Abstract
Transforming growth factor-β2 (TGF-β2) levels in rat milk are high in early lactation, whereas endogenous TGF-β1 expression in the neonatal gut increases toward midweaning. Three types of transmembrane TGF-β receptors have been identified in mammals. The receptor III (or betaglycan) binds and presents TGF-β1 or β2 to receptor II. Receptor I then interacts with receptor II, forming a signaling receptor complex, and propagates the signal. To determine whether TGF-β receptor expression in the gut is also developmentally regulated, the present study assessed ontogeny of TGF-β receptor expression in the postnatal rat small intestine. Jejunum and ileum tissues from rat pups at d 3, 10, 14, 21, and 28 of age were collected. Cryostat sections were stained with antibodies against TGF-β receptors I, II, and III, and various cell markers by immunofluorescence. In both regions, receptor I staining was seen on apical and basolateral membranes of the villus and crypt epithelium at all ages, and staining on the apical membrane increased with age; receptor II was predominantly expressed in the crypt, and staining on the villi appeared after d 10; receptor III was distributed throughout the mucosa at early ages but diminished from the epithelium postweaning by d 28. T cells, B cells, and dendritic cells in the lamina propria expressed TGF-β receptor III but lacked expression of receptor I and II. The pattern of TGF-β receptor expression changes with age in a manner that may reflect the change in ligand from TGF-β2 (milk-derived) to TGF-β1 (endogenously produced).
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Main
TGF-β is a multifunctional cytokine involved primarily in regulation of cell proliferation and differentiation, stimulation of extracellular matrix synthesis and deposition, and modulation of inflammatory and immune responses (1, 2). In the intestinal mucosa, TGF-β may be involved in the initiation of immune responses by regulation of MHC antigen expression and presentation (3). The major effects of TGF-β on the mucosal immune system seem to be regulation of IgA responses and induction of oral tolerance. For example, TGF-β induces B-cell isotype switching to IgA in murine B cells stimulated with lipopolysaccharide (4). T cells isolated from mesenteric lymph nodes, Peyer's patches, and lamina propria of orally tolerant animals had a 5–10-fold increase in their production of TGF-β together with increased amounts of IL-4 and IL-10 compared with control animals (5).
Several studies have shown that TGF-β is present in milk of various species (6–8). The total concentration of TGF-β in human milk was high in colostrum and relatively low in late lactation (6). ELISA of rat milk found no TGF-β1, whereas TGF-β2 was high in early milk and progressively declined toward weaning (8). TGF-β1, 2, and 3 have been found in normal murine intestinal tissues (9). We showed that TGF-β1 expression in the postnatal rat small intestine was very low in the first week of life and increased toward weaning by d 19 (8), indicating a reciprocal relationship between levels of TGF-β in milk and endogenous production of TGF-β in the neonatal gut. In addition, Letterio et al. (10) showed that labeled TGF-β was distributed intact in various tissues after oral administration to TGF-β1 null mice.
Three distinct TGF-β receptors have been characterized on the cell surface. TβRIII (also known as betaglycan) is a transmembrane proteoglycan containing a short cytoplasmic domain; it may not be directly involved in signaling but binds and presents TGF-β to signaling receptors (11). TβRII and I are transmembrane serine/threonine kinases, which are essential for TGF-β signaling. TβRII determines the ligand specificity, whereas TβRI interacts with TβRII and may not have a ligand-binding specificity by itself (12). TGF-β1 interacts with TβRI and II, forming a high-affinity signaling receptor complex; this interaction does not require betaglycan (13). In contrast, TGF-β2 seems to depend on betaglycan for high-affinity binding to TβRI and II. TβRI and II can distinguish between TGF-β isoforms: they bind TGF-β1 and β 3 far better than they bind TGF-β2 (14, 15). betaglycan, however, binds to TGF-β1 and β2 with equal affinity and presents them to TβRII, subsequently forming the high-affinity signaling receptor complex with TβRI (13). Indeed, by promoting TGF-β2 access to TβRII, betaglycan counteracts the intrinsic low affinity of the signaling receptors toward this isoform, thus rendering cells as sensitive to this isoform as they are to TGF-β1.
TGF-β receptors have been found in a number of intestinal epithelial cell lines as well as in fetal and adult intestinal tissues (16–19). Given the progressive changes in TGF-β levels in milk and endogenous production of TGF-β in the neonatal gut (8), a developmental change in TGF-β receptor expression in the gut may also occur from preweaning to postweaning. However, to date, no studies have assessed TGF-β receptor expression in the postnatal gut and gut-associated lymphoid tissue. The aims of the present study were 2-fold:a) to study the ontogeny of TGF-β receptor expression in the postnatal small intestine;b) to identify which cells express TGF-β receptor(s). Analysis based on these findings should provide additional insight into the role of maternal milk TGF-β in the development of the postnatal intestine and intestinal mucosal immune system.
METHODS
Tissue preparation.
Rat tissue collection was performed with the approval of the Women's and Children's Hospital Animal Ethics Committee as well as the Animal Ethics Committee of the University of Adelaide, Australia. Each litter of Hooded Wistar rat pups was culled to six and weaned at d 21 of age. Jejunum and ileum tissue samples were collected at d 3, 10, 14, 21, and 28 postpartum (four to six pups per age group). Rat pups were killed by decapitation. The intestinal tract was immediately excised and placed onto an ice-cold glass slab. Two 1-cm-long segments were collected from proximal jejunum and ileum, respectively, embedded in optimal cutting temperature (OCT) compound (Miles Inc., Elkhart, IN), frozen in liquid nitrogen, and stored at −70°C until sectioning, 8-μm-thick cryostat sections were cut and mounted onto gelatin-coated slides. As described elsewhere (20, 21), the sections were air dried, fixed in 100% acetone for 10 min at room temperature, then dried and stored at −20°C until use.
Immunofluorescence single labeling.
Before staining, the tissue sections were washed with Tris-buffered saline (TBS), and preincubated with 3% BSA (Sigma Chemical Co., St. Louis, MO) for 30 min to block nonspecific binding of the antibodies. The sections were then incubated with either rabbit anti-human Tβ RI (sc-399, Santa Cruz Biotechnology, Santa Cruz, CA) or Tβ RII (sc-1700, Santa Cruz Biotechnology), or goat anti-human Tβ RIII (AF-242-PB, R&D Systems, Minneapolis, MN) polyclonal antibodies diluted to working concentration (1 μg/mL) at room temperature for 1 h. After three washes, sections were further incubated with indocarbocyanine (Cy3) conjugated F(ab′)2 fragment donkey anti-rabbit IgG (1:800) or donkey anti-goat IgG (1:100) antibodies (Jackson ImmunoResearch, PA) as appropriate for 1 h at room temperature. Sections were then washed three times with TBS and mounted in fluorescence mounting medium (Dako, CA). Control sections were incubated without primary antibodies or IgG from the same species at the same concentration as the primary antibody. The specificity of labeling was evaluated by replacing the primary antibodies above with respective antibody solutions either preincubated with a corresponding blocking peptide (Santa Cruz Biotechnology) or preabsorbed with a recombinant receptor protein (R&D Systems).
Immunofluorescence dual labeling.
Sections were stained with antibodies against Tβ RI, II, or III as above in conjunction with antibodies to rat cell surface determinants (CD) detailed below. The chosen cell markers detect a range of immune cells including T lymphocytes, B lymphocytes, and a number of antigen-presenting cells as well as T-cell activation markers. Both indirect and direct immunofluorescence techniques were used, as some of the antibodies were not available as direct conjugates. During indirect immunofluorescence, the tissue sections were coincubated with polyclonal antibodies against TGF-β receptor molecules and MAb against cell surface markers for 1 h at room temperature. The following mouse anti-rat MAb were purchased from SEROTEC (Serotec, Oxford, England): OX-8, CD8; W3–25, CD4; OX-17, MHC class II; OX-39, IL-2R; ED5, follicular dendritic cell and OX-62, veiled dendritic cell. After initial incubation, the sections were washed thoroughly in TBS/0.05% polyoxyethylenesorbitan monolaurate 20 (Tween 20, BDH Laboratory Supplies, Poole, England) and stained with either Cy3-conjugated F(ab)2 fragment donkey anti-rabbit IgG (Jackson ImmunoResearch) plus FITC-conjugated sheep anti-mouse Ig (DDAF, Silenus, Hawthorn, Australia) or Cy3-conjugated F(ab)2 fragment donkey anti-goat IgG (Jackson ImmunoResearch) plus FITC-conjugated rabbit anti-mouse Ig (Sigma Chemical Co.) preabsorbed with 1% normal rat serum (Sigma Chemical Co.) for another 60 min at room temperature.
During direct immunofluorescence, the sections were first incubated with either rabbit anti-Tβ RI or Tβ RII (Santa Cruz Biotechnology), or goat anti-Tβ RIII (R&D Systems) for 1 h at room temperature. After washing three times in TBS/0.05% Tween 20, a further 60-min incubation with FITC directly conjugated mouse anti-rat ED-1 (macrophage), OX-26 (transferrin receptor), or OX-33 (B cell) antibodies (Serotec) was applied, together with Cy3-conjugated F(ab)2 fragment donkey anti-rabbit or donkey anti-goat IgG antibodies (Jackson ImmunoResearch). The number of double-stained cells per mm2 villus mucosa was counted using a fluorescence microscope (Leica, Wetzlar, Germany) at ×400 magnification. The average cell number was based on the scores of jejunal sections obtained from four to six animals in each group. At least three sections for each piece of tissue, 8–15 different fields of view per section, were counted.
Statistics.
The nonparametric Mann-Whitney test was used for statistical analysis. A 2-sided p< 0.05 was considered significant for differences in dual-labeled cell counts between different age groups.
RESULTS
Ontogeny of TGF-β receptor expression in rat pup jejunum.
Distinctive distribution patterns of TGF-β receptor expression were observed in the postnatal jejunum. Typical immunostaining patterns for Tβ RI, II, and III are represented in Figures 1,2, and 3 and summarized for all animals in each group (n= 6) in Table 1. As seen in Figure 1, both basolateral and apical membranes of the villus and crypt epithelium expressed Tβ RI. Staining on the apical membrane increased with age, whereas, in the basolateral membrane, the staining was relatively constant in all ages assessed. Tβ RII was abundantly expressed in both upper and lower parts of the crypt at all ages (Table 1 and Fig. 2). Staining in the villi appeared after d 10, and the pattern changed with age. At d 10, the apical membrane of the villus epithelium was stained (Fig. 2, A and B); at d 14 and 28 of age, staining was more isolated on individual enterocytes (Fig. 2, C–F). Tβ RIII was broadly expressed on the goblet cells (Fig. 3, A–D), crypt (Fig 3, A and C) and villus (Fig. 3, B and D) epithelial cells, and IEL (Fig. 3, A and C); lamina propria cells (Fig. 3, A, C, and D) and muscularis (Fig. 3C) were also stained. However, Tβ RIII staining in the epithelium and lamina propria was markedly diminished at d 28 (Fig. 3, E and F). In addition, preabsorption of antibodies to respective blocking peptide or recombinant antigen resulted in the abolition of all staining (not shown).
Expression of Tβ RI, II, and III in rat pup ileum.
Tβ RI, II, and III were also abundantly expressed in the ileum, and overall distribution patterns of immunostaining in the ileum is similar to that observed in the jejunum (Table 1 and Fig. 4). Only minor variations were seen between the jejunum and ileum. For example, Tβ RI staining of muscularis in sections from animals aged d 3 was most intense at the outer muscle layers in ileum, whereas, in jejunum, the inner circular layers were more strongly stained (Fig. 4, A and B).
TGF-β receptor-labeled immune cells in intestinal mucosa.
Double immunofluorescence showed that a number of different types of immune cells in the lamina propria and IEL expressed Tβ RIII between d 10 and 21 of age (Table 2 and Fig. 5). Although Tβ RI and II were expressed by intestinal epithelial cells, no Tβ RI or II dual-labeled immune cells were detected in this study. Controls in which isotypic IgG was used at the same concentration as the primary antibodies were negative compared with specific antibody staining (not shown). Tβ RIII-labeled OX-33 (B cell), W3/25 (CD4 T cell;Fig. 5, A and B), and OX-62 (veiled dendritic cell;Fig. 5, C and D) along with OX-17 (MHC class II) positive cells were detected as early as d 10; dual-labeled OX-8 (CD8) positive cells were detected at d 14 and 21 of age, whereas low levels of follicular dendritic cells (ED5+) expressing Tβ RIII were detected at d 21 (Table 2). Occasionally, IEL were CD8 and Tβ RIII double positive (not shown). Overall, the number of dual-labeled cells in the mucosa increased with age from d 10 to 21; no dual-labeled cells were detected at d 3 and 28 (Table 2). We found that very few immune cells were present in the lamina propria in sections from animals aged d 3. The number of TβRIII-positive B cells, CD4 T cells, veiled dendritic cells, and MHC class II+ cells was relatively low at d 10 of age but significantly increased by d 21, p< 0.05 (Table 2). Loss of double-stained cells in sections from animals aged d 28 reflects the loss of Tβ RIII staining from the epithelium and lamina propria at this age (Fig. 3, E and F).
DISCUSSION
The present study was carried out to assess the ontogeny of TGF-β receptor expression in the postnatal small intestine. Our results revealed that both Tβ RI and II were expressed in the intestinal epithelium postnatally. Tβ RIII was coexpressed with TβRI and II in the epithelium before weaning but diminished from the epithelium postweaning. The latter is in agreement with the observation that betaglycan (Tβ RIII) is less abundant in adult tissues compared with fetal tissues (22). As an accessory receptor, Tβ RIII may bind and present TGF-β to homo-oligomeric Tβ RII, which is a constitutively active serine/threonine kinase. The TGF-β /Tβ RII complex then recruits TβRI into the complex, after which Tβ RI is phosphorylated by Tβ RII, hence becoming activated, and propagates signals (23, 24). Tβ RIII binds TGF-β1 or TGF-β2 indiscriminately and greatly enhances the otherwise minimal affinity for TGF-β2 binding to the signaling Tβ RII (25). The coexistence of Tβ RI, II, and III in the gut epithelium during the suckling period could allow milk-derived TGF-β, especially TGF-β2, to be functionally active via interaction with the ligand-binding TβRIII and signaling TβRII and I. Expression of Tβ RIII in the suckling rat intestine may reflect a physiologic necessity for milk-derived TGF-β2, the predominant isoform in rat milk (8), to access signaling receptors in the gut. Lack of expression of Tβ RIII postweaning may correlate with the onset of endogenous TGF-β1 production by enterocytes at weaning (8). Norgaard et al. (26) reported that betaglycan mRNA was rapidly down-regulated, whereas Tβ RI and II mRNA were slightly increased after 24 h of treatment with TGF-β1 by small-cell lung cancer cell lines, suggesting that TGF-β1 regulates the expression of its receptors, in particular betaglycan. Unlike TGF-β2, TGF-β1 can directly interact with Tβ RII, which then leads to signal transduction in conjunction with Tβ RI (13). Once endogenous production of TGF-β1 occurs, Tβ RIII may become redundant in terms of ligand binding and presentation.
Distinctive distribution patterns of Tβ RI, II, and III in the gut epithelium were also observed related to the postnatal ages. Tβ RI was expressed on both apical and basolateral membranes of the whole epithelium, and expression on the apical membrane increased with age, whereas Tβ RII expression appeared on the apical membrane of the epithelium at d 10 and became scattered on individual enterocytes along the villi after d 14. Tβ RIII was broadly expressed across the epithelium including goblet cells, epithelial cells, and IEL before d 28. Tβ RI, II, and III coexpressed in the gut epithelium but were not necessarily situated side by side on each single cell. This is consistent with the report that no physical association of Tβ RI with Tβ RIII has been observed (27). Although TβRIII and II can be coimmunoprecipitated when bound to TGF-β (13, 25), double-labeling immunofluorescence experiments of cell surface receptors indicated that Tβ RIII and II are not detectably associated with each other (27). As suggested by others, the hetero-oligomerization between Tβ RIII and II may only be transient and restricted to a small percentage of the receptors (28), and differential regulation of Tβ RII and I expression and their signaling activities may provide the cell with a strategy to modulate TGF-β responsiveness (27).
TGF-β is a potent immunoregulator in the mucosal immune system (3–5). It is expected that TGF-β target cells would express functional TGF-β receptors. We examined various types of immune cells in the gut-associated lymphoid tissue, but none of these cells were dual-labeled with Tβ RI or II, even though Tβ RI- and II-positive cells were present in the lamina propria or gut epithelium. Mussener et al. (29) reported a similar finding in rat synovia in which cells within lymphocytic aggregates such as CD4+ cells lacked expression of Tβ RI and II. In contrast, we found immune cells including CD4+ and CD8+ T cells, veiled dendritic cells, B cells, and a small number of follicular dendritic cells in the lamina propria as well as CD8+ IEL expressing Tβ RIII, and the number of labeled cells increased significantly from d 10 to 21 of age. Tβ RIII can bind TGF-β independently of the other receptors (13, 30). Tβ RIII may function in attracting and concentrating TGF-β on the cell surface for eventual transfer to closely situated signal-transducing receptors (31, 32). It may serve to regulate the binding of TGF-β to its signal-transducing receptors by targeting TGF-β to appropriate locations in the microenvironment of cells.
In summary, there is an ontogenetic development of TGF-β receptor expression in the postnatal rat small intestine. Before weaning, Tβ RIII was coexpressed with Tβ RI and II throughout the epithelium. Over the weaning period, Tβ RI and II expression remained on the epithelium, whereas Tβ RIII gradually disappeared from the epithelium. This unique distribution pattern of TGF-β receptor expression from preweaning to postweaning may correlate with the change in ligand specificity from maternal TGF-β2 to endogenous TGF-β1 in the postnatal intestine.
Abbreviations
- TGF-β:
-
transforming growth factor-β
- Tβ RI:
-
TGF-β receptor type I
- Tβ RII:
-
TGF-β receptor type II
- Tβ RIII:
-
TGF-β receptor type III
- MHC:
-
major histocompatibility complex
- IEL:
-
intraepithelial lymphocytes
References
Sporn MB, Roberts AB 1992 Transforming growth factor-beta: recent progress and new challenges. J Cell Biol 119: 1017–1021
Shull MM, Ormsby I, Kier AB, Pawlowski S, Diebold RJ, Yin M, Allen R, Sidman C, Proetzel G, Calvin D 1992 Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease. Nature 359: 693–699
Donnet-Hughes A, Schiffrin EJ, Huggett AC 1995 Expression of MHC antigens by intestinal epithelial cells. Clin Exp Immunol 99: 240–244
Coffman RL, Lebman DA, Shrader B 1989 Transforming growth factor-beta specifically enhances IgA production by lipopolysaccharide-stimulated murine B lymphocytes. J Exp Med 170: 1039–1044
Neurath MF, Fuss I, Kelsall BL, Presky DH, Waegell W, Strober W 1996 Experimental granulomatous colitis in mice is abrogated by induction of TGF-beta-mediated oral tolerance. J Exp Med 183: 2605–2616
Saito S, Yoshida M, Ichijo M, Ishizaka S, Tsujii T 1993 Transforming growth factor-beta (TGF-beta) in human milk. Clin Exp Immunol 94: 220–224
Jin Y, Cox DA, Knecht R, Raschdorf F, Cerletti N 1991 Separation, purification, and sequence identification of TGF-beta 1 and TGF-beta 2 from bovine milk. Eur J Biochem 197: 353–358
Penttila IA, van Spriel AB, Zhang MF, Xian CJ, Steeb CB, Cummins AG, Zola H, Read LC 1998 Transforming growth factor-beta levels in maternal milk and expression in postnatal rat duodenum and ileum. Pediatr Res 44: 524–531
Barnard JA, Warwick GJ, Gold LI 1993 Localization of transforming growth factor-beta isoforms in the normal murine small intestine and colon. Gastroenterology 105: 67–73
Letterio JJ, Geiser AG, Kulkarni AB, Roche NS, Sporn MB, Roberts AB 1994 Maternal rescue of transforming growth factor-beta 1 null mice. Science 246: 1936–1938
Lopez-Casillas F, Cheifetz S, Doody J, Andres JL, Lane WS, Massague J 1991 Structure and expression of the membrane proteoglycan betaglycan. Cell 67: 785–795
Ebner R, Chen RH, Shum L, Lawlor S, Zioncheck TF, Lee A, Lopez AR, Derynck R 1993 Cloning of a type I TGF-beta receptor and its effect on TGF-beta binding to the type II receptor. Science 260: 1344–1348
Lopez Casillas F, Wrana JL, Massague J 1993 Betaglycan presents ligand to the TGF-beta signaling receptor. Cell 73: 1435–1444
Cheifetz S, Weatherbee JA, Tsang ML, Anderson JK, Mole JE, Lucas R, Massague J 1987 The transforming growth factor-beta system, a complex pattern of cross-reactive ligands and receptors. Cell 48: 409–415
Cheifetz S, Hernandez H, Laiho M, ten Dijke P, Iwata KK, Massague J 1990 Distinct transforming growth factor-beta (TGF-beta) receptor subsets as determinants of cellular responsiveness to three TGF-beta isoforms. J Biol Chem 265: 20533–20538
Ohtani H, Kagaya H, Nagura H 1995 Immunohistochemical localization of transforming growth factor-beta receptors I and II in inflammatory bowel disease. J Gastroenterology 30: 76–77
Winesett MP, Ramsey GW, Barnard JA 1996 Type II TGF-beta receptor expression in intestinal cell lines and in the intestinal tract. Carcinogenesis 17: 989–995
Linask KK, D'Angelo M, Gehris AL, Greene RM 1991 Transforming growth factor-beta receptor profiles of human and murine embryonic palate mesenchymal cells. Exp Cell Res 192: 1–9
Wang YQ, Sizeland A, Wang XF, Sassoon D 1995 Restricted expression of type-II TGF-beta receptor in murine embryonic development suggests a central role in tissue modeling and CNS patterning. Mech Dev 52: 275–289
Jeurissen SH, Dijkstra CD 1986 Characteristics and functional aspects of nonlymphoid cells in rat germinal centers, recognized by two monoclonal antibodies: ED5 and ED6. Eur J Immunol 16: 562–568
Farstad IN, Norstein J, Brandtzaeg P 1997 Phenotypes of B and T cells in human intestine and mesenteric lymph. Gastroenterology 107: 112–119
Andres JL, Ronnstrand L, Cheifetz S, Massague J 1991 Purification of the transforming growth factor-beta (TGF-beta) binding proteoglycan betaglycan. J Biol Chem 266: 23282–23287
ten Dijke P, Miyazono K, Heldin CH 1996 Signaling via hetero-oligomeric complexes of type I and type II serine/threonine kinase receptors. Curr Opin Cell Biol 8: 139–145
Wrana JL, Attisano L, Wieser R, Ventura F, Massague J 1994 Mechanism of activation of the TGF-beta receptor. Nature 370: 341–347
Moustakas A, Lin HY, Henis YI, Plamondon J, O'Connor-McCount MD, Lodish HF 1993 The transforming growth factor-beta receptors type I, II, and III form hetero-oligomeric complexes in the presence of ligand. J Biol Chem 268: 22215–22218
Norgaard P, Spang Thomsen M, Poulsen HS 1996 Expression and autoregulation of transforming growth factor-beta receptor mRNA in small-cell lung cancer cell lines. Br J Cancer 73: 1037–1043
Derynck R, Feng XH 1997 TGF-beta receptor signaling. Biochim Biophys Acta 1333: F105–F150
Henis YI, Moustakas A, Lin HY, Lodish HF 1994 The types II and III transforming growth factor-beta receptors form homo-oligomers. J Cell Biol 126: 139–154
Mussener A, Funa K, Kleinau S, Klareskog L 1997 Dynamic expression of transforming growth factor-betas (TGF-beta) and their type I and type II receptors in the synovial tissue of arthritic rats. Clin Exp Immunol 107: 112–119
Kretzschmar M, Liu F, Hata A, Doody J, Massague J 1997 The TGF-beta family mediator Smad1 is phosphorylated directly and activated functionally by the BMP receptor kinase. Genes Dev 11: 984–995
Wang XF, Lin HY, Ng-Eaton E, Downward J, Lodish HF, Weinberg RA 1991 Expression cloning and characterization of the TGF-beta type III receptor. Cell 67: 797–805
Massague J 1998 TGF-beta signal transduction. Annu Rev Biochem 67: 753–791
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Zhang, M., Zola, H., Read, L. et al. Localization of Transforming Growth Factor-β Receptor Types I, II, and III in the Postnatal Rat Small Intestine. Pediatr Res 46, 657 (1999). https://doi.org/10.1203/00006450-199912000-00017
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DOI: https://doi.org/10.1203/00006450-199912000-00017
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