CD4+CD25+ T cells expressing FoxP3 in Icelandic horses affected with insect bite hypersensitivity

Monoclonal antibodies for equine CD25 improve detection of regulatory T cells in horses

CD25, the interleukin-2 receptor α-chain, is expressed on cell surfaces of different immune cells and is commonly used for phenotyping of regulatory T cells (Tregs). CD25 has essential roles in the maintenance of hemostasis and immune tolerance and Treg cell involvement has been shown in human diseases and murine models for allergy, autoimmunity, cancer, chronic inflammation, and many others. In horses, a cross-reactive anti-human CD25 antibody has previously been used for characterizing Tregs. Here, we developed monoclonal antibodies (mAbs) to equine CD25 and compared their staining pattern with the anti-human CD25 antibody by flow cytometry. The comparison of the two reagents was performed by two separate analyses in independent laboratories. Overall, similar staining patterns for equine peripheral blood lymphocytes were obtained with the anti-human CD25 antibody and equine CD25 mAb 15-1 in both laboratories. Both reagents identified comparable CD4+CD25+ and CD4+CD25+FOXP3+ percentages after stimulation of peripheral blood mononuclear cells (PBMC) with pokeweed mitogen. However, when compared to the anti-human CD25 antibody, the equine CD25 mAb 15-1 resulted in a better staining intensity of the equine CD25+ cells and increased the percentages of Tregs and other CD25+ cells ex vivo and after culturing of PBMC without stimulation. In summary, the equine CD25 mAbs provide new, improved reagents for Tregs and CD25+ cell phenotyping in horses.

Equine allergic skin diseases: Clinical consensus guidelines of the World Association for Veterinary Dermatology

BACKGROUND

Allergic skin diseases are common in horses worldwide. The most common causes are insect bites and environmental allergens.

OBJECTIVES

To review the current literature and provide consensus on pathogenesis, diagnosis, treatment and prevention.

MATERIALS AND METHODS

The authors reviewed the literature up to November 2022. Results were presented at North America Veterinary Dermatology Forum (2021) and European Veterinary Dermatology Congress (2021). The report was available to member organisations of the World Association for Veterinary Dermatology for feedback.

CONCLUSIONS AND CLINICAL RELEVANCE

Insect bite hypersensitivity (IBH) is the best characterised allergic skin disease. An immunoglobulin (Ig)E response against Culicoides salivary antigens is widely documented. Genetics and environmental factors play important roles. Tests with high sensitivity and specificity are lacking, and diagnosis of IBH is based on clinical signs, seasonality and response to insect control. Eosinophils, interleukin (IL)-5 and IL-31 are explored as therapeutic targets. Presently, the most effective treatment is insect avoidance. Existing evidence does not support allergen-specific immunotherapy (ASIT) using commercially available extracts of Culicoides. Hypersensitivity to environmental allergens (atopic dermatitis) is the next most common allergy. A role for IgE is supported by serological investigation, skin test studies and positive response to ASIT. Prospective, controlled, randomised studies are limited, and treatment relies largely on glucocorticoids, antihistamines and ASIT based on retrospective studies. Foods are known triggers for urticaria, yet their role in pruritic dermatitis is unknown. Recurrent urticaria is common in horses, yet our understanding is limited and focussed on IgE and T-helper 2 cell response. Prospective, controlled studies on treatments for urticaria are lacking. Glucocorticoids and antihistamines are primary reported treatments.

Viral infection and allergy - What equine immune responses can tell us about disease severity and protection

Horses have many naturally occurring diseases that mimic similar conditions in humans. The ability to conduct environmentally controlled experiments and induced disease studies in a genetically diverse host makes the horse a valuable intermediate model between mouse studies and human clinical trials. This review highlights important similarities in the immune landscape between horses and humans using current research on two equine diseases as examples. First, equine herpesvirus type 1 (EHV-1) infection initiates a series of innate inflammatory signals at its mucosal entry site in the upper respiratory tract. These inflammatory markers are highly synchronized and predictable between individuals during viral respiratory infection and ultimately lead to adaptive immune induction and protection. The timing of early inflammatory signals, followed by specific adaptive immune markers correlating with immunity and protection, allow accurate outbreak tracking and also provide a foundation for understanding the importance of local mucosal immunity during other viral respiratory infections. Second, rare peripheral blood immune cells that promote allergic inflammation can be analyzed during Culicoides hypersensitivity, a naturally occurring type I IgE-mediated allergic disease of horses. Rare immune cells, such as IgE-binding monocytes or basophils, can be studied repeatedly in the horse model to unravel their larger mechanistic role in inflammation during allergic and other inflammatory diseases. We conclude with a survey of all other common equine inflammatory conditions. Together, this review serves as a reference and rationale for the horse as a non-rodent model for immunological research.

Phenotype and function of IgE-binding monocytes in equine Culicoides hypersensitivity

Human IgE-binding monocytes are identified as allergic disease mediators, but it is unknown whether IgE-binding monocytes promote or prevent an allergic response. We identified IgE-binding monocytes in equine peripheral blood as IgE+/MHCII^high/CD14^low cells that bind IgE through an FcεRI αɣ variant. IgE-binding monocytes were analyzed monthly in Culicoides hypersensitive horses and nonallergic horses living together with natural exposure to Culicoides midges. The phenotype and frequency of IgE-binding monocytes remained consistent in all horses regardless of Culicoides exposure. All horses upregulated IgE-binding monocyte CD16 expression following initial Culicoides exposure. Serum total IgE concentration and monocyte surface IgE densities were positively correlated in all horses. We also demonstrated that IgE-binding monocytes produce IL-10, but not IL-4, IL-17A, or IFN-γ, following IgE crosslinking. In conclusion, we have characterized horse IgE-binding monocytes for the first time and further studies of these cells may provide important connections between regulation and cellular mechanisms of IgE-mediated diseases.

Safety Profile of a Virus-Like Particle-Based Vaccine Targeting Self-Protein Interleukin-5 in Horses

Background: Insect bite hypersensitivity (IBH) is an eosinophilic allergic dermatitis of horses caused by type I/IVb reactions against mainly Culicoides bites. The vaccination of IBH-affected horses with equine IL-5 coupled to the Cucumber mosaic virus-like particle (eIL-5-CuMV_TT) induces IL-5-specific auto-antibodies, resulting in a significant reduction in eosinophil levels in blood and clinical signs. Objective: the preclinical and clinical safety of the eIL-5-CuMV_TT vaccine. Methods: The B cell responses were assessed by longitudinal measurement of IL-5- and CuMV_TT-specific IgG in the serum and plasma of vaccinated and unvaccinated horses. Further, peripheral blood mononuclear cells (PBMCs) from the same horses were re-stimulated in vitro for the proliferation and IFN-γ production of specific T cells. In addition, we evaluated longitudinal kidney and liver parameters and the general blood status. An endogenous protein challenge was performed in murine IL-5-vaccinated mice. Results: The vaccine was well tolerated as assessed by serum and cellular biomarkers and also induced reversible and neutralizing antibody titers in horses and mice. Endogenous IL-5 stimulation was unable to re-induce anti-IL-5 production. The CD4⁺ T cells of vaccinated horses produced significantly more IFN-γ and showed a stronger proliferation following stimulation with CuMV_TT as compared to the unvaccinated controls. Re-stimulation using E. coli-derived proteins induced low levels of IFNγ⁺CD4⁺ cells in vaccinated horses; however, no IFN-γ and proliferation were induced following the HEK-eIL-5 re-stimulation. Conclusions: Vaccination using eIL-5-CuMV_TT induces a strong B-cell as well as CuMV_TT-specific T cell response without the induction of IL-5-specific T cell responses. Hence, B-cell unresponsiveness against self-IL-5 can be bypassed by inducing CuMV_TT carrier-specific T cells, making the vaccine a safe therapeutic option for IBH-affected horses.

Immunomodulatory asthma therapy in the equine animal model: A dose-response study and evaluation of a long-term effect

INTRODUCTION

Equine asthma represents a naturally occurring animal model for human allergic neutrophilic asthma. Inhalative nanoparticle-bound cytosine-phosphate-guanosine (CpG-GNP) immunotherapy, independent of specific allergens, has already shown promising clinical and immunological results in previous studies and offers the possibility to treat the underlying cause of the disease. This study analyses the relationship between dose and response, and evaluates a possible long-term effect.

METHODS

In the prospective, randomised, double-blind clinical field study, 29 horses suffering from equine asthma received 10 inhalation treatments with either 187.5 µg CpG-GNP (CpG single dose [CpGsd]; n = 11), 375 µg CpG-GNP double dose (CpG double dose [CpGdd]; n = 9) (q48h for 20 days) or 1600 µg beclomethasone (n = 9) (q24h for 10 days). Each horse was examined three times: before the treatment (I), immediately after the 10 inhalations (II), and 8 weeks after the final inhalation (III). The three groups were compared according to clinical and laboratory parameters. The study examined the sustainability of the long-term effect of the treatment after 8 weeks, as well as the tolerability of the formula as a double dose.

RESULTS

The CpGsd resulted in a significant improvement in 82% of the parameters, the CpGdd in 72%. In the long-term evaluation, the CpGsd showed a significant improvement in 100% of the parameters in comparison to the initial values, the CpGdd in 67%. On the immunological level, the bronchoalveolar lavage revealed a significant reduction of IL-4, IL-8, and interferon-γ.

CONCLUSION

Both CpG groups displayed significant improvements in clinical and laboratory parameters, especially regarding the long-term effect of CpGsd. Doubling the CpG dose did not result in any improvement in comparison to the original single dose. On the immunological level, an anti-inflammatory, as well as an immunomodulatory effect, apart from a Th2-dominated immune response, could be observed. This immunomodulatory inhalation treatment could indicate a new possibility for human allergic asthma therapy.

Effects of allergen-specific immunotherapy on peripheral blood regulatory T cells and serum concentrations of cytokines and immunoglobulins in horses with allergic dermatitis

The aim of this study was to assess the effect of allergen-specific immunotherapy (ASIT) on the immunological responses of horses. Blood samples were taken from thirty-two horses with allergic dermatitis treated with ASIT and 10 healthy control horses at 0, 3, 6, 9 and 12 months to investigate the evolution of the percentage of regulatory T cells (Treg) in the peripheral blood and the serum levels of cytokines and immunoglobulins. Clinical improvement was appreciated by the majority of the horses' owners (56.6%). No effect of ASIT on CD4⁺CD25^High Treg cells was found during the one year treatment period. No differences in the percentage of CD4⁺ T cells were observed between the groups, and no effects of ASIT over time were observed. The percentage of CD25⁺ T cells was always higher in the ASIT group (17.9 ± 11.3%) than in the control group (7.3 ± 4.4%, p < 0.001). We did not detect any effect of ASIT on the serum levels of TGF-β, IL-10 and IFN-γ or on the serum concentrations of IgA and IgG4. A reduction in the serum levels of total IgE in the horses with allergic dermatitis was observed at the 6th month (p < 0.05), but increased again at the end of the study. The results indicate that immunotherapy was insufficient to induce significant changes that could indicate T cell tolerance, a shift in cytokine production to more protective Th1 cells. More studies are needed with new vaccine compositions and administration protocols to improve the immunological responses of the horses with allergic dermatitis.

A prospective study on insect bite hypersensitivity in horses exported from Iceland into Switzerland

BACKGROUND

Insect bite hypersensitivity (IBH) is an IgE-mediated dermatitis caused by bites of Culicoides spp., which occurs frequently in horses imported from Iceland to continental Europe. IBH does not occur in Iceland because Culicoides species that bite horses are not present. However, Simulium vittatum (S. vittatum) are found in Iceland. In Europe, blood basophils from IBH-affected horses release significantly more sulfidoleukotrienes (sLT) than those from healthy controls after in vitro stimulation with Culicoides nubeculosus (C. nubeculosus) and S. vittatum. Aims of the study were: (I) using the sLT release assay, to test if horses living in Iceland were sensitized to S. vittatum and (II) to determine in a longitudinal study in horses imported from Iceland to Switzerland whether the sLT release assay would allow to predict which horses would develop IBH.

RESULTS

Horses in Iceland, even when living in high S. vittatum areas, were usually not sensitized to S. vittatum or C. nubeculosus. Incidence of IBH in the 145 horses from the longitudinal study was 51% and mean time until IBH developed was 2.5 ± 1 year. Before import and after the first summer following import, there were no significant differences in sLT release between the endpoint healthy (H) and IBH groups. After the 2nd summer, when the number of clinically affected horses increased in the endpoint IBH group, a significantly higher sLT release after stimulation with C. nubeculosus but not with S. vittatum was observed. After the 3rd and 4th summer, the endpoint IBH group had a significantly higher sLT release with C. nubeculosus and S. vittatum than the endpoint H group. Some of the horses that remained healthy became transiently positive in the sLT release assay upon stimulation of their peripheral blood leucocytes with C. nubeculosus.

CONCLUSIONS

Horses in Iceland are not sensitized to S. vittatum. In horses that develop IBH, sensitization to S. vittatum is secondary to sensitization to C. nubeculosus and probably a result of an immunological cross-reactivity. A sLT release assay cannot be used to predict which horses will develop IBH. A transient positive reaction in the sLT release assay observed in horses that remained healthy suggests that immunoregulatory mechanisms may control an initial sensitization of the healthy horses.

Influences of intrauterine semen administration on regulatory T lymphocytes in the oestrous mare (Equus caballus)

In the mare, early pregnancy loss is common, but involvement of the maternal immune system in the pathogenesis of this condition has not been investigated in detail so far. In the present study, we assessed effects of exposure of the endometrium to semen or seminal plasma in oestrous mares on the response of regulatory T lymphocytes (Tregs) in the peripheral circulation as well as in the endometrium. Raw semen, seminal plasma or PBS (control) were introduced into the uterus of oestrous mares (n = 12). Blood was collected immediately before insemination or PBS infusion (time 0), and 12, 24 and 48 h thereafter. Endometrial biopsies were collected at 24 h. In peripheral blood, Treg (CD4⁺Foxp3⁺) cells were determined by flow cytometry. In endometrial biopsies, Tregs were assessed as cells staining positive for Foxp3 by immunohistochemistry. The percentage of Tregs in blood decreased (p < 0.05) at 12 h after exposure to seminal plasma, tended to decrease in response to raw semen (p = 0.095) but not to PBS. Leukocyte and PMN counts were not affected. In the endometrium, numbers of Foxp3 positive cells at 24 h after insemination or PBS infusion were not changed by treatment. Results of the present study provide only little evidence that maternal tolerance of pregnancy in the horse is modulated already by exposure of the oestrous endometrium to seminal plasma at mating.

Regulatory T Cells and Their Role in Animal Disease

In humans and mouse models, Foxp3(+) regulatory T cells are known to control all aspects of immune responses. However, only limited information exists on these cells' role in diseases of other animals. In this review, we cover the most important features and different types of regulatory T cells, which include those that are thymus-derived and peripherally induced, the mechanisms by which they control immune responses by targeting effector T cells and antigen-presenting cells, and most important, their role in animal health and diseases including cancer, infections, and other conditions such as hypersensitivities and autoimmunity. Although the literature regarding regulatory T cells in domestic animal species is still limited, multiple articles have recently emerged and are discussed. Moreover, we also discuss the evidence suggesting that regulatory T cells might limit the magnitude of effector responses, which can have either a positive or negative result, depending on the context of animal and human disease. In addition, the issue of plasticity is discussed because plasticity in regulatory T cells can result in the loss of their protective function in some microenvironments during disease. Lastly, the manipulation of regulatory T cells is discussed in assessing the possibility of their use as a treatment in the future.

Recombinant Culicoides obsoletus complex allergens stimulate antigen-specific T cells of insect bite hypersensitive Shetland ponies in vitro

BACKGROUND

Ponies may suffer from Insect bite hypersensitivity (IBH), an allergic IgE-mediated pruritic skin disorder, induced by allergens from biting midges of the Culicoides spp.

HYPOTHESIS/OBJECTIVES

To determine whether recombinant Culicoides obsoletus allergens are able to activate T cells of ponies exposed to C. obsoletus and whether these allergen-specific responses differ between IBH-affected and healthy ponies.

ANIMALS

Ten IBH-affected Shetland ponies and 10 age-matched healthy controls taken from the same stables, to ensure similar exposure to midges.

METHOD

Peripheral blood mononuclear cells (PBMC) were cultured with two different pools of recombinant C. obsoletus complex allergens to expand the allergen-specific T cells. These PBMC cultures were subsequently co-cultured with mature dendritic cells (DCs) loaded with the same antigens. Induction of Th1, Th2 and regulatory T (Treg) cells in these DC/PBMC co-cultures was assessed by analysis of IFN-γ, IL-4, IL-10 and FoxP3 expression levels using quantitative RT-PCR and phenotyping by flow cytometry.

RESULTS

Recombinant C. obsoletus allergens increased IFN-γ mRNA expression levels, percentages of IFN-γ expressing (Th1) cells and CD25(high) FoxP3(+) IL-10(+) Tregs compared to unstimulated DC/PBMC co-cultures. Stimulation of IL-4 expressing Th2 cells by the recombinant allergens was far less pronounced. The DC/PBMC co-cultures did not reveal significant differences between healthy and IBH-affected ponies for any of the analysed parameters, except for higher IL-4 mRNA levels in IBH affected ponies after stimulation with one of the two allergen pools.

CONCLUSION AND CLINICAL IMPORTANCE

The recombinant C. obsoletus complex allergens can stimulate antigen-specific Th1 and IL10 producing Treg cells and are therefore promising candidates for the immunotherapy of IBH.

Allergen-Specific Cytokine Polarization Protects Shetland Ponies against Culicoides obsoletus-Induced Insect Bite Hypersensitivity

The immunological mechanisms explaining development of an allergy in some individuals and not in others remain incompletely understood. Insect bite hypersensitivity (IBH) is a common, seasonal, IgE-mediated, pruritic skin disorder that affects considerable proportions of horses of different breeds, which is caused by bites of the insect Culicoides obsoletus (C. obsoletus). We investigated the allergen-specific immune status of individual horses that had either been diagnosed to be healthy or to suffer of IBH. Following intradermal allergen injection, skin biopsies were taken of IBH-affected and healthy ponies and cytokine expression was determined by RT-PCR. In addition, allergen-specific antibody titers were measured and cytokine expression of in vitro stimulated, allergen-specific CD4 T-cells was determined. 24 hrs after allergen injection, a significant increase in mRNA expression of the type-2 cytokine IL-4 was observed in the skin of IBH-affected Shetland ponies. In the skin of healthy ponies, however, an increase in IFNγ mRNA expression was found. Analysis of allergen-specific antibody titers revealed that all animals produced allergen-specific antibodies, and allergen-specific stimulation of CD4 T-cells revealed a significant higher percentage of IFNγ-expressing CD4 T-cells in healthy ponies compared to IBH-affected ponies. These data indicate that horses not affected by IBH, in contrast to the so far established dogma, are not immunologically ignorant but have a Th1-skewed allergen-specific immune response that appears to protect against IBH-associated symptoms. To our knowledge this is the first demonstration of a natural situation, in which an allergen-specific immune skewing is protective in an allergic disorder.

Multiple intravenous injections of allogeneic equine mesenchymal stem cells do not induce a systemic inflammatory response but do alter lymphocyte subsets in healthy horses

INTRODUCTION

Intravenous (IV) injection of mesenchymal stem cells (MSCs) is used to treat systemic human diseases and disorders but is not routinely used in equine therapy. In horses, MSCs are isolated primarily from adipose tissue (AT) or bone marrow (BM) and used for treatment of orthopedic injuries through one or more local injections. The objective of this study was to determine the safety and lymphocyte response to multiple allogeneic IV injections of either AT-derived MSCs (AT-MSCs) or BM-derived MSCs (BM-MSCs) to healthy horses.

METHODS

We injected three doses of 25 × 10(6) allogeneic MSCs from either AT or BM (a total of 75 × 10(6) MSCs per horse) into five and five, respectively, healthy horses. Horses were followed up for 35 days after the first MSC infusion. We evaluated host inflammatory and immune response, including total leukocyte numbers, serum cytokine concentration, and splenic lymphocyte subsets.

RESULTS

Repeated injection of allogeneic AT-MSCs or BM-MSCs did not elicit any clinical adverse effects. Repeated BM-MSC injection resulted in increased blood CD8(+) T-cell numbers. Multiple BM-MSC injections also increased splenic regulatory T cell numbers compared with AT-MSC-injected horses but not controls.

CONCLUSIONS

These data demonstrate that multiple IV injections of allogeneic MSCs are well tolerated by healthy horses. No clinical signs or clinico-pathologic measurements of organ toxicity or systemic inflammatory response were recorded. Increased numbers of circulating CD8(+) T cells after multiple IV injections of allogeneic BM-MSCs may indicate a mild allo-antigen-directed cytotoxic response. Safety and efficacy of allogeneic MSC IV infusions in sick horses remain to be determined.

Regulatory T cells in early life: comparative study of CD4+CD25high T cells from foals and adult horses

The immune system of mammals is subject to continuous development during the postnatal phase of life. Studies following the longitudinal development of the immune system in healthy children are limited both by ethical considerations and sample volumes. Horses represent a particular valuable large animal model for T regulatory (Treg) cells and allergy research. We have recently characterised Treg cells from horses, demonstrated their regulatory capability and showed both their expansion and induction in vitro. Insect bite hypersensitivity (IBH) is a common allergy in horses resembling atopic dermatitis and studies have shown that first exposure to allergens in adult life results in an increased incidence of IBH. The aim of the present study was to characterize circulating CD4⁺CD25^highFoxP3⁺cells in foals, evaluate their suppressive capability and their in vitro induction compared to adult horses. 19 foals (age range, 1–5 months), their adult mothers and six one-year-old horses (yearlings) were included in the study. The proportion of FoxP3⁺ cells within the circulating CD4⁺CD25^high population was significantly higher in foals (47%) compared to their mothers (18%) and to yearlings (26%). Treg cells from foals also displayed a higher suppressive capability. Furthermore, CD4⁺CD25^high cells in foals could be induced in vitro from CD4⁺CD25⁻ cells in a significantly higher proportion compared to mares. These cells also displayed a significantly enhanced suppressive capability. In summary these findings support the notion that exposure of horses to allergens during maturation of the immune system assists the establishment of induced (i)Treg driven tolerance.

Immune responses to ectoparasites of horses, with a focus on insect bite hypersensitivity

Horses are affected by a wide variety of arthropod ectoparasites, ranging from lice which spend their entire life on the host, through ticks which feed over a period of days, to numerous biting insects that only transiently visit the host to feed. The presence of ectoparasites elicits a number of host responses including innate inflammatory responses, adaptive immune reactions and altered behaviour; all of which can reduce the severity of the parasite burden. All of these different responses are linked through immune mechanisms mediated by mast cells and IgE antibodies which have an important role in host resistance to ectoparasites, yet immune responses also cause severe pathological reactions. One of the best described examples of such pathological sequelae is insect bite hypersensitivity (IBH) of horses; an IgE-mediated type 1 hypersensitivity to the salivary proteins of Culicoides spp. associated with T-helper-2 production of IL4 and IL13. Importantly, all horses exposed to Culicoides have an expanded population of Culicoides antigen-specific T cells with this pattern of cytokine production, but in those which remain healthy, the inflammatory reaction is tempered by the presence of FoxP3+ CD4+ regulatory T cells that express IL10 and TGF-beta, which suppresses the IL4 production by Culicoides antigen-activated T cells.

Participation of T regulatory cells in equine recurrent airway obstruction

Recurrent airway obstruction (RAO) is an equine immune-mediated disease with a high incidence worldwide. The aim of this work was to contribute to the understanding of RAO pathogenesis by studying T cells bearing regulatory markers in peripheral blood (PB) and in bronchoalveolar lavage fluid (BALF) recovered from the same group of susceptible horses before and after exposure to moldy hay, which has been shown to induce RAO signology in our horse herd. With this purpose, mononuclear cells were obtained from the BALF and PB from horses before and after antigenic challenge and were stained with fluorochrome-conjugated antibodies against CD4, CD25 and Foxp3 and subsequently analyzed by flow cytometry. The results indicated that the percentage of CD4+, Foxp3+ cells clearly increased in PB and BALF obtained from horses with RAO. In addition, the percentage of CD4+, CD25(high) cells was greatly augmented in BALF of RAO positive horses compared with a baseline. No changes were observed in the PB compartment. The percentage of CD4+, CD25(high), Foxp3+ cells in BALF increased in horses with active disease compared to horses in remission; this cell population also does not show changes in the PB compartment when RAO positive and RAO negative horses were compared. On the other hand, when the percentage of CD4, Foxp3 positive cells were compared with the percentage of CD4+, CD25(high) cells, the numbers were very similar. This observation was true for PB and BALF cells from non exposed horses as well as horses exposed to antigen. In all the experimental situations studied, the population expressing all of the markers CD4+, CD25(high), Foxp3+ represent only a minor percentage of CD4+, CD25(high) or CD4+, Foxp3 subpopulations; therefore, an significant number of CD4+, CD25(high), Foxp3- and CD4+, CD25(null), Foxp3+ cells must exist. Finally, we conclude that horses with RAO show an airway accumulation of T cells bearing regulatory markers that probably are modulating the course of this disease, and that these T cells may be involved in the resolution of immune-mediated bronchial inflammation.

Low levels of naturally occurring regulatory T lymphocytes in blood of mares with early pregnancy loss

Early pregnancy loss is a major reason for low reproductive efficiency in the horse. In humans and mice, low numbers of regulatory T cells (Treg cells) are linked to miscarriage. The percentage of Treg cells in oestrous mares at the start of the breeding season was evaluated in relation to the outcome of subsequent pregnancy. For identification and quantification of Treg cells, a highly sensitive and specific qPCR assay targeting the Treg-specific demethylated region in the equine forkhead box transcription factor (FOXP3) gene was established. In a total of 108 mares, pregnancy was followed until detection of early pregnancy loss (n = 17), abortion without identification of an infectious or apparent cause (n = 9) or birth of a viable foal (n = 82). Measured Treg-cell levels did not significantly differ between mares that conceived (82%; 1.50 ± 0.04%) or did not get pregnant (18%; 1.45 ± 0.10%). The Treg-cell percentage at oestrus before breeding was significantly different (P < 0.05) between mares that either underwent early pregnancy loss up to Day 40 of pregnancy (1.29 ± 0.07%) and mares that aborted (1.61 ± 0.15%) or gave birth to a live foal (1.52 ± 0.05%). These results suggest that low levels of Treg cells in mares can contribute to pregnancy loss up to Day 40 after ovulation.

Evaluation of a diagnostic ELISA for insect bite hypersensitivity in horses using recombinant Obsoletus complex allergens

Culicoides spp. of the Obsoletus complex belong to the most important species of midge, involved in causing insect bite hypersensitivity (IBH) in horses in The Netherlands. The aim of the current study was to evaluate seven different Obsoletus complex-derived recombinant allergens (Cul o 1-Cul o 7) and to compare these with Obsoletus complex whole body extract (WBE) in an IgE ELISA, using sera of 194 clinically-confirmed cases of IBH and 175 unaffected horses. The highest test accuracy was obtained with WBE, followed by Cul o 2, 3 and 5. Two ELISAs with a combination of recombinant allergens, Combi-1 (Cul o 3, 5 and 7) and Combi-2 (Cul o 1, 2, 5 and 7) were additionally performed and both resulted in high test accuracies close to that obtained with WBE. Combi-1 resulted in the best sensitivity and specificity, both 89%. Both Combi-1 and Combi-2 performed less well with samples collected in winter, but over 70% of the IBH-affected horses could still be identified. In conclusion, a combination of three Obsoletus complex recombinant allergens (Cul o 3, 5 and 7) could potentially replace Obsoletus complex WBE in an IgE ELISA for diagnosis of IBH in horses.

Update on equine allergies

Horses develop many skin and respiratory disorders that have been attributed to allergy. These disorders include pruritic skin diseases, recurrent urticaria, allergic rhinoconjunctivitis, and reactive airway disease. Allergen-specific IgE has been detected in these horses, and allergen-specific immunotherapy is used to ameliorate clinical signs. The best understood atopic disease in horses is insect hypersensitivity, but the goal of effective treatment with allergen-specific immunotherapy remains elusive. In this review, updates in pathogenesis of allergic states and a brief mention of the new data on what is known in humans and dogs and how that relates to equine allergic disorders are discussed.

Phospholipids in sera of horses with summer eczema: lipid analysis of the autoserum preparation used in therapy

REASONS FOR PERFORMING STUDY

Equine summer eczema, also known as insect bite hypersensitivity, affects horses recurrently during summer months. The treatment of this allergic pruritus is difficult and therefore there is a need for efficacious treatments. Autoserum therapy, based on the use of autogenous serum that is specifically prepared for oral administration and given when the animal shows clinical signs has been introduced recently. Lipids are thought to be responsible for the effect of this therapy.

OBJECTIVES

The main aim of this study was to analyse the phospholipid content of autogenous serum preparations and to further assess whether these preparations have different lipid profiles depending on the clinical status of the horse. The hypothesis is that the major serum phospholipids typical of the horse are present in the autoserum preparation.

STUDY DESIGN

Descriptive controlled clinical study.

METHODS

Sera were collected from 10 affected and 6 healthy horses, prepared in a similar fashion and the lipids contained in the resulting autoserum preparations were analysed by electrospray ionisation mass spectrometry.

RESULTS

The major phospholipid classes detected were phosphatidylcholine, sphingomyelin, phosphatidic acid and traces of lysophosphatidylcholine. Horses with summer eczema had significantly abundant concentrations of phosphatidylcholine (P = 0.042) and sphingomyelin (P = 0.0017) in comparison with healthy horses, while the concentration of phosphatidic acid was significantly higher in healthy horses (P = 0.0075).

CONCLUSIONS

The autoserum preparation contains minute amounts of the main serum phospholipids in differing concentrations in healthy horses and horses with an allergic skin disease.

The immunopathology of sepsis: pathogen recognition, systemic inflammation, the compensatory anti-inflammatory response, and regulatory T cells

Sepsis, the systemic inflammatory response to infection, represents the major cause of death in critically ill veterinary patients. Whereas important advances in our understanding of the pathophysiology of this syndrome have been made, much remains to be elucidated. There is general agreement on the key interaction between pathogen-associated molecular patterns and cells of the innate immune system, and the amplification of the host response generated by pro-inflammatory cytokines. More recently, the concept of immunoparalysis in sepsis has also been advanced, together with an increasing recognition of the interplay between regulatory T cells and the innate immune response. However, the heterogeneous nature of this syndrome and the difficulty of modeling it in vitro or in vivo has both frustrated the advancement of new therapies and emphasized the continuing importance of patient-based clinical research in this area of human and veterinary medicine.

Equine insect bite hypersensitivity: what do we know?

Insect bite hypersensitivity (IBH) is an allergic dermatitis of the horse caused by bites of insects of the genus Culicoides and is currently the best characterized allergic disease of horses. This article reviews knowledge of the immunopathogenesis of IBH, with a particular focus on the causative allergens. Whereas so far hardly any research has been done on the role of antigen presenting cells in the pathogenesis of IBH, recent studies suggest that IBH is characterized by an imbalance between a T helper 2 (Th2) and regulatory T cell (T(reg)) immune response, as shown both locally in the skin and with stimulated peripheral blood mononuclear cells. Various studies have shown IBH to be associated with IgE-mediated reactions against salivary antigens from Culicoides spp. However, until recently, the causative allergens had not been characterized at the molecular level. A major advance has now been made, as 11 Culicoides salivary gland proteins have been identified as relevant allergens for IBH. Currently, there is no satisfactory treatment of IBH. Characterization of the main allergens for IBH and understanding what mechanisms induce a healthy or allergic immune response towards these allergens may help to develop new treatment strategies, such as immunotherapy.

Immunohistochemical investigation of Foxp3 expression in the intestine in healthy and diseased dogs

Intestinal immune regulation including development of oral tolerance is of great importance for the maintenance of intestinal homeostasis. Concerning this, regulatory T cells (Tregs) occupy a pivotal role in cell-mediated immunosuppression. Dysregulation of mucosal immunology leading to an abnormal interaction with commensal bacteria is suggested to play a key role in the pathogenesis of Inflammatory Bowel Disease (IBD) in men and dogs. The aim of this study was to characterise the expression of Foxp3 in the normal canine gut of 18 dogs (mean age: 6.03 years), in 16 dogs suffering from IBD (mean age: 5.05 years), and of 6 dogs with intestinal nematode infection (mean age: 0.87 years) using immunohistochemistry. In the duodenum, Tregs in healthy dogs declined from villi (median: 10.67/62 500 μm2) to crypts (median: 1.89/62 500 μm2). Tregs were further increased in the villi of middle-aged dogs (median: 18.92/62 500 μm2) in contrast to juvenile (median: 3.50/62 500 μm2) and old (median: 9.56/62 500 μm2) individuals. Compared to healthy controls, animals suffering from IBD revealed reduced numbers of Tregs in duodenal villi (median: 4.13/62 500 μm2). Dogs with intestinal nematode infection displayed increased numbers of Tregs (median: 21.06/62 500 μm2) compared to healthy animals.Age-related changes indicate a progressive establishment of oral tolerance and immunosenescence in the canine elderly. The results further suggest that a defect in Treg homeostasis may be involved in the pathogenesis of canine IBD. In contrast, increased numbers of Tregs in the duodenum may be due to nematode infection.