paper by Fujiki et al. entitled ‘‘Quantification of greenfluorescence protein by in vivo imaging, PCR and flow cyto-metry: comparison of transgenic strains and relevance for fetalcell microchimerism’’ has a very promising approach to imagefetal cell microchimerism (1). The paper compares two typesof transgenic mice expressing green fluorescent protein (GFP)for the future study of fetal microchimerism—the processwhere fetal cells enter the maternal circulation, and in humanscan persist in the maternal blood and tissues for decades. TheGFP transgenic mice chosen for study are the C51B6/6-Tg(ACTB-EGFP) Osb/J (CAG) and the ROSA 26-EGFP. Theauthors conclude that the CAG mice have much brighter cells,but the ROSA 26-EGFP cells more consistently express GFP.The authors compare imaging, PCR, and flow cytometry(FCM) to image cells from these mice and conclude that flowcytometry is the method of choice, since ‘‘. . . due to the exist-ing status of this imaging technology and the purely quantita-tive nature of PCR amplification, FCM provides the best over-all approach for the quantitative and qualitative evaluation ofrare transgenic microchimeric fetal cells.’’The authors, however, are apparently unaware of thepower of fluorescence protein-imaging in vivo. Chishima et al.(2) pioneered this area and showed that single cancer cellsexpressing GFP could be readily imaged in autopsied miceagainst the large background of normal tissue. Subsequently,Yang et al. (3) showed that tumors could be whole-bodyimaged with GFP in live unrestrained mice. Yang et al. (4)then made two more important advances, and showed in skinflaps in live mice that single GFP cells could be imaged inmany organs. Yang et al. (5) then showed that tumor cellsexpressing red fluorescent protein (RFP) in the cytoplasm andGFP in the nucleus, as well as GFP host stromal cells, couldnoninvasively be imaged when grown in the mouse foot pad.Yamamoto et al. (6) and Yamauchi et al. (7,8) showedthat single cells labeled in the nucleus with GFP and in thecytoplasm with RFP could be imaged in mice both noninva-sively as well as in skin flaps. Yamauchi et al. (7,8) imaged thedual color cells in blood vessels as they trafficked in real time.Imaging cell trafficking was greatly enhanced by use of thevariable-magnification Olympus OV100 imaging system.Hayashi et al. (9) used the dual-colored cells and OlympusOV100 to image cells trafficking in lymphatics.Use of a high-powered variable-magnification imagingsystem, such as the OV100, rather than the IVIS 200 photoncounting device used by Fujiki et al. which does not produceimages, enables single fluorescent-protein-labeled cells to bevisualized in real time even during trafficking (10–12). Suchan approach offers many advantages over the IVIS 200 andflow cytometry, since cells can be visualized in the live animalwhich is very important for studying microchimerism (13).In parallel to the rapid development of instrumentation,many efforts have been made to optimize the existing ‘‘classical’’
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Dec 28, 2011
Arvind Dhople 
Open Access