The level of secretory immunoglobulin A (SIgA) in saliva is associated with the risk of upper respiratory infection and has been identified as a condition indicator for athletes and an indicator of mucosal immune function in the elderly. In addition, it has been suggested that non-specific polyreactive SIgA is present in human saliva and colostrum. The purpose of this study was to establish a new detection method of polyreactive salivary SIgA. Using saliva samples from eight healthy individuals, indirect ELISA was used to detect anti-LPS antibodies (LPS ELISA), and competitive ELISA was used to detect LPS antibodies after competition with DNA (LPS-DNA ELISA). The difference in SIgA concentration between LPS ELISA and LPS-DNA ELISA is thought to be the concentration of the polyreactive SIgA, which responds to both DNA and LPS. First, we determined the concentration for coating LPS and DNA as 10 μg/ml, and the saliva sample dilution was determined as 1/2. The concentration of anti-LPS antibody contained in the saliva sample, which is strongly reactive to LPS, was defined as the standard. Compared to the SIgA concentration determined by LPS ELISA, SIgA concentration of LPS-DNA ELISA did not decrease in two samples, but was reduced in 6 samples. The decrease in SIgA concentration is thought to be the concentration of polyreactive SIgA that reacts with both DNA and LPS. Notably, we found sample-to-sample differences in the concentration of polyreactive SIgA.

The present study aimed to test the hypothesis that changes in the dermal tissue dielectric constant (TDC) and biomechanical properties of the skin would be correlated with the indicators related to dehydration. Ten healthy adult men were enrolled in three trials: no fluid intake (DEH), ad libitum fluid intake (AL-HYD), and programmed fluid intake (P-HYD) after exercise in a randomised crossover design. The participants performed a pedalling exercise at 60% heart rate reserve until 2% body mass loss. At 120 min after exercise, an incremental exercise test was carried out. Aerobic capacity, body composition, TDC, biomechanical properties of the skin (pliability, viscoelasticity, and total recovery), and indicators related to dehydration in the serum and urine were measured before and 120 min after exercise. Higher values of the pliability and viscoelasticity, and lower value of the total recovery on the hand were demonstrated in the P-HYD trial compared to the DEH trial (all P < 0.05). Changes in the TDC were significantly correlated with changes in body mass, total body water, serum osmolarity, and hematocrit (all P < 0.05). Changes in the biomechanical properties of the hand were significantly correlated with changes in body mass, hematocrit, and urine specific gravity (all P < 0.05). The present study showed that the changes in skin characteristics correlated with the body water and dehydration-associated indicators in the serum and urine, thus suggesting that skin characteristics may be useful in the assessment of dehydration. Highlights. This study was the first to investigate the effect of dehydration and rehydration on the TDC and biomechanical properties of the skin upon instrumental measure, and not manual testing. . This study confirmed the decline in aerobic capacity by dehydration and immediate recovery with sufficient rehydration. . Changes in the TDC and the biomechanical properties of the skin correlated with the body water and dehydration-associated indicators in the serum and urine. . Skin characteristics may be useful in the assessment of dehydration.