Natural history of MZ B cells.

In this issue, Tull et al. (https://doi.org/10.1084/jem.20202001) and Kibler et al. (https://doi.org/10.1084/jem.20201952) track human marginal zone B cell development from early progenitors to the memory compartment, addressing changes in age and autoimmunity, the sequence of development in the gut-associated lymphoid tissue, and clonal sharing among memory cells.