Human spleen microanatomy: why mice do not suffice

Area of Science:

• Immunology
• Anatomy
• Histology

Background:

• Spleen microanatomy is primarily described in rodents, leading to terminological issues for human studies.
• The spleen comprises white pulp (lymphocytes) and red pulp (blood cells) in mice, rats, and humans.
• Rodent spleens have a distinct marginal zone absent in humans.

Purpose of the Study:

• To review and compare the splenic white and red pulp structure in rats, mice, and humans.
• To highlight species-specific microanatomical differences, particularly in humans.
• To encourage further research into lymphocyte recirculation within the human spleen.

Main Methods:

• Comparative review of microanatomical descriptions of rat, mouse, and human spleens.
• Analysis of histological features, including white pulp, red pulp, and associated vascular structures.
• Examination of cellular composition and organization within splenic compartments.

Main Results:

• Human spleens lack the rodent marginal zone; secondary follicles have germinal, mantle, and superficial zones.
• Human red pulp contains sheathed capillaries, distinct from the ellipsoids found in most vertebrates but absent in rats and mice.
• Human spleens likely possess an open circulation system, with no observed capillary-to-sinus connections in the red pulp.
• Three distinct stromal cell types are identified in the human white pulp.

Conclusions:

• Significant microanatomical differences exist between human and rodent spleens, necessitating species-specific terminology.
• Human splenic microarchitecture, including sheathed capillaries and an open circulation, supports unique lymphocyte trafficking.
• Further investigation into human splenic structure is vital for understanding immune responses and lymphocyte recirculation.