Tolerance and effectiveness of anti–tumor necrosis factor α therapies in elderly patients with rheumatoid arthritis: A population-based cohort study

OBJECTIVE

Limited data have been published on tolerance to and efficacy of classic or biologic disease-modifying antirheumatic drugs in elderly patients with rheumatoid arthritis (RA). The goal of the present study was to evaluate the tolerance to and effectiveness of anti-tumor necrosis factor (anti-TNF) agents in elderly patients (> or =65 years old) with RA (ERA) in comparison with younger patients (YRA).

METHODS

The Swiss Clinical Quality Management program for RA is a longitudinal population-based cohort. All patients who had received at least 1 dose of anti-TNF agents between January 1997 and November 2005 were included and categorized according to their age. Tolerance was assessed by analyzing discontinuation rates of anti-TNF agents. Effectiveness of these agents was assessed by analyzing RA disease activity (Disease Activity Score in 28 joints [DAS28]) and functional disability (Health Assessment Questionnaire [HAQ]) after anti-TNF initiation.

RESULTS

Among 1,571 patients with RA treated with anti-TNF agents, 344 were > or =65 years of age at treatment initiation. Drug discontinuation rates (median time 3 years) and mean change in DAS28 scores at 2 years (-0.65 versus -0.58) were identical in ERA and YRA. However, HAQ score improved significantly less in ERA (-0.02) than in YRA (-0.1) and a subsequent analysis revealed that this finding was essentially due to patients >75 years of age.

CONCLUSION

Age in itself should not interfere with the decision to treat elderly patients with RA with anti-TNF agents. In a subset of patients ages >75 years, no functional improvement according to HAQ should be expected despite improvements in disease activity.

The role of Toll-like receptor signalling in the pathogenesis of arthritis

Recent evidence highlighted the role of Toll-like receptors (TLRs) as key recognition structures of the innate immune system. The activation of TLRs initiates the production of inflammatory cytokines, chemokines, tissue destructive enzymes, and type I interferons. In addition, TLR signalling plays an important role in the activation and direction of the adaptive immune system by the upregulation of costimulatory molecules of antigen presenting cells. Considering the important role of TLR signalling as a critical link between innate and adaptive immunity it has been proposed that a dysregulation in TLR signalling might be associated with autoimmunity. In this review, recent studies on TLR signal transduction pathways activated by corresponding ligands are summarized and evidence for a possible role of TLR signalling in the pathogenesis of rheumatoid arthritis is discussed.

RNA released from necrotic synovial fluid cells activates rheumatoid arthritis synovial fibroblasts via toll-like receptor 3

OBJECTIVE

To assess the expression of Toll-like receptor 3 (TLR-3) protein in synovial tissues and cultured synovial fibroblasts obtained from patients with rheumatoid arthritis (RA) and osteoarthritis (OA) and to investigate the consequences of stimulation of cultured synovial fibroblasts with TLR-3 ligands.

METHODS

TLR-3 expression in synovial tissues was determined by immunohistochemistry and immunofluorescence, and expression in cultured RA synovial fibroblasts (RASFs) was determined by fluorescence-activated cell sorting and real-time polymerase chain reaction techniques. TLR-3 signaling was assessed by incubating RASFs with poly(I-C), lipopolysaccharide, palmitoyl-3-cysteine-serine-lysine-4, or necrotic synovial fluid cells from RA patients in the presence or absence of hydroxychloroquine or Benzonase. Subsequent determination of interferon-beta (IFNbeta), CXCL10, CCL5, and interleukin-6 (IL-6) protein production in the culture supernatants was performed by enzyme-linked immunosorbent assays.

RESULTS

TLR-3 protein expression was found to be higher in RA synovial tissues than in OA synovial tissues. TLR-3 expression was localized predominantly in the synovial lining, with a majority of the TLR-3-expressing cells coexpressing fibroblast markers. Stimulation of cultured RASFs with the TLR-3 ligand poly(I-C) resulted in the production of high levels of IFNbeta, CXCL10, CCL5, and IL-6 protein. Similarly, coincubation of RASFs with necrotic synovial fluid cells from patients with RA resulted in up-regulation of these cytokines and chemokines in a TLR-3-dependent manner.

CONCLUSION

Our findings demonstrate the expression of TLR-3 in RA synovial tissue and the activation of RASFs in vitro by the TLR-3 ligand poly(I-C) as well as by necrotic RA synovial fluid cells, and indicate that RNA released from necrotic cells might act as an endogenous TLR-3 ligand for the stimulation of proinflammatory gene expression in RASFs.

Pattern recognition receptors and their involvement in the pathogenesis of arthritis

PURPOSE OF REVIEW

Pattern recognition receptors are germ-line encoded receptors that recognize specific pathogen-associated molecules, thereby allowing the innate immune system to distinguish self from nonself structures. Pattern recognition receptors mediate activation of different signaling pathways, resulting in the production of proinflammatory cytokines and the expression of antimicrobial genes. Additionally, pattern recognition receptors play a central role in the activation and direction of the adaptive immune response. This review summarizes recent advances in research trying to elucidate the link between different pattern recognition receptors and inflammatory autoimmune disorders.

RECENT FINDINGS

The best known pattern recognition receptors, the toll-like receptors, are involved in the regulation of inflammation during infectious diseases. They affect apoptotic pathways and dendritic cell maturation, and interact with B-cell receptors in priming T-cell responses to host-derived DNA. This brought toll-like receptors and other pattern recognition receptors into focus as potential players in the induction of autoimmune diseases. Indeed, several inflammatory autoimmune diseases have been linked during the past few years to defects or polymorphisms of genes encoding pattern recognition receptors.

SUMMARY

The discovery of toll-like receptors and other groups of pattern recognition receptors, such as the caspase recruitment domains or the triggering receptors expressed by myeloid cells, allowed one to draw an increasingly complex picture of immune responses to pathogens. The growing evidence for an involvement of pattern recognition receptors in the pathogenesis of autoimmune disorders warrants further investigation of the expression and function of pattern recognition receptors to develop novel therapeutics for diseases such as rheumatoid arthritis.

Chemokine secretion of rheumatoid arthritis synovial fibroblasts stimulated by Toll-like receptor 2 ligands

To analyze the role of Toll-like receptors (TLR) in the pathogenesis of rheumatoid arthritis, we have assessed the effects of stimulation of cultured synovial fibroblasts by the TLR-2 ligand bacterial peptidoglycan. By using high density oligonucleotide microarray analysis we identified 74 genes that were up-regulated >2.5-fold. Fourteen CC and CXC chemokine genes were among the genes with the highest up-regulation. Quantitative real-time PCR analysis confirmed up-regulation of granulocyte chemotactic protein (GCP)-2, RANTES, monocyte chemoattractant protein (MCP)-2, IL-8, growth-related oncogene-2, and to a lesser extent, macrophage-inflammatory protein 1alpha, MCP-1, EXODUS, and CXCL-16. GCP-2, RANTES, and MCP-2 were detected in culture supernatants of synovial fibroblasts stimulated with peptidoglycan. Chemokine secretion induced by stimulation of rheumatoid arthritis synovial fibroblasts via TLR-2 was functionally relevant as demonstrated by chemotaxis assays. GCP-2 and MCP-2 expression, which have not been reported previously in rheumatoid arthritis, was demonstrated in synovial tissue sections of patients diagnosed with rheumatoid arthritis but not in those with osteoarthritis. Correspondingly, synovial fluid levels were significantly higher in patients diagnosed with rheumatoid arthritis as compared with osteoarthritis. Thus, we present evidence for an induction of chemokine secretion by activation of synovial fibroblasts via TLR-2, possibly contributing to the formation of inflammatory infiltrates characteristically found in rheumatoid arthritis joints.

Galectin 3 and its binding protein in rheumatoid arthritis

OBJECTIVE

To characterize the expression pattern and role of galectin 3 and galectin 3 binding protein (G3BP) in rheumatoid arthritis (RA), in comparison with galectin 1, and to explore whether soluble galectin 3 and G3BP, investigated in serum, synovial fluid, or cell culture supernatant, are associated with disease.

METHODS

Synovial tissues from patients with RA or osteoarthritis (OA), as well as from healthy controls, were analyzed for galectins 1 and 3 and G3BP by in situ hybridization and immunohistochemistry. Levels of galectin 3 and G3BP in serum and synovial fluid from patients with RA and OA and controls, as well as in cell culture supernatants, were determined by enzyme-linked immunosorbent assay (ELISA). In vitro, the intracellular expression of galectin 3 in RA and OA synovial fibroblasts after modulation with tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and anti-CD40 monoclonal antibodies was measured by flow cytometry.

RESULTS

In RA, galectin 3 messenger RNA and protein stained throughout the synovial membrane, whereas G3BP was particularly expressed at sites of bone destruction. In contrast, the expression of galectin 1 was not uniform in different RA specimens, and was never found at sites of invasion. In OA and normal synovial tissues, only a small number of cells were positive for galectins and/or G3BP. Galectin 3 was elevated in RA sera and synovial fluids, whereas G3BP was increased in RA synovial fluids only. In RA, serum galectin 3 correlated with C-reactive protein levels, whereas G3BP was associated with joint destruction and/or synovial cell activation as measured by the levels of cartilage oligomeric matrix protein. In vitro, RA synovial fibroblasts showed an increased release of galectin 3 into culture medium, as measured by ELISA, but decreased secretion of G3BP. In RA synovial fibroblasts with low basal expression of galectin 3, TNFalpha increased its intracellular level in a dose-dependent manner. In contrast, IL-1beta or anti-CD40 monoclonal antibodies showed no effect.

CONCLUSION

Our data indicate that galectin 3 and G3BP are not only involved in inflammation, but also contribute to the activation of synovial fibroblasts. The intracellular accumulation of galectin 3 can be enhanced by TNFalpha. Thus, galectin 3 and G3BP represent novel markers of disease activity in RA.

The KRN mouse model of inflammatory arthritis

In 1996 a new murine model of spontaneous arthritis was described by the group of Benoist and Mathis. Mice transgenic for a T cell receptor recognizing an epitope of bovine RNase and bred onto a NOD background developed severe destructive arthritis, which resembles human rheumatoid arthritis in many respects. The development of disease requires the presence of T and B lymphocytes and is dependent on the MHC class II molecule I-A(g7). B cell activation by antigen and an additional CD40-CD40 ligand interaction was found to give rise to the production of autoantibodies. Glucose-6-phosphate isomerase was identified as the target of the autoantibodies; moreover, the transgenic T cells were demonstrated to exhibit a dual specificity for both bovine RNase and glucose-6-phosphate isomerase. Importantly, the arthritis is serum transferable to normal recipients, enabling the examination of the pathogenic mechanisms of joint inflammation and destruction. Recent studies suggest the crucial involvement of the innate immune system in the development of antibody-induced arthritis. Complement components, Fc receptors and neutrophils are indispensable for disease induction. An overview of the existing data is given and the emerging concepts of the pathogenesis of the K/BxN arthritis are discussed with respect to their relevance for human rheumatoid arthritis. Because of the reliable and robust induction of joint inflammation by serum transfer this new disease model has been and will be a valuable means to address the as-yet-unanswered key questions related to the development of arthritis.

Selection of oligonucleotide aptamers with enhanced uptake and activation of human leukemia B cells

The clinical use of oligonucleotide (ODN) therapeutics has been hampered by their limited ability to penetrate intact cells. To identify ODN properties that would facilitate cellular uptake, we developed a repetitive selection procedure using an ODN library containing at least 10(14) different molecules and human B lymphoma cells as a target. Natural phosphodiester single-stranded DNA ODNs (R-aptamers) were obtained after 10 rounds of selection. A common feature in the R-aptamers was guanine-rich 3' terminal sequences, and many also contained potential immunostimulatory (ISS) CpG sequence motifs. Two R-aptamers (R10-60 and D-R15-8) with the predominant shared characteristics were selected for further study on primary human chronic lymphocytic leukemia (CLL) B cells, which are well known to be difficult to transfect and activate. Flow cytometry analysis of the CLL cells demonstrated that the fluorochrome-labeled R-aptamers were internalized much more efficiently than nonselected random sequence ODN. Studies on sequence modifications indicated that efficient uptake required ODN multimerization, that was promoted by guanine-rich sequences at the 3' terminus. In addition, CLL cells that were exposed to the aggregating R-aptamers containing CpG motifs were strongly activated, as indicated by upregulation of CD40 levels as compared to cells treated with nonaggregating CpG R-aptamers. Together, these findings suggest that the sequence compositions in R-aptamers that promote multimerization and contain optimal ISS CpG motifs facilitate the delivery of ISS-ODN to CLL cells and enhance the activation of these cells.

Cartilage destruction mediated by synovial fibroblasts does not depend on proliferation in rheumatoid arthritis

The aim of the study was to investigate the relationship between invasion and proliferation in rheumatoid arthritis synovial fibroblasts (RASFs). In vitro, RASFs, normal synovial fibroblasts (NSFs), and RASFs transformed with SV40 T-antigen (RASF(SV40)) were analyzed for the expression of cell surface markers (Thy1, VCAM-1, ICAM-1, CD40, CD44) and their proliferation by flow cytometry. Furthermore, colony-forming unit assays were performed and the expression of matrix metalloproteinases (MMP)-14 and cathepsin K mRNA were determined by real-time polymerase chain reaction. In vivo, in the severe combined immunodeficiency (SCID) mouse co-implantation model, RASFs, NSFs, and RASF(SV40) were tested for cartilage invasion, cellular density, and for their expression of the cell cycle-associated protein Ki67. In the SCID mouse co-implantation model, RASFs invaded significantly stronger into the cartilage than NSFs and RASF(SV40). Of note, RASF(SV40) cells formed tumor-like tissues, and the cellular density adjacent to the cartilage was significantly higher than in RASFs or NSFs. In turn, the proliferation marker Ki67 was strongly expressed in the SV40-transformed synoviocytes in SCID mice, but not in RASFs, and specifically not at sites of cartilage invasion. Using the colony-forming unit assay, RASFs and NSFs did not form colonies, whereas RASF(SV40) lost contact inhibition. In vitro, the proliferative rate of RASFs was low (4.3% S phase) in contrast to RASF(SV40) (24.4%). Expression of VCAM-1 was significantly higher, whereas of ICAM-1 was significantly lower, in RASFs than in RASF(SV40). CD40 was significantly stronger expressed in RASF(SV40), whereas CD44 and AS02 were present at the same degree in almost all synoviocytes. Expression of cathepsin K and matrix metalloproteinase-14 mRNA was significantly higher in RASFs than in the RASF(SV40). Our data demonstrate clearly that invasion of cartilage is mediated by activated RASFs characterized by increased expression of adhesion molecules, matrix-degrading enzymes, but does not depend on cellular proliferation, suggesting the dissociation of invasion and proliferation in RASFs.

Bacterial peptidoglycans but not CpG oligodeoxynucleotides activate synovial fibroblasts by toll-like receptor signaling

OBJECTIVE

To test the hypothesis that bacterial products acting as adjuvants, such as CpG oligodeoxynucleotides (ODNs) and peptidoglycans (PGs), are able to activate synoviocytes, and to determine the involvement of Toll-like receptors (TLRs) in this activation process.

METHODS

Cultured synovial fibroblasts obtained from patients with rheumatoid arthritis (RA) or osteoarthritis (OA) were stimulated with CpG ODNs or PGs. The expression of various integrins was determined by fluorescence-activated cell sorting. TLR and matrix metalloproteinase (MMP) messenger RNA (mRNA) was measured by real-time polymerase chain reaction. Additionally, levels of interleukin-6 (IL-6) and IL-8 in the culture supernatants were assessed by enzyme-linked immunosorbent assay. Blocking experiments were performed by adding anti-TLR-2 and anti-TLR-4 monoclonal antibodies to cultures stimulated with bacterial PGs.

RESULTS

Incubation of synovial fibroblasts with CpG ODNs resulted in neither up-regulation of the expression of integrins on the cell surface, up-regulation of MMP mRNA expression, nor IL-6 and IL-8 production. However, incubation of RA synovial fibroblasts as well as OA synovial fibroblasts with staphylococcal PGs led to an up-regulation of CD54 (ICAM-1) surface expression and to increased expression of MMP-1, MMP-3, and MMP-13 mRNA. Furthermore, production of the proinflammatory cytokines IL-6 and IL-8 was increased by treatment with PGs. We demonstrated that cultured synovial fibroblasts express low levels of TLR-2 and TLR-9 mRNA. TLR-2 was up-regulated after stimulation with PGs, whereas TLR-9 mRNA remained at baseline levels after stimulation with CpG ODNs. Anti-TLR-2 monoclonal antibodies significantly inhibited production of IL-6 and IL-8 induced by stimulation with PGs.

CONCLUSION

We demonstrate that bacterial PGs activate synovial fibroblasts, at least partially via TLR-2, to express integrins, MMPs, and proinflammatory cytokines. Inhibition of TLR signaling pathways might therefore have a beneficial effect on both joint inflammation and joint destruction.

Efficient T cell repertoire selection in tetraparental chimeric mice independent of thymic epithelial MHC

Nonthymic epithelial cells were compared with thymic epithelial cells for their role in T cell repertoire selection. Tetraparental aggregation chimeras were generated from T and B cell-deficient mice (H-2(d) SCID or H-2(b) Rag-/-) and thymus-deficient nude mice (H-2(b) or H-2(d)). These tetraparental mice showed primary protective CD8(+) T cell responses, after lymphocytic choriomeningitis virus infection, that were peptide-specifically restricted to either thymic or nonthymic epithelial MHC at comparable levels. These chimeras also mounted neutralizing IgG responses dependent on cognate CD4(+) T helper cell activity restricted to nonthymic epithelial MHC. Therefore, in contrast to earlier results with irradiation or thymus chimeras, these relatively undisturbed tetraparental mice reveal that the MHC of nonthymic epithelial cells efficiently selects a functional T cell repertoire.

The role of CD40 ligand and tumor necrosis factor alpha signaling in the transgenic K/BxN mouse model of rheumatoid arthritis

OBJECTIVE

Spontaneous arthritis in the KRN transgenic mouse (K/BxN) model is due to the autoreactivity of the transgenic T cell receptor and subsequent induction of autoantibodies directed against glucose-6-phosphate isomerase (G6PI). This study sought to analyze the potential of anti-CD40 ligand (anti-CD40L) and anti-tumor necrosis factor alpha (anti-TNFalpha) antibodies in preventing and treating arthritis in this murine model.

METHODS

Groups of K/BxN mice were injected with anti-CD40L and anti-TNFalpha antibodies during various stages of arthritis. Disease was assessed by clinical scoring, measurements of paw swelling, and histology. The results were correlated with the levels of autoantibodies in the serum, as assessed by enzyme-linked immunosorbent assay.

RESULTS

Anti-CD40L antibody treatment was able to diminish significantly the arthritis development in K/BxN mice when given a week before the onset of clinically apparent disease. However, no effect on disease was seen when the antibodies were administered after clinical onset. Surprisingly, neutralizing anti-TNFalpha antibodies were unable to prevent arthritis in K/BxN mice. The success of antibody treatment in preventing disease correlated with low levels of anti-G6PI antibodies in the serum.

CONCLUSION

These results suggest that anti-CD40L treatment can prevent arthritis development in a model of immunoglobulin-mediated arthritis, but anti-TNFalpha treatment cannot. The unsuccessful treatment of established disease was possibly due to the continued presence of autoreactive antibodies in the arthritic mice.

Human Rheumatoid Factor Production Is Dependent on CD40 Signaling and Autoantigen

High-affinity pathologic rheumatoid factor (RF) B cells occur in autoimmune diseases such as rheumatoid arthritis, but are deleted in healthy individuals. The reasons for the survival and differentiation of these autoreactive B cells in rheumatoid arthritis are not known. Previous studies in mice transgenic for a human IgM RF have shown that peripheral encounter with soluble human IgG leads to deletion of high-affinity RF B cells; however, deletion can be prevented when concomitant T cell help is provided. This study aimed to further discern the minimal factors necessary not only for the in vivo survival of RF B cells, but also for their differentiation into Ab-secreting cells. The combination of MHC class II-reactive T cells and Ag induced the production of RF in human IgM RF transgenic mice, while either stimulus alone was ineffective. Neutralizing Abs against CD40 ligand (CD40L), but not against IL-4 or IL-15, abrogated IgM-RF production. Moreover, blockade of CD40L-CD40 allowed IgG to delete the RF precursor cells. Most importantly, activating Abs to CD40 could substitute entirely for T cell help in promoting the survival of RF precursors and in stimulating RF synthesis in T cell deficient animals. The data indicate that CD40 signaling alone can prevent deletion of RF B cells by Ag and in the presence of IgG is sufficient to trigger RF synthesis. The results suggest that selective induction of apoptosis in high-affinity RF B cells may be achieved by blockade of CD40L-CD40 interaction.

Human rheumatoid factor production is dependent on CD40 signaling and autoantigen

High-affinity pathologic rheumatoid factor (RF) B cells occur in autoimmune diseases such as rheumatoid arthritis, but are deleted in healthy individuals. The reasons for the survival and differentiation of these autoreactive B cells in rheumatoid arthritis are not known. Previous studies in mice transgenic for a human IgM RF have shown that peripheral encounter with soluble human IgG leads to deletion of high-affinity RF B cells; however, deletion can be prevented when concomitant T cell help is provided. This study aimed to further discern the minimal factors necessary not only for the in vivo survival of RF B cells, but also for their differentiation into Ab-secreting cells. The combination of MHC class II-reactive T cells and Ag induced the production of RF in human IgM RF transgenic mice, while either stimulus alone was ineffective. Neutralizing Abs against CD40 ligand (CD40L), but not against IL-4 or IL-15, abrogated IgM-RF production. Moreover, blockade of CD40L-CD40 allowed IgG to delete the RF precursor cells. Most importantly, activating Abs to CD40 could substitute entirely for T cell help in promoting the survival of RF precursors and in stimulating RF synthesis in T cell deficient animals. The data indicate that CD40 signaling alone can prevent deletion of RF B cells by Ag and in the presence of IgG is sufficient to trigger RF synthesis. The results suggest that selective induction of apoptosis in high-affinity RF B cells may be achieved by blockade of CD40L-CD40 interaction.

Rheumatoid factor B cell tolerance via autonomous Fas/FasL-independent apoptosis

Normal individuals do not express the high-affinity autoantibodies specific for self-IgG (rheumatoid factors, RF) that are commonly seen in rheumatoid arthritis patients. Studies of transgenic mice expressing a human IgM rheumatoid factor have shown that one mechanism by which higher affinity RF B cells are tolerized to IgG is through abortive RF B cell activation followed by deletion in the absence of T cell help. We show that RF B cell deletion occurs through an intrinsic apoptotic mechanism that is independent of the Fas/FasL pathway and does not involve active killing by T cells, as it occurs in RAG-1-deficient RF transgenic mice to the same extent as in the parental RF transgenic line.

Viral peptide specific cytotoxic T lymphocytes are of high avidity to host-MHC but only low avidity to donor-MHC after allogeneic bone marrow transplantation

In the thymus maturing T lymphocytes are positively selected for efficient interaction with self-MHC molecules. Consequently, mature peripheral T cells recognize foreign (microbial) antigens in association with self-MHC molecules (known as MHC restricted recognition). In experimental bone marrow transplantation (BMT) lymphohaemopoietic stem cells from an MHC disparate donor transfused to an irradiated host give rise to mature T lymphocytes with host-MHC restriction specificity. While experiments with T cell receptor transgenic mice have largely confirmed this concept, many studies using genetically unmanipulated animals analysing polyclonal T cell repertoires have also shown donor-MHC restricted T cell activities after allogeneic BMT. To analyse this discrepancy we generated 18 virus specific cytotoxic T cell (CTL) clones, 16 from F1 into parent and two from fully allogeneic bone marrow chimeras, and analysed the MHC restriction specificity in proliferation and cytotoxicity assays. The cytotoxicity of all the clones was primarily host-MHC restricted. However, the CTL clones proliferated to viral antigen presented by both donor- or host-MHC. Our model allowed CTL cloning by cross-specific stimulation with antigen plus either donor-MHC or else host-MHC. Interestingly, even the 14 CTL clones which had been raised with donor-MHC systematically killed host-MHC but not donor-MHC expressing cells. Thus, after BMT, CTLs may proliferate crossreactively to donor-MHC but cytolysis is predominantly directed to host-MHC expressing cells. Since lytic CTL activity probably reflects high avidity CTL interaction necessary for viral clearance in vivo, the data suggest that the donor-MHC restricted CTL activity may not be protective and that virus may escape CTL surveillance in donor cells.

Peptides control the gain and loss of allele specificity by mutated MHC class I molecules

To analyze the molecular basis of MHC class I allele-restricted peptide recognition, a set of eight Ld/Lq mutants was constructed and tested for peptide recognition by allele-restricted and peptide-specific CTL. The MHC molecules H-2Ld and H-2Lq differ at six amino acid positions (95, 97, 107, 116, 155, 157) located within the alpha 2 domain of the molecule. Both molecules present the lymphocytic choriomeningitis virus (LCMV) nucleoprotein-derived peptide RPQASGVYM and the murine cytomegalovirus (MCMV) pp89-derived peptide YPHFMPTNL to the respective virus-specific CD8+ CTL is a strictly allele-restricted fashion. All mutated MHC class I molecules did still bind the LCMV peptide and seven of eight mutants retained MCMV peptide binding. The exchange Arg-->Trp at position 97 of Lq in pocket C of the peptide binding groove prevented binding of the MCMV ligand and this loss was compensated by the additional exchange of Ile-->Leu in position 95 (pocket F). Within the Lq molecule, single mutations at either position 97 on the floor of the groove or position 155 of the wall sufficed for a gain of LCMV peptide recognition by Ld-restricted CTL. Altogether, six of eight mutants resulted in a gain of recognition by CTL specific for the other allele. Thus, six of the eight mutants lost MHC-restricted recognition and were accepted by both Ld- as well as Lq-restricted CTL when presenting the LCMV peptide. Only one case of simultaneous recognition of the MCMV peptide by both Ld- as well as Lq-restricted CTL was noted. In other mutations, a gain of recognition by Ld-restricted CTL was associated with a loss of recognition of Lq-restricted CTL. Analysis of extracted MCMV peptide from mutant molecules excluded quantitative differences in presented MCMV peptide as a reason for the lack of CTL recognition. Altogether, the results show that, rather than aminoacids at certain residue positions, individual peptides govern MHC allele specificity of CTL recognition.

Peptides control the gain and loss of allele specificity by mutated MHC class I molecules

To analyze the molecular basis of MHC class I allele-restricted peptide recognition, a set of eight Ld/Lq mutants was constructed and tested for peptide recognition by allele-restricted and peptide-specific CTL. The MHC molecules H-2Ld and H-2Lq differ at six amino acid positions (95, 97, 107, 116, 155, 157) located within the alpha 2 domain of the molecule. Both molecules present the lymphocytic choriomeningitis virus (LCMV) nucleoprotein-derived peptide RPQASGVYM and the murine cytomegalovirus (MCMV) pp89-derived peptide YPHFMPTNL to the respective virus-specific CD8+ CTL is a strictly allele-restricted fashion. All mutated MHC class I molecules did still bind the LCMV peptide and seven of eight mutants retained MCMV peptide binding. The exchange Arg-->Trp at position 97 of Lq in pocket C of the peptide binding groove prevented binding of the MCMV ligand and this loss was compensated by the additional exchange of Ile-->Leu in position 95 (pocket F). Within the Lq molecule, single mutations at either position 97 on the floor of the groove or position 155 of the wall sufficed for a gain of LCMV peptide recognition by Ld-restricted CTL. Altogether, six of eight mutants resulted in a gain of recognition by CTL specific for the other allele. Thus, six of the eight mutants lost MHC-restricted recognition and were accepted by both Ld- as well as Lq-restricted CTL when presenting the LCMV peptide. Only one case of simultaneous recognition of the MCMV peptide by both Ld- as well as Lq-restricted CTL was noted. In other mutations, a gain of recognition by Ld-restricted CTL was associated with a loss of recognition of Lq-restricted CTL. Analysis of extracted MCMV peptide from mutant molecules excluded quantitative differences in presented MCMV peptide as a reason for the lack of CTL recognition. Altogether, the results show that, rather than aminoacids at certain residue positions, individual peptides govern MHC allele specificity of CTL recognition.

Peptide-induced T-cell tolerance to prevent autoimmune diabetes in a transgenic mouse model

A synthetic peptide corresponding to an immunodominant epitope of lymphocytic choriomeningitis virus glycoprotein (LCMV GP) was used to prime or to tolerize CD8+ T cells in vivo, dependent on mode of immunization. Peptide-specific tolerance was then examined in transgenic mice expressing LCMV GP in the beta islet cells of the pancreas; these mice develop CD8+ T-cell-mediated diabetes within 8-14 days after LCMV infection. Specific peptide-induced tolerance prevented autoimmune destruction of beta islet cells and diabetes in this transgenic mouse model.