Field-Deployable Lens-Free Imaging Platform for Rapid Label-Free Analysis of Natural Killer Cell Activation

Natural killer (NK) cells are important effectors of innate immunity that eliminate virus-infected and malignant cells. Monitoring NK cell activity is essential for assessing immune function. However, conventional methods, such as flow cytometry, are labor-intensive and time-consuming. This protocol describes a label-free technique for the rapid analysis of natural killer (NK) cell activity using lens-free shadow imaging technology (LSIT). NK cells isolated from peripheral blood and stimulated with a proprietary activator were analyzed using the LSIT platform within 5 min. The LSIT platform captures holographic images, known as shadow images, created by the interference of light with NK cells, and monitors their activation status by analyzing changes in shadow parameters. Key parameters derived from the shadow images, including the peak-to-peak distance (PPD) and standard deviation of the secondary maxima width (WSM-SD), quantitatively reflected the cell morphology and internal complexity. These parameters were integrated into the combined shadow parameter (CSP) and innate immunity index (I³) to provide a comprehensive assessment and quantification of NK cell activity based on morphological changes in the cells. I³, calculated as the percentage change in CSP after activation, served as a direct measure of NK cell activity. NK cells from healthy individuals consistently showed significantly higher I³ values than those from immunocompromised individuals. The LSIT platform enables fast and cost-effective immune profiling that is suitable for point-of-care diagnostics.