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-Chain Rearrangements in Streptococcal Angina and Skin Lesions of Patients with Psoriasis Vulgaris1



* Department of Dermatology, Ludwig-Maximilians-University of Munich, Munich, Germany;
Department of Dermatology, University of Rome "Tor Vergata", Rome, Italy; and
Institute for Molecular Immunology, GSF-Research Center for Environment and Health, Munich, Germany
| Abstract |
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-chain variable region gene (TCRBV) rearrangements, we compared the TCR usage of psoriatic skin lesions, blood, tonsils, and tonsillar T cells fractionated according to the expression of the skin addressin "cutaneous lymphocyte-associated Ag" (CLA). TCRBV-size spectratype analysis of the blood lymphocytes, tonsils, and the CLA-negative tonsillar T cells revealed largely unselected T cell populations. Instead, TCRBV gene families of the psoriatic lesions and skin-homing CLA-positive tonsillar T cells displayed highly restricted spectratypes. Sequencing of TCRBV cDNA identified various clonal TCRBV rearrangements within the psoriatic lesions that indicated Ag-driven T cell expansion. Several of these clonotypes were also detected within the tonsils and, in one of the patients, within the small subset of CLA-positive tonsillar T cells, suggesting that T cells from the same T cell clones were simultaneously present within skin and tonsillar tissue. Because after tonsillectomy psoriasis cleared in all three patients our observations indicate that T cells may connect psoriatic inflammation to streptococcal angina. They suggest that the chronic streptococcal immune stimulus within the tonsils could act as a source for pathogenic T cells in poststreptococcal disorders, and they may help to explain why eliminating this source with tonsillectomy may improve streptococcal-induced sequelae. | Introduction |
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-hemolytic streptococci (Streptococcus pyogenes) may cause several autoimmune disorders in susceptible individuals. Most prominent are acute rheumatic fever and rheumatic heart disease that constitute major causes of cardiovascular mortality worldwide (1). Other sequelae are Sydenhams chorea, poststreptococcal glomerulonephritis (2), and psoriasis vulgaris, which is the most common autoimmune disease of the human skin (3). The majority of guttate-psoriasis patients and a smaller fraction of chronic-plaque psoriasis patients experience first disease onset or relapses in direct association with streptococcal tonsillitis (4, 5, 6, 7, 8, 9, 10). Although the close link between infection with S. pyogenes and the poststreptococcal sequelae is well established, the precise pathogenetic mechanisms of this association remain elusive. A common hypothesis proposes that streptococcal infection may trigger a cross-reactive autoimmune response due to epitopes shared between proteins of pathogen and host (11).
In rheumatic heart disease and in psoriasis, T cells are apparently the ultimate effectors of inflammation (11, 12, 13, 14). In both disorders, the tonsils are the privileged site for the triggering streptococcal infection (2, 9). This indicates an intimate relationship between the infected tonsils on the one and the subsequent pathogenic immune reaction in contrast, and it suggests that a T cell-mediated immune response raised in the tonsils may subsequently become reactivated within the target organ of autoimmunity, i.e., the heart or the skin.
Proof of identical T cell clones as represented by defined TCR rearrangements within the tonsils and at the site of the ensuing autoimmune inflammation would strongly support this concept. To test this assumption we compared the TCR
-chain variable region gene (TCRBV)3 usage in skin lesions, blood, tonsils, and fractionated tonsillar T cells of three psoriasis patients who had undergone tonsillectomy because their onset of psoriasis and subsequent flares were closely linked to recurrent episodes of streptococcal sore throat. For this purpose, the TCR
-chain repertoire was amplified by PCR using 26 different TCRBV gene-specific primer pairs together with a dye-labeled TCR
-chain constant region gene (TCRBC)-specific primer. The PCR products covered the CDR3 which carries the Ag specificity of the TCR
-chain and differs in length according to the particular TCR-VDJ rearrangement (15). Fragment lengths analysis of the amplified TCRBV rearrangements on a genetic sequencer yields spectratypes with peaks spaced by three nucleotides, where each peak represents TCR
-chain rearrangements of the same length (16). A restricted usage of TCRBV rearrangements with a particular length of the CDR3 may denote clonal T cell expansions. The cDNA of TCRBV gene families with such evidence for clonal T cell selection within the psoriatic skin lesions was cloned and sequenced, and the TCR clonotypes identified by these means were then traced in the corresponding blood and tonsil samples. Molecular tracking of particular T cells by TCR analysis has been used as a powerful tool to dissect the pathomechanism of autoimmune diseases (17, 18, 19, 20). By this approach, we now obtained first evidence that the skin-associated lesional psoriatic T cell clones may be simultaneously present within the tonsils of patients with streptococcal-induced psoriasis. Because all three patients experienced a lasting remission of their psoriasis following tonsillectomy our data propose that T cells could represent a functional link between streptococcal angina and psoriasis. They furthermore may help to explain why eliminating this source of the pathogenic T cells by tonsillectomy may improve the course of the poststreptococcal sequelae.
| Materials and Methods |
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Three patients with histologically proven psoriasis voluntarily participated in the study which was approved by the local ethics committee. They gave written informed consent. Streptococcal infection was assessed during acute flares of tonsillitis by pharyngeal swabbing and standard methods of bacterial isolation, and by determination of anti-streptolysin O (ASLO) and anti-deoxyribonuclease B (DNase-B) serum-Ab titers (normal range <200 IU/ml each). Lesional skin biopsies and blood samples were obtained on the same day. Tonsillectomy was performed within 1 wk after the skin biopsy. The need for tonsillectomy had already been determined by otorhinolaryngology. After tonsillectomy, patients were followed for more than three years. The last control of disease activity was performed before the submission of the manuscript. Psoriasis severity was determined by the psoriasis area and severity index (PASI), which is a widely used scoring system to assess psoriasis severity in clinical trials (21).
Tissue specimens
PBL were prepared from heparinized venous blood by Ficoll density-gradient centrifugation. For the preparation of RNA PBL, skin biopsies and tonsillar tissue fragments were minced in guanidinium isothiocyanate buffer using a tissue homogenizer essentially as described previously (22, 23, 24).
To obtain single-cell suspensions, small pieces of the tonsils were repeatedly passed through a fine steel mesh using a plunger. The suspension was broken into single cells by repeatedly aspirating it through a fine needle using a syringe.
Sorting of tonsillar T cells
Tonsillar T cells were stained with a PE-labeled monoclonal CD3 Ab (V5T-CD03.05) and a FITC-conjugated mAb specific for the cutaneous lymphocyte-associated Ag (CLA) (HECA-452) (all from BD Biosciences). FACS analysis and sorting of 1 x 107 tonsillar T cells were performed on a Moflo modular flow cytometer (DakoCytomation).
Preparation of cDNA and analysis of the TCRBV repertoire by spectratyping
Extraction of RNA, preparation of cDNA, and amplification of the TCRBV gene repertoire have been described previously (22, 23, 24). For TCRBV gene repertoire analysis, cDNA was amplified using a common 6-FAM-labeled TCRBC 3' primer in conjunction with each one of 26 different 5' TCRBV gene family primers. cDNA was amplified for 35 PCR cycles as described. After adding a standard size marker (500 TAMRA; Applied Biosystems), cDNA-fragment length analysis was performed using an ABI Prism 310 Genetic Analyzer and GeneScan Analysis Software 3.1 and Sequencing Analysis Software 3.4 according to the manufacturers protocol (Applied Biosystems).
Interpretation of spectratypes
Due to the recombination events during TCR generation, the length of the TCR amplicons varies. In unselected T cell populations, CDR3-length analysis produces
510 identifiable peaks spaced by three nucleotides, with fluorescence intensity following a quasi-Gaussian distribution (25, 26). Each peak represents TCR rearrangements with an identical number of coding nucleotides (16).
The spectratype patterns were compared with each other visually. A regular spectratype profile was defined as having an approximate Gaussian bell-shaped distribution, showing a largely symmetrical profile with the highest fluorescence intensity in the middle. If discrete peaks differed from the Gaussian profile, or if particular peaks were missing the spectratype was defined as skewed. Skewing was interpreted as a selection of TCRBV gene rearrangements of a particular length that suggested clonal TCR rearrangements (16).
Cloning and sequencing of PCR products
Cloning of PCR products of lesional psoriatic TCRBV gene families was done by TA cloning (TA Cloning kit dual promoter, using the pCRII vector in One Shot TOP10F competent cells; Invitrogen Life Technologies) according to the manufacturers protocol. Negative control reactions without cDNA were set up with each primer pair.
Plasmid DNA was sequenced using the ABI BigDye terminator cycle sequencing kit and an ABI Prism 310 genetic analyzer according to the manufacturers advice (Applied Biosystems). In the manuscript, TCR rearrangements are given as deduced amino acid sequence of the CDR3. Repetitive TCR rearrangements were defined as clonotypes.
For the select amplification and sequencing of the clonal psoriatic TCRBV3 and BV13S2 rearrangements of patient 1, the following primer pairs were designed: BV3, 5'-C AGC AGT TCG TCC GGG AC-3'; BJ1.5, 5'-GAG TCG AGT CCC ATC ACC-3'; BV13S2, 5'-GCC AGC TCC AGG AGG GAC-3'; BJ 2.2, 5'-CAG CCT AGA GCC TTC TCC-3'.
| Results |
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Three patients with chronic plaque-psoriasis were included into the study (Table I). They had a history of treatment-refractory psoriasis of 1.5, 6, or 10 years, and onset and subsequent flares of their psoriasis had been closely related to recurrent episodes of streptococcal angina. All three patients had streptococcal colonization of the tonsils proven by bacterial cultures and elevated titers of anti-streptococcal serum Abs. Because of the clinically obvious link between streptococcal sore throat and psoriasis flares the patients underwent tonsillectomy. The severity of psoriasis at the time of tonsillectomy was determined by the PASI that ranges from 0 (no psoriasis) to 72 (mathematical maximum) (21). Patient 1 had a PASI of 17, patient 2 of 11.4, and patient 3 of 22.8 which is equivalent to moderate to severe psoriasis. In all three patients, tonsillectomy was followed by a long-term remission of psoriasis with a complete clearance of skin symptoms now exceeding 3 years. This obvious correlation between removal of the tonsils and recovery from psoriasis supported that the streptococcal angina had acted as a trigger for psoriasis in these patients, and it confirmed former observations that tonsillectomy may improve the course of streptococcal-driven psoriasis (27, 28, 29).
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Psoriatic skin lesion but not blood or tonsils show a highly restricted TCR usage
Several recent studies have demonstrated that psoriatic inflammation is promoted by a highly conserved clonal T cell response (22, 23, 30, 31). We therefore sought to examine the suspected relationship between streptococcal angina and psoriatic inflammation on the level of T cells. To identify the disease-related T cell clones within the psoriatic skin lesions of our patients, we determined the TCR usage of the lesional psoriatic biopsies by
-chain CDR3-length spectratype analysis and compared it to the TCR spectratypes of the blood lymphocytes and tonsils. For this purpose, TCRBV cDNA was amplified from the different specimens by PCR using TCRBV gene-specific primer pairs. The fragment length of the amplicons was analyzed on a genetic sequencer.
In all three patients, PBL showed a predominance of quasi-Gaussian repertoire
-chain lengths in most TCRBV families that reflected largely unselected T cell populations. In general, the tonsillar spectratypes showed similar numbers of peaks as the corresponding blood spectratypes. Only occasionally did they deviate from the Gaussian distribution of TCR lengths or from the blood profiles (Figs. 13).
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Sequencing identifies clonal TCRBV gene rearrangements in the psoriatic skin lesions that are simultaneously present within the tonsils
TCRBV gene spectratypes with a particularly strong evidence for clonal T cell expansion within the psoriatic skin lesions were chosen for molecular analysis of the TCR rearrangements. They were TCRBV3 (patients 1 and 3), BV13S2 (patients 13), and BV21 (patient 3) (Figs. 1A, 2A, and 3A). cDNA of these TCRBV gene families was amplified from the skin lesions and the corresponding blood and tonsil samples, randomly cloned and sequenced.
In patient 1, nucleotide-sequence analysis revealed that the lesional psoriatic TCRBV3 rearrangements (Table II) were dominated by a particular clonotype (SSGTGY, Table II), which represented 12 of 13 analyzed TCR sequences. This particular TCR rearrangement was detected twice among 40 tonsillar TCRBV3 rearrangements, but not among 45 polyclonal blood rearrangements. The lesional psoriatic BV13S2 rearrangements of patient 1 contained two major clonotypes, QH (54 of 79 rearrangements) and SRRDMN (15 of 79). The latter was identified 11 times in 77 otherwise nonrepetitive tonsillar BV13S2 rearrangements, but not in 56 polyclonal blood BV13S2 rearrangements (Table II). One particular TCRBV13S2 rearrangement was identified each once in blood and tonsils while it was not detected with the skin lesion.
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TCRBV3, BV13S2, and BV21 rearrangements from psoriatic skin lesions of patient 3 were less clonal. This corresponded to broader spectratypes, with more peaks present than in the skin spectratypes of the other patients, but still less than in the corresponding blood sample or tonsil (Fig. 3A). All three TCRBV gene families contained TCR rearrangements that were also identified within the tonsils, but not in the blood (Table II), while TCR rearrangements in blood and tonsils were completely different.
Thus, as suggested by the TCR spectratypes, sequencing of TCR
-chain rearrangements identified clonally expanded TCR rearrangements in the skin lesion of the three patients. Most interestingly, several of these TCR rearrangements were also observed within the tonsils. Therefore, our data suggest that T cells belonging to the same T cell clones may simultaneously have been present in psoriatic skin lesions and tonsils, while they were absent from the corresponding blood samples. Instead, according to the molecular analysis of TCR rearrangements TCR usages in blood and skin or blood and tonsils were largely exclusive.
Skin homing tonsillar T cells have skewed TCR repertoires and may contain the lesional psoriatic T cell clones
A T cell dependent relationship between streptococcal angina and psoriatic skin inflammation would require that the tonsillar T cells are capable of entering the skin and express particular skin homing receptors, namely the CLA (32). In psoriasis patients CLA-positive T lymphocytes preferentially migrate to the skin (33). Therefore, we wondered whether the tonsils of the psoriasis patients contained T cells expressing this skin-selective homing receptor, whether these CLA-positive T cells differed in their TCR usage from the CLA-negative tonsillar T cells, and whether within the tonsils the lesional psoriatic clonotypes might be selectively assigned to the fraction of CLA-positive tonsillar T cells.
For this purpose, single-cell suspensions were prepared from pieces of the tonsils, stained with fluorescent CD3 and CLA mAbs and sorted into CLA-positive and CLA-negative T cell populations by FACS.
In the three patients, a small fraction of 4.4, 4.5, or 5% of the tonsillar T cells expressed the CLA molecule (Table I). The sorted fractions were subjected to TCR spectratyping. Although the spectratypes of the CLA-negative T cells largely resembled those of the unfractionated tonsillar T cells, the TCRBV gene families of the CLA-positive T cells showed highly restricted spectratypes that usually were dominated by only a few peaks (Figs. 13). This indicated that other than the CLA-negative T cells, the CLA-positive T cells were subjected to a profound T cell selection pressure within the tonsils.
In patient 1, the TCRBV3 and BV13S2 spectratypes of the CLA-positive tonsillar T cells displayed particular evident overlaps with the corresponding lesional psoriatic spectratype (Fig. 1A). Therefore, this patient was exemplarily chosen to examine whether the clonal TCRBV3 and BV13S2 rearrangements of the psoriatic skin lesions might be identified within the fraction of CLA-positive tonsillar T cells. To increase the sensitivity of the assay and to corroborate an exclusive assignment to either the CLA-positive or CLA-negative T cell subset, we designed PCR primer pairs specific for the TCRBV-BJ gene recombination. With this approach, both the TCRBV3 (SSGTGY) and the BV13S2 rearrangement (SRRDMN) could be amplified from the CLA-positive tonsillar T cell fraction, while they were definitely absent from the CLA-negative T cells (Table II). These findings suggest that, within the tonsils, the lesional psoriatic T cell clones may belong to the CLA-positive T cell fraction and represent skin-homing T cells.
| Discussion |
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Several aspects of our results may contribute to the understanding of the autoimmune pathomechanisms in streptococcal-induced psoriasis and other T cell-mediated poststreptococcal disorders. Spectratyping and sequence analysis of TCR
-chain cDNA confirmed by the identification of repetitive TCRBV gene rearrangements that the lesional psoriatic immune response is dominated by clonal T cell expansions. Interestingly, several of these TCRBV gene families, namely TCRBV2, 3, 6, 9, and 13S1, had already been identified in former studies to contain disease-relevant T cell clones (22, 24, 30). The lesional psoriatic TCR clonotypes stood clearly out from the otherwise largely polyclonal TCR distributions in blood and tonsils, emphasizing Ag-driven T cell stimulation in the skin of our patients. Thus, psoriasis seems to behave like other T cell-mediated autoimmune disorders for which it is well established that, following activation by Ags, the pathogenic T cells use a limited number of TCR chains in the target organ (35).
By tracking the lesional psoriatic TCR rearrangements in blood and tonsils, our data now suggest for the first time that the lesional psoriatic T cell clones may simultaneously be present within the tonsils of patients whose psoriasis is driven by streptococcal angina. Several of the lesional TCR
-chain clonotypes were identified among the tonsillar TCRBV gene rearrangements where they represented up to 14% of the rearrangements analyzed, while they were not detected in the corresponding blood sample. This is particularly remarkable because diversity is one of the fundamental principles in the immune system and is achieved by the formation of an enormously high number of structurally different TCR molecules (15). Because thymocytes undergo proliferation between
-chain and
-chain rearrangement it would, however, be possible that the same TCR
-chain combines with different
-chains and thus belongs to different T cell clones (36, 37). Still, the simultaneous selection of several TCRBV gene rearrangements within both psoriatic skin lesions and tonsils, their obvious absence from blood, as well as the long-term remission of psoriasis after tonsillectomy support that the identical TCRBV gene rearrangements in psoriatic skin lesions and tonsils may actually reflect the occurrence of T cells from the same T cell clones at these two distinct sites.
If we assume that, like in other autoimmune disorders, the clonal T cell expansion is a consequence of Ag-specific stimulation, then our data suggest that similar antigenic stimuli could have mediated a selection of T cells from the same pathogenic T cell clones within the psoriatic skin lesions and the tonsils. Because of the lack of an appropriate animal model of infection-induced psoriasis, it will be difficult to examine whether the T cells actually spread from the angina to the integument. Because the streptococcal trigger precedes psoriasis onset by at least 1014 days, we would speculate that the pathogenic psoriatic T cells become activated first in the tonsils and then enter into the skin. A similar sequence of events in the induction of organ-specific autoimmunity has recently been demonstrated in an animal model of experimental autoimmune encephalitis (EAE). As shown by CDR3-spectratype analysis and TCR sequencing, induction of EAE by immunization with myelin basic protein in Lewis rats induced expansion of the pathogenic T cell clone first in the lymphoid organs from where the activated encephalitogenic T cells then disseminated and reached the spinal cord before the onset of EAE (38).
To enter the skin, T cells require skin-homing receptors such as CLA. A special relevance of our findings for streptococcal-induced psoriatic skin inflammation is therefore emphasized by the observation that in patient 1 the clonal psoriatic TCR
-chain rearrangements could be selectively assigned to the small subset of CLA-positive tonsillar T cells. Using primer pairs specific for the rearrangement site, the lesional psoriatic TCR clonotypes could only be amplified from the fraction of the sorted CLA-positive but not the CLA-negative tonsillar T cell fraction. Thus, within the tonsils the lesional psoriatic T cell clones may represent skin-homing T cells.
As determined by FACS analysis of cell suspensions prepared from the tonsils of the three patients, CLA was expressed by 45% of the tonsillar T cells. This frequency was lower than in tonsils of patients with palmoplantar pustulosis (PPP), another inflammatory skin disease found in direct association with streptococcal angina. In these patients, between 7.9 and 18.9% of the tonsillar T cells expressed CLA, while non-PPP patients had a frequency of 4.24.6 CLA-positive tonsillar T cells (39). In the PPP patients, CLA expression on T cells could be experimentally reproduced by stimulation of tonsillar T cells with crude streptococcal lysates via the induction of TGF-
. It is well known that CLA may be induced on memory T cells by various stimuli such as Th1-polarizing cytokines or streptococcal or staphylococcal superantigens (40, 41). Accordingly, streptococcal angina might prime and select tonsillar T cells to migrate into the skin either by the particular cytokine environment of infection-induced inflammation, or by streptococcal superantigens, as suggested recently (42). Superantigens would induce a polyclonal expansion of T cells sharing particular TCRBV regions. Because the clonal representation of some of the lesional psoriatic TCR clonotypes within the tonsils reached up to 14% of the analyzed rearrangements a relevant role of superantigens in streptococcal angina appears unlikely. Furthermore, unlike the CLA-negative tonsillar T cell fraction the CLA-positive tonsillar T cells displayed highly skewed TCR spectratypes. None of them had a Gaussian-like polyclonal distribution but all of them showed restricted fragment length distributions compatible with oligoclonal T cell expansions. Thus, within the tonsils the CLA-positive T cells were apparently subjected to an Ag-specific selection rather than superantigen-mediated stimulation.
According to these observations, T cells may represent the functional link between streptococcal tonsillitis and psoriatic inflammation. They suggest that streptococcal angina might prime and select tonsillar T cells to migrate into the skin, where they become reactivated to expand clonally and promote the formation of psoriatic skin lesions. This assumption is strongly supported by the course of psoriasis after tonsillectomy. Despite a history of permanently active, recalcitrant psoriasis of 1.5, 6, or 10 years, tonsillectomy was followed by a long-term remission of psoriatic skin inflammation >3 years in all three patients. A similar beneficial role of tonsillectomy on the course of psoriasis has been documented in several case reports and retrospective or prospective clinical trials (27, 28, 29). Furthermore, a patient with poststreptococcal arthritis who improved after tonsillectomy had identical TCR rearrangements in tonsils and inflamed joints (43). Thus, it seems that tonsillectomy may cut off the supply for the pathogenic psoriatic T cell clones when streptococcal angina is the triggering event. Our results therefore support that streptococcal angina may serve as a continuous source of the pathogenic psoriatic T cells in streptococcal-induced psoriasis, and they provide a factual basis for tonsillectomy as a therapeutic rationale in autoimmune disorders following streptococcal angina.
Taken together, our findings shed light on the pathogenetic relationship between streptococcal angina and autoimmune sequelae. They propose that in T cell-mediated poststreptococcal disorders, the ultimate effectors of autoimmune inflammation may be derived from the tonsils, and they explain why this link may be more accessible to treatment than the streptococcal infection itself. Accordingly, they might affect both the understanding and handling of streptococcal-induced autoimmunity.
| Acknowledgments |
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| Disclosures |
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| Footnotes |
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1 This work was supported by the Sonderforschungsbereich 571 of the Deutsche Forschungsgemeinschaft. L.D. was the recipient of a grant of the German Academic Exchange Service. ![]()
2 Address correspondence and reprint requests to Dr. Joerg C. Prinz, Department of Dermatology, University of Munich, Frauenlobstrasse 9-11, D-80337 Munich, Germany. E-mail address: joerg.prinz{at}med.uni-muenchen.de ![]()
3 Abbreviations used in this paper: TCRBV, TCR
-chain variable region gene; TCRBC, TCR
-chain constant region gene; ASLO, anti-streptolysin O; DNase B, antideoxyribonuclease B; PASI, psoriasis area and severity index; CLA, cutaneous lymphocyte-associated Ag; PPP, palmoplantar pustulosis; EAE, experimental autoimmune encephalitis. ![]()
Received for publication November 29, 2005. Accepted for publication March 14, 2006.
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