Somatic hypermutation of the immunoglobulin variable genes during germ
inal reactions might permit the expansion of B-cell clones with unwant
ed (e.g. autoreactive) specificity. Here, Ernst Lindhout and colleague
s propose three antigen-specific checkpoints that ensure the appropria
te antigen specificity of activated B cells is maintained by regulatin
g the activation, selection and further differentiation of B cells.