbohydrate overload-induced alimentary laminitis.Animals-22 healthy adult ponies.Procedures-Acute laminitis was induced by oral administration of corn starch/wood flour to 16 ponies, 8 of which were treated with a synthetic analogue of the platelet fibrinogen receptor antagonist peptide (RPR) RGDS (arginine-glycine-aspartic acid-serine) 110885; 6 ponies served as negative controls. Blood was collected before and at 4, 8, 12, 24, 28, and 32 hours after administration of carbohydrate overload, and PCV, total plasma protein concentration, platelet count, activated clotting time, whole blood recalcification time, spontaneous platelet aggregation, ex vivo platelet aggregation responses, in vivo platelet activation, and platelet-neutrophil aggregates were evaluated.Results-Of 16 ponies given carbohydrate, 6 of 8 untreated ponies developed laminitis and 0 of 8 ponies treated with RPR 110885 developed laminitis. The RPR 110885 treatment attenuated the increase in platelet-neutrophil aggregates observed in untreated ponies.Conclusions-Platelets are involved in the pathogenesis of equine alimentary laminitis.Clinical Relevance-Platelet aggregation inhibitors may be useful for prevention or treatment of laminitis, or both.

OBJECTIVES:To determine whether mucosal permeability is altered during the prodromal stages of alimentary laminitis.ANIMALS:15 healthy adult ponies.PROCEDURES:intestinal permeability was evaluated for control ponies (n = 5) and for ponies 4 to 12 (n = 5) and 20 to 28 (n = 5) hours after administration of carbohydrate overload. Mucosal permeability was determined by measuring the percentage of orally administered technetium Tc99m diethylenetriaminopentaacetate (99mTc-DTPA) excreted in urine during an 8-hour period, then measuring blood radioactivity at hourly intervals. Plasma endotoxin-like activity was measured by use of a chromogenic Limulus amebocyte assay.RESULTS:Urinary excretion of 99mTc-DTPA was 2.45% of administered dose for control ponies, and was 16.67% of administered dose 4 to 12 hours and 3.57% of administered dose 20 to 28 hours after administration of carbohydrate.CONCLUSIONS:A marked but transient increase in intestinal permeability was observed early in the prodromal stages of alimentary laminitis.CLINICAL RELEVANCE:Absorption of substances from the intestine may be an initiating event in alimentary laminitis.