Nikos Darzentas

Masaryk University, Brno, South Moravian Region, Czech Republic

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Publications (51)265.59 Total impact

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    ABSTRACT: Clonal CD8(+)/T-cell receptor (TCR)αβ(+) T-cell large granular lymphocyte (T-LGL) proliferations constitute the most common subtype of T-LGL leukemia. Although the etiology of T-LGL leukemia is largely unknown, it has been hypothesized that chronic antigenic stimulation contributes to the pathogenesis of this disorder. In the present study, we explored the association between expanded TCR-Vβ and TCR-Vα clonotypes in a cohort of 26 CD8(+)/TCRαβ(+) T-LGL leukemia patients, in conjunction with the HLA-ABC genotype, to find indications for common antigenic stimuli. In addition, we applied purpose-built sophisticated computational tools for an in-depth evaluation of clustering of TCRβ (TCRB) complementarity determining region 3 (CDR3) amino-acid LGL clonotypes. We observed a lack of clear TCRA and TCRB CDR3 homology in CD8(+)/TCRαβ(+) T-LGL, with only low level similarity between small numbers of cases. This is in strong contrast to the homology that is seen in CD4(+)/TCRαβ(+) T-LGL and TCRγδ(+) T-LGL and thus underlines the idea that the LGL types have different etiopathogenesis. The heterogeneity of clonal CD8(+)/TCRαβ(+) T-LGL proliferations might in fact suggest that multiple pathogens or autoantigens are involved.
    Blood Cancer Journal 01/2014; 4:e172. · 1.40 Impact Factor
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    ABSTRACT: IgG-switched chronic lymphocytic leukemia (G-CLL) is a rare variant of CLL, whose origin and ontogenetic relationship to the common IgM/IgD (MD-CLL) variant remains undefined. Here we sought for clues regarding the ontogeny of G-CLL versus MD-CLL by profiling the relevant IG gene repertoires. Using purpose-built bioinformatics methods, we performed detailed immunogenetic profiling of a multinational CLL cohort comprising 1256 cases, of which 1087 and 169 expressed IG mu/delta and gamma heavy chains, respectively. G-CLL has a highly skewed IG gene repertoire that is distinct from MD-CLL, especially in terms of: (i) overuse of the IGHV4-34 and IGHV4-39 genes; and, (ii) differential somatic hypermutation (SHM) load. Repertoire differences held also when comparing subgroups with similar SHM status and were mainly attributed to the exclusive representation in G-CLL of two major subsets with quasi-identical (stereotyped) B-cell receptors. These subsets, namely #4 (IGHV4-34/IGKV2-30) and #8 (IGHV4-39/IGKV1(D)-39), were found to display sharply contrasting SHM and clinical behavior. G-CLL exhibits an overall distinct immunogenetic signature from MD-CLL, prompting speculations about distinct ontogenetic derivation and/or immune triggering. The reasons underlying the differential regulation of SHM among G-CLL cases remain to be elucidated.
    Clinical Cancer Research 11/2013; · 7.84 Impact Factor
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    ABSTRACT: While signaling through the B cell receptor (BcR) facilitates B cell development and maintenance, it also carries intertwined risks for the development of lymphomas since malignant B cells can exploit these pathways in order to trigger and fuel clonal expansion. This corruption of the normal B cell response to antigens, leading to sustained BcR signaling, has given great impulse to investigate in detail the role of antigen in lymphomas. Suffice it to conclude from such studies, largely immunogenetics based, that the evidence implicating antigens (exogenous or self) in lymphoma development is substantial and that lymphomagenesis is functionally driven and dynamic, rather than a simple stochastic process. As the paradigm of antigen-driven lymphoma evolves, further investigation will be paramount to the identification of the inciting agent(s) that may be responsible for immunoproliferative neoplasms and also for the development of therapeutic agents targeting effectors of the BcR signaling pathway.
    Seminars in Cancer Biology 08/2013; · 7.44 Impact Factor
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    ABSTRACT: Chronic lymphocytic leukemia (CLL) patients assigned to stereotyped subset #4 possess distinctive patterns of intraclonal diversification (ID) within their immunoglobulin (IG) genes. Though highly indicative of an ongoing response to antigen(s), the critical question concerning the precise timing of antigen involvement is unresolved. Hence, we conducted a large-scale longitudinal study of 8 subset #4 cases totaling 511 and 398 subcloned IG heavy and kappa sequences. Importantly, we could establish a hierarchical pattern of subclonal evolution, thus revealing which somatic hypermutations were negatively or positively selected. In addition, distinct clusters of subcloned sequences with cluster-specific mutational profiles were observed initially, however at later time-points the minor cluster had often disappeared and hence been selected against. Despite the high intensity of ID, it was remarkable that certain residues remained essentially unaltered. These novel findings strongly support a role for persistent antigen stimulation in the clonal evolution of CLL subset #4.
    Molecular Medicine 08/2013; · 4.47 Impact Factor
  • Nikos Darzentas, Kostas Stamatopoulos
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    ABSTRACT: Roughly 30% of patients with chronic lymphocytic leukemia (CLL) carry immunoglobulin receptors with highly similar primary sequences. Highly similar, quasi-identical immunoglobulins are termed stereotyped. Patients with CLL can be assigned to different subsets expressing different types of stereotyped immunoglobulin receptors. Reliable identification of stereotypy may assist in the molecular classification of CLL and thus better-guided, compartmentalized research. In several major subsets, stereotypy extends from shared primary sequences to shared clinicobiological features and outcome. Reliable identification of stereotypy in CLL may pave the way for tailored treatment strategies applicable to each major stereotyped subset.
    Hematology/oncology clinics of North America 04/2013; 27(2):237-50. · 2.05 Impact Factor
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    Alexandros Bousios, Nikos Darzentas
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    ABSTRACT: Sireviruses are an ancient and plant-specific LTR retrotransposon genus. They possess a unique genome structure that is characterized by a plethora of highly conserved sequence motifs in key domains of the non-coding genome, and often, by the presence of an envelope-like gene. Recently, their crucial role in the organization of the maize genome, where Sireviruses occupy approximately 21% of its nuclear content, was revealed, followed by an analysis of their distribution across the plant kingdom. It is now suggested that Sireviruses have been a major mediator of the evolution of many plant genomes. However, the name 'Sirevirus' has caused confusion in the scientific community in regards to their classification within the LTR retrotransposon order and their relationship with viruses - a situation that is not unique to Sireviruses, but also affects other LTR retrotransposon genera. Here, we clarify the phylogenetic position of Sireviruses as typical LTR retrotransposons of the Copia superfamily and explain that the confusion stems from the discrepancy in the categorization of LTR retrotransposons by the two main classification systems: the International Committee on the Taxonomy of Viruses (ICTV) system and the unified classification system for eukaryotic transposable elements. While the name 'Sirevirus' has been given by ICTV, we show that the transposable element system, which is more suitable for eukaryotic genome studies, lacks an appropriate taxonomic level for describing them. We urge for this inconsistency to be addressed. Finally, we provide data suggesting that of the three ICTV-proposed genera of the Pseudoviridae (that is, Copia) family, only Sireviruses form a monophyletic group, while the phylogenetic distinction between Pseudoviruses and Hemiviruses is unclear. We conclude that because of their ongoing important contribution to the classification of transposable elements, these schemes need to be frequently revisited and revised - as shown by the example of the Sirevirus LTR retrotransposon genus.
    Mobile DNA. 03/2013; 4(1):9.
  • Nikos Darzentas, Kostas Stamatopoulos
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    ABSTRACT: Recent research has revealed the existence of subsets (clusters) of patients with different types of B-cell lymphomas and leukemias with restricted, "stereotyped" immunoglobulin (IG) variable heavy complementarity-determining region 3 (VH CDR3) sequences within their B cell receptors (BcR), suggesting selection by common epitopes or classes of structurally similar epitopes. BcR stereotypy was initially described in chronic lymphocytic leukemia (CLL), where it constitutes a remarkably frequent feature of the IG repertoire, and subsequently identified in other malignancies, including mantle cell lymphoma and splenic marginal-zone lymphoma. Of note, at least in CLL, emerging evidence indicates that the grouping of cases into distinct clusters with stereotyped BcR is functionally and prognostically relevant. Hence, the reliable identification of BcR stereotypy may assist in the investigation of the nature of the selecting antigens and immune pathways leading to lymphoma development, and also potentially pave the way for tailored treatment strategies applicable to each major stereotyped subset. In this chapter, we provide an overview of BcR stereotypy in human B-cell malignancies, and outline previous and current methodological approaches used for its identification.
    Methods in molecular biology (Clifton, N.J.) 01/2013; 971:135-48. · 1.29 Impact Factor
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    ABSTRACT: Mantle cell lymphoma (MCL) is a heterogeneous disease with most patients following an aggressive clinical course, whereas others having an indolent behavior. We conducted an integrative and multidisciplinary analysis of 177 MCL to determine whether the immunogenetic features of the clonotypic B-cell receptors (BcR) may identify different subsets of tumors. Truly unmutated (100% identity) IGHV genes were found in 24% cases, 40% were minimally/borderline mutated (99.9%-97%), 19% significantly mutated (96.9%-95%), and 17% hypermutated (<95%). Tumors with high or low mutational load used different IGHV genes, and their gene expression profiles were also different for several gene pathways. A gene set enrichment analysis showed that MCL with high and low IGHV mutations were enriched in memory and naive B-cell signatures, respectively. Furthermore, the highly mutated tumors had less genomic complexity, were preferentially SOX11-negative, and showed more frequent nonnodal disease. The best cut-off of germline identity of IGHV genes to predict survival was 97%. Patients with high and low mutational load had significant different outcome with 5-year overall survival (OS) of 59% and 40%, respectively (P = 0.004). Nodal presentation and SOX11 expression also predicted for poor OS. In a multivariate analysis, IGHV gene status and SOX11 expression were independent risk factors. In conclusion, these observations suggest the idea that MCL with mutated IGHV, SOX11-negativity, and nonnodal presentation correspond to a subtype of the disease with more indolent behavior. Cancer Res; 72(20); 5307-16. ©2012 AACR.
    Cancer Research 08/2012; 72(20):5307-5316. · 8.65 Impact Factor
  • Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K 06/2012; · 10.16 Impact Factor
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    ABSTRACT: Sireviruses are an ancient genus of the Copia superfamily of LTR retrotransposons, and the only one that has exclusively proliferated within plant genomes. Based on experimental data and phylogenetic analyses, Sireviruses have successfully infiltrated many branches of the plant kingdom, extensively colonizing the genomes of grass species. Notably, it was recently shown that they have been a major force in the make-up and evolution of the maize genome, where they currently occupy ~21% of the nuclear content and ~90% of the Copia population. It is highly likely, therefore, that their life dynamics have been fundamental in the genome composition and organization of a plethora of plant hosts. To assist studies into their impact on plant genome evolution and also facilitate accurate identification and annotation of transposable elements in sequencing projects, we developed MASiVEdb (Mapping and Analysis of SireVirus Elements Database), a collective and systematic resource of Sireviruses in plants. Taking advantage of the increasing availability of plant genomic sequences, and using an updated version of MASiVE, an algorithm specifically designed to identify Sireviruses based on their highly conserved genome structure, we populated MASiVEdb (http://bat.infspire.org/databases/masivedb/) with data on 16,243 intact Sireviruses (total length >158Mb) discovered in 11 fully-sequenced plant genomes. MASiVEdb is unlike any other transposable element database, providing a multitude of highly curated and detailed information on a specific genus across its hosts, such as complete set of coordinates, insertion age, and an analytical breakdown of the structure and gene complement of each element. All data are readily available through basic and advanced query interfaces, batch retrieval, and downloadable files. A purpose-built system is also offered for detecting and visualizing similarity between user sequences and Sireviruses, as well as for coding domain discovery and phylogenetic analysis. MASiVEdb is currently the most comprehensive directory of Sireviruses, and as such complements other efforts in cataloguing plant transposable elements and elucidating their role in host genome evolution. Such insights will gradually deepen, as we plan to further improve MASiVEdb by phylogenetically mapping Sireviruses into families, by including data on fragments and solo LTRs, and by incorporating elements from newly-released genomes.
    BMC Genomics 04/2012; 13:158. · 4.40 Impact Factor
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    ABSTRACT: Mounting evidence indicates that grouping of chronic lymphocytic leukemia (CLL) into distinct subsets with stereotyped BCRs is functionally and prognostically relevant. However, several issues need revisiting, including the criteria for identification of BCR stereotypy and its actual frequency as well as the identification of "CLL-biased" features in BCR Ig stereotypes. To this end, we examined 7596 Ig VH (IGHV-IGHD-IGHJ) sequences from 7424 CLL patients, 3 times the size of the largest published series, with an updated version of our purpose-built clustering algorithm. We document that CLL may be subdivided into 2 distinct categories: one with stereotyped and the other with nonstereotyped BCRs, at an approximate ratio of 1:2, and provide evidence suggesting a different ontogeny for these 2 categories. We also show that subset-defining sequence patterns in CLL differ from those underlying BCR stereotypy in other B-cell malignancies. Notably, 19 major subsets contained from 20 to 213 sequences each, collectively accounting for 943 sequences or one-eighth of the cohort. Hence, this compartmentalized examination of VH sequences may pave the way toward a molecular classification of CLL with implications for targeted therapeutic interventions, applicable to a significant number of patients assigned to the same subset.
    Blood 03/2012; 119(19):4467-75. · 9.06 Impact Factor
  • Blood. 2012 Mar 13. 03/2012;
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    ABSTRACT: We performed an immunogenetic analysis of 345 IGHV-IGHD-IGHJ rearrangements from 337 cases with primary splenic small B-cell lymphomas of marginal-zone origin. Three immunoglobulin (IG) heavy variable (IGHV) genes accounted for 45.8% of the cases (IGHV1-2, 24.9%; IGHV4-34, 12.8%; IGHV3-23, 8.1%). Particularly for the IGHV1-2 gene, strong biases were evident regarding utilization of different alleles, with 79/86 rearrangements (92%) using allele (*)04. Among cases more stringently classified as splenic marginal-zone lymphoma (SMZL) thanks to the availability of splenic histopathological specimens, the frequency of IGHV1-2(*)04 peaked at 31%. The IGHV1-2(*)04 rearrangements carried significantly longer complementarity-determining region-3 (CDR3) than all other cases and showed biased IGHD gene usage, leading to CDR3s with common motifs. The great majority of analyzed rearrangements (299/345, 86.7%) carried IGHV genes with some impact of somatic hypermutation, from minimal to pronounced. Noticeably, 75/79 (95%) IGHV1-2(*)04 rearrangements were mutated; however, they mostly (56/75 cases; 74.6%) carried few mutations (97-99.9% germline identity) of conservative nature and restricted distribution. These distinctive features of the IG receptors indicate selection by (super)antigenic element(s) in the pathogenesis of SMZL. Furthermore, they raise the possibility that certain SMZL subtypes could derive from progenitor populations adapted to particular antigenic challenges through selection of VH domain specificities, in particular the IGHV1-2(*)04 allele.
    Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K 01/2012; 26(7):1638-46. · 10.16 Impact Factor
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    Food Chemistry 01/2012; · 3.33 Impact Factor
  • Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K 11/2011; 26(5):1127-31. · 10.16 Impact Factor
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    ABSTRACT: Sireviruses are one of the three genera of Copia long terminal repeat (LTR) retrotransposons, exclusive to and highly abundant in plants, and with a unique, among retrotransposons, genome structure. Yet, perhaps due to the few references to the Sirevirus origin of some families, compounded by the difficulty in correctly assigning retrotransposon families into genera, Sireviruses have hardly featured in recent research. As a result, analysis at this key level of classification and details of their colonization and impact on plant genomes are currently lacking. Recently, however, it became possible to accurately assign elements from diverse families to this genus in one step, based on highly conserved sequence motifs. Hence, Sirevirus dynamics in the relatively obese maize genome can now be comprehensively studied. Overall, we identified >10 600 intact and approximately 28 000 degenerate Sirevirus elements from a plethora of families, some brought into the genus for the first time. Sireviruses make up approximately 90% of the Copia population and it is the only genus that has successfully infiltrated the genome, possibly by experiencing intense amplification during the last 600 000 years, while being constantly recycled by host mechanisms. They accumulate in chromosome-distal gene-rich areas, where they insert in between gene islands, mainly in preferred zones within their own genomes. Sirevirus LTRs are heavily methylated, while there is evidence for a palindromic consensus target sequence. This work brings Sireviruses in the spotlight, elucidating their lifestyle and history, and suggesting their crucial role in the current genomic make-up of maize, and possibly other plant hosts.
    The Plant Journal 10/2011; 69(3):475-88. · 6.58 Impact Factor
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    ABSTRACT: We examined 807 productive IGHV-IGHD-IGHJ gene rearrangements from mantle cell lymphoma (MCL) cases, by far the largest series to date. The IGHV gene repertoire was remarkably biased, with IGHV3-21, IGHV4-34, IGHV1-8, and IGHV3-23 accounting for 46.3% of the cohort. Eighty-four of 807 (10.4%) cases, mainly using the IGHV3-21 and IGHV4-34 genes, were found to bear stereotyped heavy complementarity-determining region 3 (VH CDR3) sequences and were placed in 38 clusters. Notably, the MCL stereotypes were distinct from those reported for chronic lymphocytic leukemia. Based on somatic hypermutation (SHM) status, 238/807 sequences (29.5%) carried IGHV genes with 100% germ line identity; the remainder (569/807; 70.5%) exhibited different SHM impact, ranging from minimal (in most cases) to pronounced. Shared replacement mutations across the IGHV gene were identified for certain subgroups, especially those using IGHV3-21, IGHV1-8, and IGHV3-23. Comparison with other entities, in particular CLL, revealed that several of these mutations were "MCL-biased." In conclusion, MCL is characterized by a highly restricted immunoglobulin gene repertoire with stereotyped VH CDR3s and very precise SHM targeting, strongly implying a role for antigen-driven selection of the clonogenic progenitors. Hence, an antigen-driven origin of MCL could be envisaged, at least for subsets of cases.
    Blood 07/2011; 118(11):3088-95. · 9.06 Impact Factor
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    ABSTRACT: PubMed is the most widely used database of biomedical literature. To the detriment of the user though, the ranking of the documents retrieved for a query is not content-based, and important semantic information in the form of assigned Medical Subject Headings (MeSH) terms is not readily presented or productively utilized. The motivation behind this work was the discovery of unanticipated information through the appropriate ranking of MeSH term pairs and, indirectly, documents. Such information can be useful in guiding novel research and following promising trends. A web-based tool, called MeSHy, was developed implementing a mainly statistical algorithm. The algorithm takes into account the frequencies of occurrences, concurrences, and the semantic similarities of MeSH terms in retrieved PubMed documents to create MeSH term pairs. These are then scored and ranked, focusing on their unexpectedly frequent or infrequent occurrences. MeSHy presents results through an online interactive interface facilitating further manipulation through filtering and sorting. The results themselves include the MeSH term pairs, along with MeSH categories, the score, and document IDs, all of which are hyperlinked for convenience. To highlight the applicability of the tool, we report the findings of an expert in the pharmacology field on querying the molecularly-targeted drug imatinib and nutrition-related flavonoids. To the best of our knowledge, MeSHy is the first publicly available tool able to directly provide such a different perspective on the complex nature of published work. IMPLEMENTATION AND AVAILABILITY: Implemented in Perl and served by Apache2 at http://bat.ina.certh.gr/tools/meshy/ with all major browsers supported.
    Journal of Biomedical Informatics 06/2011; 44(6):919-26. · 2.13 Impact Factor
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    ABSTRACT: To further understand flowering and flower organ formation in the monocot crop saffron crocus (Crocus sativus L.), we cloned four MIKC(c) type II MADS-box cDNA sequences of the E-class SEPALLATA3 (SEP3) subfamily designated CsatSEP3a/b/c/c_as as well as the three respective genomic sequences. Sequence analysis showed that cDNA sequences of CsatSEP3 c and c_as are the products of alternative splicing of the CsatSEP3c gene. Bioinformatics analysis with putative orthologous sequences from various plant species suggested that all four cDNA sequences encode for SEP3-like proteins with characteristic motifs and amino acids, and highlighted intriguing sequence features. Phylogenetically, the isolated sequences were closest to the SEP3-like genes from monocots such as Asparagus virgatus, Oryza sativa, Zea mays, and the dicot Arabidopsis SEP3 gene. All four isolated C. sativus sequences were strongly expressed in flowers and in all flower organs: whorl1 tepals, whorl2 tepals, stamens and carpels, but not in leaves. Expression of CsatSEP3a/b/c/c_as cDNAs was compared in wild-type and mutant flowers. Expression of the isolatedCsatSEP3-like genes in whorl1 tepals together with E-class CsatAP1/FUL subfamily and B-class CsatAP3 and CsatPI subfamilies of genes, fits the ABCE "quartet model," an extended form of the original ABC model proposed to explain the homeotic transformation of whorl1 sepals into whorl1 tepals in Liliales and Asparagales plants such as C. sativus. This conclusion was also supported by the interaction of the CsatSEP3b protein with CsatAP1/FUL and CsatAP3 proteins. In contrast, expression of both B-class CsatAP3 and CsatPI genes and the C-class CsatAGAMOUS genes together with E-class CsatSEP3-like genes in carpels, without any phenotypic effects on carpels, raises questions about the role of these gene classes in carpel formation in this non-grass monocot and requires further experimentation. Finally, taking advantage of the size and sequence differences in amplified genomic sequences of the triploid C. sativus and comparing them with the respective sequences from C. tomasii, C. hadriaticus and C. cartwrightianus, three putative wild-type diploid progenitor species, we examined the origin of CsatSEP3a sequence.
    Journal of plant physiology 05/2011; 168(14):1675-84. · 2.50 Impact Factor
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    ABSTRACT: Sézary syndrome (SS) is a cutaneous T-cell lymphoma characterized by erythroderma, lymphadenopathy and malignant clonal T cells in the skin, lymph nodes and peripheral blood. A role for superantigens in the pathogenesis of SS has been postulated before. To investigate a putative involvement of chronic (super-)antigenic stimulation in driving T-cell expansion in SS. Antigenic specificity of the T-cell receptor (TCR) was assayed by molecular analysis of the TCRA (n=11) and TCRB (n=28) genes, followed by detailed in silico analysis. Sequence analysis of clonally rearranged TCRB genes showed over-representation of Vβ8, Vβ13, Vβ17, Vβ21 and Vβ22, and under-representation of Vβ2 and Jβ1.1 when compared with healthy controls. No similarity was detected in amino acid motifs of the complementarity determining region 3 (CDR3). Analysis of TCRA rearrangements showed that there was no common Vα or Jα gene usage, and that TCRA CDR3 amino acid motifs were not highly similar. The lack of clear stereotypic TCRA and TCRB CDR3 amino acid motifs would argue against involvement of a single common antigen in the pathogenesis of SS. Nevertheless, the skewing of Vβ and Jβ gene usage does seem to point to a restricted TCR repertoire, possibly as a result of superantigenic selection prior to neoplastic transformation.
    British Journal of Dermatology 03/2011; 165(1):78-84. · 3.76 Impact Factor

Publication Stats

1k Citations
265.59 Total Impact Points

Institutions

  • 2013
    • Masaryk University
      • Výzkumná skupina Lékařská genomika
      Brno, South Moravian Region, Czech Republic
  • 2008–2013
    • Uppsala University
      • The Rudbeck Laboratory
      Uppsala, Uppsala, Sweden
  • 2012
    • Democritus University of Thrace
      Komotina, East Macedonia and Thrace, Greece
  • 2010
    • The Centre for Research and Technology, Hellas
      Saloníki, Central Macedonia, Greece
  • 2009–2010
    • Aristotle University of Thessaloniki
      • • Department of Genetics, Development and Molecular Biology
      • • School of Biology
      Thessaloníki, Kentriki Makedonia, Greece
  • 2005
    • Belgian Nuclear Research Centre
      Moll, Flanders, Belgium
  • 2003–2005
    • EMBL-EBI
      Cambridge, England, United Kingdom