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Published online before print March 12, 2004
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* Laboratory for Experimental Internal Medicine,
VU Medical Center, Departments of
Gastroenterology and Hepatology and
Surgery, Academic Medical Centre, Amsterdam, The Netherlands
1 Correspondence: Laboratory of Experimental Internal Medicine, H2-256, Academic Medical Centre, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. E-mail: a.a.tevelde{at}amc.uva.nl
| ABSTRACT |
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than CD45RBlow T lymphocytes in control patients. CD4+CD45RBlow T cells from IBD patients produced less IL-10 than CD4+CD45RBlow T lymphocytes of controls, and interferon-
production by both T lymphocyte subsets was decreased in IBD. These data indicate that CD and UC are characterized by an influx of CD4+CD45RBhigh T lymphocytes. These CD4+CD45RBhigh T lymphocytes seem to be important in the pathogenesis of IBD, as they produce more proinflammatory cytokines and less anti-inflammatory cytokines compared with CD4+CD45RBlow T lymphocytes.
Key Words: cytokines inflammation human
| INTRODUCTION |
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To study the mechanism of disease development, several mouse models of experimentally induced or spontaneously occurring colitis are available (for review, see ref. [2 ]). One of these models involves the adoptive transfer of a pathogenic CD4+CD45RBhigh T cell subpopulation into an immuno-deficient recipient. Transfer of CD4+CD45RBhigh T cells from donor mice into genetically immuno-deficient (recombination activating gene-2/) mice or severe combined immunodeficiency mice results in a spontaneous chronic and severe inflammation of the large intestines [3 ]. In contrast, cotransfer of the CD4+CD45RBlow T cell subset protects against disease [4 ] or results in a later onset of disease [5 ].
The level of expression of CD45RB on mouse CD4+ T cells is believed to distinguish naïve (CD45RBhigh) from activated/memory (CD45RBlow) cells [6 ].
In humans, two other isoforms of CD45, CD45RA and CD45RO, are used to distinguish naïve and primed/memory T cells, respectively [7 , 8 ]. However, there is also a reverse CD45RB expression on CD45RA and CD45RO cells in human peripheral blood [9 ]. In the peripheral blood, CD45RA-positive T cells express high levels of CD45RB, whereas CD45RO cells express little CD45RB. Hitherto, the role of CD45RB expression in human intestinal inflammation has not been evaluated in detail.
The expression of CD45 is essential for the activation of T lymphocytes via the T cell receptor. The intracellular domain of CD45 contains a protein tyrosine phosphatase that regulates the intracellular proteins p56lck and p59fyn on T cell activation [10 ]. T lymphocytes express different isoforms of the extracellular domain of CD45 [7 ]. The expression of the isoforms varies between subpopulations of T lymphocytes and changes upon stimulation and differentiation. The CD45 isoforms display different abilities to support T cell activation [11 ].
Conflicting reports exist concerning the distribution of memory and naïve cells in the peripheral blood cells of IBD patients. The number of memory cells was reported to be elevated in the peripheral blood of CD patients [12 ], but these observations were not confirmed in another report [13 ]. In the mucosa of the gut, almost all CD4-positive cells express the CD45RO marker and are therefore considered memory cells.
In view of the functional differences of T lymphocytes that express the various CD45 isoforms, we investigated the expression of CD45RA, CD45RO, and CD45RB by peripheral- and gut-derived T lymphocytes from IBD patients and controls. To further study the functional difference between CD45RBhigh and CD45RBlow cells, peripheral- and gut-derived T lymphocytes were sorted and stimulated with CD3/CD28. The pro- and anti-inflammatory cytokine profile of these subsets was determined.
| MATERIALS AND METHODS |
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Cell preparation of mucosal specimen
Freshly obtained mucosal specimens (3 cmx0.5 cm) were homogenized using an automated, mechanical tissue desecration device (Medimachine system, Dako, Danmark). Cell suspensions were centrifuged with Ficoll (Pharmacia, Uppsala, Sweden), and the mononuclear cells were subsequently passed through a 40-µM filter cell strainer (Becton Dickinson Transduction Laboratories, Franklin Lakes, NJ). Subsequently, cells were washed with fluorescence-activated cell sorter buffer (phosphate-buffered saline, containing 0.5% bovine serum albumin, 0.3 mmol/L EDTA, and 0.01% sodium azide) and were kept on ice for the rest of the procedure.
Flow cytometry
Four color FACSCalibur analysis was used to determine the expression of CD45RA and CD45RO within the CD45RBhigh and CD45RBlow subgroups. One million cells per well (96-well microplate, Greiner B.V. Labor Techniek, Alphen aan de Rijn, The Netherlands) were incubated with anti-CB45RB (Southern Biotechnology Associates, Birmingham, AL) and anti-immunoglobulin Gperidinin chlorophyll protein (Per CP) as secondary antibody. Subsequently, cells were incubated with anti-CD4allophycocyanin (APC)-, anti-CD45ROphycoerythrin (PE)-, and anti-CD45RAfluorescein isothiocyanate (FITC)-labeled antibody (Immunotech, Marseille, France). Isotype controls were used to determine the negative gates.
Analysis was done on a FACSCalibur in conjunction with the Cellquest Pro (BD Biosciences, Pharmingen, San Diego, CA) software, and 5000 cells were counted. CD4+CD45RBhigh and CD4+CD45RBlow subsets were defined as 40% of the highest and 40% of the lowest CD4+CD45RB-expressing cells.
Sorting of peripheral blood mononuclear cells (PBMC) and gut-derived T cells
Blood was drawn into a tube containing heparin (final concentration, 10 U/ml). PBMC were obtained using Ficoll-Hypaque (Sigma Chemical Co., St. Louis, MO) density gradient centrifugation (400 g, 20 min). Subsequently, the cells residing at the interface were washed three times and resuspended in Iscoves medium supplemented with 10% pooled human serum (BioWhittaker, Belgium) and ciproxin (10 µg/ml; Gibco-BRL, Life Technologies, Rockville, MD). Gut-derived T cells were isolated as described above under sterile conditions and resuspended in Iscoves medium supplemented with 10% pooled human serum and ciproxin. For staining, per 1 x 107 cells, 20 µl unlabeled mouse anti-human-CD45RB antibody was added, and cells were incubated for 30 min on ice. After washing with sterile medium [Iscoves medium supplemented with 10% pooled human serum (BioWhittaker)] and ciproxin (10 µg/ml), a secondary goat anti-mouseFITC-labeled antibody (Immunotech) was added and incubated for 20 min on ice in the dark. Subsequently, cells were washed, and a 10-min blocking step with normal mouse serum (CLB, Amsterdam, The Netherlands) without preservative was performed before staining with 10 µl mouse anti-humanCD4PECy5-labeled antibody (Immunotech) per 1 x 107 cells for 20 min on ice in the dark. Cells were sorted by use of the FACSVantage (BD Biosciences, Pharmingen) under sterile conditions. CD4+CD45RBhigh and CD4+CD45RBlow subsets were sorted and defined as 40% of the highest and 40% of the lowest CD4+CD45RB-expressing cells. After sorting, the subpopulations were reanalyzed on a FACScan or FACSCalibur (BD Biosciences, PharMingen), and only the populations more than 95% pure were used. The sorted cells were washed and resuspended in RPMI 1640 (BioWhittaker), supplemented with 5% pooled human serum (BioWhittaker) and antibiotics (Gibco-BRL, Life Technologies). Sorted cells were stimulated (concentration, 1x105/well) with anti-human anti-CD3 and anti-CD28 antibodies (both 1:1000, CLB) for 72 h at 37°C.
Cytokines
Supernatant of the stimulated peripheral blood cells was aspirated, and the concentration of interleukin (IL)-4, IL-10, interferon-
(IFN-
), and tumor necrosis factor
(TNF-
) was analyzed using enzyme-linked immunosorbent assay (CLB), according to the instruction of the manufacturer. For cytokine determination in the supernatants of the stimulated gut-derived T cells, the Cytometric Bead Array kit (BD Biosciences, PharMingen) was used, according to the manufacturers instructions.
Immunofluorescence staining
Double-staining was performed as described previously with some modifications [14
]. Briefly, cryostat fragments of colon tissue were cut into 46 µm sections, air-dried overnight, and fixed in acetone for 10 min at room temperature. The slides were first incubated with 5% (vol/vol) normal goat serum (CLB), then with optimal dilutions of CD45RAFITC (BD Biosciences, PharMingen), CD4PE (BD Biosciences, PharMingen), rabbit anti-PE (Biogenesis, UK), and Cy3-conjugated goat anti-rabbit (Jackson Immunoresearch Laboratories, West Grove, PA). For each fluorochrome label, negative-control antibodies were included. Fluoresence was analyzed using a Leica TCS SP (Leica Microsystems, Heidelberg, Germany) confocal system, equipped with an Ar/Kr laser combination.
Statistics
Data are provided as mean and SEM. The Mann-Whitney U-test and the Wilcoxon test were used where appropriate (SPSS for Windows, version 7.5). A double-sided P< 0.05 was considered to represent a significant difference.
| RESULTS |
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To determine the localization of these CD4+/CD45RA cells in the intestinal mucosa, cryostat sections of IBD patients were stained for CD45RA and prepared for confocal laser-scanning microscopy (Fig. 2 ). In IBD patients, CD45RA-positive cells were found in the lamina propria and in follicular structures.
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, IL-10, TNF-
, and IL-4 was determined (Fig. 3
). CD4+CD45RBlow T cells of normal controls produced fivefold more IL-10 than CD4+CD45RBhigh T cells (330.5 pg/ml±42.1 and 65.9 pg/ml±29.1, respectively). Furthermore, IL-4 production was significantly increased in CD4+CD45RBlow T cells (952.7 pg/ml±187.8 vs. 226.4 pg/ml±65.9 in CD4+CD45RBhigh T cells). In contrast, CD4+CD45RBhigh T cells produced more TNF-
(1122.3 pg/ml±198.1 and 2617.9 pg/ml±482.6). Both CD45RB subpopulations produced large amounts of IFN-
(P=0.064; 6718.0 pg/ml±1761.3 and 11981.6 pg/ml±3439.4).
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production of peripheral blood CD4+CD45RBhigh and CD4+CD45RBlow T cells was significantly reduced in CD patients compared with normal controls. In addition, the IFN-
production of CD4+CD45RBhigh cells of UC patients was significantly decreased. There was a trend toward higher production of IL-4 in CD patients (P=0.083), whereas in UC patients, the IL-4 production was significantly decreased (398.1 pg/ml±116.2 in CD and 162.1 pg/ml±78.8 in UC). No differences in TNF-
production were found among the three patient groups. The lymphocytes isolated from the gut of UC and CD patients demonstrated an enhanced CD69, CD134, CD44, and human leukocyte antigen-DR expression compared with control lymphocytes (results not shown), indicating an activated phenotype. This did not result in an enhanced, spontaneous cytokine secretion, as in the absence of CD3 and CD28, these cells did not secrete detectable levels of cytokines.
Cytokine profile of CD45RB gut-derived T cells
Cells were isolated from surgical resection specimen and sorted for the expression of the CD4+CD45RBhigh and CD4+CD45RBlow T cells. After sorting, the cells were stimulated for 72 h by anti-CD3/anti-CD28 double-stimulation, and the production of IFN-
, IL-10, TNF-
, and IL-4 was determined (Fig. 4
). The results were similar to those found in peripheral blood. CD4+CD45RBlow T cells produced more IL-10 and less TNF-
as compared with the CD4+CD45RBhigh subgroup. CD4CD45RBhigh T cells isolated from a normal, control patient produced very little. TNF-
(CD4+CD45RBlow 48.4 pg/ml and CD4+CD45RBhigh 320.4 pg/ml in controls). CD4+CD45RBlow T cells from CD patients produced 504.0 ± 226.1 pg/ml and CD4+CD45RBhigh 1933 ± 1128 pg/ml. In contrast to the low TNF-
production, control-derived cells produced high amounts of IL-10 compared with cells derived from CD patients. Control CD4+CD45RBlow T cells produced 691.3 pg/ml, as compared with 219.0 ± 73.8 pg/ml in CD patients. The CD4+CD45RBhigh and CD4+CD45RBlow subgroups produced similar amounts of IFN-
(mean production in CD: 5051±2002 pg/ml in CD45RBhigh and 4444±1419 pg/ml in CD45RBlow).
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| DISCUSSION |
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The cytokine profile differs from CD45RBhigh and CD45RBlow. The same profile was found in intestines and peripheral blood, independent of CD45RA or CD45RO expression; thus, the level of CD45RB expression may be more important than that of CD45RA or CD45RO.
In the peripheral blood of CD or UC patients and normal controls, all CD4+ CD45RBhigh T cells were CD45RA-positive, and CD4+ CD45RBlow T cells were CD45RO-positive, which is in agreement with previous reports [7 , 8 ]. Analysis of cells derived from the intestines revealed that in normal controls, the majority of the CD45RBlow and CD45RBhigh cells of control appeared to be memory cells (CD45RO+). However, in IBD patients, a significant part of the CD4+CD45RBhigh T cells were also CD45RA+, and even a higher percentage was found in UC compared with CD. Further studies will be needed to elucidate the reason why and how these naïve cells migrate to the gut mucosa in IBD patients. The preferred presence of memory cells in the gut observed in this study is in concordance with the finding that T lymphocytes within the synovial compartment of rheumatoid arthritis patients are almost exclusively CD45RO+ [13 ].
CD45RBhigh cells switch to CD45RBlow within the tissue [13 , 15 , 16 ], and when CD45RBhigh cells become CD45RBlow, the capacity to produce IL-2 is significantly reduced. The CD45RBlow cells will undergo apoptosis as a result of the loss of IL-2 [17 , 18 ]. This apoptotic process is mediated by a gradual loss of Bcl-2 and gain of CD95 [9 , 19 ]. One possible explanation for the lower percentage of CD4+CD45RBhigh T cells in CD compared with UC is that the mechanism that controls T lymphocyte activation and survival probably differs. In CD, but not in UC, lamina propria T lymphocytes are less sensitive to apoptosis as a result of a change in the Bax/Bcl-2 ratio [20 , 21 ]. Our data suggest that this resistance to apoptosis in CD is not caused by a defective switch from CD45RBhigh to CD45RBlow and probably is a result of events further downstream.
Sorting experiments further emphasized the functional significance of the CD45RBhigh and CD45RBlow expression in human intestinal inflammation. Peripheral blood and intestinal T cells were sorted for CD45RB expression, and subsequently, the cytokine pattern was analyzed. In peripheral blood and intestinal cells, different cytokine profiles were observed between CD4+CD45RBlow and CD4+CD45RBhigh. CD4+CD45RBlow cells produce high amounts of IL-4 and IL-10, whereas the CD4+CD45RBhigh T cells produce high amounts of TNF-
. The markedly different cytokine profile of the CD45 subsets is reminiscent of analog mouse T lymphocyte subsets. In the mouse transfer model of colitis, the CD45RBlow subset protects against development of colitis, which is mediated by high production of IL-10 [22
]. We now demonstrate that human CD4+CD45RBlow T cells produce significantly more IL-10 than CD4+CD45RBhigh T cells. It is interesting that in our study, the CD4+CD45RBlow subset from IBD patients produced significantly less IL-10, which has an immune-regulatory role in IBD. The pivotal importance of IL-10 as a regulatory cytokine within the mucosal environment was shown in IL-10/ mice, which develop severe colitis [23
]. IL-10 was identified as a differentiation factor for a subset of T lymphocytes, regulatory T lymphocytes (Tr1 cells). These Tr1 cells have immune-suppressive properties and were found to suppress experimental colitis induced by transfer of pathogenic CD4+/CD45RBhigh T cells [24
, 25
]. The source of IL-10 important for the development of regulatory T cells is not defined yet, but special regulatory dendritic cell populations secreting high levels of IL-10 could play a major role [26
27
28
]. Future studies will elucidate their role in IBD.
It is unexpected that CD4+CD45RBlow T cells isolated from UC patients produced low amounts of IL-4 compared with CD patients and controls. However, it was previously reported that IL-5 and not IL-4 plays an important role in UC [29
]. Although it was reported that CD45RBhigh cells produce more IFN-
[15
], we did not observe differences in IFN-
production between CD45RB subsets obtained from controls. However, the IFN-
production by the CD4+CD45RBhigh subset of IBD patients was decreased. Furthermore, the role of IFN-
in intestinal inflammation is controversial, as IFN-
-deficient and IFN-
receptor-deficient mice are susceptible to experimental 2,4,6,-trinitrobenzene sulphonic acid-induced colitis [30
, 31
].
In summary, we here report marked differences in the expression of CD45RBhigh by T lymphocytes present in the inflamed mucosa of patients with CD and UC. The CD45RBhigh and CD45RBlow differentiation could be of clinical importance, as we also observed an important, functional difference between both subgroups, not depending on CD45RA or CD45RO expression. These results indicate that CD45RB could play an important role in the maintenance of the intestinal inflammation by T cell activation.
Received August 25, 2003; revised December 24, 2003; accepted January 28, 2004.
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