Figure 3.

Immunolabeling of ICOS-positive cells in normal human lymphoid tissues. (A) Double immunoenzymatic labeling of tonsil shows, in a germinal center (GC), rare ICOS-positive (brown) cells co-expressing the regulatory T-cell associated transcription factor FOXP3 (blue, nuclear) (x400). (B) In contrast, a higher number of ICOS/FOXP3 double-positive cells are observed in the interfollicular area (X400). (A–B) The insets show examples of double-positive cells at a higher magnification (X600). (C) Triple staining for ICOS (blue), FOXP3 (brown) and the B-cell associated molecule CD79a (pink) in tissue sections of thymus reveals the presence of numerous ICOS/FOXP3 double-positive, CD79a-negative cells (as also shown at higher magnification in the inset, X600) which are mainly localized in the medulla (X200). Double immunoenzymatic labeling in tonsil (D–E) shows that rare ICOS-positive cells (brown) co-express the cytotoxic T-cell molecules CD8 (blue) (X600) and granzyme B (blue) (X600). The arrows indicate double-positive cells; (F) rare CD30-positive (blue) cells (mainly localized in the interfollicular area) co-express ICOS (brown) (X200) as also illustrated at higher magnification in the inset (X600). All staining was performed on paraffin-embedded tissue sections and hematoxylin counterstain was omitted.