Salivary Immunoglobulin A (s-IgA) and Exercise: Relevance of its Control in Athletes and Methodological Implications

The present study aimed to discuss the main findings involving salivary immunoglobulin A (s-IgA) and exercise and evidence the importance of the control in athletes. Exercise is a great modulator of immune system characteristics such as the s-IgA that exerts important defense against upper respiratory tract infections (URTI). However, more evidence is needed to confirm a direct association between low levels of s-IgA and URTI. The level of s-IgA decreases after a high-intense exercise, increasing thus, the individual's susceptibility to infection, but athletes engaged in exhausting exercise are not clinically immune-deficient compared with sedentary subjects. The changes in s-IgA are transitory returning to normal status in approximately 48-h rest. The reason of these alterations remains unclear, but many causes have been investigated: hormones stressors rise; nutrition influences; action of reactive oxygen species, psychological stress. Despite the transitory effects of the exercise on the immune system, the variability in s-IgA differs in populations with different fitness levels. Differences in exercise protocols, saliva collection, manipulation or storage methods, the method used to assess s-IgA, subject's hydration status, dietary control, competition's seasonality, acclimatization, among other factors should be considered to compare different studies. In addition, these factors could partially explain the adverse results of studies involving moderate and intermittent exercise that have found increase, decrease and no changes in s-IgA levels. Investigations of recent immunologic issues such as the toll like-receptors and the advances in technology may contribute to increase the evidence on this issue.