Splenic marginal zone B cells in humans: Where do they mutate their Ig receptor?

Abstract
Human IgM+IgD+CD27+ B cells have mutated Ig genes and harbor a splenic marginal zone (MZ) phenotype. In this issue, the group of R. Küppers has studied the expression of the enzyme activation‐induced cytidine deaminase (AID) in human spleen samples by immunocytochemistry and failed to detect a significant AID‐expressing subset in the MZ region. The consequences on the possible origin of these cells are discussed. See accompanying article: http://dx.doi.org/10.1002/eji.200535134