Lymphocyte infiltration of gut epithelium in fetal and neonatal rabbits.

Lymphocytes infiltrate the epithelium of small intestinal villi of fetal rabbits as early as day 28 of gestation. They appear within the lateral spaces between the columnar absorptive cells. At this time, the epithelial cells transport compounds, such as injected horseradish peroxidase, through these intercellular spaces to the subjacent lamina propria. The possibility for in utero interaction between intraepithelial lymphocytes and antigen in swallowed amniotic fluid is discussed. There is an increase in the number of intraepithelial lymphocytes from 1 per 500 epithelial cells on day 1 to 16 per 500 epithelial cells on day 21 of postnatal life. Each segment, duodenum, jejunum and ileum, shows an increase in the number of lymphocytes during this period.