Optimizing oral immune tolerance to Type II collagen in patients with rheumatoid arthritis: The importance of dose, Interfering medication and Genetics.

OBJECTIVES: Oral immune tolerance (OT) is a complex process with unknown genetic regulation. Our aim is to explore possible genetic control of OT in patients with rheumatoid arthritis (RA). METHODS: RA patients with increased interferon γ production invitro when their isolated peripheral blood mononuclear cells (PBMC) were cultured with type II bovine collagen α1 chain [α1 (II)] were enrolled in this study and were randomly assigned to the "Low dose" type II collagen (CII) group (30 µg/day for 10 weeks, followed by 50 µg/day for 10 weeks, followed by 70 µg/day for 10 weeks) or "High dose" CII group (90 µg/day for 10 weeks, followed by 110 µg/day for 10 weeks, followed by 130 µg/day for 10 weeks). Heparinized blood was obtained at baseline and after each of the 10 weeks treatment for analysis of the invitro production of IFNγ by their PBMC stimulated by α1(II) . Single nucleotide polymorphism (SNP) analysis of the responders and non-responders to oral CII was conducted using GeneChip Mapping 10 K 2.0 Array. RESULTS: The SNP A-15,737 was found to associate with the ability of CII to suppress IFNγ production by α1(CII)-stimulated RA PBMC. The potential for SNP A-15,737 to associate with the OT response for patients with another autoimmune disease [OT induced by oral type I bovine collagen (CI) in patients with diffuse cutaneous systemic sclersodid (dsSSc)] was also explored. CONCLUSIONS: The ROT1 region plays a role in the control of IFNγ production after oral dosing of auto-antigens, thereby determining if oral tolerance to that antigen will develop.

Role of Citrullinated Collagen in Autoimmune Arthritis.

Citrullination of proteins plays an important role in protein function and it has recently become clear that citrullinated proteins play a role in immune responses. In this study we examined how citrullinated collagen, an extracellular matrix protein, affects T-cell function during the development of autoimmune arthritis. Using an HLA-DR1 transgenic mouse model of rheumatoid arthritis, mice were treated intraperitoneally with either native type I collagen (CI), citrullinated CI (cit-CI), or phosphate buffered saline (PBS) prior to induction of autoimmune arthritis. While the mice given native CI had significantly less severe arthritis than controls administered PBS, mice receiving cit-CI had no decrease in the severity of autoimmune arthritis. Using Jurkat cells expressing the inhibitory receptor leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1), Western blot analysis indicated that while CI and cit-CI bound to LAIR-1 with similar affinity, only CI induced phosphorylation of the LAIR ITIM tyrosines; cit-CI was ineffective. These data suggest that cit-CI acts as an antagonist of LAIR-1 signaling, and that the severity of autoimmune arthritis can effectively be altered by targeting T cells with citrullinated collagen.

1,25-Dihydroxyvitamin D3 and 20-Hydroxyvitamin D3 Upregulate LAIR-1 and Attenuate Collagen Induced Arthritis.

Vitamin D plays a crucial role in regulation of the immune response. However, treatment of autoimmune diseases with 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] doses sufficient to be effective is prohibitive due to its calcemic and toxic effects. We use the collagen-induced arthritis (CIA) model to analyze the efficacy of the noncalcemic analog of vitamin D, 20S-hydroxyvitamin D3 [20S(OH)D3], as well as 1,25(OH)2D3, to attenuate arthritis and explore a potential mechanism of action. Mice fed a diet deficient in vitamin D developed a more severe arthritis characterized by enhanced secretion of T cell inflammatory cytokines, compared to mice fed a normal diet. The T cell inflammatory cytokines were effectively suppressed, however, by culture of the cells with 20S(OH)D3. Interestingly, one of the consequences of culture with 1,25(OH)2D3 or 20S(OH)D3, was upregulation of the natural inhibitory receptor leukocyte associated immunoglobulin-like receptor-1 (LAIR-1 or CD305). Polyclonal antibodies which activate LAIR-1 were also capable of attenuating arthritis. Moreover, oral therapy with active forms of vitamin D suppressed arthritis in LAIR-1 sufficient DR1 mice, but were ineffective in LAIR-1-/- deficient mice. Taken together, these data show that the effect of vitamin D on inflammation is at least, in part, mediated by LAIR-1 and that non-calcemic 20S(OH)D3 may be a promising therapeutic agent for the treatment of autoimmune diseases such as Rheumatoid Arthritis.

Leukocyte-associated immunoglobulin-like receptor 1 inhibits T-cell signaling by decreasing protein phosphorylation in the T-cell signaling pathway.

Multiple observations implicate T-cell dysregulation as a central event in the pathogenesis of rheumatoid arthritis. Here, we investigated mechanisms for suppressing T-cell activation via the inhibitory receptor leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1). To determine how LAIR-1 affects T-cell receptor (TCR) signaling, we compared 1) T cells from LAIR-1-sufficient and -deficient mice, 2) Jurkat cells expressing either LAIR-1 mutants or C-terminal Src kinase (CSK) mutants, and 3) T cells from mice that contain a CSK transgene susceptible to chemical inhibition. Our results indicated that LAIR-1 engagement by collagen or by complement C1q (C1Q, which contains a collagen-like domain) inhibits TCR signaling by decreasing the phosphorylation of key components in the canonical T-cell signaling pathway, including LCK proto-oncogene SRC family tyrosine kinase (LCK), LYN proto-oncogene SRC family tyrosine kinase (LYN), ζ chain of T-cell receptor-associated protein kinase 70 (ZAP-70), and three mitogen-activated protein kinases (extracellular signal-regulated kinase, c-Jun N-terminal kinase 1/2, and p38). The intracellular region of LAIR-1 contains two immunoreceptor tyrosine-based inhibition motifs that are both phosphorylated by LAIR-1 activation, and immunoprecipitation experiments revealed that Tyr-251 in LAIR-1 binds CSK. Using CRISPR/Cas9-mediated genome editing, we demonstrate that CSK is essential for the LAIR-1-induced inhibition of the human TCR signal transduction. T cells from mice that expressed a PP1 analog-sensitive form of CSK (CskAS) corroborated these findings, and we also found that Tyr-251 is critical for LAIR-1's inhibitory function. We propose that LAIR-1 activation may be a strategy for controlling inflammation and may offer a potential therapeutic approach for managing autoimmune diseases.

The role of Syk in peripheral T cells.

The aim of this study was to understand how Syk affects peripheral T cell function. T cells from Syk-/- chimeric mice and DR1 Sykfl/fl CD4cre conditional mice gave strong CD3-induced Th1, Th2, and Th17 cytokine responses. However, an altered peptide ligand (APL) of human CII (256-276) with two substitutions (F263N, E266D), also called A12, elicited only Th2 cytokine responses from Sykfl/fl T cells but not Sykfl/fl-CD4cre T cells. Western blots revealed a marked increase in the phosphorylation of Syk, JNK and p38 upon A12/DR1 activation in WT or Sykfl/fl T cells but not in Sykfl/flCD4-cre cells. We demonstrate that Syk is required for the APL- induction of suppressive cytokines. Chemical Syk inhibitors blocked activation of GATA-3 by peptide A12/DR1. In conclusion, this study provides novel insights into the role that Syk plays in directing T cell activity, and may shape therapeutic approaches for autoimmune diseases.

The Role of Leukocyte-Associated Ig-like Receptor-1 in Suppressing Collagen-Induced Arthritis.

Several observations implicate a critical role for T cell dysregulation as a central problem in rheumatoid arthritis. We investigated a mechanism for suppressing T cell activation by stimulating a natural inhibitory receptor called leukocyte-associated Ig-like receptor-1 (LAIR-1). The collagen-induced arthritis (CIA) model and DR-1 transgenic mice were used to study the importance of LAIR-1 in autoimmune arthritis. Splenocytes from wild-type or LAIR-1-/- mice were stimulated with soluble anti-CD3 Ab in the presence or absence of α1(II) and supernatants were collected for cytokine analysis. B6.DR1 mice were immunized with type II collagen/CFA to induce arthritis and were treated with either the stimulatory mAb to LAIR-1 or a hamster IgG control. Finally, B6.DR1/LAIR-1-/- and B6.DR1/LAIR-1+/+ mice were challenged for CIA and mean severity scores were recorded thrice weekly. Using splenocytes or purified CD4+ cells that were sufficient in LAIR-1, CD3-induced cytokine secretion was significantly suppressed in the presence of collagen, whereas LAIR-1-deficient splenocytes had no attenuation. Treatment with a stimulatory mAb to LAIR-1 also significantly attenuated CIA in the LAIR+/+ mice. When B6.DR1/LAIR-1-/- mice were immunized with type II collagen they developed more severe arthritis and had a greater percentage of affected limbs than the wild-type mice. These data demonstrate that collagen can suppress the T cell cytokine response through the action of LAIR-1. Treatment with stimulating LAIR-1 Abs suppresses CIA whereas B6.DR1/LAIR-1-/- mice develop more severe arthritis than wild-type controls. These data suggest that LAIR-1 may be a potential therapeutic target for suppressing rheumatoid arthritis.

Characterization of the Syk-Dependent T Cell Signaling Response to an Altered Peptide.

Rheumatoid arthritis is an autoimmune disorder characterized by T cell dysregulation. We have shown that an altered peptide ligand (A9) activates T cells to use an alternate signaling pathway that is dependent on FcRγ and spleen tyrosine kinase, resulting in downregulation of inflammation. In the experiments described in this study, we have attempted to determine the molecular basis of this paradox. Three major Src family kinases found in T cells (Lck, Fyn, and Lyn) were tested for activation following stimulation by A9/I-Aq Unexpectedly we found they are not required for T cell functions induced by A9/I-Aq, nor are they required for APL stimulation of cytokines. On the other hand, the induction of the second messenger inositol trisphosphate and the mobilization of calcium are clearly triggered by the APL A9/I-Aq stimulation and are required for cytokine production, albeit the cytokines induced are different from those produced after activation of the canonical pathway. DBA/1 mice doubly deficient in IL-4 and IL-10 were used to confirm that these two cytokines are important for the APL-induced attenuation of arthritis. These studies provide a basis for exploring the effectiveness of analog peptides and the inhibitory T cells they induce as therapeutic tools for autoimmune arthritis.

Peptide ligand structure and I-Aq binding avidity influence T cell signaling pathway utilization.

Factors that drive T cells to signal through differing pathways remain unclear. We have shown that an altered peptide ligand (A9) activates T cells to utilize an alternate signaling pathway which is dependent upon FcRγ and Syk. However, it remains unknown whether the affinity of peptide binding to MHC drives this selection. To answer this question we developed a panel of peptides designed so that amino acids interacting with the p6 and p9 predicted MHC binding pockets were altered. Analogs were tested for binding to I-A(q) using a competitive binding assay and selected analogs were administered to arthritic mice. Using the collagen-induced arthritis (CIA) model, arthritis severity was correlated with T cell cytokine production and molecular T cell signaling responses. We establish that reduced affinity of interaction with the MHC correlates with T cell signaling through the alternative pathway, leading ultimately to secretion of suppressive cytokines and attenuation of arthritis.

Characterization of T cell phenotype and function in a double transgenic (collagen-specific TCR/HLA-DR1) humanized model of arthritis.

INTRODUCTION: T cells orchestrate joint inflammation in rheumatoid arthritis (RA), yet they are difficult to study due to the small numbers of antigen-specific cells. The goal of this study was to characterize a new humanized model of autoimmune arthritis and to describe the phenotypic and functional changes that occur in autoimmune T cells following the induction of pathological events. METHODS: We developed a double transgenic mouse containing both the HLA-DR1 transgene and an HLA-DR1-restricted collagen-specific TCR in order to obtain large numbers of antigen-specific T cells that can be used for immunologic studies. RESULTS: In vitro, CII-specific T cells from this mouse proliferated vigorously in response to the CII immunodominant peptide A2 and the cells altered their phenotype to become predominately CD62Llow and CD44high "activated" T cells. The response was accompanied by the production of Th1, Th2, and Th17-type cytokines. Following immunization with bovine CII/CFA, these mice develop an accelerated arthritis compared to single transgenic HLA-DR1 mice. On the other hand, when the mice were treated orally with the analog peptide A12, (a suppressive analog of collagen we have previously described), arthritis was significantly suppressed, despite the fact that >90% of the CD4+ T cells express the TCR Tg. In GALT tissues taken from the A12-treated mice, IL-2, IFN-γ, and IL-17 production to the autoimmune collagen determinant dropped while high levels of IL-10 and IL-4 were produced. CONCLUSIONS: We have developed a humanized model of autoimmune arthritis that will be useful for the study of T cell directed therapies as well as T cell mediated mechanisms of autoimmune diseases.

Characterization of inhibitory T cells induced by an analog of type II collagen in an HLA-DR1 humanized mouse model of autoimmune arthritis.

INTRODUCTION: We used DR1 transgenic mice and covalently linked DR1 multimers to characterize analog-specific inhibitory T cells in collagen-induced arthritis (CIA). Because of the low numbers of antigen-specific T cells in wild-type mice, functional T-cell studies in autoimmune arthritis have been challenging. The use of T-cell receptor (TCR) transgenic mice has provided useful information, but such T cells may not represent the heterogeneous T-cell response that occurs in natural settings. Our focus was to develop tools to identify and characterize the population of immunoregulatory T cells induced in wild-type mice by an analog peptide of CII259-273, which contains amino acid substitutions at positions 263 (N) and 266 (D) (analog peptide A12). METHODS: DR1 multimers, developed by loading empty class II molecules with exogenous peptide, provide a method for visualizing antigen-specific T cells with flow cytometry. However, the low binding avidity of A12 for the major histocompatibility complex (MHC) made this strategy untenable. To overcome this problem, we generated DR1 multimers in which the analog peptide A12 was covalently linked, hoping that the low-avidity analog would occupy enough binding clefts to allow detection of the responsive T cells. RESULTS: Staining with the tetramer revealed that A12-specific T cells were readily detectable at 10 days after immunization. These CD4(+) T cells are a highly selective subset of the TCR repertoire and have a limited clonality. Analysis of cytokine expression showed that cells detected by tetramer (A12) expressed primarily suppressive cytokines (interleukin-4 (IL-4) and IL-10) in response to collagen, compared with control cells. Although they did not express Fox-p3, they were extremely effective in preventing and suppressing inflammatory arthritis. CONCLUSIONS: In summary, our studies showed that the use of covalently linked multimers allows characterization of analog-specific T cells that are otherwise difficult to detect. The suppressive character of the analog-specific T-cell response suggests that these cells attenuate autoimmunity and differ significantly in phenotype from the inflammatory T cells predominantly found in arthritic joints. Such reagents will become powerful tools to study T-cell responses in RA patients in upcoming clinical trials.

Molecular basis for T cell response induced by altered peptide ligand of type II collagen.

Mounting evidence from animal models has demonstrated that alterations in peptide-MHC interactions with the T cell receptor (TCR) can lead to dramatically different T cell outcomes. We have developed an altered peptide ligand of type II collagen, referred to as A9, which differentially regulates TCR signaling in murine T cells leading to suppression of arthritis in the experimental model of collagen-induced arthritis. This study delineates the T cell signaling pathway used by T cells stimulated by the A9·I-A(q) complex. We have found that T cells activated by A9 bypass the requirement for Zap-70 and CD3-ζ and signal via FcRγ and Syk. Using collagen-specific T cell hybridomas engineered to overexpress either Syk, Zap-70, TCR-FcRγ, or CD3-ζ, we demonstrate that A9·I-A(q) preferentially activates FcRγ/Syk but not CD3-ζ/Zap-70. Moreover, a genetic absence of Syk or FcRγ significantly reduces the altered peptide ligand induction of the nuclear factor GATA3. By dissecting the molecular mechanism of A9-induced T cell signaling we have defined a new alternate pathway that is dependent upon FcRγ and Syk to secrete immunoregulatory cytokines. Given the interest in using Syk inhibitors to treat patients with rheumatoid arthritis, understanding this pathway may be critical for the proper application of this therapy.

Administering human adipose-derived mesenchymal stem cells to prevent and treat experimental arthritis.

Rheumatoid arthritis is a chronic autoimmune disease and affecting approximately 1% of the population. Human adipose-derived mesenchymal stem cells (hASCs) were recently found to suppress effector T cell and inflammatory responses and, thus, to have beneficial effects in various autoimmune diseases. In this study, we examined whether hASCs could play a protective and/or therapeutic role in collagen-induced arthritis (CIA). We showed that hASCs both prevented and treated CIA by significantly reducing the incidence and severity of experimental arthritis. We further demonstrated that treatment with hASCs inhibited the production of various inflammatory mediators, decreased antigen-specific Th1/Th17 cell expansion, and induced the production of anti-inflammatory cytokine interleukin-10. Moreover, hASCs could induce the generation of antigen-specific Treg cells with the capacity to suppress collagen-specific T cell responses.

T cells stimulated with an analog peptide of type II collagen require the Fc receptor γ-chain to secrete interleukin-4 and suppress autoimmune arthritis in mice.

OBJECTIVE: To explore the characteristics of the T cell population that responds to an analog peptide (A9) of type II collagen and regulates autoimmunity, using the collagen-induced arthritis (CIA) model. METHODS: Analog peptide A9 is a 26-amino acid peptide analogous to the sequence of a segment of type II collagen (CII245-270) but with substitutions at amino acid positions 260 (alanine for isoleucine), 261 (hydroxyproline for alanine), and 263 (asparagine for phenylalanine). We previously showed that A9 profoundly suppressed CIA and immune responses to type II collagen. In order to determine the mechanism of suppression, we used transgenic mice whose T cells express a type II collagen-specific receptor (T cell receptor) and performed passive cell transfer experiments. RESULTS: The results demonstrated that suppression of CIA by A9 is dependent on T cells. Using multiparameter flow cytometry, we determined that the cells responsible for suppression were CD4+ and expressed high levels of Fcε receptor Iγ chain (FcRγ). To establish the significance of this finding, we obtained mice genetically deficient in FcRγ in order to perform passive transfer experiments. The resulting FcRγ-/- CD4+ T cells, when primed by culture with A9, could not transfer the suppression of arthritis or secrete cytokines in response to A9. CONCLUSION: Taken together, the results of this study suggest that the suppression of arthritis and the Th2 cytokine profile elicited by A9 is dependent on the presence of FcRγ in T cells. These findings are novel and may have therapeutic potential for patients with autoimmune arthritis.

Modulation of collagen-induced arthritis by adenovirus-mediated intra-articular expression of modified collagen type II.

INTRODUCTION: Rheumatoid arthritis (RA) is a systemic disease manifested by chronic inflammation in multiple articular joints, including the knees and small joints of the hands and feet. We have developed a unique modification to a clinically accepted method for delivering therapies directly to the synovium. Our therapy is based on our previous discovery of an analog peptide (A9) with amino acid substitutions made at positions 260 (I to A), 261 (A to B), and 263 (F to N) that could profoundly suppress immunity to type II collagen (CII) and arthritis in the collagen-induced arthritis model (CIA). METHODS: We engineered an adenoviral vector to contain the CB11 portion of recombinant type II collagen and used PCR to introduce point mutations at three sites within (CII124-402, 260A, 261B, 263D), (rCB11-A9) so that the resulting molecule contained the A9 sequence at the exact site of the wild-type sequence. RESULTS: We used this construct to target intra-articular tissues of mice and utilized the collagen-induced arthritis model to show that this treatment strategy provided a sustained, local therapy for individual arthritic joints, effective whether given to prevent arthritis or as a treatment. We also developed a novel system for in vivo bioimaging, using the firefly luciferase reporter gene to allow serial bioluminescence imaging to show that luciferase can be detected as late as 18 days post injection into the joint. CONCLUSIONS: Our therapy is unique in that we target synovial cells to ultimately shut down T cell-mediated inflammation. Its effectiveness is based on its ability to transform potential inflammatory T cells and/or bystander T cells into therapeutic (regulatory-like) T cells which secrete interleukin (IL)-4. We believe this approach has potential to effectively suppress RA with minimal side effects.

Collagen-induced arthritis.

The mouse model collagen-induced arthritis (CIA) is a widely studied autoimmune model of rheumatoid arthritis. In this model, autoimmune arthritis is induced by immunization with type II collagen (CII) emulsified in complete Freund's adjuvant. This unit describes the steps necessary for the acquisition, handling, and preparation of CII, in addition to the selection of mouse strains, proper immunization technique, and methods for evaluation of the incidence and severity of arthritis. In this model, the first signs of arthritis appear approximately 21 to 28 days after immunization. The protocols in this unit should provide the investigator with all the necessary information required to reproducibly induce a high incidence of CIA in genetically susceptible strains of mice, and to critically evaluate the pathology of the disease.

T cell receptor signaling induced by an analog peptide of type II collagen requires activation of Syk.

We have previously described an analog peptide of type II collagen (CII) that can suppress collagen-induced arthritis (CIA). This analog peptide represents CII(245-270), the immunodominant epitope of CII, but with substitutions at 260, 261, and 263 - CII(245-270) (A(260), B(261), and N(263)) (A9). To elucidate the mechanisms responsible for suppression, we used mice transgenic for a collagen-specific T cell receptor (TCR). When we found that APCs pulsed with A9 failed to induce T cell phosphorylation of TCR-zeta and ZAP-70, we explored alternative signaling pathways. We determined that A9 instead induced phosphorylation of spleen tyrosine kinase (Syk). The importance of Syk was confirmed by the use of chemical Syk inhibitors, which blocked both cytokine secretion and activation of GATA-3 mediated by peptide A9. In summary, T cells use an alternative pathway in response to A9 that involves Syk. This novel T cell pathway may represent an important means for altering T cell phenotypes.

Genetic and molecular basis of quantitative trait loci of arthritis in rat: genes and polymorphisms.

Rheumatoid arthritis (RA) is an autoimmune disease, the pathogenesis of which is affected by multiple genetic and environmental factors. To understand the genetic and molecular basis of RA, a large number of quantitative trait loci (QTL) that regulate experimental autoimmune arthritis have been identified using various rat models for RA. However, identifying the particular responsible genes within these QTL remains a major challenge. Using currently available genome data and gene annotation information, we systematically examined RA-associated genes and polymorphisms within and outside QTL over the whole rat genome. By the whole genome analysis of genes and polymorphisms, we found that there are significantly more RA-associated genes in QTL regions as contrasted with non-QTL regions. Further experimental studies are necessary to determine whether these known RA-associated genes or polymorphisms are genetic components causing the QTL effect.

A multicenter, randomized, double-blind, placebo-controlled trial of oral type I collagen treatment in patients with diffuse cutaneous systemic sclerosis: I. oral type I collagen does not improve skin in all patients, but may improve skin in late-phase disease.

OBJECTIVE: To investigate the safety and efficacy of oral bovine type I collagen (CI) treatment in patients who have had diffuse cutaneous systemic sclerosis (dcSSc; scleroderma) for

An altered peptide ligand of type II collagen suppresses autoimmune arthritis.

On the basis of the hypothesis that immunity to type II collagen (CII) contributes to joint inflammation, our goal is to develop an immunotherapy capable of selectively blocking immunity to a particular autoantigen without interfering with the beneficial functions of the immune system. CII is the major protein component of articular cartilage and autoimmunity to CII is strongly associated with rheumatoid arthritis in man. Our laboratory has previously identified a region of type II collagen (CII), CII245-270 that contains a prominent T-cell epitope in the immune response to CII. Residues critical to the I-Aq-restricted presentation of this determinant have been characterized. When synthetic analog peptides were developed that contain site-directed substitutions in critical positions, we found that that CII245-270 (A260, B261, N263) (A9), profoundly suppressed collagen-induced arthritis. When DBA/1 mice were coimmunized with CII and the analog peptide, the incidence and severity of arthritis was greatly reduced concordant with the humoral immune responses to CII. Moreover, the suppression could be transferred with A9-immune spleen cells and was accompanied by a Th2-type cytokine profile. When we compared T-cell signals in response to A9 to those of wild-type (WT) peptide, we found that APCs prepulsed with WT peptide induced strong phosphorylation of both TCR zeta chain and Zap-70, while A9 did not. Since T cells clearly respond to A9 with cytokine secretion, we hypothesize that A9 induces an alternate signaling pathway and we speculate that this pathway involves phosphorylation of Syk, a kinase ordinarily utilized by B cells. Activation of this alternative pathway is a novel observation and may represent an important means by which the phenotype of the responding T cell is altered. Elucidation of the mechanism by which A9 prevents arthritis may lead to development of novel immunotherapeutic approaches to antigen specific treatment of autoimmunity.

Crystallographic structure of a rheumatoid arthritis MHC susceptibility allele, HLA-DR1 (DRB1*0101), complexed with the immunodominant determinant of human type II collagen.

The expression of HLA-DR1 (DRB1*0101) is associated with an enhanced risk for developing rheumatoid arthritis (RA). To study its function, we have solved the three-dimensional structure of HLA-DR1 complexed with a candidate RA autoantigen, the human type II collagen peptide CII (259-273). Based on these structural data, the CII peptide is anchored by Phe263 at the P1 position and Glu266 at P4. Surprisingly, the Lys at the P2 position appears to play a dual role by participating in peptide binding via interactions with DRB1-His81 and Asn82, and TCR interaction, based on functional assays. The CII peptide is also anchored by the P4 Glu266 residue through an ionic interaction with DRB1-Arg71 and Glu28. Participation of DRB1-Arg71 is significant because it is part of the shared epitope expressed by DR alleles associated with RA susceptibility. Potential anchor residues at P6 and P9 of the CII peptide are both Gly, and the lack of side chains at these positions appears to result in both a narrower binding groove with the peptide protruding out of the groove at this end of the DR1 molecule. From the TCR perspective, the P2-Lys264, P5-Arg267, and P8-Lys270 residues are all oriented away from the binding groove and collectively represent a positive charged interface for CII-specific TCR binding. Comparison of the DR1-CII structure to a DR1-hemagglutinin peptide structure revealed that the binding of these two peptides generates significantly different interfaces for the interaction with their respective Ag-specific TCRs.