Model systems to study immunomodulation in domestic food animals

Glucocorticoids and Catecholamines Affect in Vitro Functionality of Porcine Blood Immune Cells

Simple Summary

In modern livestock husbandry, animals may face stressful events like weaning, regrouping, or transportation, all of which can impair animal welfare and health. Research in model organisms has revealed that stress hormones, such as glucocorticoids and catecholamines, strongly modulate the immune system and thus the animals’ ability to fight infections. In the pig, knowledge about this relationship is rare, and results from rodents cannot readily be transferred due to some physiological differences. Therefore, the effects of glucocorticoids and catecholamines on porcine immune cell proliferation and the production of the pro-inflammatory cytokine TNFα were investigated in an in vitro study. Blood was obtained from catheterized pigs to exclude pre-exposure to stress hormones. Glucocorticoids exerted inhibitory effects on both investigated immune functions. Catecholamines, on the other hand, showed diverse effects on lymphocyte proliferation and TNFα production of particular immune cell types. This suggests that studies from model species are not entirely transferrable to pigs. Future research should extend the preliminary findings on cytokine production and focus on the molecular mechanisms and health impacts of stress hormones in pigs.

Abstract

Stress hormones exert important modulating influences on the functionality of immune cells. Despite its major role as a livestock animal and its increasing use as an animal model, knowledge about this relationship in the domestic pig is rare. This study therefore aimed to characterize the effect of glucocorticoids and catecholamines on the proliferation and cytokine production of porcine peripheral blood mononuclear cells (PBMC). Blood was obtained from donor pigs equipped with indwelling catheters to exclude stress hormone exposition before in vitro testing. PBMC were stimulated in the presence of cortisol, adrenaline or noradrenaline at concentrations resembling low to high stress conditions. Proliferation was determined via ³H-thymidine incorporation, and TNFα producers were quantified by intracellular cytokine staining. Cortisol led to a decrease in mitogen-induced lymphocyte proliferation and the number of TNFα producing cells. In contrast, catecholamines increased proliferation while exerting repressive or no effects on the number of cytokine producers. Remarkably, in concentrations presumably found in lymphatic tissue in stress situations, noradrenaline suppressed lymphocyte proliferation completely. The shown repressive effects might especially have implications on health and welfare in pigs. The obtained results provide a preliminary database for extended studies on the molecular mechanisms of glucocorticoid and catecholamine actions on porcine immune cells.

Dexamethasone treatment did not exacerbate Seneca Valley virus infection in nursery-age pigs

BACKGROUND

Senecavirus A, commonly known as Seneca Valley virus (SVV), is a picornavirus that has been infrequently associated with porcine idiopathic vesicular disease (PIVD). In late 2014 there were multiple PIVD outbreaks in several states in Brazil and samples from those cases tested positive for SVV. Beginning in July of 2015, multiple cases of PIVD were reported in the United States in which a genetically similar SVV was also detected. These events suggested SVV could induce vesicular disease, which was recently demonstrated with contemporary US isolates that produced mild disease in pigs. It was hypothesized that stressful conditions may exacerbate the expression of clinical disease and the following experiment was performed. Two groups of 9-week-old pigs were given an intranasal SVV challenge with one group receiving an immunosuppressive dose of dexamethasone prior to challenge. After challenge animals were observed for the development of clinical signs and serum and swabs were collected to study viral shedding and antibody production. In addition, pigs were euthanized 2, 4, 6, 8, and 12 days post inoculation (dpi) to demonstrate tissue distribution of virus during acute infection.

RESULTS

Vesicular disease was experimentally induced in both groups with the duration and magnitude of clinical signs similar between groups. During acute infection [0-14 days post infection (dpi)], SVV was detected by PCR in serum, nasal swabs, rectal swabs, various tissues, and in swabs from ruptured vesicles. From 15 to 30 dpi, virus was less consistently detected in nasal and rectal swabs, and absent from most serum samples. Virus neutralizing antibody was detected by 5 dpi and lasted until the end of the study.

CONCLUSION

Treatment with an immunosuppressive dose of dexamethasone did not drastically alter the clinical disease course of SVV in experimentally infected nursery aged swine. A greater understanding of SVV pathogenesis and factors that could exacerbate disease can help the swine industry with control and prevention strategies directed against this virus.

Stress induced Salmonella Typhimurium recrudescence in pigs coincides with cortisol induced increased intracellular proliferation in macrophages

Salmonella Typhimurium infections in pigs often result in the development of carriers that intermittently excrete Salmonella in very low numbers. During periods of stress, for example transport to the slaughterhouse, recrudescence of Salmonella may occur, but the mechanism of this stress related recrudescence is poorly understood. Therefore, the aim of the present study was to determine the role of the stress hormone cortisol in Salmonella recrudescence by pigs. We showed that a 24 h feed withdrawal increases the intestinal Salmonella Typhimurium load in pigs, which is correlated with increased serum cortisol levels. A second in vivo trial demonstrated that stress related recrudescence of Salmonella Typhimurium in pigs can be induced by intramuscular injection of dexamethasone. Furthermore, we found that cortisol, but not epinephrine, norepinephrine and dopamine, promotes intracellular proliferation of Salmonella Typhimurium in primary porcine alveolar macrophages, but not in intestinal epithelial cells and a transformed cell line of porcine alveolar macrophages. A microarray based transcriptomic analysis revealed that cortisol did not directly affect the growth or the gene expression or Salmonella Typhimurium in a rich medium, which implies that the enhanced intracellular proliferation of the bacterium is probably caused by an indirect effect through the cell. These results highlight the role of cortisol in the recrudescence of Salmonella Typhimurium by pigs and they provide new evidence for the role of microbial endocrinology in host-pathogen interactions.

Influence of a hormonal preparation containing glucocorticoids (dexamethasone esters), progestagen (chlormadinone acetate) and oestrogen (ethinyl oestradiol) on testosterone, insulin-like growth factor-1 (IGF-1), IGF-binding proteins and spermatogenic cells in finishing bulls

Growth-promoters are banned by the European Community, but different hormonal cocktails are still illegally used. This experiment was therefore conducted to evaluate the effects of one of the most currently used cocktails on some hormonal parameters and spermatogenesis in finishing bulls in an attempt to provide a suitable screening technique for their illegal use. Sixteen double-muscled Belgian White Blue finishing bulls (mean ivcight: 535 (s.d. 37) kg) were blocked into control (C; no. = 7) and treated (Dex; no. = 9) groups. Animals were treated i.m. with the hormonal preparation (dexamethasone isonicotinate and phosphate, chlormadinone acetate and ethinyl oestradiol) on day 0, day 15 and day 30. Animals were slaughtered on day 45. Three h before each treatment and just prior to slaughter, jugular blood samples were collected to monitor the testosterone (T) response to an i.v. injection of gonadotropin releasing hormone (GnRH) (0·5 fig GnRH per kg body weight). Testicular tissue was also collected at slaughter. Plasma T and insulin-like growth factor-1 (IGF-1) concentrations were measured by radioimmunoassay. IGF-binding proteins (IGFBPs) were evaluated using Western ligand blotting. Daily weight gains were lower in the control group (1·29 (s.d. 0·13) kg for C v. 1·60 (s.d. 0·39) kg for Dex) but the difference ivas not significant. After treatment, spermatogonia, spermatocytes, spermatids and spermatozoa disappeared from the testis and seminiferous tubules consisted only of Sertoli cells; these observations suggest that treated animals were sterile. Moreover, plasma T concentrations in response to GnRH stimulation were suppressed fP < 0·001) in the Dex group between day 15 and day 45 (mean maximal responses: 5·4 to 7·9 μg/l in C group v. < 0·2 μg/l in Dex group at day 15, 30 and 45). Treatment did not show any prominent effect on plasma IGF-1 levels but increased IGFBPS band intensity. In conclusion, treatment with a cocktail containing dexamethasone esters, chlormadinone acetate and ethinyl oestradiol for a short period induced a number of changes in finishing bulls luhich might be possible to develop as a screening method for the identification of illegally treated animals.

Systemic dexamethasone and its effect on normal aerobic bacterial flora of cow

This study was carried out on 17 Holestein, heifers, aged between 1 to 2 years for determining the normal aerobic bacterial flora and their changes after dexamethasone injection. Swab samples were taken from eye, ear, pharynx and vagina before and 5 days after twice dexamethasone treatment. Results indicated that Bacillus cereus and Corynebacterium pseudotuberculosis had higher frequency of isolations than the other bacterial flora in eye, ear and pharynx. Actinomyces pyogenes was isolated with considerable frequency from vagina. Klebsiella pneumoniae was also isolated from pharynx and its frequency was increased significantly after dexamethasone injection (p < 0.05).

Does cortisol bias cytokine production in cultured porcine splenocytes to a Th2 phenotype?

Glucocorticoids are reported to bias the production of cytokines from a type 1 to a type 2 phenotype. However, this dogma has been advanced largely from studies utilizing potent glucocorticoid analogs, particularly dexamethasone (DEX). Although studies utilizing DEX certainly have clinical and pharmacological relevance, DEX is probably not the best glucocorticoid for studies designed to evaluate the interaction and regulation of endogenous corticosteroids with immune cells in vivo in the domestic pig. Functional measures of immune suppression suggest that the pig is relatively resistant to DEX. Furthermore, type II corticosteroid receptors exclusively bind DEX with high affinity, whereas type I receptors, the so-called mineralocorticoid receptors, have a higher affinity for cortisol. In addition, DEX is not bound by serum binding proteins as are endogenous corticosteroids. These issues prompted us to revisit glucocorticoid regulation of type 1 and type 2 cytokines in cultured pig splenocytes and to test the broad hypothesis that cortisol biases cytokine production in favor of a Th2 response. We evaluated interferon gamma (IFNgamma) (also interleukin 2 (IL-2) in one experiment) and interleukin 10 (IL-10) as representative Th1 and Th2 cytokines, respectively. Furthermore, we evaluated macrophage migration inhibitory factor (MIF) because it is reported to be an essential factor in T cell activation; it is also upregulated by glucocorticoids and reported to be a product of Th2 lymphocytes. In general, both IFNgamma and IL-10 were sensitive to cortisol inhibition early in culture. However, IFNgamma ultimately escaped cortisol inhibition, whereas IL-10 continued to be substantially suppressed by high physiological concentrations of cortisol. Similarly, MIF mRNA could be suppressed by cortisol, but only when cortisol was added to cultures after ConA (concanavalin A) stimulation of splenocytes. So, taken together, our studies do not support the hypothesis that cortisol favors a Th2 cytokine profile in cultured pig splenocytes.

Effect of Baypamun on blood leucocytes in normal and dexamathasone treated goats

The aim of this study was to determine the effect of Baypamun on selected lymphocyte subpopulations and granulocyte phagocytic activity mediated by lectin-like receptors in goats of normal immune status and in goats experimentally immunosuppressed with dexamethasone. Eighteen goats in total were used. Blood samples were collected 24 h before immunomodulation and 5 and 10 days after immunomodulation. Animals in group I were immunostimulated with Baypamun for 2 days and immunosuppressed with Dexafort for the next 2 days. Animals in group II received Dexafort first and then Baypamun. The number of leucocytes in total and in subpopulations was determined by flow cytometry. Application of Baypamun before (group I) or after (group II) immunosuppression caused significant (P < 0.001) and lasting changes in the percentage of CD2+, CD4+ and CD8+ T cells. Significant but transient changes were observed in CD19+ (B) and WC1-N2+ (null) cells. Results show that application of Baypamun to modulate non-specific defence is advisable following immunosuppression (group I). When Baypamun was applied after immunosuppression (group II), although there was no reaction during the initial phase, an increase in the activity of cells responsible for non-specific immunity was noticeable after 10 days.

Associations between function and composition of blood mononuclear leukocyte populations from Holstein bulls treated with dexamethasone

To characterize further the effects of corticosteriod-induced stress on the immune system of dairy cattle, functional and phenotypic characteristics of populations of blood mononuclear leukocytes from control and treated (0.04 mg dexamethasone/kg per d for 3 consecutive d) Holstein bulls were evaluated concurrently. In vivo administration of dexamethasone caused a > or = 97% reduction in in vitro secretion of interferon-gamma by pokeweed mitogen-stimulated mononuclear leukocytes by d 2 after the first treatment. In vitro secretion of immunoglobulin M was reduced by > 50% on d 2 and 3 after the first treatment, but returned to normal concentrations sooner than did interferon-gamma secretion. Concurrent with changes in the secretion of these proteins were changes in the mean fluorescence intensities of major histocompatibility class I and II antigens and the WC1 antigen and in the proportion of B cells, CD3 T cells, gamma delta T cells, and cells in the leukocyte population expressing major histocompatibility class II antigens. Examination of the relationships between protein secretion in vitro and the composition of the blood mononuclear leukocyte population indicated that secretion was associated positively with the proportion of CD3 T cells (primarily the gamma delta T-cell subset) and the expression of major histocompatibility class I and II molecules and associated negatively with the proportion of cells expressing major histocompatibility class II antigens. Overall, these results suggest that corticosteroid-mediated stress in dairy cattle impairs secretion of proteins that are critical to normal cellular and humoral immune responses, an effect that is strongly linked with changes in the composition of the circulating mononuclear leukocyte population.