Recently developed imaging techniques using near-infrared fluorescence (NIRF) may help elucidate the role the lymphatic system plays in cancer metastasis, immune response, wound repair, and other lymphatic-associated diseases.
The lymphatic vascular system is an important component of the circulatory system that maintains fluid homeostasis, provides immune surveillance, and mediates fat absorption in the gut. Yet despite its critical function, there is comparatively little understanding of how the lymphatic system adapts to serve these functions in health and disease1. Recently, we have demonstrated the ability to dynamically image lymphatic architecture and lymph “pumping” action in normal human subjects as well as in persons suffering lymphatic dysfunction using trace administration of a near-infrared fluorescent (NIRF) dye and a custom, Gen III-intensified imaging system2-4. NIRF imaging showed dramatic changes in lymphatic architecture and function with human disease. It remains unclear how these changes occur and new animal models are being developed to elucidate their genetic and molecular basis. In this protocol, we present NIRF lymphatic, small animal imaging5,6 using indocyanine green (ICG), a dye that has been used for 50 years in humans7, and a NIRF dye-labeled cyclic albumin binding domain (cABD-IRDye800) peptide that preferentially binds mouse and human albumin8. Approximately 5.5 times brighter than ICG, cABD-IRDye800 has a similar lymphatic clearance profile and can be injected in smaller doses than ICG to achieve sufficient NIRF signals for imaging8. Because both cABD-IRDye800 and ICG bind to albumin in the interstitial space8, they both may depict active protein transport into and within the lymphatics. Intradermal (ID) injections (5-50 μl) of ICG (645 μM) or cABD-IRDye800 (200 μM) in saline are administered to the dorsal aspect of each hind paw and/or the left and right side of the base of the tail of an isoflurane-anesthetized mouse. The resulting dye concentration in the animal is 83-1,250 μg/kg for ICG or 113-1,700 μg/kg for cABD-IRDye800. Immediately following injections, functional lymphatic imaging is conducted for up to 1 hr using a customized, small animal NIRF imaging system. Whole animal spatial resolution can depict fluorescent lymphatic vessels of 100 microns or less, and images of structures up to 3 cm in depth can be acquired9. Images are acquired using V++ software and analyzed using ImageJ or MATLAB software. During analysis, consecutive regions of interest (ROIs) encompassing the entire vessel diameter are drawn along a given lymph vessel. The dimensions for each ROI are kept constant for a given vessel and NIRF intensity is measured for each ROI to quantitatively assess “packets” of lymph moving through vessels.
We use a custom, small animal NIRF imaging system to capture images of labeled lymph vessels in mice. To construct movies of lymph movement, 300 or more images are collected. For functional analysis of lymphatics from movies, two or more ROIs are manually drawn along a lymph vessel. The dimensions of the ROIs are kept constant for each vessel and are approximately the diameter of the vessel. While whole animal spatial resolution can depict fluorescent lymphatic vessels of 100 microns or less, a macrolens for fine…
The authors have nothing to disclose.
This work was supported by the following grants to Eva Sevick: NIH R01 CA128919 and NIH R01 HL092923.
Solutions, Reagents, and Equipment | Company | Catalog Number | Comments |
Indocyanine green (ICG) | Patheon Italia S.P.A. | NDC 25431-424-02 | Reconstitute to 645 μM (5 μg/10 μL) |
Cyclic Albumin Binding Domain(cABD) | Bachem | Custom | Reconstitute to 200 μM (6.8 μg/10 μL) |
IRDye800 | Li-COR | IRDye 800CW | Reconstitute according to manufacture’s instructions; conjugate with cABD at equilmolar concentrations |
Sterile Water | Hospira, Inc., Lake Forest, IL | NDC 0409-4887-10 | |
NAIR | Church & Dwight Co., Inc. | Local Stores | www.nairlikeneverbefore.com |
Imaging System (components below) | Center for Molecular Imaging | N/A | Custom-built in our laboratories. |
Electron-multiplying charge-coupled device (EMCCD) camera | Princeton Instruments, Trenton, NJ | Photon Max 512 | |
Nikon camera lens | Nikon Inc., Melville, NY | Model No. 1992, Nikkor 28mm | |
Optical filter | Andover Corp., Salem,NH | ANDV11333 | Two 830.0/10.0 nm bandpass filters are used in front of lens |
785-nm laser diode | Intense Ltd, North Brunswick, NJ | 1005-9MM-78503 | 500 mW of optical output |
Collimating optics | Thorlabs, Newton, NJ | C240TME-B | Collimates laser output prior to cleanup filter |
Clean-up filter | Semrock, Inc., Rochester, NY | LD01-785/10-25 | Removes laser emission in fluorescence band |
Optical diffuser | Thorlabs, Newton, NJ | ED1-C20 | Diffuses the laser over the animal |
V++ | Digital Optics, Browns Bay, Auckland, New Zealand | Version 5.0 | Software used to control camera system and save images to computer. http://digitaloptics.net/ |
Analytic Software Either of the following software packages can be used for image analysis | |||
ImageJ | National Institutes of Health, Bethesda, MD | Most current version available | Freeware available at http://rsbweb.nih.gov/ij/ |
MATLAB | MathWorks, Natick, MA | Version 2008a or later | http://www.mathworks.com/ |