NATURE MEDICINE • VOLUME 9 • NUMBER 4 • APRIL 2003 453

ARTICLES

Alzheimer disease (AD) is a progressive neurodegenerative dis-order characterized by excessive deposition of amyloid-β (Aβ)peptides in the brain. One of the earliest neuropathologicalchanges in AD is the accumulation of astrocytes at sites of Aβ de-position1, but the cause or significance of this cellular responseis unclear. Here we show that cultured adult mouse astrocytesmigrate in response to monocyte chemoattractant protein-1(MCP-1), a chemokine present in AD lesions1, and cease migra-tion upon interaction with immobilized Aβ1–42. We also showthat astrocytes bind and degrade Aβ1–42. Astrocytes plated onAβ-laden brain sections from a mouse model of AD associatewith the Aβ deposits and reduce overall Aβ levels in these sec-tions. Our results suggest a novel mechanism for the accumula-tion of astrocytes around Aβ deposits, indicate a direct role forastrocytes in degradation of Aβ and implicate deficits in as-troglial clearance of Aβ in the pathogenesis of AD. Treatmentsthat increase removal of Aβ by astrocytes may therefore be acritical mechanism to reduce the neurodegeneration associatedwith AD.

The presence of large numbers of astrocytes associated with Aβdeposits in AD suggests that these lesions generate chemotacticmolecules that mediate astrocyte recruitment. In fact, AD lesionscontain MCP-1 (ref. 1), a potent chemoattractant for neonatalastrocytes in vitro2, but the cellular source of MCP-1 in the ADbrain is unclear. Whereas neonatal astrocytes from variousspecies produce MCP-1 after stimulation with Aβ1–42 in vitro3–5, as-trocytes surrounding Aβ plaques in the AD brain and in a mousemodel for AD do not express detectable levels of MCP-1 (refs. 6,7). These findings prompted us to compare Aβ1–42-stimulated re-lease of MCP-1 by astrocytes cultured from neonatal and adultmouse brains. We found that Aβ1–42-stimulated neonatal mouseastrocytes produced significantly (P = 0.05) higher amounts ofMCP-1 compared with non-stimulated controls, whereas simi-larly stimulated adult astrocytes do not (Table 1). However, bothneonatal and adult astrocytes significantly (P = 0.0001 and 0.01,respectively) increased MCP-1 release in response to lipopolysac-charide (LPS; Table 1). Because cultured adult mouse astrocytesseem to be refractory to Aβ-induced MCP-1 production, similarto astrocytes surrounding Aβ deposits in AD, we used these cellsfor most of our experiments.

We used cell culture inserts to test the ability of chemoattrac-tants MCP-1 and LPS8 to stimulate migration of adult astrocytesacross a porous membrane coated with collagen IV (CIV), an ex-tracellular matrix protein found in Aβ plaques (Fig. 1a). In the

presence of 10–8 M MCP-1, 2-fold more astrocytes migratedacross CIV-coated membranes than in the absence of MCP-1.Control experiments with LPS produced similar results (Fig. 1a).Migration of astrocytes in response to either chemoattractantwas reduced to non-stimulated levels when the membranes werecoated with CIV and Aβ1–42 (Fig. 1a). These studies indicate thatastrocytes can be recruited to sites of Aβ deposition by locally re-leased MCP-1 or other chemoattractants, and become immobi-lized when they contact Aβ in the extracellular matrix.

Immobilization of adult astrocytes upon interaction with Aβindicates that these cells adhere to Aβ-coated surfaces. To exam-ine astrocyte adhesion, we took advantage of the fact that adhe-sion of astrocytes to CIV-coated surfaces is mediated byintegrins9 and is therefore dependent on divalent cations. In theabsence of Ca2+ and Mg2+, astrocyte adhesion to CIV-coatedmulti-spot glass slides was <3% of that in the presence of Ca2+

and Mg2+ (Fig. 1b). Additional coating with human or mouseAβ1–42 promoted astrocyte adhesion even in the absence of Ca2+

and Mg2+ (Fig. 1b and data not shown). Over 90% of added cellsadhered to spots coated with 2 µg mouse or human Aβ in a dose-dependent fashion (Fig. 1c and data not shown). These findingssuggest that astrocytes associate with Aβ in the extracellular ma-trix through Ca2+- and Mg2+-independent receptor(s). One candi-date for such a receptor is scavenger receptor class B type I(SRBI), an Aβ-binding receptor expressed on astrocytes (reviewedin ref. 10). We exposed astrocytes to Cy3-labeled Aβ1–42 (Cy3-Aβ1–42) in the presence or absence of fucoidan or polyinosinicacid, substances that block scavenger receptor–mediated bindingof Aβ1–42 by a variety of cells10. Cy3-Aβ1–42–treated astrocytes dis-played a strong cell-associated fluorescence that was reducedsubstantially by fucoidan and polyinosinic acid in a concentra-tion-dependent manner (Fig. 1d). However, antibodies blockingAβ-SRBI interaction11 had no effect on Aβ binding to cells (Fig.1d). These results indicate that Aβ binds to astrocytes throughmolecules that share characteristics with scavenger receptors. Infact, other known Aβ-binding molecules present on astrocytes,including the receptor for advanced glycation end products(RAGE), low-density lipoprotein receptor–related protein ormembrane-associated proteoglycans, may synergize with scav-enger receptor–like molecules in binding Aβ, as previouslyshown for microglia11.

These observations and the presence of Aβ in astrocytes sur-rounding amyloid plaques12–15 indicated that astrocytes not onlyadhere to and are immobilized by Aβ, but also degrade it. To testthis hypothesis, we examined surfaces coated with Cy3-Aβ1–42 by

Adult mouse astrocytes degrade amyloid-β in vitro and in situ

TONY WYSS-CORAY1,2, JOHN D. LOIKE3, THOMAS C. BRIONNE2, EMILY LU3, ROMAN ANANKOV3,FENGRONG YAN4, SAMUEL C. SILVERSTEIN3 & JENS HUSEMANN3

1Geriatric Research, Education and Clinical Center, VA Palo Alto Health Care System, Palo Alto, California, USA2Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California, USA

3Department of Physiology and Cellular Biophysics, Columbia University, New York, New York, USA4Gladstone Institute of Neurological Disease, San Francisco, California, USA

Correspondence should be addressed to J.H.; e-mail: jh577@columbia.edu

Published online 3 March 2003; doi:10.1038/nm838

C-nm838.qxd 3/13/03 1:39 PM Page 453

©20

03 N

atu

re P

ub

lish

ing

Gro

up

h

ttp

://w

ww

.nat

ure

.co

m/n

atu

rem

edic

ine

454 NATURE MEDICINE • VOLUME 9 • NUMBER 4 • APRIL 2003

ARTICLES

fluorescence microscopy before (Fig. 2a) and after incubationwith adult astrocytes for 24–48 h (Fig. 2b–d). After 24 h, astro-cytes were well spread (Fig. 2b) and Cy3-Aβ1–42 had disappearedfrom the surfaces underneath and surrounding the cells but waspresent in perinuclear vesicles (Fig. 2c). After 48 h, perinuclearfluorescence disappeared almost completely (Fig. 2d). Similar ob-servations were made using surfaces coated with unlabeled Aβ1–42

followed by immunohistochemical detection of intracellular Aβwith an Aβ-specific antibody (data not shown). In contrast, as-trocytes cultured from neonatal brain were much less efficient atremoving immobilized Cy3-Aβ1–42 (Fig. 2e and f). These findingsshow that, in contrast to cultured neonatal mouse or rat astro-cytes16, adult mouse astrocytes clear immobilized Aβ.

To determine whether adult astrocytes could also process Aβdeposits from brain tissue, we plated cells on unfixed Aβ-richbrain sections from transgenic mice expressing human amyloidprecursor protein (APP). After incubation of brain sections withastrocytes for 24 h, the total hippocampal area occupied by Aβwas up to 40% lower than in untreated sections (Fig. 2g–i). Theastrocytes were spread out over the tissue (Fig. 2j) and manywere intimately associated with Aβ-immunoreactive material, asshown by confocal microscopy (Fig. 2j–l). No Aβ immunoreac-tivity was observed in astrocytes cultured on brain sections fromnon-transgenic mice (data not shown). These results indicatethat astrocytes remove Aβ deposits from brain sections in situ.

To quantitate the degradation of Aβ by adult astrocytes, we ex-posed these cells to Aβ1–42 and determined the Aβ content of thecell fraction and cell-culture supernatant by western blot analy-sis. Within 3 h, Aβ1–42 levels decreased in the supernatantand increased in the cell-associated fraction, indicatingthat astrocytes removed Aβ from the medium. After 3 h,Aβ levels in the cell fraction began to decrease, and by24–48 h there was virtually no Aβ detectable in the super-natant or the cell fraction (Fig. 3a). These findings showthat cultured adult astrocytes degrade Aβ1–42. Similar re-sults were obtained using standard ELISA procedures tomeasure Aβ1–42 levels in the same cell cultures (Fig. 3b).

Astrocytes have important metabolic and supportivefunctions in the brain, including regulation of the ionic

environment, contribution to the blood-brain barrier and mod-ulation of synaptic activity. In addition, astrocytes are migra-tory, express a variety of chemokines and cytokines and theirreceptors, and have phagocytic and proteolytic activity.

Astrocytes become rapidly ‘activated’ in response to even sub-tle changes in central nervous system homeostasis. In many dis-eases, or after injury of the nervous system, astrocyte activationhas been associated with variation in expression of cytoplasmicantigens, surface proteins and soluble factors such aschemokines. Presumably, these substances contribute to the as-trogliosis occurring as a result of central nervous system injuryor inflammation. Our data indicate that astrocytes cultured fromadult mouse brain migrate in response to MCP-1, as previouslyshown for neonatal mouse astrocytes2, and point to a crucial rolefor this chemokine in mobilizing astrocytes during astrogliosis.

Astrogliosis is one of the earliest pathological manifestationsof AD and may be a response to the increasing number of degen-erating neurons and synapses, or to the accumulation of Aβ.Astrocyte activation seems to be particularly prominent aroundAβ deposits both in the brain parenchyma and in the cere-brovasculature. It is possible that astrogliosis in AD occurs as aresponse to the MCP-1 present in these Aβ deposits1. We foundthat adult astrocytes, in contrast to neonatal astrocytes3–5, do notrespond to stimulation with Aβ by increasing their release ofMCP-1 (Table 1). This suggests that the MCP-1 found in AD le-sions is of microglial, but not astrocytic origin6. In addition, ourresults show that Aβ associated with extracellular matrix pro-teins such as CIV can bind to and directly immobilize migrating

a b c

dFig. 1 Adult mouse astrocytes cease migration upon interaction with Aβ1–42 and adhere to Aβ1–42-coated surfaces. a, Migration of astrocytes, in response to LPS or MCP-1, across porousmembranes coated with CIV alone or with CIV and Aβ1–42. Number of cells that migrated acrossCIV-coated membranes under unstimulated conditions (214 ± 74 cells/mm2; n = 4) was designatedas 100%. #, P = 0.05 compared with no chemoattractant; †, P = 0.01 compared with LPS andAβ1–42; *, P = 0.05 compared with MCP-1 and Aβ1–42. b, Adhesion of astrocytes, suspended in bufferwith (�) or without (�) Ca2+ and Mg2+, to multi-spot glass slides that were uncoated, coated withCIV or coated with CIV and Aβ1–42 (2 µg/spot). c, Adhesion of astrocytes, suspended in buffer lack-ing Ca2+ and Mg2+, to multi-spot glass slides coated with CIV and increasing amounts of Aβ1–42. d, Binding of Cy3-labeled Aβ1–42 (Cy3-Aβ1–42) to astrocytes with or without addition of 100 or 500µg/ml fucoidan, polyinosinic acid (polyI), or antibody against SRBI (SRBI). Values are mean ± s.e.m.; n = 3–5 experiments. *, P = 0.05 compared with basal; **, P = 0.01 compared with basal.

Table 1 MCP-1 production (pg/ml) by neonatal or adult mouse astrocytesafter stimulation with Aβ1–42 or LPS.

No stimulus + Aβ + LPSNeonatal astrocytes 923 ± 281 1,952 ± 500a 3,522 ± 284c

Adult astrocytes 1,208 ± 848 1,205 ± 933b 5,337 ± 1,378d

5 × 104 astrocytes were stimulated with 25 µM Aβ1–42 or 10 µg/ml LPS for 24 h. MCP-1 in themedium was determined by sandwich ELISA. Values are mean ± s.e.m.; n = 5. aP = 0.05 comparedwith non-stimulated neonatal astrocytes; bnot significant compared with non-stimulated adult as-trocytes; cP = 0.0001 compared with non-stimulated neonatal astrocytes; dP = 0.01 compared withnon-stimulated adult astrocytes.

C-nm838.qxd 3/13/03 1:39 PM Page 454

©20

03 N

atu

re P

ub

lish

ing

Gro

up

h

ttp

://w

ww

.nat

ure

.co

m/n

atu

rem

edic

ine

NATURE MEDICINE • VOLUME 9 • NUMBER 4 • APRIL 2003 455

ARTICLES

astrocytes (Fig. 1), a process that may contribute to the accumu-lation of astrocytes around Aβ deposits in the AD brain.

It is unclear whether ‘reactive’ astrocytes accumulating at sitesof Aβ deposition have neuroprotective or destructive functions(for review, see ref. 17). Whereas some studies implicate neona-tal rat astrocytes in the clearance of Aβ16, others show thatneonatal mouse astrocytes inhibit microglial phagocytosis of se-nile plaque cores isolated from AD brains18. Our current findingsshow that in contrast to neonatal mouse and rat astrocytes16,adult mouse astrocytes efficiently clear exogenously added andsurface-bound Aβ (Figs. 2 and 3) and are capable of removing Aβdeposited in brain slices from mice expressing human APP (Fig.2). These data and those in Table 1 also show that cultured adultastrocytes differ qualitatively from neonatal astrocytes. Thus,functional and phenotypic differences between cultured neona-tal and adult astrocytes must be considered when these cells areused to model astrocyte functions in normal adult brain and indiseases such as AD.

In our paradigm, exogenous adult astrocytes were able to re-move and degrade Aβ without additional stimuli such as op-

sonins or cytokines, whereas microglia seem to require stimula-tion by cytokines or the presence of opsonizing antibodies19. Ourresults are surprising because endogenous astrocytes surroundand contact Aβ deposits in AD brain but seem incapable of re-moving Aβ. They raise the possibility that dysregulation of Aβclearance by astrocytes may precede or be responsible for the ac-cumulation of Aβ in AD. Further studies are needed to determinewhether astrocytes degrade Aβ1–42 intra- or extracellularly, andwhether Aβ clearance from the brain is among the normalhomeostatic functions of astrocytes. Because astrocytes greatlyoutnumber microglia in the brain20, these cells could have amore critical role in Aβ removal than previously thought.Although numerous studies show that excessive astrocyte activa-tion can promote neurodegeneration, increasing astrocyte-me-diated clearance of Aβ may be a strategy for reducingAβ-associated toxicity and progression of AD.

MethodsCell culture. Astrocytes were purified as described4,21, with the followingmodifications. Cortices of neonatal (1–3 d) and adult (6–8 weeks) C57BL/6

a b c d

e fg h

i j k l

Fig. 2 Adult mouse astrocytes clear Aβ1–42 in vitro and in situ. a, Fluorescencemicroscopy of multi-spot glass slide coated as previously described23 withCy3-labeled Aβ1–42. b–d, Adult mouse astrocytes plated on Cy3-Aβ1–42–coatedsurfaces for 24 h (b and c) and 48 h (d), imaged by phase contrast (b) or fluo-rescence (c and d) microscopy. e and f, Neonatal mouse astrocytes plated onCy3-Aβ1–42–coated surfaces for 24 h, imaged by phase contrast (e) and fluo-rescence (f) microscopy. c, d, f, Red, Cy3-Aβ1–42 signal; blue, DAPI-stained nu-clei (arrows). g–i, Reduction of Aβ-immunoreactive area in the hippocampusof human APP–expressing mouse brain sections. Representative sections in-

cubated without (g) or with (h) adult astrocytes for 24 h and immunostainedfor Aβ with 3D6 antibody. Quantitation from 1 of 4 similar experiments (i)shows significantly less Aβ immunoreactivity in sections incubated with astro-cytes (n = 9 sections) compared with sections without astrocytes (n = 10 sec-tions). *, P = 0.05. j–l, Confocal images from a human APP–transgenic brainsection incubated with adult astrocytes. An astrocyte immunostained forS100β (green) adheres to the section (j). Aβ-immunopositive material (red)stained with Aβ-specific antibody 1280 (k) seems closely associated with theastrocyte in the merged image (l). Scale bar, 100 µm.

C-nm838.qxd 3/13/03 1:39 PM Page 455

©20

03 N

atu

re P

ub

lish

ing

Gro

up

h

ttp

://w

ww

.nat

ure

.co

m/n

atu

rem

edic

ine

456 NATURE MEDICINE • VOLUME 9 • NUMBER 4 • APRIL 2003

ARTICLES

mice were digested in Ca2+- and Mg2+-free HBSS with 0.25% trypsin and 1 mM EDTA (and 0.04 mg/ml bovine pancreatic DNase I for adult cortices),for 30 min at 37 °C in tissue culture flasks on a rotary shaker at 150 r.p.m. (4neonatal or 2 adult hemispheres per 10ml per flask). Cells were washed andreplated in DMEM/F12 complete (DMEM/F12 containing 10% heat-inacti-vated FBS, penicillin and streptomycin; Gibco, Rockville, Maryland) to gen-erate primary cultures. Astrocyte purity was >99%, as determined byimmunofluorescence using antibodies specific for glial fibrillary acidic pro-tein (Santa Cruz Biotechnology, Santa Cruz, California) and S100β (Sigma,St. Louis, Missouri). Antibodies specific to CD11b (Serotec, Raleigh, NorthCarolina) and galactocerebroside (Sigma) were used to identify microgliaor oligodendrocytes, respectively.

Aβ. Human (Bachem, Torrance, California) and mouse (Anaspec, San Jose,California) Aβ1–42 were dissolved in double-distilled water at 1 mg/ml andincubated at 37 °C (for details, see ref. 22). Human Cy3-Aβ1–42 was preparedas described23.

MCP-1 production. Astrocytes in 100 µl DMEM/F12 containing N2 supple-ments, penicillin and streptomycin were plated into 96-well plates at 5 ×104 cells/well. After 24 h, cultures were incubated in 100 µl fresh mediumwith or without 25 µM human Aβ1–42 or 10 µg/ml LPS (Sigma) for an addi-tional 24 h. Mouse MCP-1 in the supernatants was measured by ELISA(Pharmingen, San Diego, California).

Adhesion. Multi-spot glass slides (Shandon, Pittsburgh, Pennsylvania) werecoated with CIV (Fluka, Milwaukee, Wisconsin; 50 µg/ml in water for 1 h),air-dried and overlaid with various amounts of human or mouse Aβ1–42, asdescribed11. Astrocytes (5 × 104 cells/spot) suspended in HBSS with or with-out Ca2+ and Mg2+ were plated on peptide-coated spots, incubated for 45min at 37 °C and washed. Adherent cells were quantitated usingCyQuantGR (Molecular Probes, Eugene, Oregon) as described11.

Migration. Cell culture inserts (8-µm pore size; Becton Dickinson, FranklinLakes, New Jersey) were coated with CIV and overlaid with 8 µg humanAβ1–42. Astrocytes (105 cells) suspended in RPMI 1640 with 25 mM HEPESand 0.1% BSA were added to the upper chamber of the inserts; LPS (100

µg/ml) or MCP-1 (10–8 M; Leinco Technologies, St. Louis, Missouri) wasadded to the bottom chamber. After incubation at 37 °C for 6 h, non-mi-grated cells on the upper surface of the membrane were removed by scrap-ing. Cells that migrated to the lower surface of the membrane were stainedwith hematoxylin and counted with an inverted microscope.

Aβ degradation. Astrocytes (106 cells/well) in serum-free neurobasalmedium containing N2 supplement and 2 mM L-glutamine were exposedto 2 µg/ml human Aβ1–42. At various time points, Aβ levels in cell-culture su-pernatants and adherent cells were determined by immunoblotting as de-scribed24, with antibody 266 (against human Aβ13–28) or 3D6 (againsthuman Aβ1–5; 2 µg/ml; P. Seubert, Elan Pharmaceuticals, South SanFrancisco, California). Aβ1–42 levels were also measured in culture super-natants and cell fractions homogenized in 5 M guanidine buffer, usingELISA with capture antibody 21F12 (against human Aβ33–42) and biotiny-lated reporter antibody 3D6 as described24.

Binding inhibition studies. Astrocyte cultures maintained in Krebs-Ringerbuffer containing 1 mM glucose and 0.1% bovine serum albumin (KRBGA)were pretreated for 30 min at 37 °C with or without fucoidan, polyinosinicacid (100 and 500 µg/ml) or 200 µg/ml SRBI-specific rabbit antibody(Novus Biologicals, Littleton, Colorado), before adding 10 µg/ml Cy3-Aβ1–42

in KRBGA as described11. After 1 h, cells were washed with KRBGA, fixed in5% formalin and photographed. Cy3 fluorescence intensity was quantifiedusing NIH Image software (NIH, freeware at http://rsb.info.nih.gov/nih-image).

Aβ removal. Multi-spot glass slides were overlaid with DMEM/F12 contain-ing 10 µg/ml Cy3-Aβ1–42 for 1 h at 37 °C, washed with sterile water and air-dried. Astrocytes suspended in DMEM/F12 complete were plated onCy3-Aβ1–42–coated spots (5 × 103 cells per 50 µl per spot) and incubated forup to 2 d at 37 °C. Cells were fixed in 5% formalin, nuclei were stained withDAPI, and fluorescence and phase images were taken.

Clearance of Aβ from APP mouse brain slices. Brains of saline-perfused22-month-old mice expressing human APP under control of the platelet-derived growth factor B chain promoter25 (line J20; L. Mucke, GladstoneInstitute of Neurological Disease) were divided sagittally and snap frozen.Cryosections (10 µm) were mounted on poly-L-lysine-coated coverslips,transferred to 12-well plates and incubated with or without adult astrocytes(6 × 105 /well) for 24 h at 37 °C. Sections were then fixed in 4%paraformaldehyde, treated with 0.1% Triton X-100, immunostained with3D6 antibody (1:1000) and developed with diaminobenzidine and hydro-gen peroxide. Relative areas of the hippocampus occupied by 3D6 im-munoreactivity were measured for 8–15 sections per condition withBioquant 98 software (R&M Biometrics, Nashville, Tennessee). For confocalmicroscopy, sections similarly incubated with astrocytes were fixed in ace-tone and immunolabeled with rabbit antibody 1280 against human Aβ(1:1000; D. Selkoe, Harvard University, Boston, Massachusetts) and goatantibody against S100β (1:1000). After washing, sections were incubatedwith FITC- or Texas Red–conjugated secondary antibodies (VectorLaboratories, Burlingame, California), mounted and imaged by scanningconfocal microscopy. All animal experiments were performed in accor-dance with institutional guidelines.

AcknowledgmentsThis work was supported by National Institutes of Health grants AG-15871 (toT.W.-C.) and AG-19772 (to S.C.S.), the Alzheimer’s Association (T.W.-C. and

0Time (h)

Aβ

3 6 24 48 0 3 6 24 48Cell pellet Supernatant

*

a

2,000

1,500

1,000

500

00

Time (h)

3 6 24 48

Aβ 1

–42

(ng/

ml)

b

Fig. 3 Degradation of Aβ1–42 by adult mouse astrocytes as measured bywestern blot and ELISA. a and b, Astrocytes were incubated with syntheticAβ1–42, and supernatant or adherent cells (pellet) were collected after the in-dicated time points. Monomeric Aβ is detected in the cell pellet (a, leftpanel; b, �) after 3 h and disappears at 48 h in both pellet and supernatant(a, right panel; b, �). *, non-specific band. Higher molecular weight bandsin pellet and supernatant may be Aβ polymers or aggregates with otherproteins that are also degraded. One representative experiment is shown (n= 3 experiments).

C-nm838.qxd 3/13/03 1:39 PM Page 456

©20

03 N

atu

re P

ub

lish

ing

Gro

up

h

ttp

://w

ww

.nat

ure

.co

m/n

atu

rem

edic

ine

NATURE MEDICINE • VOLUME 9 • NUMBER 4 • APRIL 2003 457

ARTICLES

J.H.) and a Pilot Grant Award (to J.H.) from Columbia University’s AlzheimerDisease Research Center (through National Institutes of Health grant AG-08702).

Competing interests statementThe authors declare that they have no competing financial interests.

RECEIVED 20 NOVEMBER 2002; ACCEPTED 5 FEBRUARY 2003

1. Role of inflammatory processes and microglial activation in Alzheimer’s disease. InAlzheimer’s Disease (ed. Terry, R.D.) chap. 26, 390 (Lippincott Williams & Wilkins,Philadelphia, Pennsylvania, 1999).

2. Heesen, M. et al. Mouse astrocytes respond to the chemokines MCP-1 and KC, butreverse transcriptase-polymerase chain reaction does not detect mRNA for the KC ornew MCP-1 receptor. J. Neurosci. Res. 45, 382–391 (1996).

3. Hayashi, M., Luo, Y., Laning, J., Strieter, R.M. & Dorf, M.E. Production and function ofmonocyte chemoattractant protein-1 and other β-chemokines in murine glial cells. J.Neuroimmunol. 60, 143–150 (1995).

4. Johnstone, M., Gearing, A.J. & Miller, K.M. A central role for astrocytes in the inflam-matory response to β-amyloid; chemokines, cytokines and reactive oxygen speciesare produced. J. Neuroimmunol. 93, 182–193 (1999).

5. Rezaie, P., Trillo-Pazos, G., Everall, I.P. & Male, D.K. Expression of β-chemokines andchemokine receptors in human fetal astrocyte and microglial co-cultures: potentialrole of chemokines in the developing CNS. Glia 37, 64–75 (2002).

6. Ishizuka, K. et al. Identification of monocyte chemoattractant protein-1 in senileplaques and reactive microglia of Alzheimer’s disease. Psychiat. Clin. Neurosci. 51,135–138 (1997).

7. Mehlhorn, G., Hollborn, M. & Schliebs, R. Induction of cytokines in glial cells sur-rounding cortical β-amyloid plaques in transgenic Tg2576 mice with Alzheimerpathology. Int. J. Dev. Neurosci. 18, 423–431 (2000).

8. Tezel, G., Hernandez, M.R. & Wax, M.B. In vitro evaluation of reactive astrocyte mi-gration, a component of tissue remodeling in glaucomatous optic nerve head. Glia34, 178–189 (2001).

9. Tawil, N.J. et al. α 1 β 1 integrin heterodimer functions as a dual laminin/collagen re-ceptor in neural cells. Biochemistry 29, 6540–6544 (1990).

10. Husemann, J., Loike, J.D., Anankov, R., Febbraio, M. & Silverstein, S.C. Scavenger re-ceptors in neurobiology and neuropathology: their role on microglia and other cellsof the nervous system. Glia 40, 195–205 (2002).

11. Husemann, J., Loike, J.D., Kodama, T. & Silverstein, S.C. Scavenger receptor class B

type I (SR-BI) mediates adhesion of neonatal murine microglia to fibrillar β-amyloid. J.Neuroimmunol. 114, 142–150 (2001).

12. Wegiel, J., Wang, K.C., Tarnawski, M. & Lach, B. Microglia cells are the driving forcein fibrillar plaque formation, whereas astrocytes are a leading factor in plague degra-dation. Acta Neuropathol. (Berl.) 100, 356–364 (2000).

13. Kurt, M.A., Davies, D.C. & Kidd, M. β-amyloid immunoreactivity in astrocytes inAlzheimer’s disease brain biopsies: an electron microscope study. Exp. Neurol. 158,221–228 (1999).

14. Thal, D.R. et al. Amyloid β-protein (Aβ)-containing astrocytes are located preferen-tially near N-terminal-truncated Aβ deposits in the human entorhinal cortex. ActaNeuropathol. (Berl.) 100, 608–617 (2000).

15. Yamaguchi, H., Sugihara, S., Ogawa, A., Saido, T.C. & Ihara, Y. Diffuse plaques asso-ciated with astroglial amyloid β protein, possibly showing a disappearing stage of se-nile plaques. Acta Neuropathol. (Berl.) 95, 217–222 (1998).

16. Shaffer, L.M. et al. Amyloid β protein (A β) removal by neuroglial cells in culture.Neurobiol. Aging 16, 737–745 (1995).

17. Wyss-Coray, T. & Mucke, L. Inflammation in neurodegenerative disease—a double-edged sword. Neuron 35, 419–432 (2002).

18. DeWitt, D.A., Perry, G., Cohen, M., Doller, C. & Silver, J. Astrocytes regulate mi-croglial phagocytosis of senile plaque cores of Alzheimer’s disease. Exp. Neurol. 149,329–340 (1998).

19. Bard, F. et al. Peripherally administered antibodies against amyloid β-peptide enterthe central nervous system and reduce pathology in a mouse model of Alzheimer dis-ease. Nat. Med. 6, 916–919 (2000).

20. Savchenko, V.L., McKanna, J.A., Nikonenko, I.R. & Skibo, G.G. Microglia and astro-cytes in the adult rat brain: comparative immunocytochemical analysis demonstratesthe efficacy of lipocortin 1 immunoreactivity. Neuroscience 96, 195–203 (2000).

21. De Groot, C.J. et al. Establishment of human adult astrocyte cultures derived frompostmortem multiple sclerosis and control brain and spinal cord regions: im-munophenotypical and functional characterization. J. Neurosci. Res. 49, 342–354(1997).

22. Coraci, I.S. et al. CD36, a class B scavenger receptor, is expressed on microglia inAlzheimer’s disease brains and can mediate production of reactive oxygen species inresponse to β-amyloid fibrils. Am. J. Pathol. 160, 101–112 (2002).

23. Paresce, D.M., Ghosh, R.N. & Maxfield, F.R. Microglial cells internalize aggregates ofthe Alzheimer’s disease amyloid β-protein via a scavenger receptor. Neuron 17,553–565 (1996).

24. Wyss-Coray, T. et al. TGF-β1 promotes microglial amyloid-β clearance and reducesplaque burden in transgenic mice. Nat. Med. 7, 612–618 (2001).

25. Mucke, L. et al. High-level neuronal expression of aβ1–42 in wild-type human amyloidprotein precursor transgenic mice: synaptotoxicity without plaque formation. J.Neurosci. 20, 4050–4058 (2000).

C-nm838.qxd 3/13/03 1:39 PM Page 457

©20

03 N

atu

re P

ub

lish

ing

Gro

up

h

ttp

://w

ww

.nat

ure

.co

m/n

atu

rem

edic

ine