Common antigenic structures of HL-A antigens. 3. An HL-A common antigenic marker closely associated with HL-A alloantigenic activity and detected by use of rabbit anti-rhesus monkey cell membrane antibodies.

Rabbit antibodies formed in response to Rhesus monkey cell membranes react with a structure found on papain-solubilized HL-A molecular fragments of 48,000 Daltons. The structure or structures responsible for the reaction is common to HL-A antigen molecules of different alloantigenic specificities and appears to be one or more of the HL-A antigenic determinants shown earlier to be characteristic structural features of different HL-A antigen molecules. The structure appears to be very closely associated functionally with the alloantigenic activity. Its pH and temperature stability characteristics are very similar to those of the alloantigenic activity and it is not found on the HL-A common portion fragment of 11,000 Daltons which does not carry HL-A alloantigenic activity. In Rhesus monkeys the antigenic determinant appears to be on the major histocompatibility antigens, since it is found only on the 48,000-Dalton molecular fragment of papain-solubilized cell membrane as it is in man. The antigenic determinant of Rhesus monkey and the similar, if not identical, cross-reacting structure on the HL-A antigen molecule, may be a common, characteristic marker for the major histocompatibility antigens of man and Rhesus and possibly of other primates. This antigenic marker is not an alloantigenic determinant which is present in only certain individuals in each species.