Systemic inflammation and priming of peripheral blood leukocytes persist during clinical remission in horses with heaves.

This research article investigates the immune system response in horses suffering from heaves, even when the disease shows no symptoms. More specifically, it studies the reaction of the horse’s peripheral blood leukocytes, a type of white blood cell, to bacterial products.

Study Methodology

• The research involved a group of horses affected by heaves, but exhibiting no current symptoms (n=5-6) and healthy horses (n=4-5). Both groups were kept under similar low dust environments like pasture or shavings and pellets.
• Two cell populations were isolated from the blood. These included neutrophils and neutrophil-depleted cells which were separated using the Magnetic Activated Cell Sorting (MACS) system.
• These cells were then incubated with or without bacterial products (Lipopolysaccharide and N-formylmethionine-leucyl-phenylalanine) for 5 hours.
• The expression of cytokines, proteins that are crucial in cell signaling, and TLR4 receptor was assessed using quantitative Polymerase Chain Reaction (qPCR), a technique used to amplify and quantify targeted DNA molecules.
• The concentration of a specific type of cytokine, TNF, in the serum samples and cell culture supernatants was measured using an equine specific Enzyme-Linked Immunosorbent Assay (ELISA).
• The rate of apoptosis or cell death of resting and stimulated neutrophils was evaluated using flow cytometry with specifically AnnexinV and 7-AAD, and was correlated with the early expression rates of pro-inflammatory cytokines.

Study Findings

• The study showed that the exposure to bacterial products lead to overexpression of certain pro-inflammatory cytokines in both neutrophils and neutrophil-depleted leukocytes from horses affected by heaves.
• This overexpression of cytokines was correlated to the survival rate of neutrophils, specifically to the early expression of TNF, but not IL-8.
• Neutrophil-depleted leukocytes from heaves-affected horses also showed significantly increased basal levels of TNF mRNA.
• Moreover, the blood serum of heaves-affected horses displayed a significantly higher concentration of TNF compared to the healthy horses kept in similar conditions.

Conclusions

• The research concludes that an altered immune response to bacterial products can be observed in peripheral blood leukocytes from asymptomatic horses susceptible to heaves. This alteration is associated with high blood serum TNF concentration.
• However, the cause of this phenomenon – whether it’s due to inherent differences in innate immune responses or is triggered by systemic inflammation – is yet to be determined.