Siglec-H is expressed on pDC precursor and macrophage subsets in spleen and lymph nodes. (A-C) Spleen cryostat sections were stained with MB15 (rat anti–Siglec-H) mAb followed by goat anti–rat-FITC. Sections were counter-stained with CD4 (A), CD11c (B), or sialoadhesin (Sn), (C). Siglec-H⁺ cells are codistributed with T cells (A) and CD11c⁺ DCs (B), and some larger Siglec-H⁺ cells are present within the marginal zone, adjacent to Sn⁺ metallophilic macrophages (C). (D-E). Spleen sections were stained with biotinylated sheep anti–Siglec-H pAb and ER-TR9 mAb (rat anti–SIGN-R1) followed by streptavidin–Texas red and rabbit anti–rat immunoglobulin-FITC; panel D is low-power view, while panel E is higher-power view. In the marginal zone, there are large macrophages double labeled for both Siglec-H and SIGN-R1, as well as smaller pDC precursors that are only labeled with Siglec-H (E arrows). (F-I) Mesenteric lymph node (LN) sections were stained with sheep anti–Siglec-H–FITC and either counterstained with B220 (F) or anti-Sn (G-I). In panel F, small Siglec-H⁺ pDC precursors are labeled (arrowheads), whereas in the medullary cord (MC), larger Siglec-H⁺ cells can be seen adjacent to B220⁺ B cells. Siglec-H⁺ pDC precursors are also present in a T-cell zone (arrowheads). In panels G-I, many Siglec-H⁺ macrophages are present in the medullary cords (MCs) that colocalize with Sn (I). Siglec-H⁺ pDC precursor can also be seen in a T-cell zone(T). Magnification: 100× (A-D, F-I); 400× (E).