R-phycoerythrin-cyanine 5 tandem discerns CD72 polymorphism

By fluorescence analysis, we demonstrated that a fluorochrome tandem composed of R-phycoerythrin and cyanine 5 specifically recognized B cells from SJL, AKR, MRL/Mp, and NOD mouse strains, whereas B cells from C57BL/6, DBA/2, SWR, 129/Sv, and BALB/c were not stained. A strict correlation was observed between the fixation of the fluorochrome and the pattern of expression of the pan-B cell marker CD72, i.e., early expression in B-cell lineage development and downregulation on the terminally differentiated activated B cells. Three allelic forms, CD72a, CD72b and CD72c have been well characterized, and show a high number of amino acid substitutions concentrated in the membrane-distal extracellular domain. Using a PCR approach, we determined that all mouse strains positive for fluorochrome staining display the CD72c allelic form. Moreover, a genetic analysis showed that the fixation of the fluorochrome on the B cell is exclusively dependent on the presence of the CD72c allele. Together, these results strongly suggest that the tandem binds a molecular complex comprising the CD72c molecule or recognizes directly the CD72c molecule itself.