Phenotypic analysis of peripheral blood and bronchoalveolar lavage fluid lymphocytes in control and chronic obstructive pulmonary disease affected horses, before and after 'natural (hay and straw) challenges'

Comprehensive Flow Cytometric Characterization of Bronchoalveolar Lavage Cells Indicates Comparable Phenotypes Between Asthmatic and Healthy Horses But Functional Lymphocyte Differences

Equine asthma (EA) is a highly relevant disease, estimated to affect up to 20% of all horses, and compares to human asthma. The pathogenesis of EA is most likely immune-mediated, yet incompletely understood. To study the immune response in the affected lower airways, mixed leukocytes were acquired through bronchoalveolar lavage (BAL) and the cell populations were analyzed on a single-cell basis by flow cytometry (FC). Samples of 38 horses grouped as respiratory healthy or affected by mild to moderate (mEA) or severe EA (sEA) according to their history, clinical signs, and BAL cytology were analyzed. Using FC, BAL cells and PBMC were comprehensively characterized by cell surface markers ex vivo. An increased percentage of DH24A⁺ polymorphonuclear cells, and decreased percentages of CD14⁺ macrophages were detected in BAL from horses with sEA compared to healthy horses or horses with mEA, while lymphocyte proportions were similar between all groups. Independently of EA, macrophages in BAL were CD14⁺CD16⁺, which contrasts the majority of CD14⁺CD16^- classical monocytes in PBMC. Percentages of CD16-expressing BAL macrophages were reduced in BAL from horses with sEA compared to healthy horses. While PBMC lymphocytes predominantly contain CD4⁺ T cells, B cells and few CD8⁺ T cells, BAL lymphocytes comprised mainly CD8⁺ T cells, fewer CD4⁺ T cells and hardly any B cells. These lymphocyte subsets’ distributions were similar between all groups. After PMA/ionomycin stimulation in vitro, lymphocyte activation (CD154 and T helper cell cytokine expression) was analyzed in BAL cells of 26 of the horses and group differences were observed (p=0.01–0.11). Compared to healthy horses’ BAL, CD154⁺ lymphocytes from horses with mEA, and CD4⁺IL-17A⁺ lymphocytes from horses with sEA were increased in frequency. Activated CD4⁺ T helper cells were more frequent in asthmatics’ (mEA, sEA) compared to healthy horses’ PBMC lymphocytes. In summary, FC analysis of BAL cells identified increased polymorphonuclear cells frequencies in sEA as established, while macrophage percentages were mildly reduced, and lymphocyte populations remained unaffected by EA. Cytokine production differences of BAL lymphocytes from horses with sEA compared to healthy horses’ cells point towards a functional difference, namely increased local type 3 responses in sEA.

Giant Multinucleated Cells Are Associated with Mastocytic Inflammatory Signature Equine Asthma

Equine asthma is currently diagnosed by the presence of increased neutrophil (>5%), mast cell (>2%), and/or eosinophil (>1%) differential cell count. Macrophages are normal resident cells within the alveoli. Their presence in BALF is considered normal, but the clinical implication of the presence of activated or fused macrophages (giant multinucleated cells, GMC) is currently overlooked. We aimed to assess the prevalence, cytological determinants, and clinical significance of increased GMC counts in BALF of 34 asthmatic horses compared to 10 controls. Counts were performed on 15 randomly selected high magnification fields per cytospin slide (40×), and expressed as GMC:single macrophage (GMC:M) ratio. Regression models were used for statistical analysis. GMC was frequently observed in both asthmatic and control horses, with an increased prevalence of equine asthma (p = 0.01). GMC:M ratio was significantly higher in severe vs. mild to moderate equine asthmatic and control horses. In asthmatic horses, an increased GMC:M ratio was significantly associated with BALF mastocytosis (p = 0.01), once adjusting for age and the presence and severity of clinical signs of the horses. Tachypnea was the only clinical sign that tended to be positively associated with GMC:M ratio after adjustment (p = 0.08). In conclusion, our data suggest that a relationship might exist between molecular mechanisms regulating GMC formation and mast cell recruitment in the equine lung. The same mechanisms could lead to tachypnea even in the absence of respiratory effort at rest. We suggest including GMC count in the basic cytological assessment of BALF samples to gain more insights into their role in equine asthma.

The Immune Mechanisms of Severe Equine Asthma-Current Understanding and What Is Missing

Severe equine asthma is a chronic respiratory disease of adult horses, occurring when genetically susceptible individuals are exposed to environmental aeroallergens. This results in airway inflammation, mucus accumulation and bronchial constriction. Although several studies aimed at evaluating the genetic and immune pathways associated with the disease, the results reported are inconsistent. Furthermore, the complexity and heterogeneity of this disease bears great similarity to what is described for human asthma. Currently available studies identified two chromosome regions (ECA13 and ECA15) and several genes associated with the disease. The inflammatory response appears to be mediated by T helper cells (Th1, Th2, Th17) and neutrophilic inflammation significantly contributes to the persistence of airway inflammatory status. This review evaluates the reported findings pertaining to the genetical and immunological background of severe equine asthma and reflects on their implications in the pathophysiology of the disease whilst discussing further areas of research interest aiming at advancing treatment and prognosis of affected individuals.

Comparison of Four Different Allergy Tests in Equine Asthma Affected Horses and Allergen Inhalation Provocation Test

Potential triggers for equine asthma are allergens from hay and straw dusts, mold spores and storage mites. The contribution of these environmental trigger factors to equine asthma is still largely uncertain. The aim of this study was to compare results of four allergy tests from healthy and asthma-affected horses, and to evaluate the clinical relevance of allergens tested positive via specific inhalation provocation test. Fifteen horses were classified using a clinical scoring system as asthmatic (n = 9) or control (n = 6). Four different allergy tests (functional in vitro test, intradermal test, Fc-epsilon receptor test, and ELISA for allergen-specific IgE) were compared. A histamine inhalation provocation test as positive control was performed in all horses and the interpleural pressure was measured. In addition, two individual allergens were chosen for the allergen inhalation provocation test based on the results of the allergy tests and inhaled in increasing concentrations, until signs of dyspnea occurred. None of the four allergy tests could differentiate reliably between controls and asthma-affected horses. There was no agreement among the results of the four allergy tests. The interpleural pressure results showed a large individual variability. A clear positive reaction on the allergen inhalation provocation test was only detected in two asthma-affected horses 6 hours after allergen inhalation with Aspergillus fumigatus and Cladosporium herbarum. In most cases a purely type I immediate reaction is unlikely to be involved in causing the clinical signs of equine asthma. Because of a delayed reaction after allergen provocation in two horses, the involvement of cell-mediated type III or IV hypersensitivity may be possible. As all allergy tests used in this study can only detect IgE-mediated hypersensitivity, these tests are probably not suitable for an etiological diagnosis of equine asthma.

A comparison of nanoparticullate CpG immunotherapy with and without allergens in spontaneously equine asthma-affected horses, an animal model

INTRODUCTION

New therapeutic strategies to modulate the immune response of human and equine allergic asthma are still under extensive investigation. Immunomodulating agents stimulating T-regulatory cells offer new treatment options beyond conventional symptomatic treatment or specific immunotherapy for human and equine allergic airway diseases, with the goal of a homoeostatic T-helper cell balance. The aim of this study was to evaluate the effects of a nebulized gelatin nanoparticle-CpG formulation (CpG-GNP) with and without specific allergens for the treatment of spontaneous allergic equine asthma as a model for human asthma.

METHODS

Twenty equine asthma-affected horses were treated either with CpG-GNP alone or CpG-GNP with allergens. Two specific allergens were selected for each horse based on history and an in-vitro test. Each horse received seven administrations of the respective nebulized composition and was examined before treatment, immediately after and 6 weeks after the treatment course.

RESULTS

Clinical parameters such as breathing rate, indirect interpleural measurement, arterial blood gases, amount of tracheal mucus and percentage of neutrophils and cytokines in tracheal washes and serum samples were evaluated. Treatment with CpG-GNP alone as well as in combinations with relevant allergens resulted in clinical improvement of nasal discharge, breathing rate, amount of secretion and viscosity, neutrophil percentage and partial oxygen pressure directly after and 6 weeks after treatment. There were no significant differences between the two treatments in clinical parameters or local cytokine profiles in the tracheal wash fluid (IL-10, IFN-g, and IL-17). IL-4 concentrations decreased significantly in both groups.

CONCLUSION

Nonspecific CpG-GNP-based immunotherapy shows potential as a treatment for equine and possibly also human allergic asthma.

A review of the equine age-related changes in the immune system: comparisons between human and equine aging, with focus on lung-specific immune-aging

The equine aging process involves many changes to the immune system that may be related to genetics, the level of nutrition, the environment and/or an underlying subclinical disease. Geriatric horses defined as horses above the age of 20, exhibit a decline in body condition, muscle tone and general well-being. It is not known whether these changes contribute to decreased immune function or are the result of declining immune function. Geriatric years are characterized by increased susceptibility to infections and a reduced antibody response to vaccination as a result of changes in the immune system. Humans and horses share many of these age-related changes, with only a few differences. Thus, inflamm-aging and immunosenescence are well-described phenomena in both human and equine research, particularly in relation to the peripheral blood and especially the T-cell compartment. However, the lung is faced with unique challenges because of its constant interaction with the external environment and thus may not share similarities to peripheral blood when considering age-related changes in immune function. Indeed, recent studies have shown discrepancies in cytokine mRNA and protein expression between the peripheral blood and bronchoalveolar lavage immune cells. These results provide important evidence that age-related immune changes or 'dys-functions' are organ-specific.

Recurrent airway obstruction: a review

Recurrent airway obstruction is a widely recognised airway disorder, characterised by hypersensitivity-mediated neutrophilic airway inflammation and lower airway obstruction in a subpopulation of horses when exposed to suboptimal environments high in airborne organic dust. Over the past decade, numerous studies have further advanced our understanding of different aspects of the disease. These include clarification of the important inhaled airborne agents responsible for disease induction, improving our understanding of the underlying genetic basis of disease susceptibility and unveiling the fundamental immunological mechanisms leading to establishment of the classic disease phenotype. This review, as well as giving a clinical overview of recurrent airway obstruction, summarises much of the work in these areas that have culminated in a more thorough understanding of this debilitating disease.

Age-related changes in intracellular expression of IFN-γ and TNF-α in equine lymphocytes measured in bronchoalveolar lavage and peripheral blood

Diseases of the lower airways represent some of the most common conditions affecting horses of all ages, but the type and severity tends to follow the horses' age. The age-related dysregulation of pro-inflammatory cytokines may, in part contribute to the development of the diseases. Therefore, we hypothesize that the expression of pro-inflammatory cytokines increases with age. Peripheral blood mononuclear cells (PBMC) and bronchoalveolar lavage (BAL) cells from clinically healthy horses of different ages were used for the investigation. The cells were stimulated and the production of IFN-γ and TNF-α measured using flow cytometry. The frequency of IFN-γ producing lymphocytes in both BAL and PBMCs from old horses was significantly increased compared to the young horses. The age-related increase of TNF-α production was also found in PBMCs but not in BAL cells. In conclusion, the productions of certain pro-inflammatory cytokine are age-associated. This age-associated increase of pro-inflammatory cytokines production may be a co-factor for the pathogenesis of equine airway diseases.

Pulmonary intravascular macrophages as proinflammatory cells in heaves, an asthma-like equine disease

Heaves, an obstructive neutrophilic airway inflammation of horses, is triggered by dust components such as endotoxin and has similarities to human asthma. Pulmonary intravascular macrophages (PIMs) increase horses' sensitivity to endotoxin-induced lung inflammation; however, their role in an airborne pathology remains unknown. Therefore, we investigated the role of PIMs in the development of heaves in horses. Clinical and inflammatory responses were evaluated following induction of heaves by moldy hay exposure and PIM depletion with gadolinium chloride (GC). Mares (N = 9) were exposed to four treatments: alfalfa cubes (Cb), alfalfa cubes + GC (Cb-GC), moldy hay (MH), and moldy hay + GC (MH-GC). Clinical scores and neutrophil concentrations in bronchoalveolar lavage (BAL) fluid were higher when mares received MH compared with MH-GC. BAL cells from MH-GC-treated mares had significantly lower IL-8 and TLR4 mRNA expression compared with MH-treated mares. In vitro LPS challenge significantly increased IL-8 but not TLR4 mRNA expression in BAL cells recovered from horses fed with MH, but not from the MH-GC treatment. In summary, PIM depletion attenuated clinical scores, reduced the alveolar migration of neutrophils, and decreased the expression of proinflammatory molecules in BAL cells of heaves horses, suggesting a proinflammatory role of PIMs in the development of airborne pathology.

Comparison of genomic and proteomic data in recurrent airway obstruction affected horses using Ingenuity Pathway Analysis®

Background

Recurrent airway obstruction (RAO) is a severe chronic respiratory disease affecting horses worldwide, though mostly in the Northern hemisphere. Environmental as well as genetic factors strongly influence the course and prognosis of the disease. Research has been focused on characterization of immunologic factors contributing to inflammatory responses, on genetic linkage analysis, and, more recently, on proteomic analysis of airway secretions from affected horses. The goal of this study was to investigate the interactions between eight candidate genes previously identified in a genetic linkage study and proteins expressed in bronchoalveolar lavage fluid (BALF) collected from healthy and RAO-affected horses. The analysis was carried out with Ingenuity Pathway Analysis^® bioinformatics software.

Results

The gene with the greatest number of indirect interactions with the set of proteins identified is Interleukin 4 Receptor (IL-4R), whose protein has also been detected in BALF. Interleukin 21 receptor and chemokine (C-C motif) ligand 24 also showed a large number of interactions with the group of detected proteins. Protein products of other genes like that of SOCS5, revealed direct interactions with the IL-4R protein. The interacting proteins NOD2, RPS6KA5 and FOXP3 found in several pathways are reported regulators of the NFκB pathway.

Conclusions

The pathways generated with IL-4R highlight possible important intracellular signaling cascades implicating, for instance, NFκB. Furthermore, the proposed interaction between SOCS5 and IL-4R could explain how different genes can lead to identical clinical RAO phenotypes, as observed in two Swiss Warmblood half sibling families because these proteins interact upstream of an important cascade where they may act as a functional unit.

Increased apoptosis of CD4 and CD8 T lymphocytes in the airways of horses with recurrent airway obstruction

Recurrent airway obstruction (RAO, also known as equine heaves) is an inflammatory condition similar to human asthma caused by exposure of susceptible horses to poorly ventilated stable environments. The disease is characterized by neutrophilic airway inflammation, mucus hypersecretion and reversible bronchoconstriction. This inflammatory process is mediated by several factors, including antibodies, cytokines, resident cells of the airway and inflammatory cellular components that arrive in the respiratory tract. An increasing body of evidence has lent support to the concept that a dysregulation of T cell apoptosis may play a central role in the development of airway inflammation and the associated asthma. Therefore, the aim of this study was to investigate early and late apoptosis of CD4 and CD8 T cell subpopulations obtained from the airways of acute RAO-positive animals after exposure to hay/straw. The percentages of CD4 and CD8 T cells and their associated frequencies of apoptosis were quantified using flow cytometry. Hay/straw exposure induced clinical airway obstruction, airway neutrophilia and increased airway mucus production in RAO-positive horses. In addition, allergen exposure increased the percentage of CD4 T cells in RAO-positive horses as well as the frequency of early and late apoptosis in both CD4 and CD8 lymphocyte subpopulations. These results suggest that the higher frequency of lymphocyte apoptosis may play a role in disease progression of horses afflicted with RAO and may partially explain the characteristic remission of this pathological condition once the allergen source is removed. However, further studies are needed to clarify the role of T cell apoptosis in RAO-affected horses.

Laboratory findings in respiratory fluids of the poorly-performing horse

Any disorder impairing a performance horse's ability to ventilate its lungs and exchange oxygen compromises exercise performance in any discipline. Since bronchoalveolar lavage was described in horses in the early 1980s, laboratory evaluation of respiratory fluids, along with clinical and functional assessment of the respiratory system, has become a relevant step in the diagnosis of respiratory disease affecting performance. The aim of this review is to provide objective information to assist clinicians in interpreting laboratory findings by (1) summarising published cytological references values in both clinically healthy horses and those with various airway diseases, (2) assessing the influence of physiological circumstances, such as exercise, on the cytological evaluation, (3) discussing the relationship between cytological and microbiological analyses, clinical signs and respiratory function, and (4) suggesting how this latter relationship may affect performance.

Immunological response to long-term transport stress in mature horses and effects of adaptogenic dietary supplementation as an immunomodulator

REASONS FOR PERFORMING STUDY

Little information exists on the immunological effects of transport or the use of supplements to minimise transport stress.

OBJECTIVES

To establish baseline ranges and evaluate immunophenotypic and functional changes associated with transport and a nutritional 'adaptogen' supplement.

METHODS

Horses received either supplement (n = 10) or placebos (n = 9) during the 30 day study. After 28 days in stalls, 12 horses (6 supplement; 6 placebo) were transported for 24 h, then unloaded and recovered. Venous blood samples were collected on Days 1, 14 and 28 to establish baselines, and on Days 28, 29 and 30 to examine changes during transport and recovery.

RESULTS

Transport prompted elevations (P<0.05) in cortisol concentration, neutrophil count and white blood cell counts, while lymphocyte subpopulation counts (CD3+, CD4+, CD8+, CD21+) decreased (P<0.05). Normal phenotypic lymphocyte profiles returned within 24 h of recovery. Supplement effects on immunophenotype (CD21+ and CD8+) were observed in stabled horses (P<0.05), but not in transported horses.

CONCLUSIONS

These results provide insights into the immunological mechanisms associated with long-term transport.

POTENTIAL RELEVANCE

The existence of a small window of immunological uncertainty follows long-term transportation, enhancing the potential risk of infectious disease in susceptible individuals.

Cytokine profiles of peripheral blood and airway CD4 and CD8 T lymphocytes in horses with recurrent airway obstruction

Equine recurrent airway obstruction (RAO) is thought to result from an aberrant immune response to inhaled antigens, modulated by T lymphocytes via the secretion of pro-inflammatory cytokines. However data relating to the phenotypes of the T lymphocytes present in peripheral blood and bronchoalveolar lavage fluid of RAO horses and their cytokine profiles are contradictory. The aim of this study was to further investigate the cytokine (IL-4, IL-5, IL-13 and INF-gamma) mRNA expression profile in peripheral blood lymphocytes and bronchoalveolar lavage lymphocytes from RAO and control horses, before and at 48 h after horses were exposed to hay/straw. In contrast to previous studies, cytokine expression was quantified in populations of CD4 and CD8 T lymphocytes which were purified using magnetic bead antibody cell separation. Hay/straw exposure induced clinical airway obstruction, airway neutrophilia and airway lymphocytosis in RAO horses, and, induced a mild, but significant, airway neutrophilia in controls. However, hay/straw exposure had no significant effect on peripheral blood lymphocyte or bronchoalveolar lavage lymphocyte cytokine expression in either group. In conclusion, RAO was not associated with alterations in lymphocyte cytokine expression that are consistent with Th1 or Th2 responses, but rather with a general down-regulation in expression of the measured cytokines in peripheral blood lymphocytes and bronchoalveolar lavage lymphocytes.

Allergen challenge alters lymphocyte phosphodiesterase activity in horses with heaves

Heaves is an allergic airway disease in horses characterised by reversible airway obstruction, bronchial hyperresponsiveness and airway inflammation associated with a Th(2) response. Cyclic nucleotide-dependent signalling pathways can regulate lymphocyte function. In this study, we examined lymphocyte PDE activity comparing horses with heaves to healthy control animals. Total PDE activity and the effects of isoenzyme selective inhibitors were measured before, 5 and 24 h after the start of a 7 h allergen challenge. Allergen challenge had no effect on either total cAMP PDE activity or its inhibition by the PDE4 selective inhibitor, rolipram, and the non-selective PDE inhibitor, theophylline. In contrast, the PDE3 selective inhibitor, quazinone, caused significantly greater inhibition of cAMP PDE activity before challenge in the heaves susceptible group. Additionally, total cGMP PDE activity was significantly lower 24 h after the start of challenge in the heaves affected group (11+/-2 and 21+/-3 pmol/min/mg for heaves and control animals, respectively) and the PDE5 selective inhibitor, zaprinast, caused significantly less inhibition in the heaves group at this time point. The functional significance of these findings was explored by examining the effect of PDE3, PDE4 and PDE5 selective inhibitors on mitogen-induced mononuclear cell proliferation before and 24 h after the start of allergen challenge. Proliferation decreased after challenge in the heaves group (stimulation index=328+/-110 and 200+/-72 before and after challenge, respectively) whilst remaining constant in the control group (stimulation index=161+/-13 and 183+/-45 before and after challenge, respectively). However, all three PDE inhibitors caused a similar amount of inhibition at each time point and the effect of a combination of a PDE3 and a PDE5 inhibitor was simply additive in both groups. These results suggest differences in the control of lymphocyte PDE activity in horses with heaves.

Biochemical and functional assessment of equine lymphocyte phosphodiesterases and protein kinase C

Lymphocytes play an important role in allergic inflammation and have been implicated in the pathogenesis of equine allergic skin and respiratory disease. Targeting intracellular signalling pathways in human lymphocytes has demonstrated a role for both phosphodiesterase and protein kinase C in cell activation. The aim of this study was to measure total cyclic nucleotide hydrolysing phosphodiesterase activity and to identify the phosphodiesterase and protein kinase C isoenzymes present in equine lymphocytes. The functional significance of these isoenzymes was then investigated by examining their role in peripheral blood mononuclear cell proliferation using isoenzyme selective inhibitors. Total cyclic adenosine monophosphate hydrolysing phosphodiesterase activity was double that of cyclic guanosine monophosphate (30+/-2 pmol/min mg versus 16+/-3 pmol/min mg for cyclic adenosine and cyclic guanosine monophosphate phosphodiesterase activity, respectively). Evidence for the presence of PDE1, 3, 4 and 5 was obtained and PKCalpha, beta, delta, eta, iota, theta and zeta were identified. Selective inhibitors of PDE4, PKCdelta and conventional PKCs alpha and beta caused significant inhibition of mitogen-induced peripheral blood mononuclear cell proliferation. This study demonstrates a functional role for specific signalling isoenzymes and suggests that, in the context of allergic inflammation, targeting inflammatory cells involved in disease pathogenesis with relevant isoenzyme inhibitors may have therapeutic potential.

Recurrent airway obstruction (RAO) in horses is characterized by IFN-gamma and IL-8 production in bronchoalveolar lavage cells

In horses prone to developing recurrent airway obstruction (RAO), we tested the hypotheses that the cytokine profile in the bronchoalveolar lavage (BAL) cells of affected horses would reflect a polarized Th-2 response; that cytokine and chemokine alterations would occur within 24 h of allergen exposure; and that allergen exposure would induce alterations in the expression of the transcription factor t-bet (t-box-expressed in T-cells). The expression levels of interleukin-4 (IL-4), IL-13, Interferon-gamma (IFN-gamma), t-bet, IL-8 and granulocyte-macrophage colony stimulating factor (GM-CSF) were measured in BAL cells obtained from control and RAO-susceptible horses during an asymptomatic phase and at 24 h and 5 weeks post-stabling and hay exposure. At each sampling time, BAL neutrophil percentages in the RAO-group exceeded controls. In the RAO-group, only IL-13 expression was decreased 2-fold during the asymptomatic phase. No differences in cytokine or chemokine expression were detected during the acute exposure phase. During the chronic phase, IFN-gamma and IL-8 expression levels were 2.5- and 3-fold greater, respectively, in the RAO-group. No other differences in gene expression were detected. We conclude that the cytokine profile of the airway cells does not reflect a polarized Th-2 response; that increases in IFN-gamma result from a t-bet independent pathway and that chemokines from epithelial or interstitial cells may contribute to early neutrophil influx.

Flow cytometric analysis of peripheral blood mononuclear cells induced by experimental endotoxemia in horse

Cellular activation and functional cell surface markers were evaluated during experimentally-induced endotoxemia in healthy horses. Eight healthy adult horses were infused a low dose of endotoxin (lipopolysaccharide from Escherichia coli O26: B6, 30 ng/kg of body weight, IV) and five control horses were given an equivalent volume of sterile saline solution. Venous blood samples were collected for flow cytometric analysis of peripheral blood mononuclear cells (PBMCs) and to measure plasma endotoxin concentrations. Clinical signs of endotoxemia were recorded at 10, 20, 30, 40, 50 min, 1, 2, 3, 4, 8, 16, 24 and 48 hr after endotoxin or saline solution administration. Clinical findings characteristic of endotoxemia (tachycardia, tachypnea, increased rectal temperature, and leukopenia) occurred transiently in all horses administered endotoxin; however, plasma endotoxin concentrations were detectable in only 50% (4/8) of the endotoxin-infused horses. The percentage of CD4(+), CD5(+), and CD8(+) cells decreased while the percentage of CD14(+), IgM(+), and MHC class II(+) cells increased significantly after endotoxin infusion. Alterations in the immunophenotype of PBMCs from horses with experimentally-induced endotoxemia were associated with changes in vital signs, indicating that endotoxin altered the immuno balance.

Validity of pulmonary function indices derived from the volumetric capnogram in horses with recurrent airway obstruction (RAO)

The objective of this study was to determine the accuracy with which pulmonary function indices derived from the volumetric capnogram can diagnose different degrees of recurrent airway obstruction (RAO) in 63 warmblood horses. The sensitivity, specificity, the area under the receiver operating curve (AUC), optimal cut-off values and predictive values of the indices were calculated. The results obtained have shown that there is no single index characterised by specificity and sensitivity to differentiate with an accuracy of >90 per cent between the different degrees of RAO compared to the clinical examination. The indices A(1)/A(2) and VD(alv)/ VT(alv) (AUC=0.55 and 0.53) appeared to have the highest relative sensitivity and specificity to differentiate between healthy horses and horses suffering from subclinical or minor RAO and the indices VD(phys)/ VT and VD(Bohr)/ VT between horses suffering from subclinical or minor RAO and horses with moderate to severe RAO (AUC=0.71 and 0.70). We do not consider it acceptable to use cut off values optimised for both maximal sensitivity and specificity, because a great number of horses would have been inappropriately classified.

Cytokine induction in pulmonary airways of horses with heaves and effect of therapy with inhaled fluticasone propionate

Work in humans and laboratory animals has identified a central role for cytokines and chemokines in development and persistence of lower airway inflammation. The objectives of this study were to determine interleukin (IL)-1 beta, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha induction in bronchoalveolar lavage (BAL) of control horses and horses with heaves both during remission and exacerbation of the disease, and to determine the effect of therapy with inhaled fluticasone propionate on the cytokine profile of horses with heaves. IL-1 beta and TNF-alpha mRNA expression was significantly higher in horses with heaves after exposure to moldy hay compared to either values obtained during clinical remission or to healthy controls. IL-8 mRNA expression and protein concentrations were significantly higher in horses with heaves than in controls. Both IL-4 and IFN-gamma mRNA expression was increased at various times in heaves-susceptible horses compared to controls. IL-2, IL-5 and IL-10 mRNA expression was not detected in BAL cells of either group. Therapy with inhaled fluticasone propionate after induction of a severe heaves exacerbation resulted in complete resolution of clinical signs, normalization of pulmonary function tests, and significant decrease in BAL neutrophilia. This was associated with a significant decrease in IL-4 mRNA expression and increase in IFN-gamma/IL-4 ratio in horses with heaves. These results demonstrate the clinical efficacy of inhaled fluticasone propionate for the treatment of heaves and suggest a role for cytokines in the development of lower airway inflammation in heaves-susceptible horses.

Intradermal testing in healthy horses and horses with chronic obstructive pulmonary disease, recurrent urticaria, or allergic dermatitis

OBJECTIVE

To compare responses to a variety of intradermally injected allergens among healthy horses and horses with chronic obstructive pulmonary disease (COPD), recurrent urticaria (RU), and atopic dermatitis-insect hypersensitivity (allergic dermatitis [AD]).

DESIGN

Case-control study.

ANIMALS

86 horses.

PROCEDURE

Results of intradermal testing for horses with COPD, RU, or AD were compared with results for healthy horses.

RESULTS

Compared with healthy horses, horses with COPD, RU, and AD were significantly more likely to have positive (> or = 3+) reactions to intradermal allergens (molds, weeds, trees, grasses-crops, and insects) 30 minutes (immediate reaction), 4 hours (late-phase reactions), and 24 hours (delayed-phase reactions) after exposure. In addition, diseased horses reacted to a significantly higher number of allergens in each allergen group than did healthy horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Reactions to individual allergens should not be used to determine that horses have hypersensitivity. Overall patterns of reactivity to intradermal allergens may be helpful in management when used in conjunction with a compatible history and evidence of potential exposure to allergens in horses with conditions associated with hypersensitivity to environmental allergens.

Results of intradermal tests in horses without atopy and horses with atopic dermatitis or recurrent urticaria

OBJECTIVE

To compare results of intradermal tests (IDT) for environmental allergens at 30 minutes and 4, 6, and 24 hours after injection in horses without atopy and horses with atopic dermatitis (AD) or recurrent urticaria (RU).

ANIMALS

22 horses without atopy, 10 horses with RU, and 7 horses with AD.

PROCEDURE

In all horses, medical history was obtained, and results of physical examination, hematologic examination, serum biochemical analyses, examination of bronchoalveolar lavage fluid, and IDT with 73 allergens were examined.

RESULTS

Horses with AD or RU had a significantly greater mean number of positive reactions for IDT, compared with horses without atopy. Horses with AD had a significantly greater number of positive reactions than horses without atopy in every allergen group at all time periods, except for molds at 4 and 24 hours. Horses with RU had a significantly greater number of positive reactions than horses without atopy in every allergen group, except for molds at 30 minutes and 4 and 6 hours, trees at 4 and 6 hours, and grasses at 4 hours.

CONCLUSIONS AND CLINICAL RELEVANCE

A significantly greater number of positive reactions for IDT in horses with AD or RU, compared with horses without atopy, provides evidence of type-I IgE-mediated hypersensitivity for these diseases. Evaluation of results of IDT performed in horses with AD or RU is useful in determining specific allergens for the formulation of immunotherapy along with providing identification of allergens that could be useful when creating avoidance strategies.

Comparison of immediate intradermal test reactivity with serum IgE quantitation by use of a radioallergosorbent test and two ELISA in horses with and without atopy

OBJECTIVE

To compare a radioallergosorbent test and 2 ELISA with intradermal testing for the determination of environmental allergen hypersensitivity in horses with and without atopic diseases.

DESIGN

Prospective clinical study.

ANIMALS

10 horses with recurrent urticaria, 7 with atopic dermatitis, 16 with chronic obstructive pulmonary disease, and 22 without atopy.

PROCEDURE

History, physical examination, hemogram, serum biochemical analyses, bronchoalveolar lavage, and an intradermal test (used as the criterion standard) with a regional panel of 73 allergens were performed in all horses. Serum was analyzed by use of the 3 in vitro assays of allergen-specific IgE.

RESULTS

An ELISA based on the alpha chain of the high-affinity IgE receptor, the Fcepsilon receptor immunoglobin epsilon chain (FcepsilonRIalpha) for IgE, had the overall highest kappa statistic (0.238), positive predictive value (49%), and negative predictive value (78%). Overall agreement between the FcepsilonRIalpha-based ELISA and the intradermal test was fair. The highest kappa statistic was obtained by the FcepsilonRIalpha-based ELISA in horses with atopic dermatitis (0.330). Kappa statistics for the radioallergosorbent test and a polyclonal antibody-based ELISA agreed slightly with that of the intradermal test at best.

CONCLUSIONS AND CLINICAL RELEVANCE

None of the 3 serum allergy tests reliably detected allergen hypersensitivity, compared with the intradermal test. The FcepsilonRIalpha-based ELISA performed significantly better overall than the other 2 tests. Low sensitivity of all 3 assays indicates the need for continued study to elucidate a more sensitive test for the determination of potentially pathogenic allergens in horses.

Results of intradermal tests in horses without atopy and horses with chronic obstructive pulmonary disease

OBJECTIVE

To compare results of intradermal tests (IDT), conducted using environmental allergens, in horses without atopy and horses with chronic obstructive pulmonary disease (COPD).

ANIMALS

38 horses (22 horses without atopy and 16 horses with COPD).

PROCEDURE

All horses were examined (physical examination, hematologic examination, serum biochemical analyses, examination of bronchoalveolar lavage fluid). An IDT was conducted, using a full panel of 73 allergens consisting of grasses, weeds, trees, molds, and insects. Results of the IDT were evaluated 30 minutes and 4, 6, and 24 hours after injection of allergens. Horses without atopy were euthanatized, and gross and histologic changes of lung parenchyma were assessed.

RESULTS

Horses without atopy had a greater number of positive immediate and late-phase reactions than did horses with COPD. Horses with COPD did not have a significantly greater number of positive reactions than horses without atopy at any time period for any allergen group (grasses, weeds, trees, molds, and insects).

CONCLUSIONS AND CLINICAL RELEVANCE

Positive results of IDT document allergen-specific hypersensitivity but do not necessarily distinguish clinically relevant reactions from subclinical reactivity in horses with COPD. Interpreting the clinical relevance of results of IDT requires a thorough knowledge of the medical history, physical examination findings, and environment of each animal.

Tracheobronchial mucus viscoelasticity during environmental challenge in horses with recurrent airway obstruction

The goal of this study was to compare the rheological properties of mucus from horses with recurrent airway obstruction (RAO) to that from healthy controls during environmental challenge by stabling in stalls with straw as bedding and hay as feed. We determined viscoelasticity (log G* dyn/cm2, at 10 radian/s) and calculated mucociliary clearability index (MCI) and cough clearability index (CCI), which are derivative parameters of G* and the ratio of viscosity and elasticity measured at 1 and 100 radian/s, respectively. We also investigated the solids content of mucus, and cytology of bronchoalveolar lavage fluid (BALF). Samples were obtained before (0 h) and 6, 24 and 48 h after environmental challenge. The central findings were rheological changes in airway mucus, which occurred over time in RAO-affected animals, but not in controls. Mucus rheology was similar in both groups at 0 and 6 h. In RAO-affected horses, mucus viscoelasticity, as measured by log G*, increased from 2.49 +/- 0.18 dyn/cm2 (mean +/- s.e.) at 0 h to 3.05 +/- 0.13 dyn/cm2 at 24 h after environmental challenge, and was accompanied by significant decreases in MCI and CCI. Percent solids of mucus did not differ significantly between the 2 groups, nor over time. Rheological values did not correlate with BALF cytology. We conclude that viscoelastic properties of tracheal mucus samples from RAO horses in remission do not differ from those of normal horses. However, environmental challenge causes clinical signs of small airway disease and a concurrent increase in mucus viscoelasticity only in RAO horses. Therefore, we infer that unfavourable changes in mucus rheology may contribute to stasis and accumulation of mucus in RAO horses in exacerbation, but not in clinical remission.

The effect of high intensity exercise on the functional capacity of equine pulmonary alveolar macrophages and BAL-derived lymphocytes

The effect of strenuous exercise on the functional capacity of pulmonary alveolar macrophages (PAM) and bronchoalveolar lavage-derived lymphocytes was determined in eight horses prior to and after 7 weeks of training. Strenuous exercise had no effect on the total cell count or the percentage of live cells in bronchoalveolar lavage (BAL) samples prior to or following training. However, training was associated with a significant increase in the total cell count of pre-exercise BAL samples and a significant reduction in the percentage of live cells in post-exercise samples. Strenuous exercise was associated with impaired phagocytosis by PAM after 7 weeks of training but had no effect on similar samples obtained from untrained horses. The oxidative burst activity of PAM was significantly increased following strenuous exercise for both untrained and trained horses. BAL -derived lymphocyte oxidative burst was similarly affected following training. These results suggest that strenuous exercise and training may influence pulmonary immune cell function.

Characterization of peripheral blood and pulmonary leukocyte function in healthy foals

Studies in infants and foals indicate an age-dependent maturation of peripheral lymphocyte subsets. The age-dependent relationship for maturation of cellular immune responses, such as phagocytosis and lymphocyte responses of the peripheral and pulmonary-derived leukocytes, has not been characterized in foals. Lymphocyte subpopulations, mitogen stimulation response of lymphocytes, lymphokine-activated killing cell activity, phagocytosis and oxidative burst activity, and serum immunoglobulin (Ig) classes G and M concentrations were determined in developing foals. This study illustrates age-dependent changes in immunoglobulin class concentrations, lymphocyte subsets, and EqMHC Class II expression in cells of the peripheral blood and lungs of developing neonatal-to-weanling foals. The increase in peripheral blood and BAL B-lymphocytes and serum immunoglobulins in developing foals suggests expansion of immune cell populations during a time in which environmental pathogen exposure is great. General immune function, mitogenic responses, LAK cell activity, opsonized phagocytosis, and oxidative burst activity of newborns was similar to the adult horse. Total immune-cell numbers, rather than function, seemed to be the limiting factor in the development of the equine neonatal immune system. There was an age-related percent increase in the appearance of pulmonary lymphocytes, but a percent decrease in macrophages. Although development of the respiratory immune system follows changes in the peripheral blood, cellular expansion, activation, and migration may occur at a slower pace, making the respiratory environment susceptible to pathogens prior to optimal immune system maturity.

Studies on pulmonary and systemic Aspergillus fumigatus-specific IgE and IgG antibodies in horses affected with chronic obstructive pulmonary disease (COPD)

Inhalant exposure to Aspergillus fumigatus (Asp. f.) antigens induces marked inflammatory and immunological alterations in the lungs of horses affected with chronic obstructive pulmonary disease (COPD). In this study we investigated the role of specific allergen(s) present in Asp. f. on systemic and pulmonary IgE and IgG responses in control and COPD-affected horses, using an enzyme-linked immunosorbent assay (ELISA) and immunoblotting techniques. Compared with controls, horses affected with COPD had significantly higher levels of BALF IgE and IgG to somatic Asp. f. antigens as well as to the allergen 1/a (Asp. f. 1/a). Serum levels of IgE and IgG against these antigens did not differ between control and COPD-affected horses. Antigen specific IgE and IgG levels did not correlate between BALF and serum. Scanning of Asp. f. and IgE and IgG blots revealed bands that are recognised by both IgE- and IgG-specific antibodies. Additionally, all horses responded with BALF IgE- and IgG-specific for 93, 35, 31 and 23 kDa allergens, suggesting that these antigens are involved in the induction of airway IgE and IgG responses. These allergens may have the potential to be used as biomarkers for the diagnosis of Asp. f. related exacerbations of equine COPD.

Flow cytometric determination of oxidative burst activity of equine peripheral blood and bronchoalveolar lavage-derived leucocytes

Flow cytometric techniques were developed for the evaluation of oxidative burst activity in equine peripheral blood neutrophils and lymphocytes, as well as bronchoalveolar lavage derived pulmonary alveolar macrophages and lymphocytes. The oxidation of dichlorofluorescin was measured by the increased fluorescence of cells stimulated with phorbol myristate acetate or a variety of other stimulants. Flow cytometry was a suitable method for the evaluation of the intracellular oxidation in all cell populations evaluated. Analysis was rapid and cell separation before analysis was not required. Heterogenous cell populations with differing responsiveness to phorbol myristate acetate stimulated oxidative burst were identified in peripheral blood neutrophil and alveolar macrophage populations. The current study characterizes flow cytometric techniques for the evaluation of oxidative burst activity in equine peripheral blood and bronchoalveolar lavage-derived leucocytes.

The flow cytometric evaluation of phagocytosis by equine peripheral blood neutrophils and pulmonary alveolar macrophages

Flow cytometry was used to assess the phagocytosis of fluorescent-labelled bacteria by equine peripheral blood neutrophils and pulmonary alveolar macrophages. Cell populations were prepared from venous blood following ammonium chloride lysis and from washed bronchoalveolar lavage derived samples. Discrete clusters of cells, corresponding to different leucocyte groups, were readily identified on the basis of differing light scattering properties and could thus be discriminated, negating the need for prior cell separation. Cells able to associate with fluorescent-labelled bacteria (by attachment to the cell membrane or by internalization within the cell) acquired increased fluorescence and were readily differentiated from cells unable to interact with bacteria. The fluorescence of bacteria attached to the cell surface was quenched by the addition of trypan blue or counterstained by the addition of ethidium bromide to the assay, thus permitting identification of cells which were able to internalize bacteria.

Immune therapy in respiratory disease

Pharmacologic manipulation of pulmonary immunity plays an important role in primary and adjunct therapy for equine respiratory disease. Frequent exposure to respiratory viral pathogens, strenuous exercise, long distance transport, and inhalation of harmful substances destroy various aspects of the pulmonary defense system and predispose performance horses to development of infectious and noninfectious respiratory disease. Pulmonary immunity may be bolstered by nonspecific immunostimulants to combat primary or secondary immunodeficiency. State of the art technology improves active and passive-specific immunity for prevention of common infectious respiratory diseases in horses. Immuno-suppressive therapy can attenuate hyperreactive pulmonary immune responses in horses with allergic airway disease.

Comparative analysis of equine lymphocyte subsets in whole blood and gradient-purified samples

In the present study, two methods of lymphocyte preparation, whole blood lysis and Ficoll-Paque separation, prior to FACS analysis were compared. The comparison was done with single and dual-colour staining techniques. Monoclonal antibodies (mAb) against eCD4, eCD5, eCD8 and eMHC class II were used. There was no significant difference in the results obtained by these two methods.

Heterogeneity of porcine alveolar macrophages in experimental pneumonia

The aim of the study was the morphological and the phenotypic characterization of the porcine non-lymphocytic bronchoalveolar lavage (BAL) cell population of unaffected- and intrabronchial with Pasteurella multocida- (P.m.) infected swine using flow cytometry. Three non-lymphocytic cell populations of the porcine bronchoalveolar lavage could be differentiated: (1) large, high autofluorescent cells, (LHC); (2) small, high autofluorescent cells, (SHC); (3) small, low autofluorescent cells, (SLC). In comparison with the control animals, the percentage of the LHC and SHC within the whole non-lymphocytic cell population was decreased, whereas the SLC was significantly enhanced after infection. In order to investigate the phenotype of these cell populations, monoclonal antibodies against porcine antigens (SWC1, SWC3a, MHC class II, 2G6 (against macrophages)) were used. The results showed that the cells of the SLC seem to belong to the granulocytes, whereas the LHC and the SHC are lung macrophages. After the infection of the animals the percentage of the SWC1 positive cells of LHC and SHC were significantly increased, indicating an entrance of more immature macrophages. The percentage of the MHC class II antibody binding cells of all three non-lymphocytic populations was-decreased after infection, indicating a restricted MHC class II dependent antigen recognition in P.m. pneumonia.

Immunophenotypic analysis of foal bronchoalveolar lavage lymphocytes

The purpose of this study was to define the normal immunophenotype of equine lymphocytes present within the pulmonary air spaces, and to determine if this changes as foals age from one to ten weeks. Six pairs of mares and foals underwent sequential bronchoalveolar lavage (BAL) between 1 and 10 weeks of age. Data were grouped according to foal age (1, 1-3, 3-6, or 6-10 weeks of age) and were compared to adult control values obtained from the mares. BAL cells were harvested and stained with antibodies to the equine homologues of CD5, CD4, CD8, CD44, MHC I, MHC II and to equine IgG. Data, including percent positive staining and mean fluorescence intensity, were acquired on a flow cytometer gated for viable lymphocytes. All foals had significantly fewer CD5+ lymphocytes than mares, with the largest differences in the youngest animals. The percentage of CD4+ lymphocytes increased as the foals aged, approaching adult levels by 3 weeks of age, while the percentage of CD8+ lymphocytes increased more slowly and approached adult levels by 10 weeks of age. The CD4:CD8 ratio changed from 1.26 at one week of age to 0.78 by 10 weeks of age, compared to an adult value of 0.66. Lymphocytes from foals less than 6 weeks of age expressed MHC II and CD44 at lower levels than adults. The lymphocytic populations within the airways of foals are significantly different from adult animals. This may account for the susceptibility of foals to certain respiratory infections during the first few months of life.

Phenotypic characterization of lymphocyte subpopulations in horses affected with chronic obstructive pulmonary disease and in normal controls

The alterations in lymphocyte subsets in chronic obstructive pulmonary disease (COPD) in the horse were investigated by using monoclonal antibodies to identify CD3+, CD4+, CD8+, and surface immunoglobulin positive (sIg+) lymphocytes in peripheral blood, bronchoalveolar lavage fluid (BALF), and pulmonary biopsy frozen tissue sections. COPD-affected horses (n = 5) and normal controls (n = 5) were sampled prestabling and 14 days poststabling, at which time the COPD-affected horses wee exhibiting clinical signs of COPD. The peripheral blood absolute CD4+ lymphocyte count was significantly elevated in the COPD-affected horses pre- and poststabling. The CD4:CD8 ratio in peripheral blood of COPD-affect horses was unaffected by stabling, but the same ratio in the control horses was significantly decreased. These findings support a hypothesis of deficient regulation of a systemic immune response to indoor air in the COPD-affected horses. A large population of leukocytes in pulmonary biopsy immunohistochemical sections from both groups of horses appeared to be CD3+ CD4- CD8-, an uncommon phenotype in both the peripheral blood and BALF.

Lower respiratory tract disease

Lower respiratory tract disease is an important source of poor performance and exercise intolerance in racehorses and middle-aged sport horses. Horses that perform high-intensity exercise are predisposed to development of infectious and noninfectious respiratory disease. Diagnostic aids for investigation of lower respiratory tract disease include thorough thoracic auscultation with rebreathing, endoscopic examination, bronchoalveolar lavage (BAL), and thoracic radiographic examination. The therapeutic approach for horses with lower respiratory tract diseases often can be directed by cytologic evaluation of BAL fluid. Conservative management techniques may reduce the risk or severity of respiratory disease in horses performing high-intensity exercise.

The pathogenesis of chronic obstructive pulmonary disease of horses

Present evidence suggests that chronic obstructive pulmonary disease (COPD) of horses is a delayed hypersensitivity response to inhaled antigens, particularly the thermophilic moulds and actinomycetes that grow in damp hay. Within several hours of exposing COPD-susceptible horses to such hay, neutrophils invade the lung and accumulate in the lumens of airways, particularly bronchioles. The inflammatory response is accompanied by increased levels of histamine in bronchoalveolar lavage fluid, increased plasma levels of the inflammatory mediators thromboxane and 15-hydroxyeicosatetraenoic acid (15-HETE), and a decrease in the production of prostaglandin (PG) E2 by the airway mucosa. During acute exacerbations of COPD, airways exhibit nonspecific hyperresponsiveness and become obstructed as a result of bronchospasm and the accumulation of mucus and exudates. Bronchospasm is due largely to activation of smooth muscle muscarinic receptors by acetylcholine (ACh). Because the in vitro response of smooth muscle to ACh is unaltered, the increase in airway smooth muscle tone is probably a result of activation of airway reflexes by inflammatory mediators and decreases in inhibitory mechanisms such as the intrapulmonary nonadrenergic noncholinergic nervous system and the production of PGE2 in affected horses. The diffuse airway obstruction leads to uneven distribution of ventilation, ventilation/perfusion mismatching, and hypoxaemia. As a result of the increased respiratory drive caused by hypoxaemia and the presence of airway obstruction, horses adopt a characteristic breathing strategy in which very high peak flows at the start of exhalation rapidly diminish as exhalation proceeds.

Quantitative characterization of lymphocyte populations in bronchoalveolar lavage fluid and peripheral blood of normal adult Arabian horses

Bronchoalveolar lavage fluid (BALF) and peripheral blood were obtained from each of 17 adult Arabian mares and absolute numbers and relative lymphocyte proportions were determined for total T lymphocytes, using CD2 as a marker, CD4 + T lymphocytes, CD8 + T lymphocytes, CD5 + lymphocytes, and sIgM + B lymphocytes. The marked variation in BALF cell recovery resulted in wide variation in absolute values for each lymphocyte subset. The relative proportions of gated BALF lymphocytes were much less variable and provided a basis for comparison of lymphocyte subsets between the BALF and peripheral blood in normal horses. The total lymphocyte population was comprised predominantly of T cells in both BALF (83 +/- 11% CD2 + lymphocytes) and peripheral blood (70 +/- 8% CD2 + lymphocytes). There was a significantly greater percentage of total T lymphocytes and a significantly lower percentage of B lymphocytes in BALF as compared with peripheral blood collected at the same time. The increase in total T lymphocytes in BALF reflected a significantly higher percentage of CD8 + T lymphocytes in BALF (39 +/- 7%) as compared with peripheral blood (18 +/- 5%). The mean percentages of CD4 + T lymphocytes (58 +/- 13% in BALF; 62 +/- 8% in peripheral blood) and CD5 + lymphocytes (78 +/- 11% in BALF; 71 +/- 7% in peripheral blood), a population composed primarily of T lymphocytes but also including a subset of sIgM + B lymphocytes, were not significantly different between the two compartments. These normal values in Arabian mares provide a basis for detection of disease associated changes in the lymphocyte populations and for determination of effects of age and breed on lymphocyte subpopulations in the BALF and peripheral blood.

Overview of equine pruritus

Pruritus is a common complaint associated with equine dermatoses. Self-mutilation results in alopecia, excoriations, scaling, and crusting; the aesthetic appearance of the horse is often ruined and the horse may be unfit for riding or showing. This article specifically addresses those pruritic dermatoses caused by allergies, including food allergy/intolerance, atopy and contact allergy, as well as by two ectoparasites, stick-tight fleas and rhabditic mange. The clinical signs, diagnostic tests, and treatment recommendations are discussed for each disorder. Insect hypersensitivity and pruritus associated with the other more common ectoparasites are covered in depth elsewhere in this issue.

Quantitation of alpha-1 proteinase inhibitor in the pulmonary epithelial lining fluid of horses with chronic obstructive pulmonary disease

The concentration of alpha-1 proteinase inhibitor (API) was measured in the pulmonary epithelial lining fluid (PELF) of horses with chronic obstructive pulmonary disease (COPD) while they had clinical signs and while they had none. The concentrations of total protein, albumin and API were significantly higher in the PELF of animals with clinical signs of COPD. The correlation between albumin and API in the PELF suggested that most of the API was derived from the serum.

Molecular weight alterations of alpha-1 proteinase inhibitor in equine bronchoalveolar lavage fluid

The equine alpha-1 proteinase inhibitor (alpha 1PI) system differs from that of man in that the equine system consists of four closely-linked genes (Spi1-Spi4) whereas in man, a single gene encodes for alpha 1PI. We have previously found differences in the proportion of the Spi proteins in equine serum and bronchoalveolar lavage fluid (BALF). We therefore wished to determine whether, as reported in man, there was any molecular weight difference between the Spi proteins in serum and BALF. alpha 1PI and albumin from equine BALF migrated further towards the anode compared with serum alpha 1PI on native polyacrylamide gel electrophoresis (PAGE) although the difference was only significant for alpha 1PI. Sodium dodecyl sulphate-PAGE (SDS-PAGE) showed that a mean decrease in molecular weight of 1.5 kDa for alpha 1PI and 1.3 kDa for albumin had occurred in BALF. These findings were observed in control animals and in those with symptomatic or asymptomatic chronic obstructive pulmonary disease. The mechanism of this decrease in molecular weight of alpha 1PI is likely to differ from reports of alpha 1PI cleavage by bacterial proteinases in man since the molecular weight change was relatively small and loss of trypsin inhibitory activity did not occur. Nor, in our system, was there evidence of bacterial infection. Damage by endogenous proteinases or glycosidases at a site other than the reactive site may be involved but the resultant effect on the efficiency of the antiproteinase screen of the lower respiratory tract is uncertain.

Local and systemic antibody production in horses affected with chronic obstructive pulmonary disease

An enzyme-linked immunosorbent assay (ELISA) was used to quantify isotype-specific antibody to Micropolyspora faeni and to Aspergillus fumigatus in the sera and bronchoalveolar lavage fluid (BALF) of normal horses, horses with chronic obstructive pulmonary disease (COPD) and horses with other chronic respiratory diseases. Elevated antibody levels were not detected in the sera of affected horses. However, both IgE and IgA antibody to both allergens was significantly elevated in BALF in COPD affected horses sampled both when symptomatic and asymptomatic. Elevated levels were also found in animals that developed a chronic cough after an acute onset with symptoms compatible with a respiratory virus infection. In one animal a ten fold increase in IgE antibody to the two allergens developed after an interval of 7 weeks. These findings are supportive of a central role of local IgE antibody to mould allergens in the immunopathogenesis of COPD, and also suggest that respiratory viral infection may predispose to the development of COPD in some horses.

Comparison of cellular and molecular components of bronchoalveolar lavage fluid harvested from different segments of the equine lung

A comparison was made of the cellular and molecular components of bronchoalveolar lavage fluid (BALF) harvested from the left and right diaphragmatic lobes, the accessory lobe of the right lung and the apical lobe of the left lung, of seven control horses and six horses with symptomatic chronic obstructive pulmonary disease (COPD). Neither control nor symptomatic COPD affected horses showed significant regional differences in BALF recovery volumes, total and differential BALF cell counts, albumen adjusted total and absolute BALF cell counts, total and absolute pulmonary epithelial lining fluid (PELF) cell counts, and BALF albumen and urea concentrations. This suggests that the composition of PELF is uniform throughout the lungs of normal horses and horses with symptomatic COPD and that a single BALF sample is representative of the entire lung in these horses.

Quantification of histamine in plasma and pulmonary fluids from horses with chronic obstructive pulmonary disease, before and after 'natural (hay and straw) challenges'

A commercial radioimmunoassay kit was used to quantify histamine concentrations of plasma, bronchoalveolar lavage fluid (BALF) and pulmonary epithelial lining fluid (PELF) of normal horses and horses with chronic obstructive pulmonary disease (COPD), before and after 'natural (hay and straw) challenge' (NC). There were no significant changes in the concentrations of histamine in plasma or BALF at 0.5 or 5 h after NC, but the PELF histamine concentration of COPD affected horses was significantly increased at 5 h, but not at 0.5 h, following NC. As the histamine concentrations of whole BALF lysates were significantly correlated with the numbers of metachromatically staining cells, presumed to be mast cells and/or basophils, these findings support involvement of a late phase, IgE mediated, hypersensitivity reaction in the pathogenesis of equine COPD.