Inexpensive upgrading of a FACS I and isolation of rare somatic variants by double-fluorescence sorting

We have modified a FACS I by addition of a tunable dye laser and an optical system for fluorescence detection that allows physically independent measurement of green and red immunofluorescence. These modifications are inexpensive and should be applicable to most single-laser systems. By using the modified machine and double-fluorescence activated selection with H-2Kk-specific monoclonal antibodies labelled with FITC or Texas Red, we have isolated from a murine T-cell lymphoma line variant subclones expressing structurally altered histocompatibility class I (H-2Kk) molecules.