Human marginal zone B cells.

Human marginal zone (MZ) B cells are, in a sense, a new entity. Although they share many properties with their mouse counterpart, they also display striking differences, such as the capacity to recirculate and the presence of somatic mutations in their B cell receptor. These differences are the reason they are often not considered a separate, rodent-like B cell lineage, but rather are considered IgM memory B cells. We review here our present knowledge concerning this subset and the arguments in favor of the proposition that humans have evolved for their MZ B cell compartment a separate B cell population that develops and diversifies its Ig receptor during ontogeny outside T-dependent or T-independent immune responses.