The changes in the number, distribution, and ultrastructure of globule
leukocytes (GL) during postnatal development were investigated in the
intestinal epithelium of non-infected healthy rats. Intestinal GL wer
e abundant in normal newborn rats even in the absence of infection. Th
ey subsequently decreased markedly to the adult level by the fourth we
ek. Ultrastructurally, morphological variations suggesting maturation
of the cells were observed in the GL during development. These changes
could be noted neither in the mucosal mast cells (MMC) nor in the gra
nular intra-epithelial lymphocytes. Morphological differences between
GL and other cells were evident in adult animals. Most notably, paracr
ystalline structures were found exclusively in the granules of the GL.
Immunohistochemically, both the GL and MMC were stained with anti-ser
otonin, but not with anti-IgE. Degranulation of GL in developing rats
was caused by repeated intraperitoneal administration of dexamethasone
. Neither GL nor MMC were affected by compound 48/80. These results in
dicate that (1) the GL and MMC are derived from a common ancestral cel
l toward the end of embryonic development, (2) the immature GL migrate
from the lamina propria into the epithelium to differentiate, mature,
and proliferate, and (3) the immature GL have specific functions duri
ng the neonatal period.