SYNERGY TEST FOR RECOGNITION OF EPITOPES ON SOLUBLE-PROTEINS - ITS APPLICATION IN THE STUDY OF CD21 AND CD23 ANTIGENS AND THEIR RESPECTIVE ANTIBODIES

Antigens such as CD21 and CD23, which express only one copy of an epit ope require two monoclonal antibodies (mAbs) for their detection and e stimation. This requirement is exploited in two ways in a technique ba sed on the chromic chloride haemagglutination test. For simple titrati on of antigen two portions of red cells each coated with one of a pair of synergising mAbs are used in a 1:1 combination. For testing the an tigenic specificity of a mAb and assessing its region of epitope bindi ng, the mAb under test is serially diluted in fluid containing a stand ard amount of antigen and red cells are added to which have been attac hed a different mAb. If the red cell-bound mAb recognises a determinan t topographically distinct from that of the soluble mAb, red cell aggl utination to high titre occurs. In titrations of ascitic fluid contain ing approximately 1 mg/ml mAb, tires of log(2)9 to log(2)16 xwere reco rded from a starting dilution of 1 in 200. Hence the test is very sens itive and only minute amounts of a mAb are required for testing. The s ame test system can be used for assessing the relative display of epit opes on antigen obtained from different sources, e.g., culture superna tes and body fluids. The method is of general applicability to monomer ic antigens and its use is illustrated by analysis of CD21 and CD23 an tigens and antibodies.