RESUMO
Strenuous exercise is recognized as a stress, which may induce functional immunodeficiency and increase individual susceptibility to infection. It has been shown in equine athletes, that alterations in leukocyte functions occur after moderate and submaximal exertion, however, no data deal with the effect of extreme physical exertion. In this study, we evaluated leukocyte functions (neutrophil oxidative burst and lymphocyte proliferation activity in response to mitogens) in horses following the CEI 3* 162 km endurance ride. Exercise-induced stress was manifested as neutrophilic leukocytosis and lymphopaenia resulting in a significant increase in neutrophil:lymphocyte ratio. The alterations in neutrophil function were expressed as a lower percentage of the cells undergoing oxidative burst. The spontaneous lymphocyte proliferation was very high, however, the cells failed to respond to mitogens. Although a decrease in lymphocyte proliferation in response to mitogens has been reported previously, the pattern determined in our study was unique. It may suggest that during the extreme physical exercise immune cells receive an excessive stimulation from yet undetermined factor(s), which renders them unresponsive to extraneous mitogens. The differences between alterations in leukocyte activities induced by extreme exertion may reflect the exercise type and duration as well as the training status of the horses.