The defined antigen substrate spheres (DASS) system and some of its applications.

A quantitative immunofluorescent technique based on the covalent coupling of protein to Sepharose beads, the so-called defined antigen substrate spheres (DASS) system is described, and the main technical aspects are discussed. The method proved to be reproducible and has a lower detection limit equivalent to the amount of antigen, present per bead, that can bind 1 pg fluorescent labeled antibody. The DASS system has many applications, and some of them are discussed, such as the quantitation of antibodies and antigens with Sepharose-coupled antigens or antibodies. Not only antigen-antibody interactions but also any reaction that results in a stable complex can be studied, provided antisera against one of the constituents are available. An example is given by the complement fixation to Sepharose-coupled IgG. For the quantitation of hydrophobic antigens, hydrophobic Sepharise can be used.