Used in immunological research to quantify levels of decay acceleration factor (DAF/CD55) in biological samples such as serum, plasma, or cell culture supernatants. Enables assessment of DAF/CD55 expression in studies related to complement system regulation, autoimmune diseases, transplant rejection, and infectious diseases where pathogens exploit CD55 for immune evasion. Commonly applied in clinical research and drug development to monitor disease progression or evaluate therapeutic efficacy targeting complement-mediated pathways.