Aggregate of nonneoplastic lymphocytes in a bone marrow specimen involved by T-cell GLL.

(A) Immunoperoxidase stain for CD3. Most of the lymphocytes in the aggregate are CD3⁺ T cells. Aminoethyl carbazol chromogen, hematoxylin counterstain; original magnification: × 80. (B) Immunoperoxidase stain for CD20. The lymphoid aggregate contains few CD20⁺ B cells. Aminoethyl carbazol chromogen, hematoxylin counterstain; original magnification: × 80. (C) Immunoperoxidase stain for granzyme B. Virtually none of the neoplastic granzyme B⁺ granular lymphocytes are present in the lymphoid aggregate, but they can be seen in the bone marrow interstitium and the blood vessels at the periphery of the aggregate. Aminoethyl carbazol chromogen, hematoxylin counterstain; original magnification: × 80.