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Kaposi's sarcoma-associated herpesvirus (KSHV) is the infectious cause of Kaposi's sarcoma (KS) and certain lymphoproliferations particularly in the context of human immunodeficiency virus (HIV) type 1-induced immunosuppression. The introduction of effective therapies to treat HIV has led to a decline in the incidence of KS, suggesting that immune responses may play a role in controlling KSHV infection and pathogenesis. Cytotoxic-T-lymphocyte (CTL) activity against KSHV proteins has been demonstrated; however, the identification of KSHV CTL epitopes remains elusive and problematic. Although the herpesvirus genomic layout is generally conserved, KSHV encodes a unique hypervariable protein, K1, with intense biological selection pressure at specific amino acid sites. To investigate whether this variability is partly driven by cellular immunity, we designed K1 peptides that match only the unique viral sequence for every individual studied here (autologous peptides). We identified functional CTL epitopes within K1's most variable areas, and we show that a given individual responds only to autologous peptides and not to peptides from other individuals. Furthermore, these epitopes are highly conserved sequences within KSHV isolates from a specific strain but are not conserved between different strains. We conclude that CTL recognition contributes to K1, and therefore to KSHV, evolution. [ABSTRACT FROM AUTHOR]

Crystallographic studies have suggested that the cysteine at position 67 (Cys(67)) in the B pocket of the MHC molecule HLA-B*2705 is of importance for peptide binding, and biophysical studies have documented altered thermodynamic stability of the molecule when Cys(67) was mutated to serine (Ser(67)). In this study, we used HLA-B27.Cys(67) and HLA-B27.Ser(67) tetramers with defined T cell epitopes to determine the contribution of this polymorphic, solvent-inaccessible MHC residue to T cell recognition. We generated these HLA-B27 tetramers using immunodominant viral peptides with high binding affinity to HLA-B27 and cartilage-derived peptides with lower affinity. We demonstrate that the yield of refolding of HLA-B27.Ser(67) molecules was higher than for HLA-B27.Cys(67) molecules and strongly dependent on the affinity of the peptide. T cell recognition did not differ between HLA-B27.Cys(67) and HLA.B27.Ser(67) tetramers for the viral peptides that were investigated. However, an aggrecan peptide-specific T cell line derived from an HLA-B27 transgenic BALB/c mouse bound significantly stronger to the HLA-B27.Cys(67) tetramer than to the HLA-B27.Ser(67) tetramer. Modeling studies of the molecular structure suggest the loss of a SH ... pi hydrogen bond with the Cys-->Ser substitution in the HLA-B27 H chain which reduces the stability of the HLA-B27/peptide complex. These results demonstrate that a solvent-inaccessible residue in the B pocket of HLA-B27 can affect TCR binding in a peptide-dependent fashion.

The pathology of ankylosing spondylitis, reactive arthritis, and other spondyloarthropathies (SpA) is closely associated with the human leukocyte class I Ag HLA-B27. A characteristic finding in SpA is inflammation of cartilage structures of the joint, in particular at the site of ligament/tendon and bone junction (enthesitis). In this study, we investigated the role of CD8+ T cells in response to the cartilage proteoglycan aggrecan as a potential candidate autoantigen in BALB/c-B27 transgenic mice. We identified four new HLA-B27-restricted nonamer peptides, one of them (no. 67) with a particularly strong T cell immunogenicity. Peptide no. 67 immunization was capable of stimulating HLA-B27-restricted, CD8+ T cells in BALB/c-B27 transgenic animals, but not in wild-type BALB/c mice. The peptide was specifically recognized on P815-B27 transfectants by HLA-B27-restricted CTLs, which were also detectable by HLA tetramer staining ex vivo as well as in situ. Most importantly, analysis of the joints from peptide no. 67-immunized mice induced typical histological signs of SpA. Our data indicate that HLA-B27-restricted epitopes derived from human aggrecan are involved in the induction of inflammation (tenosynovitis), underlining the importance of HLA-B27 in the pathogenesis of SpA.

Reports of the use of HLA-B27/peptide tetrameric complexes to study peptide-specific CD8+ T cells in HLA-B27+-related diseases are rare. To establish HLA-B27 tetramers we first compared the function of HLA-B27 tetramers with HLA-A2 tetramers by using viral epitopes. HLA-B27 and HLA-A2 tetramers loaded with immunodominant peptides from Epstein-Barr virus were generated with comparable yields and both molecules detected antigen-specific CD8+ T cells. The application of HLA-B27 tetramers in HLA-B27-related diseases was performed with nine recently described Chlamydia-derived peptides in synovial fluid and peripheral blood, to examine the CD8+ T cell response against Chlamydia trachomatis antigens in nine patients with Chlamydia-triggered reactive arthritis (Ct-ReA). Four of six HLA-B27+ Ct-ReA patients had specific synovial T cell binding to at least one HLA-B27/Chlamydia peptide tetramer. The HLA-B27/Chlamydia peptide 195 tetramer bound to synovial T cells from three of six patients and HLA-B27/Chlamydia peptide 133 tetramer to synovial T cells from two patients. However, the frequency of these cells was low (0.02-0.09%). Moreover, we demonstrate two methods to generate HLA-B27-restricted T cell lines. First, HLA-B27 tetramers and magnetic beads were used to sort antigen-specific CD8+ T cells. Second, Chlamydia-infected dendritic cells were used to stimulate CD8+ T cells ex vivo. Highly pure CD8 T cell lines could be generated ex vivo by magnetic sorting by using HLA-B27 tetramers loaded with an EBV peptide. The frequency of Chlamydia-specific, HLA-B27 tetramer-binding CD8+ T cells could be increased by stimulating CD8+ T cells ex vivo with Chlamydia-infected dendritic cells. We conclude that HLA-B27 tetramers are a useful tool for the detection and expansion of HLA-B27-restricted CD8+ T cells. T cells specific for one or more of three Chlamydia-derived peptides were found at low frequency in synovial fluid from HLA-B27+ patients with Ct-ReA. These cells can be expanded ex vivo, suggesting that they are immunologically functional.

The illustrated clinical and experimental results demonstrate the strong relationship between the MHC class I antigen HLA-B27 and synovial CD8+ T cells with specificity for bacterial and possible self-antigen in SpA. These new aspects obtained in recent experimental and clinical studies might also provide clues to the pathomechanisms of joint inflammation in SpA. In particular, the newly developed techniques will be of great relevance in the near future. New and more precise bioalgorithms reflecting new insights in the biology and biochemistry of proteins as recently presented [98, 99] can be helpful (e.g., a program with an improved prediction of the features of immunoproteasomes). Intracellular and secreted cytokine staining by FACScan allows examination of a great number of cells expressing certain antigens in response to certain stimuli. The analysis of T-cell responses with tetramer/peptide complexes can be useful to screen tissue sections for TCR, recognizing foreign or self-derived epitopes on those complexes loaded with selected (e.g., bacterial) peptides. Identification of arthritogenic peptides and a further understanding of the immunology of the pathomechanisms in SpA might open ways to design new peptide vaccines to prevent inflammation, autoimmunity, and other diseases by early intervention [100].