The human spleen cells that strongly express PrP^C have an immunophenotype consistent with myeloid DCs.

(A-H) Identification of PrP^C-expressing cells by dual-color immunolocalization. PrP^C was identified using rabbit antiserum R26 and detected using Texas red-labeled antirabbit immunoglobulin (red) in all cases. Lineage-restricted mouse monoclonal antibodies (as indicated) to normal splenic cell types were detected using FITC-labeled antimouse immunoglobulin (green). Cell nuclei were identified by DAPI (blue). Sensitivity of the detection system was adjusted to identify only the strongly expressing cells. Strong PrP^C-expressing cells are rarely found in the T-cell area (panel A, CD3) or B-cell area (panel B, CD20); the antigen is not strongly expressed on FDCs (panel C, CR4/23). Cells strongly expressing PrP^C are clearly separate from surrounding monocytes/macrophages (panel D, CD68). Unstained cells (top right) represent an adjacent lymphoid area. Coexpression of PrP^Cwith CD13 (panel E and detail panel G) and CD11c (panel F and detail panel H) confirms myeloid origin and is indicated by an orange-yellow tone. Note that for CD11c (panel H) the cells coexpress PrP^C and CD11c, but the intracellular localization is not identical. CD13⁺ or CD11c⁺, which do not express PrP^C, are likely to represent monocyte-macrophage cells (panels E and F).