TRENDS
B-G: we know what it is, but what does it do? Jim Kaufman and Jan Salomonsen
The major histocompatibility complex (MHC) of chickens was first described as the serologically polymorphic B blood group locus. The alloantisera presumably detected mainly B-G antigens on red blood cells. Only later were B-F (class I) antigens, B-L (class II) antigens, graft rejection, graft-versus-host reaction and mixed lymphocyte reaction found to cosegregate with the B locus. Although B-G antigens were considered to be confined to the red blood cell lineage, and were thus considered of less interest than class 1 and class 11 antigens, they were found to have just as many aileles as class I and class II antigens I,-'. In addition, B-G antigens were associated with certain immunological phenomena, in particular the "adjuvant effect', the 'preferential response' and 'natural antibody reactions'. These three phenomena were discovered during attempts to make alloantisera and monoctonal antibodies to chicken red blood cell surface molecules. In the 'adjuvant effect', the antibody response to poorly inmmnogenic molecules is much improved by the presence of allogeneic B-G molecules on the same cell (or liposome). While this is, in principle, like 'intermolecular help', it appears that only B-G molecules mediate this effect for other molecules on red blood cells. The 'preferential response' describes the observation that the primary antibodv response to B-G molecules is faster and higher titer than to other red blood cell molecules. This seems to be true both for chicken alloantibodies and mouse monoclonal antibodies. These phenomena may be due to the presence of 'natural antibodies' to B-G molecules in unimnmnized animals. These 'natural antibodies' have been described in chickens, in alligators and, interestingly, in several mammals. The
B-G molecules are pol),morphic ceil surface proteins that are encoded by the chicken MHC Here, .lira K,mfina, and Jan Salomonsen brie/Ty summarize developments in the molecular genetics, the structure and the tissue distribution of B-G molecules, and discuss possible functions of this intriguing multigene family. 'natural antibodies' mav also be responsible for the rapid clearance of red blood cells and the appearance of bursal tumors ascribed to B-(;region-encoded molecules I,~ Recently, it has become clear that B-G molecules are encoded by a large multigenc family, that thev have a wide tissue distribution and that they have a complcx and interesting structure. Here we review this progrcss and speculatc about the possible functions of B-(i molecules. A more complete revie\~' of the literature is given in Ref. I.
Molecular genetics The first Southern blots of chicken gcnomic DNA with B-(; eDNA
clones revealed malt, more hvbridizmg fragments than were expected from the number of proteins on red blood culls. Analysis of MHC congenie and trisomic chickens showed that all of these hybridizing fragments originate fronl the 8Mbp MHC microcilromosome, with most of them in the B-(; region. (The B-(; and B-FilJ-I. regions arc defined by serological and functional assays (if certain chicken stratus with recombinant MHC chromosomes)~._'.s.
B-G: we know what it is, but what does it do? Jim Kaufman and Jan Salomonsen
The major histocompatibility complex (MHC) of chickens was first described as the serologically polymorphic B blood group locus. The alloantisera presumably detected mainly B-G antigens on red blood cells. Only later were B-F (class I) antigens, B-L (class II) antigens, graft rejection, graft-versus-host reaction and mixed lymphocyte reaction found to cosegregate with the B locus. Although B-G antigens were considered to be confined to the red blood cell lineage, and were thus considered of less interest than class 1 and class 11 antigens, they were found to have just as many aileles as class I and class II antigens I,-'. In addition, B-G antigens were associated with certain immunological phenomena, in particular the "adjuvant effect', the 'preferential response' and 'natural antibody reactions'. These three phenomena were discovered during attempts to make alloantisera and monoctonal antibodies to chicken red blood cell surface molecules. In the 'adjuvant effect', the antibody response to poorly inmmnogenic molecules is much improved by the presence of allogeneic B-G molecules on the same cell (or liposome). While this is, in principle, like 'intermolecular help', it appears that only B-G molecules mediate this effect for other molecules on red blood cells. The 'preferential response' describes the observation that the primary antibodv response to B-G molecules is faster and higher titer than to other red blood cell molecules. This seems to be true both for chicken alloantibodies and mouse monoclonal antibodies. These phenomena may be due to the presence of 'natural antibodies' to B-G molecules in unimnmnized animals. These 'natural antibodies' have been described in chickens, in alligators and, interestingly, in several mammals. The
B-G molecules are pol),morphic ceil surface proteins that are encoded by the chicken MHC Here, .lira K,mfina, and Jan Salomonsen brie/Ty summarize developments in the molecular genetics, the structure and the tissue distribution of B-G molecules, and discuss possible functions of this intriguing multigene family. 'natural antibodies' mav also be responsible for the rapid clearance of red blood cells and the appearance of bursal tumors ascribed to B-(;region-encoded molecules I,~ Recently, it has become clear that B-G molecules are encoded by a large multigenc family, that thev have a wide tissue distribution and that they have a complcx and interesting structure. Here we review this progrcss and speculatc about the possible functions of B-(i molecules. A more complete revie\~' of the literature is given in Ref. I.
Molecular genetics The first Southern blots of chicken gcnomic DNA with B-(; eDNA
clones revealed malt, more hvbridizmg fragments than were expected from the number of proteins on red blood culls. Analysis of MHC congenie and trisomic chickens showed that all of these hybridizing fragments originate fronl the 8Mbp MHC microcilromosome, with most of them in the B-(; region. (The B-(; and B-FilJ-I. regions arc defined by serological and functional assays (if certain chicken stratus with recombinant MHC chromosomes)~._'.s.
