Direct identification of the murine pluripotential stem cell using rabbit anti-mouse brain serum

Previous studies have shown that antisera prepared in rabbits against mouse brain tissue (RAMBS) contain activity against the murine bone marrow colony-forming unit (CFU-s) or pluripotential hemotopoietic stem cell. In the present study, the F(ab')2 portion of RAMBS was examined for its potential efficacy in the identification of the mouse CFU-s when used in an indirect immunofluorescence-labeling technique. After separation of mouse bone marrow cells by a discontinuous bovine serum albumin density gradient, fluorescent cells were observed only in those bands which, by the splenic colony-forming assay, demonstrated CFU-s. Furthermore, the quantity of CFU-s demonstrated by the spleen colony-forming assay approximated the number of fluorescent cells observed in the corresponding band. It appears that the F(ab')2 portion of RAMBS used in an immunofluorescent assay may provide a method for the direct quantitation and identification of the CFU-s content of murine bone marrow.