Active macromolecule uptake by lymph node antigen-presenting cells: a novel mechanism in determining sentinel lymph...

Area of Science:

• Oncology
• Immunology
• Surgical Pathology

Background:

• Sentinel lymph node (SLN) biopsy is crucial for staging melanoma and breast cancer.
• Technique-related controversies persist in SLN biopsy.
• The role of antigen-presenting cells (APCs) in differential radiotracer retention in SLNs requires clarification.

Purpose of the Study:

• To investigate if active particle uptake by APCs explains differential radioactivity retention in SLNs versus nonsentinel lymph nodes (NSLNs).

Main Methods:

• Pigs were injected with vital blue dye, FITC-labeled human serum albumin (FITC-HSA), and 99mTc-labeled tracers (macromolecule or sulfur colloid).
• In vitro APC uptake of FITC-HSA was assessed using fluorescence-activated cell sorting (FACS).
• SLNs and NSLNs were analyzed via fluorescence microscopy and FACS, with leukocyte markers for cell identification.

Main Results:

• Both radiotracers proved effective for SLN mapping.
• APCs demonstrated rapid uptake of FITC-HSA in vitro.
• Microscopy revealed FITC-HSA in SLN subcapsular sinuses and interfollicular areas; FACS confirmed increasing SLN uptake over time.
• APCs expressing MHC class II were identified as the primary cells responsible for uptake.

Conclusions:

• Active macromolecule uptake by APCs is a key mechanism determining SLN status.
• Understanding this mechanism is vital for optimizing SLN biopsy procedures.