Optimization and use of near infrared imaging to guide lymph node collection in rhesus macaques (Macaca mulatta)

Background Identification of lymph nodes (LNs) draining a specific site or in obese macaques can be challenging. Methods Indocyanine Green (ICG) was administered intradermal (ID), intramuscular, in the oral mucosa, or subserosal in the colon followed by Near Infrared (NIR) imaging. Results After optimization to maximize LN identification, intradermal ICG was successful in identifying 50-100% of the axillary/inguinal LN at a site. Using NIR, collection of peripheral and mesenteric LNs in obese macaques was 100% successful after traditional methods failed. Additionally, guided collection of LNs draining the site of intraepithelial or intramuscular immunization demonstrated significantly increased numbers of T follicular helper (Tfh) cells in germinal centers of draining compared to nondraining LNs. Conclusion These imaging techniques optimize our ability to evaluate immune changes within LNs over time, even in obese macaques. This approach allows for targeted serial biopsies that permit confidence that draining LNs are being harvested throughout the study.