Lymphocyte proliferation activity after limited (Light class) and long (CEI) distance endurance rides in horses

Abstract

Long lasting or high-intensity exercise has been shown to suppress immune response by alterations in the number and functions of leukocytes. Several reports confirmed diminished neutrophil activity in human and equine athletes, but variable results on lymphocyte functions are presented. In this study, we evaluated the mitogen-induced proliferation activity of lymphocyte isolated from horses taking part in endurance competition. Twenty four horses competed on limited distance (Light class) or long distance (CEI) rides were examined. Exercise induced changes in leukocyte number manifested in all horses as neutrophilic leukocytosis and an increase in neutrophil to lymphocyte ratio after both types of rides. Completing limited distance rides did not produced any changes in lymphocyte proliferation activity, but clear alterations in lymphocyte functions have been detected in the horses taking part in long distance rides, even before the start. The reaction to mitogen stimulation in most cases was equal to the activity of unstimulated cells, indicating a kind of unresponsiveness to mitogens. However, the spontaneous activity of the cells was low or high and three patterns of reaction have been shown. It can be concluded, that competing or even preparing to long distance rides may be conductive to alterations in the lymphocyte functions, that can be recognized as immunosuppression. The reaction is highly heterogeneous and seems of limited importance in the evaluation of the suppression of immune response in endurance horses.