Used in immunological research to detect and quantify C4d, a stable breakdown product of complement component C4, in biological samples. The kit helps assess activation of the classical and lectin pathways of the complement system, which plays a key role in immune response and inflammation. Commonly applied in studies of autoimmune diseases such as systemic lupus erythematosus (SLE), transplant rejection, and other conditions involving complement activation. Provides a reliable, sensitive, and specific method for measuring C4d levels in serum, plasma, or tissue eluates, supporting both clinical research and diagnostic development.