T-cell Receptor Variable Beta Research Articles

Oligoclonal CD4+CD57+ T-Cell Expansions Contribute to the Imbalanced T-Cell Receptor Repertoire of Rheumatoid Arthritis Patients

AbstractA peculiar feature of rheumatoid arthritis patients is that they carry clonally expanded CD4+ and CD8+ cells in the peripheral blood. While the distortion of the repertoire of CD8+ cells has been ascribed to the increase of CD8+CD57+ large granular lymphocytes, often detected in these patients, the mechanism responsible for the clonal expansion of CD4+ cells remains unexplained. Here, we report that CD4+CD57+ cells, that in healthy individuals represent a small subset of peripheral CD4+ lymphocytes, are significantly expanded in the peripheral blood of a considerable percentage of rheumatoid arthritis patients. Furthermore, the expansion of these lymphocytes appears to correlate with the presence of rheumatoid factor. The molecular analysis of the T-cell receptor variable beta segments expressed by the CD4+CD57+ cells enriched in rheumatoid arthritis patients showed that they use restricted repertoires, that partially overlap with those of their CD4−CD57+ counterpart. The structural feature of the receptor ligand expressed by these cells revealed that their expansion is most likely mediated by strong antigenic pressures. However, since we also found that CD4+CD57+ and CD4−CD57+ cells can share the same clonal specificity, it is likely that their selection is not mediated by conventional major histocompatibility complex restricted mechanisms. Thus, while our data demonstrate that CD4+CD57+ cells play an important role in establishing the imbalance of the CD4+ cell repertoire observed in rheumatoid arthritis patients, they also suggest that these cells have common features with mouse CD4+CD8−NK1.1+/T cells.

On simple repetitive DNA sequences and complex diseases.

Simple repetitive DNA sequences are abundantly interspersed in eukaryote genomes and therefore useful in genome research and genetic fingerprinting in plants, fungi and animals, including man. Recently, simple repeats were also identified in some prokaryotic genomes. Hence the same probes can be applied for multilocus DNA fingerprinting in medically relevant bacteria. Simple repeats including composite dinucleotide microsatellites are differentially represented in different compartments of eukaryote genomes. Expanded triplet blocks in and around certain genes may, for example, cause so-called trinucleotide diseases in man. As a consequence, simple repetitive sequences should also be characterized with respect to their influences on the DNA structure, gene expression, genomic (in)stability and their development on an evolutionary time scale. Here three examples of microsatellites in the human major histocompatibility complex (HLA) are investigated, a (GT)n microsatellite situated 2 kb 5' off the lymphotoxin alpha (LTA) gene, a (GAA)n block in the 5' part of the HLA-F gene and a composite (GT)n(GA)m stretch in the second intron of HLA-DRBl genes. Grossly differing mutation rates are evident in these elements as well as varying linkage disequilibria. The unfolding of these simple repeats in distant human populations is covered including Caucasians, Bushmen and South American Indians. Furthermore, implications of simple repeat neighboring genes are discussed for the multifactorial diseases multiple sclerosis (MS), rheumatoid arthritis (RA) and early onset pauciarticular arthritis (EOPA). Polymorphisms of HLA-DRBl and T cell receptor beta variable (TCRBV) genes confer susceptibility for these autoimmune diseases as demonstrable by intronic simple repeat variability. Microsatellite polymorphisms within the TNF region reveal linkage disequilibria with HLA-DRBl and different promotor alleles of the TNFA gene. Disease associations with TNFA microsatellite alleles are, on the one hand, secondary to associations with HLA-DRBl genes (in MS) or they represent additional risk factors (in RA, EOPA) on the other hand. Evolutionary persistence, various structural conformations and the specific binding of nuclear proteins to several simple repeat sequences refute the preconceptions of biological insignificance for all of these ubiquitously interspersed elements.

Engrafted Maternal T Cells in a Severe Combined Immunodeficiency Patient Express T-Cell Receptor Variable Beta Segments Characterized by a Restricted V-D-J Junctional Diversity

To better understand the peculiar functional behavior of engrafted maternal T cells in a severe combined immunodeficiency (SCID) patient, we characterized, at the molecular level, the T-cell repertoire of a SCID child with a high number of engrafted, mature, activated lymphocytes. We found that, although these transplacentally acquired T cells express a random set of T-cell receptor variable beta (TCRBV) segments, the TCRBV transcripts are characterized by an extremely restricted V-D-J junctional diversity. Only a few cDNA clones were dominant among the TCRBV4+, TCRBV6+, and TCRBV20+ populations in engrafted cells, whereas the same TCRBV chains expressed by the mother's lymphocytes had the expected junctional hetero-geneity. Highly diverse and polyclonal junctions were also expressed by maternal cells activated in mixed lymphocyte reaction by Epstein-Barr virus (EBV)-transformed B lymphocytes from the patient, indicating that the strong clonal selection that characterizes the engrafted cells repertoire is probably not due to allorecognition. Furthermore, we report that the repertoire of the transplacentally acquired lymphocytes is dynamic over time and is characterized by waves of expression and contraction of selected clones, expressing different TCRBV segments. These results help to explain some of the abnormal functional behaviors of engrafted maternal cells and raise new questions regarding the mechanisms responsible for the restricted clonal diversity.

Phenotypic and clonal analysis of T lymphocytes in childhood immune thrombocytopenic purpura

In an attempt to identify and characterize T-lymphocyte immunoregulatory abnormalities in immune thrombocytopenic purpura (ITP), we have performed phenotypic and clonal analysis on peripheral T lymphocytes from 23 children with ITP. Quantitation of lymphocyte subpopulations showed that children with acute ITP had higher numbers of CD45RA+ and lower numbers of CD45RO+ T cells than children with chronic ITP or controls, but these differences may be age related. Analysis of T-cell receptor variable beta gene usage identified 2 boys with chronic ITP and elevated numbers of V beta 8+ T cells. Eight T- cell clones were established (6 CD4+, 4B4+ helper-inducer lines and 2 CD8+ lines) that showed in vitro proliferation against allogeneic platelets. The addition of autologous antigen-presenting cells enhanced the proliferation of six clones, but not for two clones that coexpressed natural killer (NK) markers. Four of seven positive clones also had measurable interleukin (IL)-2 secretion following platelet stimulation, providing further evidence for T-cell reactivity. Our results provide the first evidence that patients with ITP may have platelet-reactive T lymphocytes identifiable at the clonal level, supporting the hypothesis that autoreactive peripheral T lymphocytes may mediate or participate in the pathogenesis of this disorder.

Phenotypic and Clonal Analysis of T Lymphocytes in Childhood Immune Thrombocytopenic Purpura

In an attempt to identify and characterize T-lymphocyte immunoregulatory abnormalities in immune thrombocytopenic purpura (ITP), we have performed phenotypic and clonal analysis on peripheral T lymphocytes from 23 children with ITP. Quantitation of lymphocyte subpopulations showed that children with acute ITP had higher numbers of CD45RA+ and lower numbers of CD45RO+ T cells than children with chronic ITP or controls, but these differences may be age related. Analysis of T-cell receptor variable beta gene usage identified 2 boys with chronic ITP and elevated numbers of V beta 8+ T cells. Eight T-cell clones were established (6 CD4+, 4B4+ helper-inducer lines and 2 CD8+ lines) that showed in vitro proliferation against allogeneic platelets. The addition of autologous antigen-presenting cells enhanced the proliferation of six clones, but not for two clones that coexpressed natural killer (NK) markers. Four of seven positive clones also had measurable interleukin (IL)-2 secretion following platelet stimulation, providing further evidence for T-cell reactivity. Our results provide the first evidence that patients with ITP may have platelet-reactive T lymphocytes identifiable at the clonal level, supporting the hypothesis that autoreactive peripheral T lymphocytes may mediate or participate in the pathogenesis of this disorder.