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From: Terry S. Singeltary Sr. (
Subject: Re: Chronic Lymphocytic Inflammation Specifies the Organ Tropism of Prions (kidney, pancreas and liver)
Date: January 25, 2005 at 9:08 am PST

In Reply to: Chronic Lymphocytic Inflammation Specifies the Organ Tropism of Prions (kidney, pancreas and liver) posted by TSS on January 20, 2005 at 2:14 pm:

-------- Original Message --------
Subject: Chronic Lymphocytic Inflammation Specifies the Organ Tropism of Prions [FULL TEXT]
Date: Tue, 25 Jan 2005 10:45:51 -0600
From: "Terry S. Singeltary Sr."
Reply-To: Bovine Spongiform Encephalopathy

##################### Bovine Spongiform Encephalopathy #####################

Chronic Lymphocytic Inflammation Specifies the Organ Tropism of Prions

Mathias Heikenwalder,1* Nicolas Zeller,1* Harald Seeger,1* Marco
Prinz,1* Peter-Christian Klöhn,2 Petra
Schwarz,1 Nancy H. Ruddle,3 Charles Weissmann,2 Adriano Aguzzi1!

1Institute of Neuropathology, University Hospital of Zürich, CH-8091
Zürich, Switzerland. 2Medical Research Council Prion
Unit, Department of Neurodegenerative Diseases, Institute of Neurology,
Queen Square, London WC1N 3BG, UK. 3Department
of Epidemiology and Public Health and Section of Immunobiology, Yale
University School of Medicine, New Haven, CT
06520, USA.

*These authors contributed equally to this work.
Present address: Institute of Neuropathology, Georg-August-Universität,
D-37073 Göttingen, Germany.
!To whom correspondence should be addressed. E-mail:

Prions typically accumulate in nervous and lymphoid
tissues. Because proinflammatory cytokines and immune
cells are required for lymphoid prion replication, we
tested whether inflammatory conditions affect prion
pathogenesis. We administered prions to mice with five
inflammatory diseases of kidney, pancreas or liver. In all
cases, chronic lymphocytic inflammation enabled prion
accumulation in otherwise prion-free organs.
Inflammatory foci consistently correlated with
lymphotoxin upregulation and ectopic induction of PrPCexpressing
FDC-M1+ cells, whereas inflamed organs of
mice lacking lymphotoxin-? or its receptor did not
accumulate PrPSc nor infectivity upon prion inoculation.
By expanding the tissue distribution of prions, chronic
inflammatory conditions may act as modifiers of natural
and iatrogenic prion transmission.

Although transmissible spongiform encephalopathies
selectively damage the central nervous system (CNS), the
infectious agent (termed prion) is detectable in lymphoid
organs long before clinical symptoms (1). PrPSc, a proteaseresistant
isoform of the host protein PrPC, accumulates mostly
in CNS and lymphoid organs of infected organisms, and may
represent the infectious principle (2, 3). In addition to PrPC
(4), splenic prion replication requires follicular dendritic cells
(FDCs) (5), whose maintenance depends on B cells
expressing tumor necrosis factor (TNF) and lymphotoxins
(LT) ? and ? (68). Accordingly, LT/TNF inhibition
antagonizes peripheral prion replication (911). However,
most cellular requirements for peripheral prion replication
remain unknown (12).

Chronic inflammatory conditions present with organized
collections of B and T lymphocytes, FDCs, dendritic cells
(DCs), as well as marginal-zone and tingible-body
macrophages (1315). Extranodal follicles are also prevalent
in naturally occurring infections of free-ranging ruminants
(16). Besides participating in chronic inflammatory
conditions, FDCs, B lymphocytes, and other components of
the immune system are involved in prion replication (610,
17). We therefore reasoned that inflammation may affect
prion pathogenesis. We studied this question in various
transgenic and spontaneous mouse models of chronic
inflammation, including nephritis, pancreatitis, and hepatitis.
First, we generated bitransgenic mice expressing LT? and
LT? in liver under the control of the albumin promoter (fig.
S1A) (18, 19). C57BL/6-Tg(LTab)1222 and C57BL/6-
Tg(LTab)1223 mouse lines contained one copy/haploid
genome of both AlbLT? and AlbLT? transgenes (fig. S1B),
with expression restricted to liver and absent from thymus,
spleen, mesenteric lymph node (MLN), pancreas and kidney
(Fig. 1A). C57BL/6-Tg(LTab)1223 mice (henceforth termed
AlbLT?? mice) were identified as the highest expressors
(Fig. 1B) and were selected for further experiments.

4-6 month-old AlbLT?? livers displayed highly organized
aggregates of B220+ B lymphocytes, CD3+, CD4+ and CD8+
T cells, FDC-M1+ and CD35+ networks, MOMA-1+ marginal
zone-like festoons, CD68+ tingible body macrophages, IgD+
and IgG1+ lymphocytes, ERTR9+ cells, and NLDC-145+ DCs
(Fig. 2, A and B) (fig. S1C). AlbLT?? sinusoids exhibited
F4/80+ Kupffer cell hyperproliferation and upregulation of the
adhesion molecules I-CAM and V-CAM (fig. S1C).
Occasionally, PNA+ clusters indicative of germinal center B
cells were found (fig. S1C; arrowheads). None of the above
features were found in livers of wild-type littermates (fig.
S1C), nor could we detect abnormal histopathological
features in AlbLT?? kidneys, spleens and thymuses.

Transgenic mice expressing LT? under control of the rat
insulin promoter (RIP) in pancreatic beta islet cells and renal
proximal convoluted tubules (2022) developed interstitial
and capsular follicles in kidney and pancreatic islets with
discrete B220+ areas and CD35+/FDC-M1+ networks (20, 21)
(Fig. 2A). Renal and pancreatic inflammatory foci in RIPLT?
and hepatic foci in AlbLT?? mice were essentially identical
in their cellular composition, and expressed various
complement components (Fig. 2) (fig. S1D). Splenic and
lymph nodal microarchitecture of RIPLT? (n=5), AlbLT??
(n=3) and wild-type mice (n=3) were indistinguishable upon
immunostaining with an exhaustive panel of immunological
markers (23).

We then studied mice expressing the homeostatic
chemokine TCA4/SLC/CCL21 under the control of the rat
insulin promoter (22). These mice (henceforth termed
RIPSLC) contain follicles in the pancreas with organized T
and B cell zones, DCs, ER-TR7+ and CD35+ cells, and small
FDC-M1+ networks (Fig. 2) (23).

NZBxNZW-F1 (henceforth termed NZBW) and NODLtJ
mice are considered models for systemic lupus erythematosus
(SLE) and autoimmune diabetes, respectively. NZBW mice
develop interstitial nephritis and glomerulonephritis with
distinct B and T cell areas, small FDC-M1+ clusters, DCs,
small PNA+ clusters and IgG1+ cells (Fig. 2) (fig. S1E).
Infiltrates lacked MAdCAM-1+ expression but contained
MOMA-1+ cells (fig. S1E). Deposits of C1q, C3, and C4 were
identified within glomeruli of kidneys of NZBW mice, but
not in parental NZW mice, which did not develop nephritis
and were used as controls (Fig. 2) (fig. S1E) (23). NODLtJ
mice develop spontaneous autoimmune insulitis with
lymphoid follicles similar to those developing in NZBW
kidneys (2426); NODB10.H2b mice, which do not develop
insulitis despite the presence of the NOD locus (27), were
used as controls.

Real-time RT-PCR analysis of LT? and LT? expression in
inflamed and appropriate control tissues revealed that 6-8
week old AlbLT?? livers overexpressed LT? ?45-fold and
LT? 8-10-fold (Fig. 1C). LT expression declined in 8-12
month-old transgenic mice, in parallel with cirrhotic
hepatocyte replacement. No other organs of AlbLT?? mice
showed LT overexpression. RIPLT? mice overexpressed
LT? and, to a lower extent, LT? in kidney and pancreas,
while RIPSLC mice slightly upregulated LT? expression in
pancreas and kidney. LT? and LT? were strongly
upregulated in NODLtJ pancreases, and LT? was
overexpressed in NZBW kidneys and pancreases. In
summary, we detected LT upregulation in every instance of
chronic inflammation.

RIPLT?, RIPSLC, NZBW, NODLtJ, and isogenic or
congenic control mice were inoculated with prions
intraperitoneally (103 LD50) or intracerebrally (3x102 LD50).
RIPLT?, RIPSLC, and control mice showed similar
incubation times and attack rates of disease (Fig. 3A), and the
extent of terminal PrPSc deposition was similar (fig. S2, A and
B). Topography and intensity of spongiosis, gliosis, and PrP
deposits was found by immunohistochemistry to be similar in
brains of all terminally sick mice (23). Thus chronic
pancreatitis or nephritis did not influence susceptibility to
intracerebrally or peripherally administered prions, prion
titers, or neuroinvasion speed. Scrapie incubation times of
NZBW and NODLtJ mice could not be determined as they
exceeded their natural life span. The extent and morphology
of inflammation in RIPLT? and RIPSLC kidneys and
pancreases, as well as in AlbLT?? livers, were compared to
age-matched mock-infected controls at several time points
from 60 days post inoculation (dpi) to terminal disease. We
did not detect any modulation of the inflammatory
pathologies by prion infection, and intraperitoneal glucose
tolerance was unaltered in prion-inoculated RIPLT? mice
(fig. S2C).

We then asked whether inflammation influences the
distribution of prion infectivity during the preclinical phase of
infection. AlbLT??, RIPLT?, RIPSLC, NZBW, NZW (8-12
weeks old), NODLtJ, NODB10 (6 months old), and C57BL/6
mice were inoculated i.p. with scrapie prions (5 logLD50) and
sacrificed at 60, 75, 90 or 100 dpi. Spleen homogenates were
assayed for prion infectivity by mouse bioassay (MBA),
consisting of intracerebral inoculation of tga20 indicator mice
(28) and comparison of scrapie incubation times to a
calibration curve (29). All spleens displayed comparably high
titers of prion infectivity: 4.5-6 (wild-type), 3.5-5 (RIPLT?),
4.2-6.1 (AlbLT??), and 3.9-5.7 logLD50/g (RIPSLC). Attack
rates of indicator mice were 100% at all time points (Fig. 3B).
Nephritis and pancreatitis do not affect splenic prion

Prion loads of kidneys, pancreases and livers from prioninfected
presymptomatic mice were also determined by MBA
(Fig. 3B). Titers were regarded as borderline if attack rates
were <100%. At 60 dpi, wild-type pancreases and kidneys
homogenates lacked measurable infectivity, whereas RIPLT?
kidney and pancreas titers ranged between borderline and 1.4
logLD50/g. At 75 dpi RIPLT? pancreas and kidney titers were
3.3 or 4 logLD50/g, whereas wild-type pancreases and kidneys
were non-infectious.

At 90 dpi, all RIPSLC and RIPLT? pancreases and one
RIPLT? kidney had prion titers approaching those of spleens
(?3.7 logLD50/g in pancreas and ?2.4logLD50/g in kidney),
whereas wild-type organs displayed undetectable or
borderline infectivity (Fig. 3B). Infectivity of wild-type
livers, kidneys, and AlbLT?? kidneys was borderline or
below detectability, whereas AlbLT?? livers had titers of 3.1-
3.4 logLD50/g (Fig. 3B). NZBW kidneys were found to
contain 2.5-3.5 logLD50/g prion infectivity (n=2), whereas
NZW kidneys were non-infectious (Fig. 3C).

We subjected organ extracts to scrapie cell assays in end
point format (SCEPA) or to conventional scrapie cell assays
(SCA), which allow for quantification of prion infectivity
with sensitivity similar to MBAs (30). SCEPA and MBA
results with RIPLT? homogenates (60 and 90 dpi) were
almost completely congruent (fig. S2D and table S1). Wildtype
kidneys and pancreases contained no detectable
infectivity (<2.54 logLD50/g), whereas prion titers in the
corresponding RIPLT? extracts were high (table S1).
AlbLT?? liver prion titers (75 dpi) were >3.4logLD50/g tissue
in 3/3 liver homogenates, whereas no infectivity was detected
in wild-type livers (<2. 4logLD50/g) (fig. S2E).

We then administered 5 logLD50 scrapie prions i.p. to 6-
month old NODLtJ mice and NODB10 mice. Pancreases of
hyperglycemic NODLtJ mice contained ?2 logLD50/g prion
infectivity at 50 dpi, whereas control NODB10 mice harbored
no or borderline infectivity (Fig. 3D). All tga20 mice (n=7)
that had developed clinical scrapie upon exposure to
pancreatic homogenates (50 dpi) displayed spongiosis, gliosis
and PrPSc in immunoblots (figs. S3 and S4), confirming
transmission of scrapie infectivity. Similarily, all tga20 mice
that had developed clinical scrapie upon exposure to renal,
pancreatic and hepatic homogenates (AlbLT??, RIPLT?,
RIPSLC, NZBW) showed spongiosis, gliosis and PrPSc in
immunoblots (figs. S3 and S4), confirming transmission of
infectivity. However, at 100 dpi (?10 months of age)
pancreatic infectivity was no longer detectable in either
genotype, consistently with progressive islet elimination and
consecutive regression of pancreatitis in NODLtJ mice (Fig.
3D) (23).

We then determined PrPSc loads in organ extracts. Samples
negative by conventional immunoblotting were reanalyzed
after phosphotungstate (PTA) precipitation of PrPSc (31),
enhancing sensitivity (32). At 60, 75 and 90 dpi, PrPSc was
detectable in similar amounts in all spleens of each genotype,
but not in livers, kidneys or pancreases of wild-type mice
(Fig. 4, A and B). At 60 dpi PrPSc was undetectable in livers,
kidneys or pancreases of any genotype. At 75 dpi we found
robust PrPSc immunoreactivity in 2 of 3 AlbLT?? livers, but
not in RIPLT? kidneys and pancreases (Fig. 4A). At 90 dpi,
PrPSc was readily detectable in all AlbLT?? livers (Fig. 4A),
RIPLT? kidneys, and RIPLT? pancreases (n=6, Fig. 4B).
Possible PrPSc traces were found in one wild-type kidney at
90 dpi (fig. S2F).

PTA-enhanced immunoblot analysis identified PrPSc in
NZBW (n=2) but not in NZW (n=2) kidneys (90 dpi) (Fig.
4C) (23). In contrast, PTA-enhanced immunoblotting failed
to reveal PrPSc in NODLtJ and NODB10 pancreases at all
time points (50 and 100 dpi), consistent with the low
infectivity titers of NODLtJ pancreases at 50 dpi (Fig. 3D).
By which mechanism does inflammation create novel
prion reservoirs? PrPC is necessary for prion replication (4):
hence its expression might be rate-limiting. We thus
investigated PrPC expression in wild-type and RIPLT?
kidneys and pancreases. Quantitative immunoblot analysis
revealed ?20% increase in total PrPC of RIPLT? kidneys, and
no significant changes in transgenic pancreases (fig. S1F). In
contrast, immunohistochemical analysis revealed foci of high
PrP expression in all analyzed AlbLT?? livers, RIPLT?
kidneys and pancreases, RIPSLC pancreases, NZBW
kidneys, and NODLtJ pancreases (Fig. 2B), but not in organs
of the appropriate control mice. These foci mostly colocalized
with FDC-M1+ networks (Fig. 2B).

To characterize the topography of PrPSc in inflamed prioninfected
organs, we assayed (33) wild-type, RIPLT??,NZBW
and NZW kidneys as well as RIPSLC pancreases by
histoblotting. RIPLT? kidneys and pancreases (90 dpi)
displayed PrPSc deposits colocalizing with inflammatory
infiltrates, whereas neither feature was found in scrapieinfected
wild-type kidneys or pancreases (Fig. 4D). RIPSLC
pancreases and NZBW kidneys (90 dpi) also showed small
PrPSc positive areas colocalizing with inflammatory
infiltrates, whereas controls were devoid of PrPSc positive
areas (23).

Inflammatory conditions cause immune cells to migrate
into parenchymal sites of pathology. Some of these immune
cells, including activated B lymphocytes, express
lymphotoxins which in turn trigger differentiation of FDCs.
Lymphotoxin-triggered events, most likely including PrPC
upregulation in stromal FDC precursors, appear to confer
prion replication competence to sites of inflammation.
Lymphotoxin might thus represent a crucial link between
inflammation and prion distribution. We tested this prediction
by administering prions intraperitoneally to 6-8 month-old
LT?-/- and LT?R-/- mice, which suffer from spontaneous
inflammatory pathologies (34), and to age-matched controls.
Despite severe multifocal chronic lymphocytic hepatitis with
disseminated PNA+ clusters (fig. S5, A and B), livers of
prion-inoculated LT?-/- and LT?R-/- mice were found to be
consistently devoid of prion infectivity (fig. S5C) and PrPSc
(fig. S5D).

The above results indicate that chronic follicular
inflammation, induced by a variety of causes, specifies prion
tropism for otherwise prion-free organs. In most instances
infectivity tended to rise with time, suggesting local prion
replication. Organ-specific expression of one single proinflammatory
cytokine (LT?) or chemokine (SLC) sufficed to
establish unexpected prion reservoirs, suggesting
differentiation of ubiquitous stromal constituents into prionreplication
competent cells. In several instances, prion
concentration in individual inflamed organs approached that
of spleen long before any clinical manifestation of scrapie.
Inflamed non-lymphoid organs not only accumulated PrPSc,
but transmitted bona fide prion disease when inoculated into
healthy recipient mice.

Knowledge of the distribution of prions within infected
hosts is fundamental to consumer protection and prevention
of iatrogenic accidents. Based on the failure to transmit BSE
infectivity from any tissue but central nervous system,
intestinal, and lymphoid tissue (35), the risk to humans of
contracting prion infection from other organs has been
deemed small even in countries with endemic BSE. It may be
important now to test whether superimposed viral, microbial
or autoimmune pathologies of farm animals trigger
unexpected shifts in the organ tropism of prions. Conversely,
the lack of infectivity in burned out postinflammatory
pancreases suggests that anti-inflammatory regimens may
abolish ectopic prion reservoirs.

References and Notes
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36. We thank S. Nedospasov and D. Kuprash for providing
LT?/? cDNA, D. Lo for providing Ins-TCA4/SLC mice,
C. Sigurdson, G. Miele, M. Zabel, F. Montrasio and M. Le
Hir for discussions, as well as A. Gaspert and W. Jochum
for histopathological advice, B. Odermatt, R. Moos and G.
Bosshard for support with immunohistochemistry and
SCA. AA is supported by grants of the Bundesamt für
Bildung und Wissenschaft, the Swiss National Foundation,
and the NCCR on neural plasticity and repair. MH is
supported by the foundation for Research at the Medical
Faculty, University of Zurich, a generous educational grant
of the Catello family, and a grant of the Verein zur
Förderung des akademischen Nachwuchses. PK and CW
are supported by the Medical Research Council, UK. NHR
is supported by NIH grant NCI R01 CA 16885.
Supporting Online Material
Materials and Methods
Figs. S1 to S5
Table S1
18 October 2004; accepted 6 December 2004
Published online 20 January 2005; 10.1126/science.1106460
Include this information when citing this paper.
Fig. 1. Molecular and phenotypic characterization of
AlbLT?? mice. (A) RT-PCR analysis for transgenic LT?,
using primers 1 and 2 (see fig. S1A) (450bp), and primers 4
and 5 (see fig. S1A) for transgenic LT? (390bp) confirmed
liver specific transgene expression in AlbLT?? mice (neg.
ctrl.: master mix and H2O; pos. ctrl.: transgenic plasmid DNA
(10ng). (B) Transgene specific real-time RT-PCR analysis
identifying C57BL/6-Tg(LTab)1222 as low LT? expressor
and C57BL/6-Tg(LTab)1223 as high expressor. (C) Realtime
RT-PCR identifying total LT? and LT? expression in
organs of mice with naturally occurring or transgenetically
induced inflammatory and autoimmune diseases. Each value
represents the fold change (log2) in individual organs as
compared to the average expression in two respective organs
of control mice of the appropriate genotype. Each
measurement was normalized against ?-actin by the ??Ct
/ / 20 January 2005 / Page 4 / 10.1126/science.1106460
method. Grey and black symbols denote inflamed and noninflamed
organs, respectively. LT? and/or LT? were
overexpressed not only in LT transgenic organs, but also in
inflamed organs of RIPSLC, NZBW and NODLtJ mice.
Fig. 2. Inflammatory foci in AlbLT?? livers, RIPLT?
kidneys, as well as NZBW and RIPSLC pancreases.
Consecutive frozen sections of AlbLT?? liver, RIPSLC
pancreas and RIPLT? and NZBW kidneys. (A) Follicular
inflammatory foci displaying organized collections of B cells
(B220) and complement receptor 1-expressing cells (CD35).
Scale bar: 200 µm. (B) Two-color immunofluorescence
analysis. PrP (antiserum XN, red) mainly colocalizes with
FDC networks (antibody FDC-M1, green) within follicular
infiltrates in all models of follicular inflammation. Scale bar:
20 µm.
Fig. 3. The distribution of PrPSc and prion infectivity is
influenced by inflammatory conditions. (A) Survival plots of
prion-infected RIPLT???RIPSLC and wild-type (wt) mice,
showing similar incubation times after i.p.
(RIPLT?:?229±10?days; wt: 234±6;? RIPSLC: 243±8) or i.c.
inoculation (RIPLT?:?192±2days; wt: 185±6; RIPSLC:
174±2?. (B) Prion infectivity titers in spleens (circles),
pancreases (squares), kidneys (triangles), and livers (crosses)
of wild-type (wt) (blue), RIPLT? (red), AlbLT?? mice (pink)
and RIPSLC (green) were determined by transmission to
indicator mice at 60, 75 and 90 dpi. Each column lined by
vertical dotted lines represents one mouse. Datapoints below
the dotted horizontal line indicate attack rates of <100% and
were regarded as borderline infectivity. Error bars were
drawn when standard deviation exceeded 0.75 log units.
Except for one RIPLT? kidney that elicited an attack rate of
75%, RIPLT? kidneys, pancreases, RIPSLC pancreases and
AlbLT?? livers led to 100% attack rate with high prion titers
at 90 dpi. In contrast, wild-type kidneys, pancreases, and
livers contained undetectable or at best borderline prion
infectivity. (a) One of 4 tga20 mice died shortly after
inoculation. (C and D) Prion infectivity titers in kidneys
(triangles) of NZW (black), NZBW (brown), NODB10
(orange) and NODLtJ mice (striped) were determined by
transmission assay or SCEPA. At 90 dpi NZBW kidneys
harbored reasonably high infectivity titers, whereas NZW
mice lacked prion infectivity (C). At 50 dpi NODLtJ mice
displayed borderline or moderate prion infectivity, whereas
NODB10 mice showed no or borderline infectivity. At 100
dpi NODLtJ mice were devoid of detectable prion infectivity,
consistently with progressive islet elimination and
consecutive regression of pancreatitis (D) (23).
Fig. 4. PrPSc accumulates in inflamed organs of prioninfected
mice. (A) Immunoblot analysis of liver homogenates
after PTA precipitation at 75 (upper blot) and 90 dpi (lower
blot). No PrPSc in 4/4 individual wild-type livers, but clear
PrPSc signal in 4/5 AlbLT?? livers. Control samples (ctrl.)
included undigested healthy brain, PK-digested healthy brain,
and PK-digested terminally scrapie-sick brain. PK: Proteinase
K, PTA: sodium phosphotungstate precipitation. (B)
Immunoblot analysis showed strong PrPSc signal in spleen,
kidney and pancreas of prion-infected RIPLT? mice (90 dpi),
whereas PrPSc was confined to spleens of wild-type mice. (C)
Immunoblot of NZBW and NZW mice. PrPSc was detected in
kidneys of NZBW but not NZW mice. (D) Histoblot analysis
of prion-infected kidneys. Capsular and subcapsular deposits
of PrPSc co-localize with follicular infiltrates in RIPLT?
kidneys. Consecutive sections display colocalization of PrPSc
deposits with follicular infiltrates (H&E).
/ / 20 January 2005 / Page 5 /

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