Exercise and Immunity: A Review with Emphasis on the Horse

Abstract

Exercise has been recognized as a stress, which can significantly alter the host's immune response and, therefore, its susceptibility to disease. Whereas research in this area has previously focused primarily on human subjects and laboratory animals, it has more recently extended to domestic animals, especially the equine athlete. Despite several studies, defining the relationship among exercise, the immune response, and disease has proven difficult due to a number of factors, including the complexity of the immune system and the variable nature of exercise itself. It now appears that exercise has dual effects on the immune system. Supn association between exercise and disease susceptibil-A ity was recognized as early as 1918, when it was reported that pneumonia was more common in human athletes than in sedentary individuals, and that strenuous exercise increased the risk of upper respiratory tract infections progressing to pneumonia.' Since that time, several studies have investigated the relationship among exercise, the immune response, and disease, leading to recognition that the stress of exercise has profound but variable effects on the immune Although comparatively little is known about the specific effects of exercise on immunity in domestic animals, the strenuous exercise that horses and other performance animals routinely engage in makes this subject of importance in veterinary medicine. In this article, we review the literature examining the relationship between exercise and immunity, and its clinical relevance. Effects of Exercise on the Immune SystemConsiderable research has investigated the effects of exercise on the immune system, and while it has been established that virtually every aspect of both the nonspecific and specific immune systems can be affected by exercise, the definitive results of these studies often appear conflicting.*-"' Several factors contribute to the variability among studies, including the complexity of the immune system and differences in experimental design. Function of the immune system depends on a number of cell types, receptor systems, soluble mediators, and their interactions. The effects of exercise on isolated components of the immune system may not reflect a change in the overall immune status. Likewise, because variations in the intensity, duration, or specific type of activity can have significant effects on the response of the immune system, the nature of the exercise being studied

Lower serum IgA levels in horses kept under intensive sanitary management and physical training

“…Athlete horses are born and kept under controlled conditions such as concrete individual stalls, standardized industrialized -E-mail: mmcamar@usp.br food, multiple vaccination and vermifugation protocols, easy access to antimicrobial therapy and daily supervised physical training. It is conceivable that such conditions, which are much cleaner but physically demanding when compared to those found in a free-ranging farm, underlie the higher frequency of upper respiratory and digestive tracts infections found in athlete animals (Hines et al, 1996). Herein, we worked with the hypothesis that intensive handling associated with chronic strenuous exercise results in mucosal humoral immunosuppression in horses.…”

U-Shaped Dose-Responses in Biology, Toxicology, and Public Health

“…Although several significant reviews have documented the occurrence of U-shaped dose-responses in biological and toxicological systems (9,10,17,18,22), such responses have also been commonly seen in numerous pharmacological investigations (8) as well as for endpoints of considerable public health significance, including body weight and longevity (1-3, 20, 30, 36, 40, 48, 62, 63, 80-83, 89), cholesterol and longevity (28, 47), alcohol consumption and cardiovascular disease incidence (33,49,50,52,54,56), and exercise intensity/duration and immune responsive disease resistance (6,29,39,53,57,71). The occurrences of U-shaped dose-responses are thus widely and independently observed phenomena.…”

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

“…This condition is believed to result from alterations in the number and functions of circulating leukocytes. Several reports confirmed the diminished neutrophil function during this period in human and equine athletes [2,5,7,8]. However, variable results on the lymphocyte response after exercise have been presented, suggesting that it is highly heterogeneous [8][9][10].…”

“…The assay represents an in vitro model, which is believed to mimic events that occur after antigen stimulation of lymphocytes in vivo [2,[8][9][10]. In human many reports have proved that lymphocyte proliferation is changed by exercise, but the response have been seen either elevated, reduced or unchanged [9].…”