Dual Y chromosome painting and in situ cell-specific immunofluorescence staining in lung tissue: An improved method of identifying donor marrow cells in lung following bone marrow transplantation

Several recent studies have demonstrated localization of donor bone marrow-derived cells in recipient lungs following transplantation from male to female mice or patients. Donor cells are identified by detection of the Y chromosome by fluorescence in situ hybridization (FISH). However, protein digestion pretreatments usually required for tissue FISH significantly limit the ability to detect cell type-specific markers by immunohistochemistry. We have used an alternative protein digest approach that entails heating the slides in 10 mM sodium citrate rather than utilizing a protease digestion. This approach preserves cell proteins following FISH, and allows lung tissue to remain intact for subsequent detection of cell-specific markers by immunohistochemistry. We have examined this technique in mouse lungs using a Y chromosome paint and three cell-specific markers, a pancytokeratin for epithelial cells, PECAM-1 for endothelial cells, and CD45 for leukocytes. Excellent visualization of both the Y chromosome and cell-specific surface protein markers was obtained on a single slide. This approach will significantly enhance the ability to detect and identify donor bone marrow cells in recipient mouse lungs following male to female transplantation.