Identification of chicken Bu-1 alloantigens using the monoclonal antibody AV20

The genetically polymorphic chicken antigen Bu-1 (chB6) has been identified by alloantisera raised against RPL line 63 (Bu-1a) and line 72 (Bu-1b) birds and subsequently by monoclonal antibodies (mAbs) which identify individual alloantigens. We have produced a monoclonal antibody, AV20, which recognises a monomorphic determinant on the antigen Bu-1. AV20 identifies a marker on both bursal and peripheral B cells. Staining characteristics on bursa, spleen, thymus and peripheral blood lymphocytes are similar to those of the allotypic antibodies which identify Bu-1a and Bu-1b. However, AV20 identified B cells in partially inbred birds as well as inbred lines including line 61 and line 72, indicating that it recognises a monomorphic determinant. AV20 immunoprecipitated an antigen with a Mwr of 150 kDa under non-reducing conditions and 70–75 kDa under reducing conditions indicating it is a homodimer. Serial immunoprecipitations of bursal-cell lysates from line 61 or line 72 confirmed that AV20 recognised the same antigen as mAbs against Bu-1a and Bu-1b in the respective lines.