Histologic features and CD21 expression in 3 histologic patterns of AITL.

Panels A and B show case 2 with histologic pattern I, panels C and D show case 10 with histologic pattern II, and panels E and F show case 28 with histologic pattern III. (A,C,E) Hematoxylin and eosin–stained sections showing 3 different histologic patterns. Inset in panel C highlights a depleted follicle. Follicular architecture is retained in pattern I (A) and II (C) but is completely lost in pattern III (E). (B,D,F) Immunostaining for CD21 in 3 histologic patterns. There is only focal proliferation of FDCs in pattern I (B, upper panel; arrow); in patterns II and III (panels D and F), there is increasing FDC proliferation. Original magnification A-F, × 40; C inset, × 200.