Figure 4. IgG distribution in mouse visceral yolk sac.
Photomicrographs of representative tissue sections dual labeled with (green) Alexa-488 goat IgG anti-mouse IgG and chicken anti-CAV1 antibody followed by (red) Alexa-594 goat IgG anti-chicken IgY secondary antibody. Panel A: FcRn+/+ yolk sac in which green signal is seen in endodermal cells (thick arrows) as well in mesenchymal areas (thin arrows). Anti-CAV1 labels both the endothelium in mesenchyma and the mesothelium (broken arrows). The inset, which contains a higher magnification view of the small outlined area of yolk sac, shows labeling of IgG in mesenchyma, indicated by arrowheads. Panel B: FcRn−/− yolk sac showing bright green staining of the endodermal cells (thick arrow) but no IgG staining in the mesenchyma (thin arrow). The mesothelium (red) is marked with broken arrows. The inset, containing a higher magnification view of the outlined area of yolk sac, shows with arrowheads the lack of IgG in the mesenchyma. For orientation of arrows with histologic features, the center two panels show combined DIC and DAPI images of yolk sac from FcRn+/+ (C) and FcRn−/− (D) conceptuses. Bar = 20 μm. Panels E and F: Quantification of immunofluorescence images. Multiple images such as those in panels A and B were quantified as in Figure 2C. The relative morphologic distribution and the fluorescence intensity of IgG staining in yolk sac cells were quantified and compared (expressed as mean fluorescence intensity ± SD) from recorded fluorescence intensity measurements of both endodermal (E) and mesenchymal (F) areas of tissue sections. Matched yolk sacs from 3 FcRn+/+ and 3 FcRn−/− conceptuses were studied simultaneously. In panel F, the average intensity per unit area for FcRn−/− is 0.0193 with SD of 0.023.