Immune Response in Young Thoroughbred Racehorses under Training

Abstract

Training has a great impact on the physiology of an athlete and, like all stressful stimuli, can trigger an innate immune response and inflammation, which is part of a wider coping strategy of the host to restore homeostasis. The Thoroughbred racehorse is a valid animal model to investigate these changes thanks to its homogeneous training and highly selected genetic background. The aim of this study was to investigate modifications of the innate immune response and inflammation in young untrained Thoroughbred racehorses during the first training season through haematological and molecular investigations. Twenty-nine Thoroughbred racehorses were followed during their incremental 3-month sprint exercise schedule. Blood collection was performed at time 0 (T0; before starting the intense training period), 30 days after T0 (T30), and 90 days after T0 (T90). Haematological parameters (red and white blood cells, haemoglobin, and platelets) were evaluated and haematocrit (HCT), mean corpuscular haemoglobin concentration (MCHC), and red cells width distribution + standard deviation (RDW-SD) were calculated. Moreover, via RT-qPCR, we investigated the expression of, Interleukin 1β (IL-1β), Interleukin 4 (IL-4) Interleukin 6 (IL-6), Interleukin 2 (IL-2), Interleukin 3 (IL-3), Interleukin 5 (IL-5) Interleukin 8 (IL-8), Trasformig Growth Factor β and α (TGF-β), Tumor necrosis factor α (TNF-α), and Interferon γ (IFN-γ)genes. Main corpuscular volume (MCV) showed a significant (p = 0.008) increase at T90. Main corpuscular haemoglobin (MCH) and haemoglobin concentration (MCHC) values were significantly augmented at both T30 (p < 0.001) and T90 (p < 0.001). Basophils were significant increased at T30 (p = 0.02) and eosinophils were significantly increased at T90 (p = 0.03). Significant differences in gene expression were found for all the genes under study, with the exception of IFN-γ and TNF-α. In particular, IL-2 (T30, p = 0.011; T90, p = 0.015), IL-4 (T30, p = 0.009; T90, p < 0.001), and IL-8 (T30, p < 0.001; T90, p < 0.001) genes were significantly upregulated at both T30 and T90 with respect to T0, TGF-β was intensely downregulated at T30 (p < 0.001), IL-5 gene expression was significantly decreased at T90 (p = 0.001), while IL-1β (p = 0.005) and IL-3 (p = 0.001) expression was strongly augmented at the same time. This study highlighted long-term adjustments of O2 transport capability that can be reasonably traced back to exercise adaptation. Moreover, the observed changes of granulocyte numbers and functions and inflammatory cytokine gene expression confirm a major role of the innate immune system in the response to the complex of stressful stimuli experienced during the training period.

Effect of First Long-Term Training on Whole Blood Count and Blood Clotting Parameters in Thoroughbreds

“…Interestingly, in our study, we detected an increase in both platelet and eosinophil counts, in addition to enhanced IL1B expression (data reported in our previous study [ 4 , 43 ], during the entire training period. These parameters could be closely interrelated since, at least from the functional point of view, the two cells have been proven to strictly cooperate [ 3 , 43 ]. In this regard, eosinophils have recently been reported to accumulate in human thrombi [ 53 ] and to express tissue factor, a strong trigger of blood coagulation [ 54 ].…”

“…Literature data suggest that an increased leukocytes count is among the most consistent responses to exercise, generally occurring after all types of exercise. Exercise-induced leukocytosis is often compared with an inflammation-like reaction and the increase is quantitatively related to the response induced by physiological insults to the immune system [ 3 , 43 ]. Exercise-induced leukocytosis is also considered as pseudoleukocytosis because it does not seem to be connected with the production of new cells but rather due to the increase in the number of lymphocytes as a result of increased adrenaline secretion consequent to their release in blood from the spleen and, to a minor degree, from the bone marrow and lymph nodes [ 39 ].…”

“…Recently, it has been reported both in a murine model and in horses that exercise training can promote the immune response by a proliferation of peripheral lymphocytes [ 43 , 44 , 45 ]. In humans and horses, it was previously observed that interleukin IL-8 increases in the blood of athletes performing exercise and this might explain the increased lymphocytes counts [ 43 , 44 , 45 , 46 ].…”

“…Recent data show that hypereosinophilic human patients indeed suffer from an increased incidence of atypical thrombotic events [ 56 ]. Evidence supporting a direct contribution of eosinophils to the hemostatic process has recently been obtained in humans and in a murine model [ 3 , 43 ]. In particular, it has been shown that eosinophils are able to autonomously generate thrombin by expressing tissue factor and 12/15-lipoxygenase (12/15-LO), a key enzyme promoting the generation of procoagulant phospholipids at their surface [ 57 ].…”

The Physical Activity-Dependent Hematological and Biochemical Changes in School Horses in Comparison to Blood Profiles in Endurance and Race Horses

“…On the other hand, the AST activity increased only in endurance horses, thus may be connected with the highest muscle fatigue during this type of exercise. Besides, the CPK and AST values are related to muscle mass and composition [ 38 , 39 ], which were not included in this study.…”