The development of the adaptive immune system has been studied in the mouse primarily
because it is easier to access fetal tissues and because there exists a rich array of probes for
analysis of various components of the immune system. While much has been learned from
this exercise, it is also clear that different species show substantial temporal variation in the
development of the immune system during early life. In mice, for instance, mature α/β T cells
first appear in the periphery during the final stages of fetal gestation and only increase in …