Figure 4.

Proliferation and apoptosis in thyroid LFs. a: Immunofluorescence staining for Ki67 in an intrathyroidal LF, showing abundant proliferating cells polarized toward the dark zone (GD, case TB228). b: Double-immunofluorescence staining for IgD (green) and Ki67 (red), demonstrating that most proliferating cells are in the light zone of the GC and are either negative or slightly positive for IgD, as in the case of centroblasts. c: Demonstration of the existence of apoptotic cells by the terminal dUTP nick-end labeling technique and hematoxylin counterstain. Most positive cells were found in the GC area; no positive cells were seen in the epithelium of the thyroid follicles (data not shown). d and e: Double immunofluorescence for bcl-2 and IgD. The level of expression of apoptosis inhibitor bcl-2 is high in the MZ but is also expressed in the GC cells. The staining for IgD shows the distribution of mature B cells in the MZ. f: Double exposure of double-immunofluorescence staining for IgD (green) and CD95/Fas (red). Notice that Fas is mainly expressed in the CG, whereas IgD is expressed in the MZ, as is the case in normal LNs.