Specificity of T cells in synovial fluid: high frequencies of CD8(+) T cells that are specific for certain viral epitopes

The ELISPOT assay: an easily transferable method for measuring cellular responses and identifying T cell epitopes

Characterization of human leukocyte antigen (HLA) class I restricted epitopes derived from viral pathogens is imperative for formulating therapeutic interventions, as well as for vaccine design and monitoring. Sensitive, easy and cost-effective assays that measure the frequency of antigen-specific T lymphocytes are crucial for evaluating and improving vaccines and therapies. This paper reviews the ELISPOT technique that allows for quantifying HIV-specific T lymphocytes at the single cell level from peripheral blood by detection of antigen-induced cytokine secretion. The assay can be used successfully to quantify T cell immune responses in humans infected with different pathogens and to assess T cell immunogenicity of vaccines in phase I/II and III clinical trials. This review focuses on the ELISPOT methodology and discusses how it can be standardized and potentially used by multiple international laboratories attached to clinical trial sites.

HLA-B27 and pathogenesis of spondyloarthropathies

Although the influence of HLA-B27 on the development of spondyloarthropathies is undisputed, its role in pathogenesis remains unclear. New ideas have focused on abnormal characteristics of HLA-B27 resulting from aberrant folding, disulfide bond formation, or both, rather than a predilection for selecting arthritogenic peptides. This reflects, in part, unanswered questions about whether immunologic recognition of HLA-B27 is required for disease. Recent studies suggest that CD4+ T cells, immunomodulatory killer cell Ig receptors, and Ig-like transcript receptors may recognize aberrant forms of HLA-B27. Other reports suggest that HLA-B27 expression can alter cytokine production from monocytes and T cells-effects that appear unrelated to antigen presentation. Novel bioinformatics approaches have led to the identification of HLA-B27-restricted pathogen-derived peptides and may prove useful in determining whether HLA-B27 presents arthritogenic peptides. Elucidating the role of HLA-B27 in the pathogenesis of these conditions will require an integration of information from animal models, genome-wide screens for susceptibility alleles, and translational studies using human samples.

CD8 T cells are required for the formation of ectopic germinal centers in rheumatoid synovitis

The assembly of inflammatory lesions in rheumatoid arthritis is highly regulated and typically leads to the formation of lymphoid follicles with germinal center (GC) reactions. We used microdissection of such extranodal follicles to analyze the colonizing T cells. Although the repertoire of follicular T cells was diverse, a subset of T cell receptor (TCR) sequences was detected in multiple independent follicles and not in interfollicular zones, suggesting recognition of a common antigen. Unexpectedly, the majority of shared TCR sequences were from CD8 T cells that were highly enriched in the synovium and present in low numbers in the periphery. To examine their role in extranodal GC reactions, CD8 T cells were depleted in human synovium-SCID mouse chimeras. Depletion of synovial CD8 T cells caused disintegration of the GC-containing follicles. In the absence of CD8 T cells, follicular dendritic cells disappeared, production of lymphotoxin-alpha1beta2 markedly decreased, and immunoglobulin (Ig) secretion ceased. Immunohistochemical studies demonstrated that these CD8 T cells accumulated at the edge of the mantle zone. Besides their unique localization, they were characterized by the production of interferon (IFN)-gamma, lack of the pore-forming enzyme perforin, and expression of CD40 ligand. Perifollicular IFN-gamma+ CD8 T cells were rare in secondary lymphoid tissues but accounted for the majority of IFN-gamma+ cells in synovial infiltrates. We propose that CD8+ T cells regulate the structural integrity and functional activity of GCs in ectopic lymphoid follicles.

Immunodominant CD8 T cell response to Epstein-Barr virus

Epstein-Barr virus (EBV) provides one of the most informative systems for analysing cytotoxic T lymphocyte responses in humans. The viral infection and its persistence are the results of an alternation of lytic and latent phases that are controlled by the immune response. Using a transient COS transfection assay that permits semi-quantitative estimation of CD8 T cell responses against a large number of HLA/viral protein combinations, we analyzed responses to EBV within a large number of polyclonal T cell lines. This allowed a rapid identification of major epitopes and the demonstration that EBV-specificT cells were mainly directed against a restricted set of immunodominant epitopes, primarily generated during the early lytic cycle. Knowledge of the antigen specificity of CDB T cell responses against EBV should help generate cytotoxic T cell lines to this herpesvirus, and more generally to study the molecular basis of immunodominance.

Epitope specificity of clonally expanded populations of CD8+ T cells found within the joints of patients with inflammatory arthritis

OBJECTIVE

To investigate the hypothesis that clonality of synovial T cells from patients with rheumatoid arthritis is at least partly due to the presence of virus-specific T cells expressing a restricted repertoire of T cell receptors (TCRs).

METHODS

Using fluorescently labeled HLA class I-peptide tetramers, populations of virus-specific CD8+ T cells were identified in samples of peripheral blood and synovial fluid taken from 4 patients with inflammatory arthritis. The TCR repertoire of the virus-specific T cells in the synovial fluid was analyzed using a panel of TCR beta variable region-specific monoclonal antibodies. Where T cells expressing a particular Vbeta chain dominated the response to a viral epitope, the sequences of these Vbeta chains were derived from sorted populations of antigen-specific T cells by reverse transcription-polymerase chain reaction.

RESULTS

CD8+ T cells specific for Epstein-Barr virus, cytomegalovirus, and influenza virus were enriched in synovial fluid compared with peripheral blood. Clonal or oligoclonal populations of CD8+ T cells were found to dominate the responses to these viral epitopes in synovial fluid.

CONCLUSION

The results support the hypothesis that restricted T cell receptor usage by large populations of virus-specific T cells provides one explanation for the presence of clonally expanded CD8+ T cells within the joints of patients with inflammatory arthritis. Thus, T cell clonality at a site of inflammation may reflect enrichment for memory T cells specific for foreign antigens, rather than proliferation of autoreactive T cells specific for self antigens.

MHC class I multimers

T lymphocytes play a key role in the immune response to both foreign and self peptide antigens, which they recognize in combination with MHC molecules. In the past it has been difficult to analyse objectively the specificity, frequency and intensity of T cell responses. The recent application of fluorescent-labelled MHC class I multimers, however, has provided a powerful experimental approach to the direct visualisation of antigen-specific T cells. As a result, our perspective of how T cells respond to both viruses and other antigens in vivo has been greatly enhanced.