(A) HIV-HD LD subtype (case 25). Most RS cells show a distinct pattern of staining for anti-CD40 MoAb 89: a strong membranous staining is associated with a dot-like cytoplasmic positivity in Bouin-fixed, paraffin-embedded tissue section. (B, C, D) HIV-HD MC subtype (case 9). Serial Bouin-fixed, paraffin-embedded sections show that in the same area containing RS cells (arrows), numerous CD3⁺ (B) and CD8⁺ (C) small lymphocytes are present in the cellular background, where cells positive for CD4 (D) are scarce. (E) HIV-HD MC subtype (case 1). CD40L positivity is manifested on frozen section as dot-like staining on scattered lymphocytes (arrows). An RS cell surrounded by CD40L⁻lymphocytes is also shown (arrowhead). (A, E) APAAP immunostaining; (B, C, D) ABC immunostaining; (A-E) hematoxylin counterstain. Original magnification ×250 (A), ×320 (B-D), and ×400 (E).