Effects of two commercially available immunostimulants on leukocyte function of foals following ex vivo exposure to Rhodococcus equi

Pharmacologic Interventions to Immunologic and Immune-Mediated Conditions in Horses

Immunomodulators can stimulate, suppress, or regulate one or many aspects of the immune response. Use of a variety of immunostimulants, immunosuppressors, and anti-inflammatory drugs are described in horses, but the evidence supporting their efficacy is variable. Corticosteroids and nonsteroidal anti-inflammatory drugs are the best characterized immunomodulators in horses, but further study is needed to fully define their ideal dosing protocols and indications and to characterize the efficacy of other immunomodulators in equine medicine.

Orally administered β-glucan improves the hemolytic activity of the complement system in horses

Background and Aim:

Immune-modulating molecules mainly act on innate immune cells, which are central to early defense against invading pathogens and contribute to developing adaptive immunity. Yeast-extracted β-glucan, a model immune-modulating molecule, is widely used in several animal species; however, its effect on horse immune parameters has not been thoroughly investigated yet. This study aimed to evaluate the effects of orally administered β-glucan on selected innate immune parameters in horses.

Materials and Methods:

Eighteen thoroughbred horses were assigned equally into three groups as follows: One control group (no β-glucan) and two β-glucan experimental groups (one received 125 mg and the other 2 g of β-glucan per day for 28 days). Blood samples were collected before and at the end of the experiment for hematological analysis, whole blood phagocytosis, respiratory burst assays, and to assess the serum lysozyme and complement hemolytic activities.

Results:

At the end of the experiment, significant decreases (p<0.05) in monocyte numbers were observed in the control horses (258.8±45.9 vs. 115.3±41.5) and in those fed 125 mg/day of β-glucan (208.8±72.3 vs. 99.2±60.7), whereas a significant increase in numbers was noted in the horses that were fed 2 g/day of β-glucan (303.5±45.8 vs. 429.8±86.0; p<0.05). The natural hemolytic activity of the complement was higher only in horses fed 2 g/day of β-glucan (p=0.018) compared to the other groups. The hemolytic activity in the classical pathway was higher in those fed 125 mg/day (p=0.0035) and 2 g/day of β-glucan (p=0.0001).

Conclusion:

β-glucan improves important innate immune parameters and might be fed to horses before stressful events.

Equine PBMC Cytokines Profile after In Vitro α- and γ-EHV Infection: Efficacy of a Parapoxvirus Ovis Based-Immunomodulator Treatment

Equine herpesviruses (EHV) infect horses early during life and the persistence of these viruses through establishment of latency represents a real risk. A better understanding of the immune response to EHV infection is necessary to improve our methods of prevention and decrease the risk of transmission. The objectives of this study were to characterise the cytokine gene expression profile of peripheral blood mononuclear cells (PBMC) after in vitro EHV-1, EHV-4, and EHV-2 infection and to determine the efficacy of inactivated Parapoxvirus ovis (iPPVO) against these 3 viruses. PBMC were isolated from 3 horses and infected in vitro with EHV-1, EHV-4, or EHV-2 in the presence or absence of iPPVO. In vitro culture of PBMC with EHV-1, EHV-4, and iPPVO induced a significant increase of IFN-α, IFN-β, and IFN-γ gene expression. EHV-4 also triggered a significant increase of IL-6 and TNF-α mRNA. EHV-2 triggered a significant increase of IFN-α, IFN-β, IFN-γ, IL-1β, IL-6, and TNF-α mRNA. The presence of iPPVO induced an earlier and stronger expression of IFN-α, IFN-β, and IFN-γ mRNA during EHV infection and reduced the inflammatory response induced by EHV-2. In conclusion, this study suggests that the presence of iPPVO potentiates the development of the immune response to in vitro EHV infection.

Effects of age and macrophage lineage on intracellular survival and cytokine induction after infection with Rhodococcus equi

Rhodococcus equi, a facultative intracellular pathogen of macrophages, causes life-threatening pneumonia in foals and in people with underlying immune deficiencies. As a basis for this study, we hypothesized that macrophage lineage and age would affect intracellular survival of R. equi and cytokine induction after infection. Monocyte-derived and bronchoalveolar macrophages from 10 adult horses and from 10 foals (sampled at 1-3 days, 2 weeks, 1 month, 3 months, and 5 months of age) were infected ex vivo with virulent R. equi. Intracellular R. equi were quantified and mRNA expression of IL-1β, IL-4, IL-6, IL-8, IL-10, IL-12 p40, IL-18, IFN-γ, and TNF-α was measured. Intracellular replication of R. equi was significantly (P<0.001) greater in bronchoalveolar than in monocyte-derived macrophages, regardless of age. Regardless of the macrophage lineage, replication of R. equi was significantly (P=0.002) higher in 3-month-old foals than in 3-day old foals, 2-week-old foals, 1-month-old foals, and adult horses. Expression of IL-4 mRNA was significantly higher in monocyte-derived macrophages whereas expression of IL-6, IL-18, and TNF-α was significantly higher in bronchoalveolar macrophages. Induction of IL-1β, IL-10, IL-12 p40, and IL-8 mRNA in bronchoalveolar macrophages of 1-3-day old foals was significantly higher than in older foals or adult horses. Preferential intracellular survival of R. equi in bronchoalveolar macrophages of juvenile horses may play a role in the pulmonary tropism of the pathogen and in the window of age susceptibility to infection.

Inactivated Parapoxvirus ovis induces a transient increase in the expression of proinflammatory, Th1-related, and autoregulatory cytokines in mice

The immunostimulatory properties of inactivated Parapoxvirus ovis (iPPVO) have long been investigated in different animal species and experimental settings. In this study, we investigated the effects of iPPVO on cytokine expression in mice after intraperitoneal inoculation. Spleen and sera collected from iPPVO-treated mice at intervals after inoculation were submitted to cytokine mRNA determination by real-time PCR (qPCR), serum protein concentration by ELISA, and interferon (IFN)-α/β activity by bioassay. The spleen of iPPVO-treated animals showed a significant increase in mRNA expression of all cytokines assayed, with different kinetics and magnitude. Proinflammatory cytokines interleukin (IL)-1β, tumor necrosis factor-alpha (TNF-α), and IL-8 mRNA peaked at 24 hours postinoculation (hpi; 5.4-fold increase) and 48 hpi (3- and 10-fold increases), respectively. A 15-fold increase in IFN-γ and 6-fold IL-12 mRNA increase were detected at 48 and 24 hpi, respectively. Increased expression of autoregulatory cytokines (Th2), mainly IL-10 and IL-4, could be detected at later times (72 and 96 hpi) with peaks of 4.7- and 4.9-fold increases, respectively. IFN-I antiviral activity against encephalomyocarditis virus was demonstrated in sera of treated animals between 6 and 12 hpi, with a >90% reduction in the number of plaques. Measurement of serum proteins by ELISA revealed increased levels of IL-1, TNF-α, IL-12, IFN-γ, and IL-10, with kinetics similar to those observed by qPCR, especially for IL-12 and IFN-γ. These data demonstrate that iPPVO induced a transient and complex cytokine response, initially represented by Th1-related cytokines followed by autoregulatory and Th2 cytokines.

A systematic review of the immune-modulators Parapoxvirus ovis and Propionibacterium acnes for the prevention of respiratory disease and other infections in the horse

Inactivated Parapoxvirus ovis (iPPVO) and Propionibacterium acnes (P. acnes) are currently used in equine medicine as immune-modulators for prophylactic treatment or adjunct to conventional therapy in order to improve immune defences, to prevent or treat infectious diseases. Their mode of action relies on a non-antigen specific interaction with the innate and/or adaptive immune responses. iPPVO stimulates and regulates cytokine secretion by leucocytes, while P. acnes acts primarily through the activation of macrophages. This report aims to describe their activity as immune-modulators and to summarise the scientific literature and reports available about their use in horses, particularly in the prevention or treatment of equine respiratory diseases. This systematic review regroups articles published in peer-review journals, clinical trials reports, conference proceedings and other information made available in the last 2 decades.

The effect of an immunomodulator (parapoxvirus ovis) on cell-mediated immunity (CMI) in abruptly weaned foals

The weaning process of foals involves a period of considerable stress which likely contributes to an increased risk of infectious disease in these young horses. Mechanisms responsible for this heightened risk of infection remain unknown, although likely due to compromised cell-mediated immunity. Parapoxvirus ovis (PPVO), an immmunomodulator, has been shown to limit the severity of infectious disease outbreaks among horses and has been shown to enhance CMI responses. Thus, an objective of this study was to investigate the effect of PPVO therapy on cell-mediated immune (CMI) responses of abruptly weaned foals. A group of foals (n=6) were given an intramuscular injection of PPVO on days -2, 0 (weaning) and 9. An additional group of foals (n=5) received the diluent only on the same days serving as controls. Peripheral blood samples were collected from all foals prior to weaning (day 0) and on days 1, 3, 5, 7, 9, 11, 14, and 21 after weaning. Whole blood samples were prepared to determine in vivo cytokine mRNA expression by reverse transcription and real-time PCR (RT-PCR). Peripheral blood mononuclear cells (PBMC) were isolated and stimulated to determine in vitro cytokine production by intracellular staining using flow cytometry and gene expression was measured by RT-PCR. Cytokines analyzed in this study were interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α) and interleukin-10 (IL-10). Regardless of PPVO treatment, foals undergoing the weaning process showed a significant decrease in both in vivo and in vitro cytokine (IFN-γ, TNF-α and IL-10) production. These results indicate that abrupt weaning significantly impacts CMI of the foal which may increase susceptibility to infectious agents.