Mucosal immunity and respiratory illness in elite athletes.

This review focuses on studies of immunity in elite athletes and specifically addresses the role of mucosal immunity in respiratory illness and associations with the intensity, volume and duration of exercise. Investigations of mucosal immunity have mostly studied the response of salivary immunoglobulins to exercise, although nasopharyngeal secretions and breast milk have also been examined. Habitual exercise at an intense level can cause suppression of mucosal immune parameters. Salivary IgA and IgM concentrations decline immediately after a bout of intense exercise and usually recover within 24 h. Training at an intense level can result in a chronic suppression of mucosal immunoglobulin levels over many years, and in some endurance sports a decline over a training season has been observed. The degree of suppression is associated with the intensity of the exercise and the duration or volume of the training. Low levels of salivary IgM and IgA, particularly the IgA1 subclass, are associated with an increased risk of respiratory illness. Monitoring mucosal immune parameters during critical training periods and establishing personal profiles for individual athletes may provide an assessment of the risk status of an athlete for URTI and allow effective management by the athlete and coach. Despite suppression of mucosal immune parameters, elite athletes are capable of normal responses to novel oral vaccinations, indicating that mucosal immune mechanisms are intact. The mechanisms underlying the mucosal immune suppression are unknown but most likely reflect alterations in T-lymphocyte cytokine control mechanisms.