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

Area of Science:

• Developmental Biology
• Gastrointestinal Histology

Background:

• The human fetal appendix's early histological development is not fully understood.
• Investigating the appendix's immune cell presence during gestation is crucial for understanding its role.

Purpose of the Study:

• To characterize the ultrastructural development of the human fetal appendix epithelium and lamina propria.
• To identify the emergence and distribution of immune cells within the fetal appendix during early gestation.

Main Methods:

• Electron microscopy was employed to examine appendix tissue samples.
• Human fetal appendix specimens were collected from 7.5 to 18 weeks of gestation.

Main Results:

• At 7.5 weeks, stratified columnar epithelium and mesenchymal cells were observed.
• By 13.5 weeks, simple columnar epithelium with microvilli, goblet cells, and argentaffin cells developed.
• Lymphocytes were present in the lamina propria and epithelium by 13.5 weeks, increasing in density by 18 weeks, but no lymphoid follicles formed.

Conclusions:

• The human fetal appendix undergoes significant epithelial differentiation between 7.5 and 18 weeks of gestation.
• Immune cell presence, specifically lymphocytes, is established within the fetal appendix during this period.
• The absence of lymphoid follicles suggests a delayed development of organized gut-associated lymphoid tissue in the appendix.