Peyers patches (PPs) play a critical role in the induction and dissemi
nation of immune responses at mucosal surfaces. However, increasing ev
idence shows that, in some species, they are also a major site for the
production of the systemic B-cell pool and for the generation of the
primary immunoglobulin repertoire. Here, Philip Griebel and Wayne Hein
compare the structural, functional and developmental heterogeneity of
PPs in different species.