The effect of free and carrier-bound cortisol on equine neutrophil function

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.

Effects of intravenous administration of peripheral blood-derived mesenchymal stromal cells after infusion of lipopolysaccharide in horses

BACKGROUND

A systemic and dysregulated immune response to infection contributes to morbidity and mortality associated with sepsis. Peripheral blood-derived mesenchymal stromal cells (PB-MSC) mitigate inflammation in animal models of sepsis. Allogeneic PB-MSC administered IV to horses is well-tolerated but therapeutic benefits are unknown.

HYPOTHESIS

After IV lipopolysaccharide (LPS) infusion, horses treated with PB-MSC would have less severe clinical signs, clinicopathological abnormalities, inflammatory cytokine gene expression, and oxidative stress compared to controls administered a placebo.

ANIMALS

Sixteen horses were included in this study.

METHODS

A randomized placebo-controlled experimental trial was performed. Sixteen healthy horses were assigned to 1 of 2 treatment groups (1 × 10⁹  PB-MSC or saline placebo). Treatments were administered 30 minutes after completion of LPS infusion of approximately 30 ng/kg. Clinical signs, clinicopathological variables, inflammatory cytokine gene expression, and oxidative stress markers were assessed at various time points over a 24-hour period.

RESULTS

A predictable response to IV LPS infusion was observed in all horses. At the dose administered, there was no significant effect of PB-MSC on clinical signs, clinicopathological variables, or inflammatory cytokine gene expression at any time point. Antioxidant potential was not different between treatment groups, but intracellular ROS increased over time in the placebo group. Other variables that changed over time were likely due to effects of IV LPS infusion.

CONCLUSIONS AND CLINICAL IMPORTANCE

Administration of allogeneic PB-MSC did not cause clinically detectable adverse effects in healthy horses. The dose of PB-MSC used here is unlikely to exert a beneficial effect in endotoxemic horses.

Effects of administration of ascorbic acid and low-dose hydrocortisone after infusion of sublethal doses of lipopolysaccharide to horses

Background

Sepsis is associated with ascorbic acid (AA) depletion and critical illness‐related corticosteroid insufficiency (CIRCI) in humans.

Hypotheses

Intravenous infusion of lipopolysaccharide (LPS) would (a) decrease endogneous AA concentrations, (b) induce CIRCI and (c) administration of a combination of AA and hydrocortisone (HC) would have decreased indices of inflammation compared to either drug alone.

Animals

Thirty‐two healthy horses.

Methods

Randomized placebo‐controlled experimental trial. Horses were assigned to 1 of 4 groups (saline, AA and HC, AA only, or HC only). Treatments were administered 1 hour after completion of LPS infusion. Clinical signs, clinicopathological variables, pro‐inflammatory cytokine gene expression and production, and plasma AA concentrations were assessed at various time points. Serum cortisol concentrations and ACTH stimulation tests were used to detect CIRCI.

Results

There was no effect of drug on clinical signs or pro‐inflammatory cytokine gene expression or production compared to controls at any time point. Administration of AA was associated with higher blood neutrophil counts 6 hours after LPS infusion (11.01 ± 1.02 K/μl) compared to other groups (8.99 ± 0.94 K/μL; P < .009). Adminstration of HC was associated with higher blood neutrophil counts 12 hours after LPS infusion (10.40 ± 0.75 K/μl) compared to other groups (6.88 ± 0.68 K/μl; P < .001). Serum cortisol increased from 5.11 ± 1.48 μg/dL before LPS administration to 9.59 ± 1.83 μg/dL 1 h after completion of LPS infusion (T1) without an effect of treatment (P = 0.59).

Conclusions and Clinical Importance

Ascorbic acid and HC appeared to protect against LPS‐induced neutrophil depletion and could be considered as adjunctive therapy in horses with endotoxemia.

The effect of foal or adult horse plasma on equine monocyte-derived dendritic cell phenotype and function

Immunological and endocrine immaturity in foals increases foal morbidity and mortality from bacterial sepsis. Dendritic cells (DC) are critical in activating the adaptive immune response, but foal DC are phenotypically and functionally different than those of adult horses. Age-related variations in availability of some soluble plasma factors, such as hormones, might govern some age-related differences in DC function. Effects of exposure to plasma factors on equine DC phenotype and function have not been described. We hypothesized that exposure to plasma from foals or adult horses would differentially impact monocyte-derived DC (MoDC) phenotype and function. Eight healthy adult horses and 8 healthy foals were divided into pairs of one adult horse and one foal. Blood was collected from each pair for MoDC generation when foals were 1 and 30 days of age. MoDC from horses and foals were then exposed to killed whole-cell bacteria in the presence of their own age-matched plasma, plasma from the opposite-aged animal in the pair, and serum-free medium alone (control). Expression of DC-relevant surface markers (MHC class-II, CD86, and CD14) and endocytosis capability were measured by flow cytometry. Supernatant cytokine concentrations (IL-4, IL-17, IFN-γ, and IL-10) were quantified with a validated bead-based immunoassay. Data were analyzed using linear mixed-effects and Tobit regression models (P < 0.05). The percentage of MoDC expressing surface markers MHC class-II and CD86 was reduced in MoDC derived from 1-day-old foals in comparison to adult horse MoDC when cultured in medium alone or with either source of plasma (P = 0.0001). Foal and adult horse MoDC cultured in either source of plasma expressed more CD86 and less CD14 than cells cultured in serum-free medium alone (P ≤ 0.02). Adult horse and foal MoDC exposed to bacterial antigen in the presence of 1-day-old foal plasma secreted less IL-10 (P ≤ 0.0008) compared to those cultured in adult horse plasma. Endogenous production of IL-17 by MoDC from foals at day 1 of age cultured in adult plasma was increased compared to foal MoDC cultured in serum-free medium (P = 0.004). Phagocytosis of killed, labeled Staphylococcus aureus was reduced when MoDC generated from foals or adult horses were exposed to plasma from foals at day 1 or 30 of age (P ≤ 0.03). Age-related variation in soluble plasma factors appear to regulate equine MoDC function, but specific plasma factors capable of regulating MoDC phenotype or function were not defined in this study.

The effect of age on foal monocyte-derived dendritic cell (MoDC) maturation and function after exposure to killed bacteria

Neonatal foals are uniquely susceptible to certain infections early in life. Dendritic cells (DC) are vital in the transition between the innate and adaptive immune response to infection, but DC biology in foals is not fully characterized. Monocyte-derived DC represent a suitable in vitro model similar to DC that differentiate from monocytes recruited from circulation. We hypothesized that foal monocyte-derived DC (MoDC) would exhibit age-dependent phenotypic and functional differences compared to adult horse MoDC. MoDC generated from 9 horses (collected once) and from 8 foals (collected at 1, 7, and 30 days-of-age) were exposed to killed whole cell Escherichia coli or Staphylococcus aureus bacteria. MoDC expression of MHC class II (MHC class-II), CD86, and CD14 were measured by flow cytometry, and supernatant cytokine concentrations of IL-4, IL-17, IFN-γ, and IL-10 were quantified with a validated immunoassay. The percentage of MoDC expressing MHC class-II and CD86 was lower and CD14 was higher for cells generated from 1-day-old foals compared to cells generated from adult horses (P < 0.0001). Bacterial exposure increased the percentage of cells expressing CD86 at all ages (P < 0.0001). Bacteria-exposed MoDC from 1-day-old foals produced significantly less IL-4, IL-17, and IFN-γ than adult MoDC produced in response to bacterial exposure (P ≤ 0.04). Following bacterial exposure, foal MoDC phenotype and cytokine secretion were different than those of mature horses. These differences could reduce the ability of foals to generate a protective immune response against bacterial infection.