|
|
||||||||
CUTTING EDGE |


*
Laboratory of Immunology and Vascular Biology, Departments of Pathology and
Surgery, and
Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, CA 94305;
§
Center for Molecular Biology and Medicine, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304; and
¶
Millenium Pharmaceuticals, Cambridge, MA 02142
| Abstract |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
Here we describe mucosae-associated epithelial chemokine (MEC), a novel chemokine ligand for CCR10. MEC is most homologous to CTACK, displaying about 40% identity, and is expressed not in the skin, but, instead, in diverse mucosal tissues. MEC attracts subsets of memory lymphocytes as well as eosinophils. Analysis of cultured cell lines and laser capture microdissected epithelia reveals constitutive MEC expression by epithelial, but not endothelial, fibroblastic or lymphoid cells. Our findings suggest that MEC may play an important role in the physiology and/or recruitment of specialized cells into mucosal tissues, including the respiratory and oral mucosa and colon.
| Materials and Methods |
|---|
|
|
|---|
TBLASTN searches of the GenBank dbEST database with the sequences of known CC chemokines identified the expressed sequence tag for human MEC. IMAGE consortium clone 136910 was obtained from American Type Culture Collection (Manassas, VA) as an EcoRI-NotI insert in the pT7T3D-Pac vector. The nucleotide sequence was confirmed by automated sequencing. Protein similarity and dendrogram analysis were performed using ClustalW. BLASTN searches of the high throughput genome database using the MEC cDNA sequence revealed two BAC clones from human chromosome 5, CTD-2282F8 and CTD-2202K16, that encode the human MEC gene.
Synthesis of MEC
The signal sequence of MEC was predicted by the SignalP
server (http://www.cbs.dtu.dk/signal/cbssignalp.html). The predicted
105-aa mature protein (aa 23127 of the coding sequence) was
synthesized by F-moc chemistry (automated 433 peptide synthesizer, PE
Biosystems, Foster City, CA). A biotin moiety (aminocaproic
acid-biotin) was added to lysine 124. The purity (>95%) and molecular
integrity of the purified folded chemokine were determined by
analytical C18 reverse phase HPLC as well as by
mass spectrometry. Synthesized MEC had an experimentally determined
m.w. of 12408.7 (vs a theoretical weight of 12409.5). CTACK, TECK, and
other chemokines were synthesized, and stromal cell-derived factor
(SDF)-1
, TARC, and eotaxin were purchased from PeproTech (Rocky
Hill, NJ).
Blood cells and cell lines
A panel of 15 known chemokine receptor and 12 orphan G protein-coupled receptor stable transfectants were generated in the murine pre-B lymphoma cell line L1/2 as previously described (7, 8). The CCR10 (GPR-2) full-length sequence was provided by Dr. Craig Gerard (9). L1/2 cells were stimulated overnight with 10 mM butyric acid before performing chemotaxis assays. Peripheral blood mononuclear leukocytes and eosinophils were isolated from whole blood as described previously (8, 10).
Chemotaxis of L1/2 transfectants and blood lymphocytes
Chemotaxis assays were performed using 24-well Transwell
plates (Corning Costar, Cambridge, MA; 3-µm pores for L1/2 cells and
eosinophils and 5-µm pores for lymphocytes) as previously
described (8, 10). L1/2 cells were incubated from 5 h
to overnight, and lymphocytes and eosinophils were
incubated for 1.5 h. Migrated cells were quantitated by flow
cytometry, where FACS cell number corresponds to events acquired in a
fixed time of 30 s. Migrated cells were stained with CD4-APC or
CD8-APC, CD45RA-Cy, cutaneous lymphocyte Ag (CLA)-FITC, and
4ß7-PE to analyze T
cells, IgD-FITC, CD19-PE, and CD45RA-Cy for B cell analysis or CD49d-PE
and CD16-FITC for eosinphil analysis (all conjugated Abs purchased from
PharMingen, San Diego, CA). Four-color flow cytometry was performed on
a FACSCalibur (Becton Dickinson, San Jose, CA) using CellQuest
software, version 3.1 (Becton Dickinson). For gradient disruption
experiments, chemotaxis was conducted identically, except that 3 times
the optimal chemotactic dose of chemokine was added to the cells in the
top well, and for Ab blockade experiments, 50 µg/ml of blocking mAb
(clone 7B11, mouse IgG2a) or control mAb (isotype control or
eosinophil-binding anti-L-selectin mAb) was added to
the top well.
Laser capture microdissection
Eight-micron sections from normal human salivary gland and colon (obtained from patients undergoing elective surgery at Stanford University Medical Center, Stanford, CA) embedded in OCT (Miles, Elkhart, IN) were cut and immediately fixed in 70% ethanol/diethylpyrocarbonate (DEPC)-treated water for 30 s. Sections were counterstained with toludine blue (Sigma, St. Louis, MO)/DEPC-treated water for 30 s, dehydrated in increasing concentrations of ethanol/DEPC-treated water, and cleared in xylene. Laser capture microdissection was performed on a PixCell II (Arcturus Engineering, Mountain View, CA). Epithelial and nonepithelial cells were captured from each tissue, lysed in guanidinium buffer, and placed on ice for later RT-PCR and Southern analysis. Total RNA was isolated and subjected to a semiquantitative RT-PCR analysis as previously described (11). The PCR primers for human MEC were 5'-CCATCGTGGCCTTGGCTGTCTGTG-3' and 5'-GCCGTATGTTTCGTGTTTCCCCTG-3'.
Northern analysis for MEC mRNA
Human epithelial cells derived from bronchus-associated epithelium or mammary gland epithelium were obtained from Clonetics (Walkersville, MD) and cultured in a complete medium according to the manufacturers instructions. EA.hy926, a hybrid HUVEC line, was a gift from Dr. Edgell (University of North Carolina, Chapel Hill, NC). Poly(A)+ RNA from these cell lines was isolated using a Fasttrack Kit (Invitrogen, Carlsbad, CA). Poly(A)+ RNA from various human tissues was purchased from Clontech (Palo Alto, CA) or Clemente Associates (Madison, WI). RNA was separated on a 1.5% formaldehyde-agarose gel and quantitated by Northern blot analysis according to a standard protocol.
| Results and Discussion |
|---|
|
|
|---|
A BLAST search of the GenBank human EST database with the coding
region of CTACK revealed an EST encoding a novel chemokine, here termed
MEC. The MEC-coding sequence displays 49 and 45% nucleotide identity
with CTACK and TECK, respectively (Fig. 1
A). Interestingly, unlike
CTACK on chromosome 9 and TECK on chromosome 19, MEC is encoded on
human chromosome 5 by at least four exons separated by large introns
(Fig. 1
B). At the protein level, MEC displays
40% amino
acid identity in the common homology region with CTACK and is also
closely related to TECK, but MEC has a longer C terminus than CTACK and
contains six cysteines (Fig. 1
C).
|
|
(CXCL12), and the phenotype of the starting
population and that of the chemokine-recruited cells were analyzed by
flow cytometry. As shown in Fig. 2
300 nM), MEC was
more efficacious at this dose (Fig. 2
Consistent with its ability to attract CCR3 transfectants, MEC also
attracts blood eosinophils (Fig. 2
C). The
optimal chemotactic concentration of MEC for both CCR3 transfectants
(Fig. 2
A) and eosinophils (Fig. 2
C)
was in the range of 300400 nM. Eotaxin-3 (PTEC, CCL26), another CCR3
ligand, is also maximally active at this concentration, as are several
chemokines active on lymphocytes, including SLC and ELC for CCR7
(10) and TECK for CCR9 (12). Moreover, MEC
completely inhibits [125I]eotaxin (CCL11)
binding to eosinophils with an IC50
of about 23 nM, whereas CTACK does not compete for eotaxin binding
even at 500 nM (data not shown). Migration of eosinophils
to MEC could be completely inhibited by a blocking mAb to CCR3 (Fig. 2
C), but was unaffected by control mAbs, indicating that MEC
activates eosinophils through CCR3 and not CCR10. This
activity distinguishes MEC from CTACK, as CTACK fails to attract either
eosinophils or CCR3 transfectants (Ref. 6 and
D. Soler, unpublished observations).
Mucosal epithelial cell expression of MEC
Dot blot and Northern blot analyses revealed that
MEC message is most abundant in salivary gland, but is also expressed
in other tissues associated with mucosal epithelial surfaces, including
trachea, mammary gland, colon and rectum (Fig. 3
, A and B).
Interestingly, MEC message was poorly expressed in skin (compare
expression of CTACK and MEC in Fig. 3
B), and appeared
relatively less abundant in small intestine than in the colon or rectum
(compare TECK and MEC expression in Fig. 3
B). However, the
dot blot results suggest that there may be variable low expression of
MEC in different segments of the small intestine and in the stomach,
pancreas, thyroid gland, and prostate as well (Fig. 3
A). In
the Northern blots, we found that our MEC cDNA probe detected five MEC
transcripts of different sizes (0.8, 1, 3, 3.5, and 6 kb), with the
3-kb transcript being the most abundant (data not shown). The abundance
of the other transcripts is correlated with that of the 3-kb
transcript, and there were no obvious tissue-specific transcripts in
any tissues examined. These transcripts may represent splice variants
of MEC and/or variations in polyadenylation sites.
|
We conclude that MEC is a novel epithelial cell-expressed chemokine ligand for CCR10 and CCR3 with a unique pattern of tissue expression. Chemokines can modulate tissue physiology at multiple levels, including regulation of cell proliferation and differentiation as well as modulation of adhesion, locomotion, and chemotaxis. MEC may therefore participate in the physiology of mucosal tissues through any number of different mechanisms. The recent demonstration of CCR10 mRNA in Peyers patches, colon, and stomach (9, 14) is consistent with the coordinate presence of MEC and CCR10+ cells in these mucosal sites. Clearly, however, additional studies will be required to define the role(s) of MEC in the physiology of mucosal tissues and in the specialization of their immune responses.
The close relationship of MEC to CTACK suggests that these chemokines may be products of a relatively recent gene duplication event. Several other clusters or pairs of closely related chemokines that share a common receptor have been described: notably the CCR7 ligands ELC (15) and two nearly identical variants of SLC (16, 17), and the CCR4 ligands TARC and macrophage-derived chemokine (18). In each case, the homologous chemokines display highly distinctive patterns of expression in vivo, suggesting that the evolutionary pressure for gene duplication may have facilitated selective chemokine regulation and tissue or cell type-specific expression (19).
In addition to their distinctive patterns of tissue expression, MEC and CTACK differ in their ability to attract cells via CCR3. MEC, but not CTACK, stimulates migration of CCR3 transfectants as well as eosinophils. In this context, MEC may play a role, in conjunction with other regulatory elements, in the recruitment of eosinophils and, potentially, of rare CCR3+ T cells into mucosal tissues, including trachea and bronchi.
In the context of chemokine regulation of lymphocyte trafficking,
it is reasonable to postulate that MEC may play a role in the
recruitment and/or microenvironmental localization of specialized
CCR10-expressing memory and effector lymphocyte subsets. For example,
the high levels of MEC expression in salivary glands may be relevant to
the migratory patterns of a population of CLA+
lymphocytes, as the buccal mucosa is known to be a site of localization
of CLA+ T cells (20, 21). (In
contrast, it is unlikely that MEC recruits CLA+ T
cells to the colon, as CLA+ T cells lack the
necessary homing receptors to interact with and arrest on intestinal
vascular endothelium.) It is likely that additional
CCR10+ lymphocyte populations exist, populations
that may be relatively poorly represented in blood. Subsets of
CCR10+ gut-associated lymphocytes, for example,
might express
4ß7 but
lack CLA, and thus would have the opportunity to respond to
gut-associated MEC (but not to skin keratinocyte-expressed CTACK). In
the context of the multistep process required for
lymphocyte-endothelial recognition, diapedesis, and recruitment from
the blood (22), MEC and CTACK could thus play parallel
roles in facilitating lymphocyte diapedesis into mucosal tissues and
skin, but in each site would be acting on different lymphocyte subsets,
whose availability would be determined by prior vascular interaction
(i.e., capture, rolling, activation, and firm adhesion).
Another group has independently identified CCL28, reporting its expression by epithelial cells and activity on CCR10 (but not CCR3) (23).
In conclusion, its unique pattern of mucosal epithelial expression and of chemokine receptor usage suggests that MEC may play important roles in the physiology and pathophysiology of diverse mucosal tissues.
| Acknowledgments |
|---|
| Footnotes |
|---|
2 The human MEC sequence was submitted to GenBank under accession number AF266504. ![]()
3 J.P. and E.J.K. contributed equally to this work. ![]()
4 Address correspondence and reprint requests to Dr. Eugene C. Butcher, Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305-5324. ![]()
5 Abbreviations used in this paper: SLC, secondary lymphoid-tissue chemokine; MEC, mucosae-associated epithelial chemokine; DEPC, diethylpyrocarbonate; CLA, cutaneous lymphocyte Ag; ELC, EBI1-ligand chemokine; TECK, thymus-expressed chemokine; TARC, thymus and activation-regulated chemokine; SDF, stromal cell-derived factor; CTACK, cutaneous T cell-attracting chemokine. ![]()
Received for publication May 26, 2000. Accepted for publication July 14, 2000.
| References |
|---|
|
|
|---|
and MIP-3ß. J. Immunol. 158:1033.[Abstract]
eß7 integrins are expressed by mononuclear cells in skin and oral lichen planus. J. Oral Pathol. Med. 26:402.[Medline]
This article has been cited by other articles:
![]() |
M. Hansson, M. Hermansson, H. Svensson, A. Elfvin, L.-E. Hansson, E. Johnsson, A. Sjoling, and M. Quiding-Jarbrink CCL28 Is Increased in Human Helicobacter pylori-Induced Gastritis and Mediates Recruitment of Gastric Immunoglobulin A-Secreting Cells Infect. Immun., July 1, 2008; 76(7): 3304 - 3311. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. Miles, E. Liaskou, B. Eksteen, P. F. Lalor, and D. H. Adams CCL25 and CCL28 promote {alpha}4{beta}7-integrin-dependent adhesion of lymphocytes to MAdCAM-1 under shear flow Am J Physiol Gastrointest Liver Physiol, May 1, 2008; 294(5): G1257 - G1267. [Abstract] [Full Text] [PDF] |
||||
![]() |
A.-K. Shirakawa, D. Nagakubo, K. Hieshima, T. Nakayama, Z. Jin, and O. Yoshie 1,25-Dihydroxyvitamin D3 Induces CCR10 Expression in Terminally Differentiating Human B Cells J. Immunol., March 1, 2008; 180(5): 2786 - 2795. [Abstract] [Full Text] [PDF] |
||||
![]() |
N. Iijima, M. M. Linehan, S. Saeland, and A. Iwasaki Vaginal epithelial dendritic cells renew from bone marrow precursors PNAS, November 27, 2007; 104(48): 19061 - 19066. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. Shaykhiev and R. Bals Interactions between epithelial cells and leukocytes in immunity and tissue homeostasis J. Leukoc. Biol., July 1, 2007; 82(1): 1 - 15. [Abstract] [Full Text] [PDF] |
||||
![]() |
N. Feng, M. C. Jaimes, N. H. Lazarus, D. Monak, C. Zhang, E. C. Butcher, and H. B. Greenberg Redundant Role of Chemokines CCL25/TECK and CCL28/MEC in IgA+ Plasmablast Recruitment to the Intestinal Lamina Propria After Rotavirus Infection J. Immunol., May 15, 2006; 176(10): 5749 - 5759. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. E. John, M. S. Thomas, A. A. Berlin, and N. W. Lukacs Temporal Production of CCL28 Corresponds to Eosinophil Accumulation and Airway Hyperreactivity in Allergic Airway Inflammation Am. J. Pathol., February 1, 2005; 166(2): 345 - 353. [Abstract] [Full Text] [PDF] |
||||
![]() |
D. Alvarez, G. Harder, R. Fattouh, J. Sun, S. Goncharova, M. R. Stampfli, A. J. Coyle, J. L. Bramson, and M. Jordana Cutaneous Antigen Priming via Gene Gun Leads to Skin-Selective Th2 Immune-Inflammatory Responses J. Immunol., February 1, 2005; 174(3): 1664 - 1674. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. Ogawa, M. Iimura, L. Eckmann, and M. F. Kagnoff Regulated production of the chemokine CCL28 in human colon epithelium Am J Physiol Gastrointest Liver Physiol, November 1, 2004; 287(5): G1062 - G1069. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. Wilson and E. C. Butcher CCL28 Controls Immunoglobulin (Ig)A Plasma Cell Accumulation in the Lactating Mammary Gland and IgA Antibody Transfer to the Neonate J. Exp. Med., September 20, 2004; 200(6): 805 - 809. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Hieshima, Y. Kawasaki, H. Hanamoto, T. Nakayama, D. Nagakubo, A. Kanamaru, and O. Yoshie CC Chemokine Ligands 25 and 28 Play Essential Roles in Intestinal Extravasation of IgA Antibody-Secreting Cells J. Immunol., September 15, 2004; 173(6): 3668 - 3675. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. Schaerli, L. Ebert, K. Willimann, A. Blaser, R. S. Roos, P. Loetscher, and B. Moser A Skin-selective Homing Mechanism for Human Immune Surveillance T Cells J. Exp. Med., May 3, 2004; 199(9): 1265 - 1275. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. Hanamoto, T. Nakayama, H. Miyazato, S. Takegawa, K. Hieshima, Y. Tatsumi, A. Kanamaru, and O. Yoshie Expression of CCL28 by Reed-Sternberg Cells Defines a Major Subtype of Classical Hodgkin's Disease with Frequent Infiltration of Eosinophils and/or Plasma Cells Am. J. Pathol., March 1, 2004; 164(3): 997 - 1006. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. Nakayama, K. Hieshima, D. Nagakubo, E. Sato, M. Nakayama, K. Kawa, and O. Yoshie Selective Induction of Th2-Attracting Chemokines CCL17 and CCL22 in Human B Cells by Latent Membrane Protein 1 of Epstein-Barr Virus J. Virol., February 15, 2004; 78(4): 1665 - 1674. [Abstract] [Full Text] [PDF] |
||||
![]() |
X. Zhao, A. Sato, C. S. Dela Cruz, M. Linehan, A. Luegering, T. Kucharzik, A.-K. Shirakawa, G. Marquez, J. M. Farber, I. Williams, et al. CCL9 Is Secreted by the Follicle-Associated Epithelium and Recruits Dome Region Peyer's Patch CD11b+ Dendritic Cells J. Immunol., September 15, 2003; 171(6): 2797 - 2803. [Abstract] [Full Text] [PDF] |
||||
![]() |
N. H. Lazarus, E. J. Kunkel, B. Johnston, E. Wilson, K. R. Youngman, and E. C. Butcher A Common Mucosal Chemokine (Mucosae-Associated Epithelial Chemokine/CCL28) Selectively Attracts IgA Plasmablasts J. Immunol., April 1, 2003; 170(7): 3799 - 3805. [Abstract] [Full Text] [PDF] |
||||
![]() |
D. Soler, T. L. Humphreys, S. M. Spinola, and J. J. Campbell CCR4 versus CCR10 in human cutaneous TH lymphocyte trafficking Blood, March 1, 2003; 101(5): 1677 - 1682. [Abstract] [Full Text] [PDF] |
||||
![]() |
V. J. Cavanaugh, Y. Deng, M. P. Birkenbach, J. S. Slater, and A. E. Campbell Vigorous Innate and Virus-Specific Cytotoxic T-Lymphocyte Responses to Murine Cytomegalovirus in the Submaxillary Salivary Gland J. Virol., February 1, 2003; 77(3): 1703 - 1717. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. Nakayama, K. Hieshima, D. Izawa, Y. Tatsumi, A. Kanamaru, and O. Yoshie Cutting Edge: Profile of Chemokine Receptor Expression on Human Plasma Cells Accounts for Their Efficient Recruitment to Target Tissues J. Immunol., February 1, 2003; 170(3): 1136 - 1140. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Hieshima, H. Ohtani, M. Shibano, D. Izawa, T. Nakayama, Y. Kawasaki, F. Shiba, M. Shiota, F. Katou, T. Saito, et al. CCL28 Has Dual Roles in Mucosal Immunity as a Chemokine with Broad-Spectrum Antimicrobial Activity J. Immunol., February 1, 2003; 170(3): 1452 - 1461. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. Wilson, J. F. Hedges, E. C. Butcher, M. Briskin, and M. A. Jutila Bovine {gamma}{delta} T Cell Subsets Express Distinct Patterns of Chemokine Responsiveness and Adhesion Molecules: A Mechanism for Tissue-Specific {gamma}{delta} T Cell Subset Accumulation J. Immunol., November 1, 2002; 169(9): 4970 - 4975. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. W. Zuercher, H.-Q. Jiang, M. C. Thurnheer, C. F. Cuff, and J. J. Cebra Distinct Mechanisms for Cross-Protection of the Upper Versus Lower Respiratory Tract Through Intestinal Priming J. Immunol., October 1, 2002; 169(7): 3920 - 3925. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. Nakayama, R. Fujisawa, D. Izawa, K. Hieshima, K. Takada, and O. Yoshie Human B Cells Immortalized with Epstein-Barr Virus Upregulate CCR6 and CCR10 and Downregulate CXCR4 and CXCR5 J. Virol., February 22, 2002; 76(6): 3072 - 3077. [Abstract] [Full Text] [PDF] |
||||
![]() |
Y. K. Gruijthuijsen, P. Casarosa, S. J. F. Kaptein, J. L. V. Broers, R. Leurs, C. A. Bruggeman, M. J. Smit, and C. Vink The Rat Cytomegalovirus R33-Encoded G Protein-Coupled Receptor Signals in a Constitutive Fashion J. Virol., February 1, 2002; 76(3): 1328 - 1338. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. P. Bowman, N. A. Kuklin, K. R. Youngman, N. H. Lazarus, E. J. Kunkel, J. Pan, H. B. Greenberg, and E. C. Butcher The Intestinal Chemokine Thymus-expressed Chemokine (CCL25) Attracts IgA Antibody-secreting Cells J. Exp. Med., January 22, 2002; 195(2): 269 - 275. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. M. Lilly and B. L. Daugherty A Novel LPS-Inducible CCR3 Activator . Why So Many CCR3 Ligands? Am. J. Respir. Cell Mol. Biol., December 1, 2001; 25(6): 673 - 675. [Full Text] [PDF] |
||||
![]() |
C. Penido, H. C. Castro-Faria-Neto, A. Vieira-de-Abreu, R. T. Figueiredo, A. Pelled, M. A. Martins, P. J. Jose, T. J. Williams, and P. T. Bozza LPS Induces Eosinophil Migration via CCR3 Signaling Through a Mechanism Independent of RANTES and Eotaxin Am. J. Respir. Cell Mol. Biol., December 1, 2001; 25(6): 707 - 716. [Abstract] [Full Text] [PDF] |
||||
![]() |
Y. Reiss, A. E. Proudfoot, C. A. Power, J. J. Campbell, and E. C. Butcher CC Chemokine Receptor (CCR)4 and the CCR10 Ligand Cutaneous T Cell-attracting Chemokine (CTACK) in Lymphocyte Trafficking to Inflamed Skin J. Exp. Med., November 19, 2001; 194(10): 1541 - 1547. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. S. POBER, M. S. KLUGER, and J. S. SCHECHNER Human Endothelial Cell Presentation of Antigen and the Homing of Memory/Effector T Cells to Skin Ann. N.Y. Acad. Sci., September 1, 2001; 941(1): 12 - 25. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||