Page 1356 - Veterinary Immunology, 10th Edition

Regular moderate exercise boosts immune function. For example,
VetBooks.ir increased antibody responses are seen in mice that get moderate

exercise, compared with unexercised control mice. Exercise also
raises blood neutrophil counts, enhances NK cell activity, promotes

lymphocyte responses to mitogens, and increases blood levels of IL-
1, IL-6, and TNF-α. Although mild exercise is good for immune
function, high-intensity exercise, prolonged exhaustive exercise, or
overtraining may induce a functional immunodeficiency. In horses,

blood lymphocytes show a decreased proliferative response for up
to 16 hours after a race. Acute exercise in the unfit animal can be
especially stressful. Unfit horses subjected to strenuous exercise
showed significantly raised steroid levels, resulting in reduced

lymphocyte responses to mitogens or influenza virus antigens and
reduced neutrophil chemotactic responsiveness and respiratory
burst activity (Fig. 40.10). These animals show a decline in their
CD4/CD8 ratio as well as in both the number and activity of their

NK cells. The age of an animal may moderate the effect of exercise
on immune responses. For example, strenuous exercise significantly
reduces lymphocyte proliferative responses in young horses, yet
has much less effect on older animals. This resistance of older

horses to exercise-induced immunosuppression may be due to their
reduced steroid production.

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