Figure 4. PrP^Sc is detected only in inflamed sheep mammary glands containing newly formed lymphoid follicles.

Inflammatory cell immunophenotyping in serial paraffin-embedded sections of mammary glands from sheep simultaneously affected by scrapie and lymphofollicular, lymphoproliferative/non-lymphofollicular, or granulomatous mastitis. A normal ovine palatine tonsil is also shown for comparison. CNA-42, CD3, and CD79 were used as markers for FDCs, T cells, and B cells (Panel A), while CD172a, CD68, and CD11c were used for activated macrophages and DCs (Panel B), respectively. In panel C, a representative set of negative controls are shown. These were obtained by omitting all the primary antibodies used on the tonsil sections (photos 1, 2, 3, 4, 6, and 7), as well as from granulomatous mastitis (photo 5). The omitted primary antibodies are indicated on each photo. It is noteworthy that the relative positioning of these cell populations was similar in newly formed lymphoid follicles and constitutive follicles normally hosted inside the palatine tonsil. CD172a⁺ macrophages were the most representative cell population in granulomatous mastitis, which also displayed a moderate presence of T and B cells and DCs. CD3⁺ T cells were the most abundant cellular component in the context of lymphoproliferative/non-lymphofollicular mastitis. PrP^Sc deposition occurred in co-localization with CD79⁺ B cells and the CNA42⁺ FDC network both in palatine tonsil and in newly formed lymphoid follicles. Immune reactions were visualized by 3-3′-diaminobenzidine (DAB) chromogen, with F99 primary MoAb being used for PrP^Sc detection. Mayer’s hematoxylin counterstain. Scale bar = 100 µm.