Genetic control of the human V beta 13.2 T cell repertoire: importance of allelic variation outside the coding regions of the TCRBV13S2 gene

Cyclosporin A and Tacrolimus (FK506) Differentially Alter T-cell Receptor ExpressionIn Vivo

Cyclosporin A (CSA) and tacrolimus (FK506) are two common immunosuppressive agents used post blood and marrow transplantation. Despite similarity in their accepted modes of action, we observed polarized effects of CSA and FK506 on the in vivo human T cell repertoire. To determine the possible mechanism for this difference, the effects of CSA and FK506 on cell viability, cell proliferation, interleukin-2 production, and calcineurin inhibition were determined in vitro. Our data suggest that a secondary mechanism of action exists for the different T-cell repertoire induced by exposure to CSA and FK506.

Variability in TRBV haplotype frequency and composition in Caucasian, African American, Western African and Chinese populations

The polymorphic T-cell receptor Vbeta (TRBV) genes encode much of the variable region of the T-cell receptor beta chain. Analysis of allele frequencies of three closely linked polymorphic TRBV genes, TRBV7-3, TRBV9 and TRBV6-4, was undertaken in several populations. The frequencies of these alleles are not significantly different in populations of Caucasians, African Americans and Western Africans. However, Chinese population is extremely homogenous at all three loci. The current study identifies the existence of haplotypic relationships between alleles of these genes in the Caucasian population. The ORF allele TRBV7-3*A3 is found exclusively on chromosomes bearing TRBV9*A2 and TRBV6-4*A2 in this cohort. In contrast, TRBV7-3*A1 and the null allele TRBV7-3*A2 are associated only with TRBV9*A1 and TRBV6-4*A1. This pattern of linkage disequilibrium (LD) is altered in the African American and Western African populations. In these cohorts, there is a marked reduction in LD between alleles of TRBV7-3 and TRBV9. This study is consistent with previous population genetic studies wherein African-derived samples have a greater level of genetic diversity compared to Caucasians. These data also demonstrate that patterns of LD are not consistent across the entire TRBV locus.

Diagnostic role of tests for T cell receptor (TCR) genes

Rapid advances in molecular biological techniques have made it possible to study disease pathogenesis at a genomic level. T cell receptor (TCR) gene rearrangement is an important event in T cell ontogeny that enables T cells to recognise antigens specifically, and any dysregulation in this complex yet highly regulated process may result in disease. Using techniques such as Southern blot hybridisation, polymerase chain reaction, and flow cytometry it has been possible to characterise T cell proliferations in malignancy and in diseases where T cells have been implicated in the pathogenesis. The main aim of this article is to discuss briefly the process of TCR gene rearrangement and highlight the disorders in which expansions or clonal proliferations of T cells have been recognised. It will also describe various methods that are currently used to study T cell populations in body fluids and tissue, their diagnostic role, and current limitations of the methodology.

Antigen triggering selectively increases TCRBV gene transcription

When the TCR binds Ag it is phosphorylated, internalized, and degraded. We wished to examine whether this process was accompanied by a specific concomitant increase in TCR mRNA levels. To do this, PBMC and a T cell clone were cultured with a series of superantigens and an alloantigen. Only T cells specifically responding to an antigenic stimulus had increased levels of TCR beta-chain variable (TCRBV)-specific mRNA. This response was apparent after 48 h, peaked around 72 h, and was still elevated after 7 days. Increased gene transcription appeared to be driven solely by Ag as specific Ag depletion prevented culture supernatants transferring this effect. The level of TCRBV mRNA elevation was not influenced by the stimulating Ag, but appeared dependent on the gene encoding the stimulated TCR. Reporter gene assays, using cloned TCRBV gene promoters, confirmed both that TCR gene transcription rises after stimulation and that basal and stimulated levels of TCR transcription vary between different TCRBV genes. These data conclusively demonstrate that there is no direct relationship between TCRBV mRNA and T cell number, and that future repertoire studies must take both factors into account.

Identification of domains involved in superantigenicity of streptococcal pyrogenic exotoxin F (SpeF)

A series of 11 synthetic peptides of 30 amino acids, each with 10 amino acids overlap which spanned the entire sequence of streptococcal pyrogenic exotoxin F (SpeF), were employed in proliferation studies on human peripheral blood mononuclear cells (PBMCs). Regions 41-70, 141-170 and 181-210 were identified as important for SpeF-induced lymphocyte activation. Secondary structure predictions of these peptides showed similarities to regions in other superantigens known to be important for T cell mitogenicity. Furthermore, antisera specific to peptides covering amino acids 1-70 and 181-228 were able to inhibit SpeF-induced mitogenicity by 25% when pre-incubated with SpeF prior to PBMC activation.

Development of Human Peripheral TCRBJ Gene Repertoire

Previous studies of TCRBJ gene repertoires of human peripheral T lymphocytes showed that all TCRBV family transcripts had some common features in BJ gene usage, and nevertheless, transcripts of each BV family gene had a distinct pattern. To discern how the development of the peripheral BJ repertoire is controlled, the effects of preferential BJ gene rearrangement, thymic selection, and peripheral stimulation on the repertoire formation were investigated. A PCR-ELISA technique was used to examine the immature CD3−CD4+CD8−, and mature CD3+CD4+CD8− and CD3+CD4−CD8+ thymocytes, and peripheral CD4+ and CD8+ T lymphocytes for their BJ gene repertoires. Analogous to the peripheral repertoire, the BJ gene repertoires of the immature thymocytes displayed common features, and each BV transcript had a distinct pattern. All features were conserved well by those of mature thymocytes and peripheral T lymphocytes. In addition, the BJ gene repertoires of mature CD4 and CD8 thymocytes and peripheral lymphocytes with the same coreceptors were apparently different in a few BV-BJ combinations. The results showed that the overall BJ gene repertoire pattern was developed before antigenic selection. Thus, the preferential BJ gene expression, primarily based on preferential use of certain BJ gene rearrangements, dictates the peripheral BJ gene repertoire, which is then further modified by thymic selection and peripheral stimulation.

Synergy between T cell receptor beta gene polymorphism and HLA-DR4 in susceptibility to rheumatoid arthritis

OBJECTIVE

To investigate the etiologic significance of germline polymorphisms in the T cell receptor beta variable region 6S7 (TCRBV6S7) gene segment and adjacent loci in susceptibility to rheumatoid arthritis (RA).

METHODS

Ten TCRB allelic polymorphisms were analyzed from 3 groups of white women: 112 with RA, 72 with systemic lupus erythematosus, and 70 healthy controls. All participants were also HLA typed.

RESULTS

HLA-DR4+ RA patients showed significantly increased frequencies of TCRBV6S7*1, 13S5P*1 (an allelic variant of BV13S5 promoter), and 12S4*2, compared with healthy controls. The combination of DR4 with either BV6S7*1, 13S5P*1, or 12S4*2 conferred greater risk for RA than HLA-DR4 alone. Pairwise analyses showed a high degree of linkage disequilibrium (P = 10(-5)-10(-8)) between these 3 TCRBV loci that span 47 kilobases (kb).

CONCLUSION

Our data suggest that a TCR gene segment in or linked to this 47-kb region may be involved in genetic susceptibility to RA through an interaction with HLA-DR4.

TCR gene polymorphisms and autoimmune disease

Autoimmunity may result from abnormal regulation within the immune system. As the T cell is the principal regulator of the immune system and its normal function depends on immune recognition or self/non-self discrimination, abnormalities of the idiotypic T-cell receptor (TCR) may be one cause of autoimmune disease. The TCR is a clonally distributed, cell-surface heterodimer which binds peptide antigen when complexed with HLA molecules. In order to recognize the variety of antigens it may possibly encounter, the TCR, by necessity, is a diverse structure. As with immunoglobulin, it is the variable domain of the TCR which interacts with antigen and exhibits the greatest amount of amino acid variability. The underlying genetic basis for this structural diversity is similar to that described for immunoglobulin, with TCR diversity relying on the somatic recombination, in a randomly imprecise manner, of smaller gene segments to form a functional gene. There are a large number of gene segments to choose from (particularly the TCRAV, TCRAJ and TCRBV gene segments) and some of these also exhibit allelic variation. Finally, polymorphisms in non-coding regions of TCR genes, leading to biased recombination or expression, are also beginning to be recognized. All these factors contribute to the polymorphic nature of the TCR, in terms of both structure and repertoire formation. It follows that inherited abnormalities in either coding or regulatory regions of TCR genes may predispose to aberrant T-cell function and autoimmune disease. This review will outline the genomic organization of the TCR genes, the genetic mechanisms responsible for the generation of diversity, and the results of investigations into the association between germline polymorphisms and autoimmune disease.

Differential patterns of T-cell receptor BV-specific activation of T cells by gp120 from different HIV strains

Studies by several groups have suggested that HIV infection in vivo results in a BV-specific alteration of the TCR repertoire and that this might play a role in the pathogenesis of AIDS. Our earlier studies demonstrated that both a crude extract of HIV451 as well as purified gp 160 from HIV451 could specifically activate, in vitro, T cells expressing a common set of TCRBV segments (TCRBV3, 12, 14, 15, and sometimes BV17 and 20) in individuals of disparate HLA type. Furthermore, purified gp120 from HIV451 was shown to have a similar ability to activate T cells, although with a slightly different TCRBV-specific pattern. In order to determine whether gp120 from other HIV strains could similarly activate T cells in a TCRBV-specific pattern, PBMC from HIV seronegative individuals of disparate HLA type were stimulated with gp120 from three strains of HIV (451, IIIB, and MN). The authors found that gp120 from all three strains activate T cells bearing TCRBV2 and BV3 in nearly every individual. T cells expressing other BV segments are also activated, but this is more variable and appears to be unique to each individual. Furthermore, gp120(451) and gp120 from HIVIIIB and HIVMN differ in their ability to activate T cells expressing these other TCRBV segments. These observations suggest that variation in the structure of gp120 and in the genetic and/or environmental background of the individual play an important role in determining which TCRBV segments are 'triggered' by gp120. Furthermore, these observations may have important implications for the rate of disease progression in HIV-infected individuals.

A subset of Sjögren's syndrome associates with the TCRBV13S2 locus but not the TCRBV2S1 locus

HGPSS associates with the TCRBV6S7 locus within the TCR beta-chain gene complex. However, V beta 6.7 T cells, encoded by this locus, have never been implicated in the salivary gland destruction that characterizes primary Sjögren's syndrome. Both V beta 13 and V beta 2 T cells have been implicated in glandular destruction. We therefore analyzed the association of HGPSS with both TCRBV2S1, the only TCRBV2 locus, and the TCRBV13S2 locus (the TCRBV13 family member which lies closest to TCRBV6S7). Our results show that the prevalence of TCRBV13S2*2 homozygotes is significantly increased in HGPSS and that there is a high degree of linkage disequilibrium between this locus and TCRBV6S7 not previously described across the TCR beta-chain gene complex. However, HGPSS does not associate with the TCRBV2S1 locus. These results suggest that it is the V beta 13.2 T cell which may be responsible for the autoimmune destruction that characterizes HGPSS and that the previous association of this condition with the TCRBV6S7 locus is primary due to the linkage disequilibrium that exists between it and TCRBV13S2.