Immunolabeling of PrPScin the hemal nodes from a scrapie-infected sheep. PrPSc immunolabeling (dark red) was visible in the secondary follicles of abdominal hemal nodes (animal ID 3777) when labeled with anti-prion mAbs 12B2 (A), P4 (B), 1E4 (C), 8G8 (D), L42 (E), SAF84 (F), F184.108.40.206 (G) and retropharyngeal lymph nodes labeled with SAF84 (I). The FDC-type of PrPSc immunolabeling was visible in the hemal nodes of this animal with 12B2 and SAF84 mAbs. PrPSc immunolabeling was not observed in the hemal nodes’ secondary follicles when anti-prion mAbs were replaced with isotype-matched control immunoglobulins (H; same tissue block shown in A-G). Scale bar = 50 μm.