Figure 1.

Transplantation of unfractionated bone marrow ubiquitously labeled with GFP (B-actin–GFP). Representative lung frozen tissue section from a recipient analyzed 1 yr after transplantation of 10 million unfractionated GFP+ bone marrow cells. At the time of analysis this recipient had 88% GFP+ peripheral blood chimerism. (A) DAPI nuclear counterstaining (blue); (B) immunostaining with an antibody against a specific alveolar type II (AT2) pneumocyte cell marker (Cy3 anti-pro–SP-C; red); and (C) fluorescence of GFP (B-actin–GFP; green) are merged in D, illustrating the 1 cell (of 200 AT2 cells examined on this section) that appeared to express both markers (arrows). The number of cells that are “double-labeled” with GFP fluorescence and AT2-specific red immunostaining in this recipient lung is no different than the number of cells per section that show background autofluorescence on negative control sections (shown in Figure 3 below).