Used to measure the concentration of CD28 protein in human biological samples such as serum, plasma, or cell culture supernatants. This ELISA kit is commonly applied in immunological research to study T-cell activation and immune response regulation. CD28 is a key co-stimulatory receptor on T cells, and its detection helps in understanding immune system function, autoimmune diseases, cancer immunotherapy, and the effects of immunomodulatory drugs. The assay enables quantitative analysis, supporting both clinical research and drug development.