Separation of Pancreatic Islets by Fluorescence-Activated Sorting

To allow clinical pancreatic islet transplantation, the yield and purity of islets must be improved. Intravital staining of islets with neutral red is a specific, nontoxic technique for labeling islets of various species. Using neutral red-stained rat islets, we investigated the known fluorescence absorbance and emission spectra in comparison with unstained exocrine tissue and have shown that stimulation with light of wavelength between 500 and 560 nm produces detectable emission >610 nm, which is absent from unstained exocrine tissue. The PARTEC cell sorter is an inexpensive alternative to currently available fluorescence-activated cell sorters and has a sorting mechanism based on a piezoelectric valve. We made extensive modifications to this machine to allow passage of particles up to 300 μm diam. Using rat pancreas stained intravitally with neutral red and dispersed by intraductal collagenase technique, we have shown that islets can be accurately identified in a high-speed flow system and sorted to a purity of >90% islet tissue. The islets remain intact and viable as determined by supravital staining and isogeneic transplantation to the kidney capsule site. These studies prove the feasibility of separating intact islets by fluorescence-activated sorting.