Micro- and Macro-Anatomical Frameworks of Lymph Nodes Indispensable for the Lymphatic System Filtering Function

Area of Science:

• Immunology
• Vascular Biology
• Anatomy

Background:

• Lymph nodes (LNs) are crucial for filtering lymph-borne substances.
• Their filtering capacity relies on resident macrophages and sinus structures.
• The functional significance of LN microarchitecture and arrangement in a chain is not fully understood.

Purpose of the Study:

• To investigate the mechanistic and histo-anatomical significance of LNs as lymph fluid filters.
• To explore the role of LN microarchitecture and cellular composition in lymphatic filtration.
• To understand the cooperative function of LNs in a chain system.

Main Methods:

• Subcutaneous injection of fluorescent tracers into mice.
• Qualitative and quantitative examination of lymphatic transport to LNs.
• Analysis of tracer accumulation in specific LN regions and cellular components.

Main Results:

• Tracers selectively accumulated in the MARCO+ subcapsular-medullary sinus border (SMB) of LNs.
• Reticular lymphatic endothelial cells and CD169+F4/80+ macrophages form a dense meshwork barrier in the SMB.
• Stepwise filtration via the LN chain prevented tracer leakage into the blood.
• Inflammatory responses remodeled LN tissue and lymphatic pathways, enhancing filtration capacity.

Conclusions:

• Specialized tissue infrastructure and systematic orchestration in LNs create an integrated filtering system.
• The LN chain provides cooperative, stepwise filtration, crucial for lymphatic recirculation.
• Understanding LN structure and function is key to lymphatic system defense and health.