CD45⁺ SP tip cells from liver (Li) are phenotypically distinct from bone marrow (BM) SP cells. (A) Effects of enzyme digestion (collagenase and dispase) on c-kit immunostaining in BM SP cells. Despite diminished intensity of c-kit surface immunostaining after enzyme digestion, 61% of BM SP cells still exhibit c-kit immunofluorescence above background. (B) After identical enzyme digestion, c-kit immunostaining is readily detected above background in CD45-Li non-SP cells and minimally detected in few CD45-LiSP cells. In contrast, no CD45⁺ SP tip cells from liver exhibit c-kit surface staining. IgG indicates immunoglobulin G. (C) Multiplex RT-PCR assay for c-kit and GAPDH gene expression shows no detectable c-kit mRNA in multiple sorted samples of CD45⁺ LiSP tip cells. In contrast, c-kit expression is easily detected in samples prepared from identical numbers of sorted BM SP and BM main population (MP). Expression of the housekeeping gene GAPDH is present in all samples. Numbers in dot plots represent percentage of cells contained in each quadrant.