For a period of two months during the competitive season the effects of endurance
training in cross-country skiers were evaluated in order to compare the adaptive and
innate immune systems between 10 competitive athletes, 10 moderately trained athletes
and 10 untrained healthy controls. The main results were as follows: the peripheral
T-lymphocyte count of the competitive athletes was decreased. In contrast the number
of peripheral blood NK cells was increased in this group. These data imply a diminution
of the adaptive immune system due to repeated bouts of intense exercise and contemporaneous
reinforcement of the innate immune response. Moreover the inducible IL-12-expression
following monocyte stimulation was significantly decreased in competitive athletes.
Compared with the other two groups, the moderately trained athletes showed a significantly
increased production of IFN-γ upon T-cell stimulation. These data suggest that the
immune system may profit from moderate endurance training by an increased capacity
to generate IFN-γ while the immune situation following repeated exhausting exercise
of competitive athletes tends to deteriorate through downregulation of IFN-γ and IL-12.
Endurance training, infection, humoral and cellular immune response, cytokines.
