Optical clearing based cellular-level 3D visualization of intact lymph node cortex.

Area of Science:

• Immunology
• Biomedical Imaging
• Optical Engineering

Background:

• Lymph nodes (LNs) are crucial immune organs with complex 3D cellular and vascular structures.
• Conventional histology limits 3D analysis of LNs due to tissue disruption.
• Confocal microscopy offers 3D imaging but is limited by light scattering in biological tissues.

Purpose of the Study:

• To establish an optical clearing procedure for lymph nodes (LNs) to enable deep 3D imaging.
• To overcome the limitations of light scattering in intact LN tissue.
• To visualize cellular structures, vasculature, and metastatic cells within the entire LN cortex.

Main Methods:

• Developed and optimized an optical clearing protocol specifically for lymph node tissue.
• Utilized confocal microscopy for 3D volumetric imaging of cleared LN samples.
• Employed transgenic mice (H2B-GFP/actin-DsRed) and fluorescently labeled cells (B cells, T cells, melanoma) for visualization.
• Used fluorescently conjugated antibodies (anti-CD31, anti-LYVE-1) for vascular and lymphatic labeling.

Main Results:

• Achieved 3D volumetric visualization of the entire lymph node cortex, significantly improving imaging depth (over 4x).
• Successfully visualized key immune structures: T-cell zones, B-cell follicles, and germinal centers.
• Visualized metastatic melanoma cell colonies, vasculature, and lymphatic vessels within the LN cortex in 3D.

Conclusions:

• The established optical clearing method enables unprecedented deep 3D imaging of intact lymph nodes.
• This technique facilitates detailed analysis of immune microenvironments and disease processes, such as cancer metastasis.
• The method provides a powerful tool for studying LN structure-function relationships and immune responses.