Introduction
URTIs
RESPIRATORY TRACT INFECTIONS, RHEUMATISM
Edited by: Francesco Di Pierro, Velleja Research S.r.l., ItalyReviewed by: Andrey Kruglov, German Rheumatism Research Center (DRFZ), Germany; Mariarosaria Matera, Azienda USL Toscana Sud Est, Italy; Qiang Wang, Wuhan University of Science and Technology, ChinaThis article was submitted to Microbial Immunology, a section of the journal Frontiers in ImmunologyUpper respiratory tract infections (URTI) are the most common illnesses affecting athletes, causing absences from training and competition. Salivary immunoglobulin A (sIgA) is the main immune factor in saliva, and a consistent association between low concentrations of sIgA and an increased incidence of URTIs has been reported. The oral probiotic 