 To collect a sufficient quantity of saliva, we used Salivette cotton swabs Salimetrics, State College, PA, USA, which were stored in double-layer plastic tubes with a lid. When participants chew a swab for about 2 to 3 minutes, saliva flow is stimulated to a sufficient amount 1 mL for collection. After the tube was centrifuged at 1000 x g for 2 minutes, saliva was stored at -80C until assay for salivary cortisol and IgA concentrations. 