In contrast, it is postulated that high-intensity exercise may promote a suppressive effect on the immune response, reducing the secretion rate of salivary immunoglobulin A (IgA-S) and leading to a transient decrease in the IFN-γ/IL-4 ratio, creating an “open window” for infections (Walsh et al., 2011; Zhao et al., 2012). This evidence concerns the gene IL4 and infection.