Epithelium and associated lymphocytes of developing human fetal appendix. Electron microscopic study.

The epithelium and lamina propria of the human fetal appendix between 7.5 and 18 weeks of gestation was examined with electron microscopy. At 7.5 weeks the epithelium was composed of stratified columnar cells; scattered mesenchymal cells appeared in the lamina propria. By 13.5 weeks of gestation the epithelium was composed of simple columnar cells with a microvillous surface, goblet cells containing numerous mucinogen granules and argentaffin cells with elongated electron-dense granules. Also at 13.5 weeks of gestation some free lymphocytes were observed within the lamina propria as well as an occasional migrating lymphocyte within the epithelium between the columnar cells. At 18 weeks of gestation the simple columnar epithelial cells were tightly packed, the goblet cells were secretory and lymphocytes again appeared singly within the epithelium and lamina propria. No evidence of groups of lymphocytes or developing primary follicles within the lamina propria was observed in this study.