Structure and permeability differ in subepithelial villus and Peyer's patch follicle capillaries

Area of Science:

• Gastrointestinal physiology
• Immunology
• Vascular biology

Background:

• Laminin is present in the basement membrane of both villus and Peyer's patch epithelia.
• Differences in basement membrane labeling suggested variations in subepithelial capillary permeability.

Purpose of the Study:

• To compare the fine structure and macromolecular permeability of capillaries beneath mouse villus and Peyer's patch epithelia.
• To investigate the role of endothelial fenestrae in differential permeability.

Main Methods:

• Electron microscopy of tissue sections and freeze-fracture replicas to assess capillary fenestrae.
• Intravenous injection of horseradish peroxidase and hemoglobin to evaluate macromolecular transport.

Main Results:

• Villus capillaries exhibited abundant fenestrae, while Peyer's patch dome capillaries had very few.
• Macromolecular tracers (horseradish peroxidase, hemoglobin) readily accessed the pericapillary space of villus capillaries but were significantly restricted in dome capillaries.
• Permeability differences were quantified, with significantly lower tracer localization in dome capillaries compared to villus capillaries.

Conclusions:

• Subepithelial capillaries in mouse Peyer's patch domes generally lack endothelial fenestrae.
• The Peyer's patch dome capillary network demonstrates reduced permeability to certain macromolecules compared to the villus capillary network.
• Endothelial fenestration is a key determinant of differential macromolecular transport in the small intestine.