Heterogeneity in intraepithelial lymphocyte subpopulations in fetal and postnatal human small intestine.

Intraepithelial lymphocytes (IEL) are present in fetal human small intestine from 14 weeks' gestation independent of exogenous dietary or microbial antigens. We have now studied the heterogeneity of IEL in 18-22-week-old human fetal intestine and in postnatal small intestine by single and sequential immunoenzyme histochemistry. In normal children and adults, there were 6-27 CD3+ IEL per 100 epithelial cells, whereas in fetal gut there were 3-5 CD3+ IEL per 100 epithelial cells. Postnatal intestine contained a population of CD3-,7+, non-T cell IEL (7-25% of total CD7+). These cells were absent from fetal IEL but were occasionally seen in the fetal lamina propria. About 6% of CD3+ postnatal IEL were CD4-,8-. In contrast in the fetus, 35-70% of CD3+ IEL were subset negative. Since CD3 and CD7 are always co-expressed on fetal IEL, 28-58% of fetal IEL were also CD7+,4-,8-. Only about 20% of the CD3+ IEL expressed the gamma delta chains of the T cell antigen receptor. We conclude from these studies that CD3+,4-,8- T cells migrate to the epithelium in the absence of exogenous antigen and that there is a population of CD3-,7+ non-T cells in postnatal gut which is absent in fetal gut.