NIRF-guided capture of lymph sacs. Dextran-500,000 MW-Cy5.5 was administered in the pelvic floor underneath the urinary bladder. Two hours after dextran-Cy5.5, the abdomen was opened and the gastrointestinal tract was removed, and representative photomicrographs were taken in black-and-white (A) or artificially-colored to provide a gradation of fluorescence distribution (B). Fluorescent lymph sacs (white circle in A and B) were captured and dissected under fluorescence, and subsequently frozen for histology. C is a composite of an H&E stained cross-section (originally at ×100) of a lymph sac showing an interesting pattern of concentric paths of smooth muscle (dotted black circle) that can be appreciated at higher magnification in D. A region with high concentration of lymphocytes was also visible (wavy black line in figure C). This region was processed for fluorescent Immunohistochemistry and at the confocal level, it was possible to determine the presence of CD-31-positive blood vessels (E; green) and LYVE-1-positive lymphatic vessels (F; green) draining this region. In figures E and F, the red represents Cy5.5 accumulation and the blue stain is DAPI. Original magnifications were: C = ×100, D = ×400, E = ×400, and F = ×400.