Expression pattern of PU.1 in reactive lymphoid tissue and in classical Hodgkin disease.

(A) Uniform nuclear expression of PU.1 by germinal center and follicular mantle B cells in tonsillar lymphoid tissue. (B) Hodgkin and Reed-Sternberg cells show absent PU.1 expression, whereas small B cells and occasional histiocytes express the protein in the nuclei (immunostains using a PU.1 monoclonal antibody and the EnVision method using diaminobenzidine as chromogen, brown reaction product). Isotype-matched irrelevant antibodies did not show positive staining patterns on the same tissues. Original magnification A, × 100; B, × 250.