Comparison of histopathological features in scrapie-infected C57BL/10 mice and homozygous anchorless PrP transgenic mice (tg44+/+).

aPartially protease-resistant PrP (PrPres) is a hallmark of TSE/prion diseases. Most researchers including ourselves rely on the correlation between the immunoblot detection of PrPres and the immunohistochemical detection of PrP with staining properties and regional distribution found only in prion-infected animals, and thus refer to such disease-associated PrP as PrPres or PrPd.bIn most mouse scrapie models PrPres has a diffuse fine punctate staining pattern which is negative for staining with the amyloid stain, Thioflavin S. In both homozygous and heterozygous anchorless PrP transgenic mice the PrPres has a coarse dense plaque-like staining pattern and is Thioflavin S-positive.cDistortion of neuroanatomical features such as the hippocampal and cerebrocortical neuronal layers was associated with the presences of large PrPres amyloid plaques. Such distortion was accompanied by neuronal loss (Figure 4H–L). This feature was seen in tg44+/+ and tg23+/+ mice, but was less frequent in heterozygous transgenic mice. Brain distortion appeared to be the result of the large amounts of PrPres amyloid present in homozygous transgenic mice (Figure 3).dAbnormal staining with anti-APP indicates axonal or neuronal damage. This is easily seen in infected tg44+/+ mice, but is minimal in infected C57BL/10 mice. Antibodies reactive with phosphorylated or non-phosphorylated neurofilament protein (NFP) both showed abnormal staining in infected tg44+/+ mice compared to C57BL/10 mice (Figure 4L vs 4M).eTSE vacuoles in gray matter are a hallmark of classical prion diseases. At the ultrastructural level they are characterized by fragmentation of the inner limiting membrane and presence of membrane fragments hanging into the vacuole, and by electron microscopy PrPres detectable by immunogold labeling is not found to be colocalized with these vacuoles ([13], [17], [7]).fSeveral ultrastructural abnormalities, including spiral membranes, invaginated membranes, increased and fused clathrin-coated pits and membrane microfolds, have been found to be unique to TSE diseases, all of which co-localize with disease-associated membrane accumulations of PrPres. These changes are present in mice infected with different murine scrapie strains [17], in sheep scrapie [18] and in cattle BSE [7], and were not seen in infected homozygous or heterozygous tg44 or tg23 mice.gIn white matter distended empty myelin sheaths were seen, and these were often large enough to be noted as “vacuoles” by light microscopy.