A lympho-follicular microenvironment is required for pathological prion protein deposition in chronically inflamed tissues from scrapie-affected sheep

PLoS One. 2013 May 3;8(5):e62830. doi: 10.1371/journal.pone.0062830. Print 2013.

Abstract

In sheep scrapie, pathological prion protein (PrP(Sc)) deposition occurs in the lymphoreticular and central nervous systems. We investigated PrP(Sc) distribution in scrapie-affected sheep showing simultaneous evidence of chronic lymphofollicular, lymphoproliferative/non-lymphofollicular, and/or granulomatous inflammations in their mammary gland, lung, and ileum. To do this, PrP(Sc) detection was carried out via immunohistochemistry and Western Blotting techniques, as well as through inflammatory cell immunophenotyping. Expression studies of gene coding for biological factors modulating the host's inflammatory response were also carried out. We demonstrated that ectopic PrP(Sc) deposition occurs exclusively in the context of lymphofollicular inflammatory sites, inside newly formed and well-organized lymphoid follicles harboring follicular dendritic cells. On the contrary, no PrP(Sc) deposition was detected in granulomas, even when they were closely located to newly formed lymphoid follicles. A significantly more consistent expression of lymphotoxin α and β mRNA was detected in lymphofollicular inflammation compared to the other two types, with lymphotoxin α and β signaling new lymphoid follicles' formation and, likely, the occurrence of ectopic PrP(Sc) deposition inside them. Our findings suggest that, in sheep co-affected by scrapie and chronic inflammatory conditions, only newly formed lymphoid follicles provide a suitable micro-environment that supports the scrapie agent's replication in inflammatory sites, with an increased risk of prion shedding through body secretions/excretions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Dendritic Cells, Follicular / immunology
  • Dendritic Cells, Follicular / pathology*
  • Female
  • Gene Expression
  • Ileum / immunology
  • Ileum / pathology*
  • Inflammation
  • Lung / immunology
  • Lung / pathology*
  • Lymphoid Tissue / immunology
  • Lymphoid Tissue / pathology*
  • Lymphotoxin-alpha / genetics
  • Lymphotoxin-alpha / immunology
  • Lymphotoxin-beta / genetics
  • Lymphotoxin-beta / immunology
  • Mammary Glands, Animal / immunology
  • Mammary Glands, Animal / pathology*
  • PrPSc Proteins / genetics*
  • PrPSc Proteins / immunology
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Scrapie / genetics
  • Scrapie / immunology
  • Scrapie / pathology*
  • Sheep, Domestic

Substances

  • Lymphotoxin-alpha
  • Lymphotoxin-beta
  • PrPSc Proteins
  • RNA, Messenger

Grants and funding

This work was supported by IZS SA 04/09 and IZS SA 05/09 RC grants from the Italian Ministry of Health, as well as by an EMIDA ERA-NET 2011 Research Project. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.