Validation of a Novel Method for Measuring Sweat-Derived Immunoglobulin A.

INTRODUCTION: Immunoglobulin A (IgA) is a major antibody responsible for mucosal immunity, abundant in saliva, tears, airways, and the gastrointestinal tract, where it functions as the first line of defense against pathogens. In recent years, simple and non-invasive methods for monitoring IgA levels have become increasingly important for health management and disease prevention. Blood and saliva are routinely used to detect IgA levels; however, blood sampling is invasive, and saliva is strongly influenced by psychological states, limiting high-frequency or real-time monitoring. This study evaluated the feasibility of measuring IgA from sweat using a non-invasive skin surface collection method. METHODS: The study included 60 non-medical undergraduate and graduate students (25 males, 35 females; mean age 20.5 ± 1.4 years). Participants with skin disorders, immune dysfunctions, or active infections were excluded. Sweat samples were collected during three periods in 2023 (June, July-August, November) in a laboratory setting maintained at 18-25°C. After hand washing and disinfection, 100 µL of phosphate-buffered saline (PBS) was applied to the fingertip with a cap fixed by medical tape and exposed for one, three, five, or 30 min. PBS was recovered, frozen at -20°C, and analyzed for secretory IgA (s-IgA) using enzyme-linked immunosorbent assays (ELISA). Two commercial kits (Yanaihara Institute and Abcam) were used, with all assays conducted by the same investigator. Short exposure conditions (1-5 min) yielded IgA below the detection threshold. However, under the 30-minute exposure condition, IgA was successfully detected. In the third collection period using the Abcam kit, quantification success rates were 83%, 90%, and 90% across three repeated measurements. RESULTS: Mean IgA concentrations were 5.37 ± 11.27, 5.81 ± 10.10, and 7.96 ± 12.47 ng/mL. Although some samples exceeded the upper or lower detection limits, reproducibility was acceptable, showing that sweat IgA can be reliably measured. To the best of our knowledge, this study is the first to demonstrate successful detection of sweat IgA using a simple, non-invasive PBS exposure method. Compared with blood or saliva testing, this technique is less invasive and suitable for routine use. Integration with biosensing and wearable technologies may enable real-time monitoring of immune function in daily life. Challenges remain, including individual variability, environmental influences, and standardization of procedures. Future research should focus on the following objectives: increasing reproducibility, clarifying the role of lifestyle and gut microbiota in sweat IgA dynamics, and reducing the collection time for practical application. CONCLUSION: This study presents a novel method for non-invasive measurement of IgA from sweat, providing a technological foundation for applications in health monitoring and preventive medicine. With further refinement, sweat IgA monitoring could become a valuable tool for routine immune assessment, early disease detection, and personalized medical care.