Immunohistochemical staining with anti-HGAL monoclonal antibody in tonsil tissues. (A-B) GCs are highlighted in a normal tonsil; an increased intensity of staining is seen within cells of the proliferating pole or dark zone of GCs, whereas mantle and marginal zones lack staining. Inset shows a higher magnification of HGAL staining in germinal-center cells. (C) Double immunohistologic labeling for HGAL (red cytoplasmic stain) and BCL6 (brown nuclear stain) are colocalized in a significant number of cells within the GC. (D) A subset of GC cells shows coexpression of BCL6 (arrow) and HGAL (arrowhead). (E) A subset of GC cells located in the proliferative pole of the GC shows staining for BCL6 but not for HGAL. (F) Double immunohistologic labeling for HGAL (red cytoplasmic stain, arrowhead) and CD10 (brown membrane stain, arrow) show that a majority of GC cells coexpress these 2 proteins although cells expressing only HGAL or CD10 are also present. Original magnifications: A, ×30; B and C, ×150; D-F and B inset, ×600.