Determining the role of follicular dendritic cells in TSE agent neuroinvasion
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McCulloch2011.doc (28.63Mb)
Date
25/11/2011Author
McCulloch, Laura
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Abstract
Transmissible spongiform encephalopathies (TSEs), such as scrapie and variant
Creutzfeldt-Jakob disease are infectious, fatal, neurodegenerative diseases. Following
peripheral infection TSE agents usually accumulate in lymhoid tissues before
spreading to the central nervous system. In mice, follicular dendritic cells (FDCs)
expressing the host prion protein (PrPC) are essential for scrapie agent accumulation
in lymphoid tissues. The accumulation of the scrapie agent on FDCs is critical for the
efficient spread of infection to the brain. However, it is unknown whether FDCs
themselves actively replicate the scrapie agent, or simply accumulate it following
production by other cells types such as neurones, lymphocytes or other stromal cell
populations. To definitively address this issue a transgenic mouse model was created
in which PrPC is switched on or off exclusively on FDCs.
Expression of cre-recombinase (Cre) under the action of cell-specific gene promoters
can be used to induce or delete the expression of a target gene in specific cell
populations. In this model, Cre expression is driven by the complement receptor type
2 gene (Cr2/CD21) which is expressed by FDCs and mature B lymphocytes.
Characterisation of the CD21-cre mouse line was achieved by crossing with a
ROSA26 reporter strain. The CD21-cre mouse line was subsequently crossed with
floxed-PrP mouse lines to produce compound transgenic mouse lines in which PrPC
expression was switched on or off, only in FDCs. Cre expression by B lymphocytes
was eliminated by γ-irradiation and grafting recipient mice with Cre-deficient bone
marrow. Immunohistochemical analysis confirmed the expression PrPC had been
switched on or off exclusively on FDCs. Subsequently, the mice were challenged
with scrapie by intra-peritoneal injection to determine the precise role of FDCs in the
accumulation of scrapie in lymphoid tissues.
Switching off PrPC expression exclusively on FDCs prevented the accumulation of
TSE agent specific disease-associated PrPSc in the spleen after i.p inoculation.
Conversely, in mice in which PrPC was expressed only on FDC, successful replication
of the agent occurred on the FDC network in the spleen. Taken together, these data
show PrPC-expressing FDCs alone are sufficient to support the accumulation of the
scrapie agent within lymphoid tissues. Furthermore, these data suggest FDC replicate
the TSE agent and do not simply accumulate it following synthesis by other cell
types.