The origin of CD5(+) B cells remains controversial. The differential respon
se to ligation of CD5 resulting in apoptosis or proliferation provides insi
ght into its roles in distinct human B cells. Here,Pierre Youinou, Christop
he Jamin and Peter Lydyard review current knowledge of B-1 and B-2 cells, a
nd proposer that CD5 has different functions when expressed by different B-
cell subpopulations.