CHICKEN B-CELL MARKER CHB6 (BU-1) IS A HIGHLY GLYCOSYLATED PROTEIN OFUNIQUE STRUCTURE

The chB6 molecule is expressed on chicken B cells throughout most of t heir development, as well as on some non-lymphoid cells. It has long b een used as an allotypic marker in important studies of B-cell develop ment, though its function is unknown. We isolated a chB6 cDNA by expre ssion cloning and sequenced two further alleles following polymerase c hain reaction amplification. The results show that chB6 is a typical t ype I transmembrane protein, highly glycosylated in the extracellular region and carrying a large intracellular region. It has no recognizab le similarity to known mammalian molecules and thus represents a uniqu e B-cell marker. Its presence in chickens may be related to difference s in the properties of B-cell development between chickens and mammali an species. The sequences of the different alleles of this gene reveal ed a higher level of polymorphism than expected. A restriction fragmen t length polymorphism linked to the CHB6 gene has been used to determi ne its location on the linkage map of the chicken genome, which will a llow the definitive evaluation of reported associations with disease r esistance.