Bu-1b Monoclonal Antibody for Flow Bu-1b, a product of the Bu-1b allele, is expressed on the cell surface as a disulfide-linked homodimer. In 10-week-old H.B15 and H.B2 chickens, Bu-1 is found on 85-90% of bursal cells, 2-8% of thymocytes, 15-27% of sple