Yeast display of MHC-II enables rapid identification of peptide ligands from protein antigens (RIPPA)

CD4+ T cells orchestrate adaptive immune responses via binding of antigens to their receptors through specific peptide/MHC-II complexes. To study these responses, it is essential to identify protein-derived MHC-II peptide ligands that constitute epitopes for T cell recognition. However, generating cells expressing single MHC-II alleles and isolating these proteins for use in peptide elution or binding studies is time consuming. Here, we express human MHC alleles (HLA-DR4 and HLA-DQ6) as native, noncovalent αβ dimers on yeast cells for direct flow cytometry-based screening of peptide ligands from selected antigens. We demonstrate rapid, accurate identification of DQ6 ligands from pre-pro-hypocretin, a narcolepsy-related immunogenic target. We also identify 20 DR4-binding SARS-CoV-2 spike peptides homologous to SARS-CoV-1 epitopes, and one spike peptide overlapping with the reported SARS-CoV-2 epitope recognized by CD4+ T cells from unexposed individuals carrying DR4 subtypes. Our method is optimized for immediate application upon the emergence of novel pathogens.

Molecular mimicry between varicella, measles virus and Hsp60 in type 1 diabetes associated HLA-DR3/DR4 molecules

BACKGROUND AND AIMS

Type 1 diabetes (T1D) is a multifactorial autoimmune disease that combines genetics and environmental factors. The aim of this study is to determine the environmental risk factors and to investigate how virals infections are risks factors for type 1 diabetics whom have HLA DR3/DR4 predisposition in our population.

METHODS

This study includes 233 subjects, 145 diabetics and 88 controls from regions of the extreme western of Algeria. All the informations related to the disease were collected using predesigned questionnaire. Using in silico approach, we attempt to improve the understanding of this analytical result by molecular mimicry, which is associated with the breakdown of several autoimmune pathologies.

RESULTS

The statistical study showed that history of varicella and measles infection and T1D related inheritance and type 2 diabetes are risk factors for T1D in the population of Tlemcen. We have determined the homologous antigenic regions between the glycoprotein "gE" of the varicella virus, the "hemagglutinin" of measles and the human protein "HSP60" at the level of their sequence and 3D structure. These cross-reactive epitopes bind to MHC class II molecules (HLA DR3/DR4) that predispose to T1D but not to MHC class II molecules (HLA DR2) that protect against T1D. This epitopes induce Th2 cells but only "hemagglutinin" and "Hsp60" can activate Th1 differentiation. This indicates their potential to destroy pancreatic cells β.

CONCLUSION

Our study can allow us to adapt biological markers to genetically predisposed T1D and to establish a preventive strategy for healthy genetic predisposed individuals in Tlemcen population.

Aire is not essential for regulating neuroinflammatory disease in mice transgenic for human autoimmune-diseases associated MHC class II genes HLA-DR2b and HLA-DR4

The human autoimmune disease-associated HLA alleles HLA-DR2b (DRB1*1501) and HLA-DR4 (DRB1*0401) are strongly linked to increased susceptibility for multiple sclerosis (MS) and rheumatoid arthritis (RA), respectively. The underlying mechanisms are not fully understood, but these MHC alleles may shape the repertoire of pathogenic T cells via central tolerance. The transcription factor autoimmune regulator (AIRE) promotes central T cell tolerance via ectopic expression of tissue-specific antigens (TSAs). Aire deficiency in humans causes autoimmune polyendocrinopathy syndrome type 1 (APS1), and Aire knockout mice (Aire-/-) develop spontaneous autoimmune pathology characterized by multi-organ lymphocytic infiltrates. Here, we asked whether impaired TSAs gene expression in the absence of Aire promoted spontaneous MS- or RA-like autoimmune pathology in the context of human HLA alleles in HLA-DR2b or HLA-DR4 transgenic (tg) mice. The results show that reduced TSAs gene expression in the thymus of Aire-deficient HLA-DR2b or HLA-DR4 tg mice corresponded to mild spontaneous inflammatory infiltrates in salivary glands, liver, and pancreas. Moreover, Aire-deficiency modestly enhanced experimental autoimmune encephalomyelitis (EAE) in HLA-DR tg mice, but the animals did not show signs of spontaneous neuroinflammation or arthritis. No significant changes were observed in CD4+ T cell numbers, T cell receptor (TCR) distribution, regulatory T cells (Treg), or antigen-induced cytokine production. Abrogating Treg function by treatment with anti-CTLA-4 or anti-CD25 mAb in Aire-deficient HLA-DR tg mice did not trigger EAE or other autoimmune pathology. Our results suggest a redundant role for Aire in maintaining immune tolerance in the context of autoimmune disease-associated human HLA alleles.

Collateral Damage: Insulin-Dependent Diabetes Induced With Checkpoint Inhibitors

Insulin-dependent diabetes may occur in patients with cancers who are treated with checkpoint inhibitors (CPIs). We reviewed cases occurring over a 6-year period at two academic institutions and identified 27 patients in whom this developed, or an incidence of 0.9%. The patients had a variety of solid-organ cancers, but all had received either anti-PD-1 or anti-PD-L1 antibodies. Diabetes presented with ketoacidosis in 59%, and 42% had evidence of pancreatitis in the peridiagnosis period. Forty percent had at least one positive autoantibody and 21% had two or more. There was a predominance of HLA-DR4, which was present in 76% of patients. Other immune adverse events were seen in 70%, and endocrine adverse events in 44%. We conclude that autoimmune, insulin-dependent diabetes occurs in close to 1% of patients treated with anti-PD-1 or -PD-L1 CPIs. This syndrome has similarities and differences compared with classic type 1 diabetes. The dominance of HLA-DR4 suggests an opportunity to identify those at highest risk of these complications and to discover insights into the mechanisms of this adverse event.

A Comparative Analysis of the Peptide Repertoires of HLA-DR Molecules Differentially Associated With Rheumatoid Arthritis

OBJECTIVE

To evaluate similarity of the peptide repertoires bound to HLA-DR molecules that are differentially associated with rheumatoid arthritis (RA), and to define structural features of the shared peptides.

METHODS

Peptide pools bound to HLA-DRB1*01:01, HLA-DRB1*04:01, and HLA-DRB1*10:01 (RA associated) and those bound to HLA-DRB1*15:01 (non-RA-associated) were purified and analyzed by liquid chromatography (LC) matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MS) and LC-ion-trap MS. Peptide pools from each allotype were compared in terms of size, protein origin, composition, and affinity (both theoretical and experimental with some peptides). Finally, 1 peptide sequenced from DR1, DR4, and DR10, but not from DR15, was modeled in complex with all 4 HLA-DRB1 molecules and HLA-DRB5*01:01.

RESULTS

A total of 6,309 masses and 962 unique peptide sequences were compared. DR10 shared 29 peptides with DR1, 9 with DR4, and 1 with DR15; DR1 shared 6 peptides with DR4 and 9 with DR15; and DR4 and DR15 shared 4 peptides. The direct identification of peptide ligands indicated that DR1 and DR10 were the most similar molecules regarding the peptides that they could share. The peptides common to these molecules contained a high proportion of Leu at P4 and basic residues at P8 binding core positions.

CONCLUSION

The degree of overlap between peptide repertoires associated with different HLA-DR molecules is low. The repertoires associated with DR1 and DR10 have the highest similarity among the molecules analyzed (∼10% overlap). Among the peptides shared between DR1 and DR10, a high proportion contained Leu(4) and basic residues at the P8 position of the binding core.

Sugar intake is associated with progression from islet autoimmunity to type 1 diabetes: the Diabetes Autoimmunity Study in the Young

AIMS/HYPOTHESIS

Dietary sugar intake may increase insulin production, stress the beta cells and increase the risk for islet autoimmunity (IA) and subsequent type 1 diabetes.

METHODS

Since 1993, the Diabetes Autoimmunity Study in the Young (DAISY) has followed children at increased genetic risk for type 1 diabetes for the development of IA (autoantibodies to insulin, GAD or protein tyrosine phosphatase-like protein [IA2] twice or more in succession) and progression to type 1 diabetes. Information on intake of fructose, sucrose, total sugars, sugar-sweetened beverages, beverages with non-nutritive sweetener and juice was collected prospectively throughout childhood via food frequency questionnaires (FFQs). We examined diet records for 1,893 children (mean age at last follow-up 10.2 years); 142 developed IA and 42 progressed to type 1 diabetes. HLA genotype was dichotomised as high risk (HLA-DR3/4,DQB1*0302) or not. All Cox regression models were adjusted for total energy, FFQ type, type 1 diabetes family history, HLA genotype and ethnicity.

RESULTS

In children with IA, progression to type 1 diabetes was significantly associated with intake of total sugars (HR 1.75, 95% CI 1.07-2.85). Progression to type 1 diabetes was also associated with increased intake of sugar-sweetened beverages in those with the high-risk HLA genotype (HR 1.84, 95% CI 1.25-2.71), but not in children without it (interaction p value = 0.02). No sugar variables were associated with IA risk.

CONCLUSIONS/INTERPRETATION

Sugar intake may exacerbate the later stage of type 1 diabetes development; sugar-sweetened beverages may be especially detrimental to children with the highest genetic risk of developing type 1 diabetes.

Coexisting ankylosing spondylitis and rheumatoid arthritis: a case report with literature review

A 30-year-old female patient with coexisting ankylosing spondylitis and rheumatoid arthritis was diagnosed and treated. The human leukocyte antigen (HLA)-B27 is a predisposing factor of ankylosing spondylitis and HLA-DR4 is a predisposing factor of rheumatoid arthritis. This patient was HLA-B27 and HLA-DR4 positive, and ankylosing spondylitis manifested before rheumatoid arthritis. After disease modifying anti-rheumatic drugs successfully arrested ankylosing spondylitis activity the patient conceived and delivered a healthy baby. One year later, she developed peripheral polyarthritis and was diagnosed with rheumatoid arthritis. We hypothesized that pregnancy may be one of the environmental factors that can activate rheumatoid arthritis, and that disease modifying anti-rheumatic drugs play an important role in keeping the disease under control.

Review on monogenic diabetes

PURPOSE OF REVIEW

The goal of this review is to provide an update on the different forms of monogenic diabetes, including maturity-onset diabetes of the young (MODY) and neonatal diabetes (permanent and transient neonatal diabetes).

RECENT FINDINGS

Monogenic diabetes accounts for approximately 1-2% of diabetes cases and results from mutations that primarily reduce β-cell function. Individuals with islet autoantibody negative youth-onset forms of diabetes should be evaluated for either glucokinase-MODY or transcription factors MODY. The mild-fasting hyperglycemia found in glucokinase-MODY typically does not necessitate pharmacological treatment, whereas patients with MODY caused by transcription factor mutations can often be successfully treated with low-dose sulfonylurea. Neonatal diabetes is defined as diabetes onset within the first 6 months of life and most individuals with permanent neonatal diabetes can be treated with high-dose sulfonylurea.

SUMMARY

The discovery of the genetic cause of monogenic diabetes has greatly advanced our understanding and management of these uncommon forms of diabetes.

Design of glycopeptides used to investigate class II MHC binding and T-cell responses associated with autoimmune arthritis

The glycopeptide fragment CII259–273 from type II collagen (CII) binds to the murine A^q and human DR4 class II Major Histocompatibility Complex (MHC II) proteins, which are associated with development of murine collagen-induced arthritis (CIA) and rheumatoid arthritis (RA), respectively. It has been shown that CII259–273 can be used in therapeutic vaccination of CIA. This glycopeptide also elicits responses from T-cells obtained from RA patients, which indicates that it has an important role in RA as well. We now present a methodology for studies of (glyco)peptide-receptor interactions based on a combination of structure-based virtual screening, ligand-based statistical molecular design and biological evaluations. This methodology included the design of a CII259–273 glycopeptide library in which two anchor positions crucial for binding in pockets of A^q and DR4 were varied. Synthesis and biological evaluation of the designed glycopeptides provided novel structure-activity relationship (SAR) understanding of binding to A^q and DR4. Glycopeptides that retained high affinities for these MHC II proteins and induced strong responses in panels of T-cell hybridomas were also identified. An analysis of all the responses revealed groups of glycopeptides with different response patterns that are of high interest for vaccination studies in CIA. Moreover, the SAR understanding obtained in this study provides a platform for the design of second-generation glycopeptides with tuned MHC affinities and T-cell responses.

[Association of HLA-DR4, PAD4, and STAT4 expression in the peripheral blood with disease activity in patients with rheumatoid arthritis]

OBJECTIVE

To explore the association of the expressions of human leukocyte antigen (HLA)-DR4, peptidyl arginine deiminase type4(PAD4), and signal transducer and activator of transcription 4 (STAT4) in the peripheral blood with the disease activity in patients with rheumatoid arthritis (RA).

METHODS

Twenty-four RA patients in active stage (DAS28 score>or=2.6) and 14 RA patients in remission stage (DAS28 score<2.6) were enrolled in this study, with 12 healthy volunteers as the control. The QuantiGene Plex method was used to measure the expression level of HLA-DR4, PAD4, and STAT4 mRNA, and the relationship between the expressions of these genes and the DAS28 score, levels of anti-cyclic citrullinated peptide antibody (anti-CCP antibody) and rheumatoid factor (RF) was analyzed.

RESULTS

The expressions of HLA-DR4, PAD4, and STAT4 were significantly higher in RA patients than in the healthy controls (P<0.05). The level of HLA-DR4 mRNA in the two RA groups showed no significant difference, but was significantly higher than that in the healthy controls. HLA-DR4 expression was not found to correlated to DAS28 score, anti-CCP antibody level or RF in the RA patients. The expressions of PAD4 and STAT4 were significantly different between the two RA groups (P<0.05). In the RA patients, PAD4 mRNA expression was positively correlated to DAS28 and anti-CCP antibody level (P<0.05), and STAT4 expression showed positive correlations to DAS28 and RF levels (P<0.05).

CONCLUSION

HLA-DR4, PAD4 and STAT4 are overexpressed in RA patients and may be involved in the pathogenesis of RA. The expressions of PAD4 and STAT4, but not HLA-DR4, are closely related to the disease activity of RA. Detection of peripheral blood PAD4 and STAT4 expressions can be helpful for evaluating the disease activity of RA.

Identification of an altered peptide ligand based on the endogenously presented, rheumatoid arthritis-associated, human cartilage glycoprotein-39(263-275) epitope: an MHC anchor variant peptide for immune modulation

We sought to identify an altered peptide ligand (APL) based on the endogenously expressed synovial auto-epitope of human cartilage glycoprotein-39 (HC gp-39) for modulation of cognate, HLA-DR4-restricted T cells. For this purpose we employed a panel of well-characterized T cell hybridomas generated from HC gp-39-immunized HLA-DR4 transgenic mice. The hybridomas all respond to the HC gp-39(263–275) epitope when bound to HLA-DR4(B1*0401) but differ in their fine specificities. First, the major histocompatibility complex (MHC) and T-cell receptor (TCR) contact residues were identified by analysis of single site substituted analogue peptides for HLA-DR4 binding and cognate T cell recognition using both T hybridomas and polyclonal T cells from peptide-immunized HLA-DR4 transgenic mice. Analysis of single site substituted APL by cognate T cells led to identification of Phe265 as the dominant MHC anchor. The amino acids Ala268, Ser269, Glu271 and Thr272 constituted the major TCR contact residues, as substitution at these positions did not affect HLA-DR4(B1*0401) binding but abrogated T cell responses. A structural model for visualisation of TCR recognition was derived. Second, a set of non-classical APLs, modified at the MHC key anchor position but with unaltered TCR contacts, was developed. When these APLs were analysed, a partial TCR agonist was identified and found to modulate the HC gp-39(263–275)-specific, pro-inflammatory response in HLA-DR4 transgenic mice. We identified a non-classical APL by modification of the p1 MHC anchor in a synovial auto-epitope. This APL may qualify for rheumatoid arthritis immunotherapy.

Associations between serum anti-CCP antibody, rheumatoid factor levels and HLA-DR4 expression in Hungarian patients with rheumatoid arthritis

BACKGROUND

The presence of anti-cyclic citrullinated peptide autoantibody is highly specific for rheumatoid arthritis. Certain HLA-DR4 (HLA-DRB1*04) alleles, also known as the "shared epitope," are associated with increased susceptibility to RA. In addition, these alleles may also have relevance for disease outcome. Anti-CCP antibody positivity has been associated with the presence of HLA-DR4 alleles in patients with RA. However, there is little information regarding a relationship between quantitative anti-CCP production (serum anti-CCP concentrations) and the shared epitope.

OBJECTIVES

To determine the association between anti-CCP antibody production and various HLA-DRB1 alleles.

METHODS

Serum anti-CCP, rheumatoid factor and C-reactive protein levels were assessed in 53 RA patients. All these patients underwent HLA-DRB1 genotyping.

RESULTS

Of the 53 patients 33 (62%) were positive for anti-CCP antibody. We found significant correlations between anti-CCP and RF positivity (chi-square = 6.717, P < 0.01), as well as between anti-CCP and HLA-DRB1*04 positivity (chi-square = 5.828, P < 0.01). There was no correlation between RF positivity and serum levels, CRP serum levels and HLA-DRB1*04 positivity. When quantitatively comparing serum anti-CCP levels with shared epitope positivity, patients carrying one or two copies of HLA-DRB1*04 alleles had significantly higher anti-CCP concentrations (530.0 +/- 182.6 U/ml) compared to DRB1*04-negative patients (56.8 +/- 27.4 U/ml) (P < 0.01). There was no difference in serum anti-CCP antibody concentrations between patients carrying only one HLA-DRB1*01 allele but no HLA-DRB1*04 allele (12.0 +/- 8.6 U/ml) compared to SE-negative patients (76.8 +/- 56.2 U/ml). Regarding non-SE HLA-DRB1 genotypes, all 6 patients (100%) carrying DRB1*15 alleles and 6 of 7 (85%) patients carrying DRB1*13 were anti-CCP positive. In addition, patients with HLA-DRB1*13 (282.5 +/- 23.8 U/ml) and DRB1*15 (398.7 +/- 76.2 U/ml) produced significantly more anti-CCP than did any other non-SE HLA-DRB1 subtypes (P < 0.01).

CONCLUSIONS

There is significant association between anti-CCP and RF, as well as between anti-CCP and SE positivity in RA. In addition, the presence of one or two copies of HLA-DRB1*04 alleles has been associated with higher serum anti-CCP antibody levels. Thus, patients carrying HLA-DRB1*04 alleles exhibited an overall tenfold increase in serum anti-CCP antibody levels in comparison to HLA-DRB1*04-negative subjects. Increased anti-CCP production may also be associated with other non-SE HLA-DRB1 genotypes, such as DRB1*13 or DRB1*15. In reports by other investigators, both anti-CCP concentrations and SE positivity were related to more rapid disease progression and unfavorable outcome.

Ligand design by a combinatorial approach based on modeling and experiment: application to HLA-DR4

Combinatorial synthesis and large scale screening methods are being used increasingly in drug discovery, particularly for finding novel lead compounds. Although these "random" methods sample larger areas of chemical space than traditional synthetic approaches, only a relatively small percentage of all possible compounds are practically accessible. It is therefore helpful to select regions of chemical space that have greater likelihood of yielding useful leads. When three-dimensional structural data are available for the target molecule this can be achieved by applying structure-based computational design methods to focus the combinatorial library. This is advantageous over the standard usage of computational methods to design a small number of specific novel ligands, because here computation is employed as part of the combinatorial design process and so is required only to determine a propensity for binding of certain chemical moieties in regions of the target molecule. This paper describes the application of the Multiple Copy Simultaneous Search (MCSS) method, an active site mapping and de novo structure-based design tool, to design a focused combinatorial library for the class II MHC protein HLA-DR4. Methods for the synthesizing and screening the computationally designed library are presented; evidence is provided to show that binding was achieved. Although the structure of the protein-ligand complex could not be determined, experimental results including cross-exclusion of a known HLA-DR4 peptide ligand (HA) by a compound from the library. Computational model building suggest that at least one of the ligands designed and identified by the methods described binds in a mode similar to that of native peptides.

T84-intestinal epithelial exosomes bear MHC class II/peptide complexes potentiating antigen presentation by dendritic cells

BACKGROUND & AIMS

Intestinal epithelial cells release antigen-presenting vesicles (exosomes) bearing major histocompatibility complex class II/peptide complexes stimulating specific immune responses in vivo. To characterize further the role of human epithelial exosomes in antigen presentation, their capacity to load antigenic peptides, bind immune target cells, and induce T-cell activation was analyzed in vitro.

METHODS

The capacity of exosomes derived from the HLA-DR4-expressing, intestinal epithelial cell line T84 to load the HLA-DR4-specific peptide (3)H-HSA 64-76 and to activate a HLA-DR4-restricted T-cell hybridoma was tested in the presence or absence of human monocyte-derived dendritic cells (DCs). Interaction of fluorescein isothiocyanate-labeled exosomes with T cells and DCs was analyzed by flow cytometry and confocal microscopy.

RESULTS

T84-derived exosomes, enriched in CD9, CD81, CD82, and A33 antigen, were capable of binding specifically human serum albumin (HSA) 64-76 peptide on HLA-DR4 molecules and of interacting preferentially with DCs. HSA-loaded exosomes were unable to activate the T-cell hybridoma directly but induced a productive T-cell activation through DCs. When HSA peptide was bound to exosomal HLA-DR4 molecules instead of in a soluble form, the threshold of peptide presentation by DCs was markedly decreased (x10(-3)).

CONCLUSIONS

Exosomes released by intestinal epithelial cells bear exogenous peptides complexed to major histocompatibility complex class II molecules and interact preferentially with DCs, strongly potentiating peptide presentation to T cells. Epithelial exosomes constitute a powerful link between luminal antigens and local immune cells by mediating the transfer of tiny amounts of luminal antigenic information and facilitating immune surveillance at mucosal surfaces.

New humanized HLA-DR4-transgenic mice that mimic the sex bias of rheumatoid arthritis

OBJECTIVE

To generate a mouse model that can mimic human rheumatoid arthritis (RA). A major difference between RA in humans and collagen-induced arthritis (CIA) in mice is the lack of sex bias and autoantibodies in the animal model. We used DRB1*0401-transgenic mice to understand the role of DR4 in susceptibility and sex bias in RA.

METHODS

A transgenic mouse was generated that lacked all endogenous mouse class II genes (AE(o)) and expressed the RA susceptibility allele HLA-DRB1*0401. These transgenic mice were tested for incidence, severity, and sex distribution of CIA.

RESULTS

DRB1*0401.AE(o) mice developed CIA predominantly in females and produced rheumatoid factors, similar to the features of human RA. Another feature similar to human RA is the expression of class II molecules on antigen-presenting cells as well as T cells. Activated and sorted CD4(+) T cells can present DR4-restricted type II collagen (CII)-derived peptide in vitro, but cannot process the antigen. This suggests a role for these cells in epitope presentation locally in joints, which affects disease severity. After challenge with CII, female mice had higher cellularity and increased T cell proliferation and produced higher levels of proinflammatory cytokines than did the male mice.

CONCLUSION

DR4.AE(o) mice expressed HLA similar to humans and displayed increased arthritis susceptibility in females, thus mimicking RA in humans. This model may be valuable for studying sex differences observed in humans and for understanding why autoimmunity is increased in women. These mice may also be useful for developing future therapeutic strategies.

Analog peptides of type II collagen can suppress arthritis in HLA-DR4 (DRB1*0401) transgenic mice

Rheumatoid arthritis (RA) is an autoimmune disease associated with the recognition of self proteins secluded in diarthrodial joints. We have previously established that mice transgenic for the human DR genes associated with RA are susceptible to collagen-induced arthritis (CIA) and we have identified a determinant of type II collagen (CII(263-270)) that triggers T-cell immune responses in these mice. We have also determined that an analog of CII(263-270) would suppress disease in DR1 transgenic mice. Because the immunodominant determinant is the same for both DR1 transgenic and DR4 transgenic mice, we attempted to determine whether the analog peptide that was suppressive in DR1 transgenic mice would also be effective in suppressing CIA in DR4 transgenic mice. We treated DR4 transgenic mice with two analog peptides of CII that contained substitutions in the core of the immunodominant determinant: CII(256-276) (F263N, E266D) and CII(256-270) (F263N, E266A). Mice were observed for CIA, and T-cell proliferative responses were determined. Either peptide administered at the time of immunization with CII significantly downregulated arthritis. Binding studies demonstrated that replacement of the phenylalanine residue in position 263 of the CII peptide with asparagine significantly decreased the affinity of the peptide for the DR4 molecule. In contrast, replacement of the glutamic acid residue in position 266 with aspartic acid or with alanine had differing results. Aspartic acid reduced the affinity (35-fold) whereas alanine did not. Both peptides were capable of suppressing CIA. With the use of either peptide, CII(256-276) (F263N, E266D) or CII(256-270) (F263N, E266A), the modulation of CIA was associated with an increase in T-cell secretion of IL-4 together with a decrease in IFN-gamma. We have identified two analog peptides that are potent suppressors of CIA in DR4 transgenic mice. These experiments represent the first description of an analog peptide of CII recognized by T cells in the context of HLA-DR4 that can suppress autoimmune arthritis.

Evidence for a Domain-Swapped CD4 Dimer as the Coreceptor for Binding to Class II MHC

CD4 is a coreceptor for binding of T cells to APC and the primary receptor for HIV. The disulfide bond in the second extracellular domain (D2) of CD4 is reduced on the cell surface, which leads to formation of disulfide-linked homodimers. A large conformational change must take place in D2 to allow for formation of the disulfide-linked dimer. Domain swapping of D2 is the most likely candidate for the conformational change leading to formation of two disulfide-bonds between Cys130 in one monomer and Cys159 in the other one. Mild reduction of the extracellular part of CD4 resulted in formation of disulfide-linked dimers, which supports the domain-swapped model. The functional significance of dimer formation for coreceptor function was tested using cells expressing wild-type or disulfide-bond mutant CD4. Eliminating the D2 disulfide bond markedly impaired CD4's coreceptor function. Modeling of the complex of the TCR and domain-swapped CD4 dimer bound to class II MHC and Ag supports the domain-swapped dimer as the immune coreceptor. The known involvement of D4 residues Lys318 and Gln344 in dimer formation is also accommodated by this model. These findings imply that disulfide-linked dimeric CD4 is the preferred coreceptor for binding to APC.

Influenza virus haemagglutinin-derived peptides inhibit T-cell activation induced by HLA-DR4/1 specific peptides in rheumatoid arthritis

OBJECTIVE

To investigate whether influenza virus haemagglutinin (HA)-derived altered peptide ligands (APLs) could abrogate T-cell responses to wild type HA308-317 or type II collagen (CII) 263-272 peptides and explore the potential inhibitory effects of the altered HA308-317 peptides on T-cell activation in rheumatoid arthritis (RA).

METHODS

Altered HA308-317 peptides containing substitutions of T-cell receptor (TCR)-contact residues were synthesized. Peripheral blood mononuclear cells (PBMC) were obtained from 27 HLA-DR4/1-positive RA patients. Impact of the altered HA308-317 peptides on T-cell responses and the inhibitory effects on T-cell activation were determined by using PBMC from RA.

RESULTS

The results showed that the altered HA308-317 peptides could bind to HLA-DR4/1 on cell surface and had no effects on T-cell proliferation and CD25 expression. Moreover, all the altered HA308-317 peptides inhibited T-cell proliferative responses to wild type HA308-317 or CII263-272. In addition, Th1 type cytokine profile was found when PBMC were cultured with wild type HA308-317 or CII263-272, but not the altered HA 308-317 peptides.

CONCLUSIONS

It is suggested that altered HA308-317 peptides bind to the RA-associated HLA-DR4/1 with no stimulating effects on T cells and might be potentially important in inhibition of T-cell activation in RA.

Altered collagen II peptides inhibited T-cell activation in rheumatoid arthritis

It has been reported that collagen II (CII)-derived peptide induced T-cell activation via its amino acids responsible for T-cell receptor (TCR) recognition. In this study, three altered CII263-272 peptide ligands (APL) containing multiple substitutions of TCR contact residues were synthesized. Their roles in inhibition of T-cell activation were evaluated in peripheral blood lymphocytes (PBL) of rheumatoid arthritis (RA) in vitro. It was shown that 41% (25/61) of RA patients were responsive to the wild-type antigenic CII263-272. In contrast, marginal or silent T-cell responses to the three APLs were found, accompanied by inhibitory effects on secretion of Th1 type cytokines and expression of cell surface markers, CD69 and CD25. In addition, T-cell activation induced by the wild-type antigenic CII263-272 was inhibited by all the three APLs in a dose-dependent manner. It is demonstrated that APLs with substitutions of TCR contact residues are capable of down-regulating T-cell responses in PBLs of RA, suggesting that the CII-derived APLs are potentially therapeutic in RA.

Inhibitory effects on HLA-DR1-specific T-cell activation by influenza virus haemagglutinin-derived peptides

Collagen (CII) 263-272 peptide, an autoantigen in rheumatoid arthritis, is a specific human leukocyte antigen (HLA)-DR1/4-binding peptide recognized by T-cell receptors (TCR). The affinity of influenza virus haemagglutinin (HA) 306-318 peptide for the antigen-binding groove of HLA-DR1/4 molecules is higher than that of CII263-272. The HLA-DR1/4-binding residues of HA306-318 are located in the region 308-317. Altered HA308-317 peptides with substitutions of TCR-contact residues may inhibit HLA-DR1/4-specific T-cell activation by blocking the antigen-binding site of HLA-DR1/4 molecules. To evaluate the role of altered HA308-317 peptides in HLA-DR1-restricted T-cell activation, we synthesized three altered HA308-317 peptides. The specific binding of altered HA308-317 peptides to HLA-DR1 molecules was examined using flow cytometry. Effects of altered HA308-317 peptides on HLA-DR1-specific T-cell hybridoma were studied by measuring T-cell proliferation and surface expression of CD69 or CD25. The results showed that altered HA308-317 peptides were able to bind to HLA-DR1 molecules and competed with CII263-272 or wildtype HA308-317 peptide. Compared with wildtype CII263-272 or HA308-317, altered HA308-317 peptides did not stimulate significant T-cell proliferation and CD69 or CD25 expression. Furthermore, the altered HA308-317 peptides inhibited HLA-DR1-specific T-cell activation induced by CII263-272 or wildtype HA308-317 peptide, which may suggest an effective therapeutic strategy in inhibition of HLA-DR1-specific T-cell responses in autoimmunity.

HLA Class II molecules on haplotypes associated with type 1 diabetes exhibit similar patterns of binding affinities for coxsackievirus P2C peptides

Enteroviruses such as coxsackievirus B4 (CVB4) are proposed as possible environmental triggers or accelerants of the autoimmune process that leads to type 1 diabetes mellitus. One putative mechanism to account for this association is mimicry between virus components and islet autoantigens. Particular interest has focused on the CVB4 non-structural protein P2C, which we previously showed to be a major target of the effector memory anti-CVB4 CD4 T-cell response, and which harbours a region of sequence similarity with the islet autoantigen, glutamic acid decarboxylase (GAD65). Since several distinct human leucocyte antigen (HLA) Class II molecules are associated with development of type 1 diabetes, we hypothesized that for functional mimicry to be important, any potential region(s) of mimicry in P2C should bind to each of these susceptibility molecules. In the present study therefore we examined the affinity of 20-mer overlapping P2C peptides for soluble HLA-DR4, -DR3, -DQ2 and -DQ8. We identified one discrete region of P2C with high binding affinities for all of these HLA Class II molecules. Moreover, the binding affinity of P2C peptides was significantly correlated between HLA molecules present on the same susceptibility haplotype (e.g. DR4 and DQ8, P =0.0076; DR3 and DQ2 P = 0.002). We conclude that possession of these haplotypes favours restricted presentation of viral epitopes, and speculate that this could promote the potential for mimicry between microbial proteins and islet autoantigens.

Ultrasensitive Detection and Phenotyping of CD4+ T Cells with Optimized HLA Class II Tetramer Staining

HLA class I tetramers have revolutionized the study of Ag-specific CD8+ T cell responses. Technical problems and the rarity of Ag-specific CD4+ Th cells have not allowed the potential of HLA class II tetramers to be fully realized. Here, we optimize HLA class II tetramer staining methods through the use of a comprehensive panel of HIV-, influenza-, CMV-, and tetanus toxoid-specific tetramers. We find rapid and efficient staining of DR1- and DR4-restricted CD4+ cell lines and clones and show that TCR internalization is not a requirement for immunological staining. We combine tetramer staining with magnetic bead enrichment to detect rare Ag-specific CD4+ T cells with frequencies as low as 1 in 250,000 (0.0004% of CD4+ cells) in human PBLs analyzed directly ex vivo. This ultrasensitive detection allowed phenotypic analysis of rare CD4+ T lymphocytes that had experienced diverse exposure to Ag during the course of viral infections. These cells would not be detectable with normal flow-cytometric techniques.

The insulin A-chain epitope recognized by human T cells is posttranslationally modified

The autoimmune process that destroys the insulin-producing pancreatic β cells in type 1 diabetes (T1D) is targeted at insulin and its precursor, proinsulin. T cells that recognize the proximal A-chain of human insulin were identified recently in the pancreatic lymph nodes of subjects who had T1D. To investigate the specificity of proinsulin-specific T cells in T1D, we isolated human CD4⁺ T cell clones to proinsulin from the blood of a donor who had T1D. The clones recognized a naturally processed, HLA DR4–restricted epitope within the first 13 amino acids of the A-chain (A1–13) of human insulin. T cell recognition was dependent on the formation of a vicinal disulfide bond between adjacent cysteine residues at A6 and A7, which did not alter binding of the peptide to HLA DR4. CD4⁺ T cell clones that recognized this epitope were isolated from an HLA DR4⁺ child with autoantibodies to insulin, and therefore, at risk for T1D, but not from two healthy HLA DR4⁺ donors. We define for the first time a novel posttranslational modification that is required for T cell recognition of the insulin A-chain in T1D.

Modeling Ligand−Receptor Interaction for Some MHC Class II HLA-DR4 Peptide Mimetic Inhibitors Using Several Molecular Docking and 3D QSAR Techniques

The ligand-receptor interaction between some peptidomimetic inhibitors and a class II MHC peptide presenting molecule, the HLA-DR4 receptor, was modeled using some three-dimensional (3D) quantitative structure-activity relationship (QSAR) methods such as the Comparative Molecular Field Analysis (CoMFA), Comparative Molecular Similarity Indices Analysis (CoMSIA), and a pharmacophore building method, the Catalyst program. The structures of these peptidomimetic inhibitors were generated theoretically, and the conformations used in the 3D QSAR studies were defined by docking them into the known structure of HLA-DR4 receptor through the GOLD, GLIDE Rigidly, GLIDE Flexible, and Xscore programs. Some of the parameters used in these docking programs were selected by docking an X-ray ligand into the receptor and comparing the root-means-square difference (RMSD) computed between the coordinates of the X-ray and docked structure. However, the goodness of a docking result for docking a series of peptidomimetic inhibitors into the HLA-DR4 receptor was judged by comparing the Spearman's rank correlation coefficient computed between each docking result and the activity data taken from the literature. The best CoMFA and CoMSIA models were constructed using the aligned structures of the best docking result. The CoMSIA was conducted in a stepwise manner to identify some important molecular features that were further employed in a pharmacophore building process by the Catalyst program. It was found that most inhibitors of the training set were accurately predicted by the best pharmacophore model, the Hypo1 hypothesis constructed. The deviation or conflict found between the actual and predicted activities of some inhibitors of both the training and the test sets were also investigated by mapping the Hypo1 hypothesis onto the corresponding structures of the inhibitors.

Design and synthesis of a novel potent myelin basic protein epitope 87-99 cyclic analogue: enhanced stability and biological properties of mimics render them a potentially new class of immunomodulators

A cyclic analogue, [cyclo(87-99)MBP(87)(-)(99)], of the human immunodominant MBP(87)(-)(99) epitope, was designed based on ROESY/NMR distance information and modeling data for linear epitope 87-99, taking into account T-cell (Phe(89), Lys(91), Pro(96)) and HLA (His(88), Phe(90), Ile(93)) contact side-chain information. The cyclic analogue was found to induce experimental allergic encephalomyelitis (EAE), to bind HLA-DR4, and to increase CD4 T-cell line proliferation, like that of the conformationally related linear MBP(87)(-)(99) epitope peptide. The mutant cyclic peptides, the cyclo(91-99)[Ala(96)]MBP(87)(-)(99) and the cyclo(87-99)[Arg(91)Ala(96)]MBP(87)(-)(99), reported previously for suppressing, to a varying degree, autoimmune encephalomyelitis in a rat animal model, were found in this study to possess the following immunomodulatory properties: (i) they suppressed the proliferation of a CD4 T-cell line raised from a multiple sclerosis patient, (ii) they scored the best in vitro TH2/TH1 cytokine ratio in peripheral blood mononuclear cell cultures derived from 13 multiple sclerosis patients, inducing IL-10 selectively, and (iii) they bound to HLA-DR4, first to be reported for cyclic MBP peptides. In addition, cyclic peptides were found to be more stable to lysosomal enzymes and Cathepsin B, D, and H, compared to their linear counterparts. Taken together, these data render cyclic mimics as putative drugs for treating multiple sclerosis and potentially other Th1-mediated autoimmune diseases.

Dissection of the HLA-DR4 peptide repertoire in endocrine epithelial cells: strong influence of invariant chain and HLA-DM expression on the nature of ligands

Class II MHC (MHC II) expression is restricted to professional APCs and thymic epithelium but it also occurs in the epithelial cells of autoimmune organs which are the unique targets of the CD4 autoreactive T cells in endocrine autoimmune diseases. This specificity is presumably conditioned by an epithelium-specific peptide repertoire associated to MHC II at the cell surface. MHC II expression and function is dependent on the action of two main chaperones, invariant chain (Ii) and DM, whose expression is coregulated with MHC II. However, there is limited information about the in vivo expression levels of these molecules and uncoordinated expression has been demonstrated in class II-positive epithelial cells that may influence the MHC-associated peptide repertoires and the outcome of the autoimmune response. We have examined the pool of peptides associated to DR4 molecules expressed by a neuroendocrine epithelial cell and the consequences of Ii and DM coexpression. The RINm5F rat insulinoma cell line was transfected with HLA-DRB1*0401, Ii, and DM molecules in four different combinations: RIN-DR4, -DR4Ii, -DR4DM, and -DR4IiDM. The analysis of the peptide repertoire and the identification of the DR4 naturally processed ligands in each transfected cell were achieved by mass spectrometry. The results demonstrate that 1) the expression of Ii and DM affected the DR4 peptide repertoires by producing important variations in their content and in the origin of peptides; 2) these restrictions affected the stability and sequence of the peptides of each repertoire; and 3) Ii and DM had both independent and coordinate effects on these repertoires.

Vogt-Koyanagi-Harada syndrome and keratoconjunctivitis sicca

PURPOSE

To discover a relationship between Vogt-Koyanagi-Harada (VKH) syndrome and Sjögren syndrome.

DESIGN

Observational case-control study.

METHODS

Sixteen Italian patients with VKH syndrome and 16 controls with diffuse uveitis underwent tear analysis and rheumatologic evaluation. Biopsy specimens of the minor salivary glands were obtained or salivary gland scintigraphy was performed in patients with xerostomia.

RESULTS

The Schirmer test (P <.0001), break-up time (P <.0001), the Ferning test (P <.001), and fluorescein and rose bengal staining (P <.0001) resulted in changes in VKH. Biopsy was positive in two patients and scintigraphy in four. Human leukocyte antigen DR4 was found in 68.75% of VKH cases and in 83.3% of the cases with Schirmer test less than 3 mm.

CONCLUSIONS

The incidence of keratoconjunctivitis sicca was higher in VKH syndrome patients than in controls. Two patients satisfied the criteria for Sjögren syndrome, and two others had scintigraphy indicative of salivary gland involvement. The association of these two autoimmune disorders is suggested by the low incidence of VKH syndrome in Italy and might be related to HLA DR4.

Collagen-Induced Arthritis Mediated by HLA-DR1 (*0101) and HLA-DR4 (*0401)

Although associations between the expression of particular HLA genes and susceptibility to specific autoimmune diseases has been known for some time, the role HLA molecules play in the autoimmune response is unclear. Through the establishment of chimeric HLA-DR/I-E transgenes, the authors examined the function of the rheumatoid arthritis (RA) susceptibility alleles HLA-DR1 (DRB1*0101) and DR4 (DRB1*0401) in presenting antigenic peptides derived from the model antigen, type II collagen (CII), and in mediating an autoimmune response. As a transgene, these chimeric DR molecules confer susceptibility to an autoimmune arthritis induced by immunization with human CII. Both the DR1 and DR4-restricted T cell responses to CII are focused on an immunodominant determinant CII(263-270). Peptide binding studies revealed that the majority of the CII-peptide binding affinity for DR1 and DR4 is controlled by the Phe at 263 and, unexpectedly, the adjacent Lys. Only these 2 CII amino acids were found to provide binding anchors. Amino acid substitutions at the remaining positions had either no effect or significantly increased the affinity of the hCII peptide. These data indicate that DR1 and DR4 bind this CII peptide in a nearly identical manner and that the primary structure of CII may dictate a different binding motif for DR1 and DR4 than has been described for other peptides. In all, these studies demonstrate that DR1 and DR4 are capable of binding peptides derived from human type II collagen (hCII) and support the hypothesis that autoimmune responses to hCII play a role in the pathogenesis of RA.

Autoreactive T cell responses show proinflammatory polarization in diabetes but a regulatory phenotype in health

According to the quality of response they mediate, autoreactive T cells recognizing islet beta cell peptides could represent both disease effectors in the development of type 1 diabetes (T1DM) and directors of tolerance in nondiabetic individuals or those undergoing preventative immunotherapy. A combination of the rarity of these cells, inadequate technology, and poorly defined epitopes, however, has hampered examination of this paradigm. We have identified a panel of naturally processed islet epitopes by direct elution from APCs bearing HLA-DR4. Employing these epitopes in a sensitive, novel cytokine enzyme-linked immunosorbent spot assay, we show that the quality of autoreactive T cells in patients with T1DM exhibits extreme polarization toward a proinflammatory Th1 phenotype. Furthermore, we demonstrate that rather than being unresponsive, the majority of nondiabetic, HLA-matched control subjects also manifest a response against islet peptides, but one that shows extreme T regulatory cell (Treg, IL-10-secreting) bias. We conclude that development of T1DM depends on the balance of autoreactive Th1 and Treg cells, which may be open to favorable manipulation by immune intervention.

Expansion and Functional Relevance of High-Avidity Myelin-Specific CD4+T Cells in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease in which myelin-specific T cells are believed to play a crucial pathogenic role. Nevertheless, so far it has been extremely difficult to demonstrate differences in T cell reactivity to myelin Ag between MS patients and controls. We believe that by using unphysiologically high Ag concentrations previous studies have missed a highly relevant aspect of autoimmune responses, i.e., T cells recognizing Ag with high functional avidity. Therefore, we focused on the characterization of high-avidity myelin-specific CD4+ T cells in a large cohort of MS patients and controls that was matched demographically and with respect to expression of MHC class II alleles. We demonstrated that their frequency is significantly higher in MS patients while the numbers of control T cells specific for influenza hemagglutinin are virtually identical between the two cohorts; that high-avidity T cells are enriched for previously in vivo-activated cells and are significantly skewed toward a proinflammatory phenotype. Moreover, the immunodominant epitopes that were most discriminatory between MS patients and controls differed from those described previously and were clearly biased toward epitopes with lower predicted binding affinities to HLA-DR molecules, pointing at the importance of thymic selection for the generation of the autoimmune T cell repertoire. Correlations between selected immunological parameters and magnetic resonance imaging markers indicate that the specificity and function of these cells influences phenotypic disease expression. These data have important implications for autoimmunity research and should be considered in the development of Ag-specific therapies in MS.

Detection of major histocompatibility complex/human cartilage gp-39 complexes in rheumatoid arthritis synovitis as a specific and independent histologic marker

OBJECTIVE

Peptide 263-275 is the immunodominant epitope of human cartilage (HC) gp-39, a candidate autoantigen in rheumatoid arthritis (RA). We recently generated and characterized a monoclonal antibody (mAb) called 12A, which is directed against HLA-DR4/HC gp-39(263-275) complexes and inhibits specific T cell responses in vitro. The aim of the present study was to analyze whether presentation of the immunodominant epitope of HC gp-39 by shared epitope-positive synovial dendritic cells is a specific event in the development of chronic synovial inflammation in RA.

METHODS

Staining with mAb 12A was performed on synovium obtained from clinically swollen joints in 65 patients with RA and 67 non-RA controls and from joints without clinical effusion in 9 additional patients with RA.

RESULTS

Monoclonal antibody 12A staining was observed in the synovium of 40 of the 65 patients with RA. Histologically, expression of HC gp-39, lymphoid aggregates, CD3, and CD1a as well as the global inflammation score were higher in mAb 12A-positive RA synovium than in mAb 12A-negative synovium, indicating a follicular synovitis in these samples. Accordingly, mAb 12A stained dendritic cells in the close vicinity of lymphoid aggregates. No mAb 12A staining was detected in synovium obtained from RA joints without effusion. Clinically, there were no correlations between mAb 12A staining and clinical or biologic parameters in RA. However, positive staining was observed in 61.5% of the inflamed RA synovial samples compared with only 3.0% of the control samples (P < 0.001). This mAb 12A staining was not related to intracellular citrullinated peptides, which are another specific histologic marker for RA.

CONCLUSION

Presentation by synovial dendritic cells of the immunodominant epitope of HC gp-39, in the context of the shared epitope, is associated with characteristic histologic features of follicular synovitis and is highly specific for RA. This suggests a contribution to the autoimmune-related tissue inflammation and provides a new and independent tool for the immunopathologic diagnosis of RA.

Generation of autologous cytotoxic and helper T-cell responses against the B-cell leukemia-associated antigen HB-1: relevance for precursor B-ALL-specific immunotherapy

Tumor relapses in patients with precursor B-cell acute lymphoblastic leukemia (BALL) occur frequently after primary treatment. Therefore, development of additional treatment modalities to eliminate residual tumor cells is needed. Active immunotherapy using dendritic cells (DCs) loaded with tumor-associated antigens is a promising approach to induce specific T-cell immunity in patients with cancer. In previous studies, we described HB-1 as a B-cell lineage-specific antigen that is recognized by donor-derived cytotoxic T lymphocytes (CTLs) on allogeneic B-ALL tumor cells. Here, we investigated the potential use of the HB-1 antigen as an autologous T-cell vaccine target. To determine whether HB-1-specific CTL precursors are present within the T-cell repertoire, we induced expansion of CD8+ T cells using mature monocyte-derived DCs pulsed with the previously identified HB-1.B44 antigenic peptide. In 6 of 8 donors, CD8+ CTL lines have been generated that exert cytotoxicity against target cells exogenously pulsed with peptide or endogenously expressing the HB-1 antigen. From one of these HB-1-specific T-cell lines, we isolated a CD8+ CTL that produces interferon-gamma on stimulation with B-ALL tumor cells. Interestingly, the HB-1 antigen also induced CD4+ T-helper responses on activation with protein-loaded mature monocyte-derived DCs. We identified 2 novel epitopes recognized in the context of HLA-DR4 and HLA-DR11 with the use of HB-1-specific CD4+ T-cell clones generated from different donors. These present data, that HB-1 induces both helper and cytotoxic T-cell responses, indicate that the HB-1 antigen is a candidate target to induce T-cell-mediated antitumor immunity in patients.

Inhibition of T-cell activation with HLA-DR1/DR4 restricted Non-T-cell stimulating peptides

It has been reported that collagen II (CII) derived peptide CII263-272 induced T-cell activation via its amino acids responsible for T-cell receptor (TCR) recognition. The impact of substitution of the TCR contacting amino acids of CII263-272 on T-cell activation was evaluated in this study using a panel of altered CII263-272 peptides. Computer modeling revealed that the side chains of 263F and 266E in CII263-272 were coupled with amino acids on alpha1 and beta1 chains of HLA-DR1 or -DR4, mainly via hydrogen bonds, whereas the side chains of 267Q and 270K protrude out of the cleft and might be recognized by TCR. Intracellular delivery of the altered peptides, and their binding to HLA-DR1 and -DR4 molecules on cell surface, were demonstrated by confocal microscopy and flow cytometry. The results also revealed that the substitution of 267Q, 268G, 269P, and 270K individually or consecutively by alanine (A) or glycine (G) led to weak or non-T-cell responses. Furthermore, the altered peptides with 270K substitution (270A) or with consecutive substitution of 268G, 269P, and 270K (sub268-270) dramatically inhibited T-cell activation. It is suggested that the altered peptides derived from CII263-272 with substitution of amino acids responsible for TCR contact might be of inhibitory effect on T-cell responses.

Cutting edge: the conversion of arginine to citrulline allows for a high-affinity peptide interaction with the rheumatoid arthritis-associated HLA-DRB1*0401 MHC class II molecule

Rheumatoid arthritis (RA) is genetically associated with MHC class II molecules that contain the shared epitope. These MHC molecules may participate in disease pathogenesis by selectively binding arthritogenic peptides for presentation to autoreactive CD4(+) T cells. The nature of the arthritogenic Ag is not known, but recent work has identified posttranslationally modified proteins containing citrulline (deiminated arginine) as specific targets of the IgG Ab response in RA patients. To understand how citrulline might evoke an autoimmune reaction, we have studied T cell responses to citrulline-containing peptides in HLA-DRB1*0401 transgenic (DR4-IE tg) mice. In this study, we demonstrate that the conversion of arginine to citrulline at the peptide side-chain position interacting with the shared epitope significantly increases peptide-MHC affinity and leads to the activation CD4(+) T cells in DR4-IE tg mice. These results reveal how DRB1 alleles with the shared epitope could initiate an autoimmune response to citrullinated self-Ags in RA patients.

Toxicity of the staphylococcal enterotoxin B mutants with histidine-to-tyrosine substitutions

In this study we made a series of site-directed mutants of staphylococcal enterotoxin B (SEB), in which histidine residues in the molecule were replaced by tyrosine. The mutant genes were cloned and expressed, and the corresponding proteins were purified. These mutant proteins were tested for binding to human HLA-DR4 and for mitogenetic activity in mouse splenocyte culture. Toxicity of the proteins in vivo was evaluated in the actinomycin D-primed C3H/HeJ mouse model. We found that SEB mutant proteins with fewer than four histidine-to-tyrosine (his-to-tyr) substitutions retained toxic properties similar to wild-type SEB. However, studies showed that his-to-tyr substitution of four consecutive histidine residues eliminated SEB toxicity. Our results clearly show that this genetically modified SEB protein is non-toxic and justifies its further development as a component of a new, safer vaccine to prevent SEB intoxication.

Low-avidity recognition by CD4+ T cells directed to self-antigens

Self-reactive T cells populate the peripheral immune system, and likely form the reservoir from which autoreactive cells are derived. We analyzed a panel of self and non-self peptides presented by HLA-DR4, a class II molecule associated with autoimmunity, by immunization of mice transgenic for HLA-DR4. Significant structural avidity for T cell recognition, as measured by MHC class II tetramer binding to CD4(+) T cells was only observed in mice immunized with the non-self antigens. T cell hybridomas were generated from mice immunized with the naturally processed self-peptide hGAD65 (552-572) and also from mice immunized with an influenza-derived non-self epitope (HA 306-318). T cells specific for the self peptide failed to bind tetramers and exhibited low functional avidity as measured by the peptide concentration required to reach half-maximum proliferation values. In contrast, T cells specific for the non-self HA (306-318) peptide exhibited high structural and functional avidity profiles. As recently described in studies of murine CD8(+) T cell function, the predominance of low avidity recognition of self-peptide epitopes may be a characteristic feature of CD4(+) T cells responding to autoantigens.

Promiscuous binding of proinsulin peptides to Type 1 diabetes-permissive and -protective HLA class II molecules

AIMS/HYPOTHESIS

Presentation of peptide epitopes derived from beta-cell autoantigens, such as insulin and its precursor molecules, by MHC class II molecules to autoreactive T-cells is believed to play a role in the development of Type 1 diabetes. However, little is known about the interaction between peptides of (prepro)insulin and MHC class II molecules permissive and protective for Type 1 diabetes. In this study therefore, peptides spanning the human preproinsulin sequence were assessed for their binding characteristics to Type 1 diabetes-protective and -permissive HLA molecules.

METHODS

HLA-DR2, -DQ6.2 (Type 1 diabetes-protective) and HLA-DR4, -DQ8 (Type 1 diabetes permissive) molecule binding affinity for overlapping synthetic 20mer peptides spanning human preproinsulin was measured in a direct competition binding assay against a biotinylated indicator peptide.

RESULTS

All HLA molecules tested showed similarity in their binding characteristics across the preproinsulin molecule, with regions of the insulin A-chain showing the highest affinity and C-peptide regions the lowest affinity for all HLA molecules tested. Furthermore, an insulin peptide implicated as a major CD4+ T-cell target in disease pathogenesis (B9-23) had high affinity binding to both protective and permissive HLA molecules but did not represent the highest affinity region of (prepro)insulin identified in either case.

CONCLUSION/INTERPRETATION

The results suggest that peptide binding affinity alone is unlikely to be the major determinant of disease susceptibility in relation to interactions between (prepro)insulin epitopes and HLA molecules. The identification of epitopes derived from beta-cell autoantigens that bind promiscuously to diabetes-permissive HLA molecules could be important in the design of peptide-based immunotherapeutic strategies for the prevention of Type 1 diabetes.

T cell recognition and therapeutic effect of a phosphorylated synthetic peptide of the 70K snRNP protein administered in MR/lpr mice

Modifications of self antigens that occur during apoptosis might be involved in the generation of neo-antigens, which can break tolerance and induce autoimmunity. We have previously identified an epitope at residues 131-151 of the U1-70K snRNP protein, recognized by IgG antibodies and CD4+ T cells from at least two strains of lupus mice. With the aim of investigating the possible role of phosphorylation on the antigenicity of peptide 131-151 and to gain a better understanding of how this peptide can drive autoimmune response, we synthesized two peptides phosphorylated on Ser137 and 140, respectively. We show here that peptide P140 phosphorylated on Ser140 is recognized by both CD4+ T cells and antibodies from MRL/lpr mice. Furthermore, intravenous administration to lupus-prone MRL/lpr mice of P140 in saline (but not of the non-phosphorylated peptide) decreased proteinuria and anti-DNA antibody production, and significantly prolonged survival of treated mice. We further demonstrated that P140 is recognized by antibodies from lupus patients and binds to various HLA DR molecules, offering new hope for manipulating T cell response in humans.

Formation of two peptide/MHC II isomers is catalyzed differentially by HLA-DM

Major histocompatability class II proteins are transmembrane alphabeta-heterodimers that present peptides to T-cells. MHC II may bind exogenous peptides directly at the cell surface. Alternatively, peptides derived from processing of endosomal protein may bind to MHC II in endosomal compartments. There, HLA-DM catalyzes the formation of peptide/MHC complexes, which are then transported to the cell surface. Here we report evidence that the peptide Ii CLIP 81-104 binds to DR*0404 in two alternate registries, whose dissociation rates, while kinetically indistinguishable at pH 5.3 and 37 degrees C, are kinetically resolved in the presence of HLA-DM. In one registry isomer, CLIP Met 91 is placed in the N-terminal P1 pocket of DR*0404, and peptide dissociation is readily catalyzed by HLA-DM. In a second proposed registry, likely with CLIP Leu 97 in the P1 pocket, the complex is substantially less sensitive to HLA-DM catalysis. Without HLA-DM, or at pH 7, the fraction of each isomer formed in solution is relatively insensitive to the duration of incubation with peptide. However, with HLA-DM, the fraction of the DM-insensitive isomer is dramatically influenced by peptide incubation time. The mechanism of isomer formation appears to be determined by the HLA-DM-modified relative association to the two registries, followed by HLA-DM-catalyzed dissociation of each isomer and rebinding, leading to a final isomer composition determined by these kinetic constants. Intramolecular isomer interconversion does not appear to be involved. The behavior of these complexes may provide a model for peptide editing by DM in endosomes.

Differential MHC class II-mediated presentation of rheumatoid arthritis autoantigens by human dendritic cells and macrophages

Rheumatoid arthritis is characterized by synovial joint infiltration of activated CD4(+) T cells and MHC class II(+) APC, and is linked to specific HLA-DR alleles. Candidate autoantigens in synovial fluid and cartilage include type II collagen (CII) and cartilage gp39 (HCgp39). Using preparations of native Ag and T cells derived from Ag-immunized DR4-transgenic mice, we determined that human ex vivo differentiated DR4(+) dendritic cells (DC) and macrophages (Mphi) can mediate MHC class II presentation of CII or HCgp39 epitopes. The form of the Ag (soluble, partially degraded, or particulate) delivered to the APC influenced its presentation by DC and Mphi. DC efficiently presented partially degraded, but not native CII alpha-chains, while Mphi presentation was most efficient after phagocytosis of bead-conjugated CII. Both DC and Mphi presented soluble HCgp39, and activated Mphi from some donors presented epitopes derived from endogenously synthesized HCgp39. When synovial fluid from rheumatoid arthritis patients was used as a source of Ag, DC presentation of HCgp39 and CII epitopes was efficient, indicating that synovial fluid contains soluble forms of CII and HCgp39 amenable to internalization, processing, and presentation. These data support the hypothesis that CII and HCgp39 are autoantigens and that their class II-mediated presentation by DC and Mphi to T cells in vivo has a critical role in the pathogenesis of human rheumatoid arthritis.

Evaluation of the role of MHC class II alleles, haplotypes and selected amino acid sequences in primary sclerosing cholangitis

BACKGROUND AND AIMS

Genetic susceptibility to primary sclerosing cholangitis is associated with several different HLA haplotypes, though a single "shared" susceptibility allele has yet to be identified. Most recently, attention has focussed on the MICA alleles in close proximity to the HLA class I, B locus. However, although there are strong associations with MICA*008, implicating this or a closely linked allele as major risk factors, this explanation alone does not account for all of the MHC-encoded susceptibility and resistance to PSC. The present study re-examines HLA class II associations in a large single centre series of well-characterised PSC patients. The specific aims of the study were to test existing associations and to develop hypotheses which together may account for all, or the majority, of the MHC-encoded susceptibility in PSC.

METHODS

A total of 148 adult white northern European patients and 134 control subjects were studied. HLA DRB1, DQA1, DQB1 alleles and DRB1*04, DRB1*13 and DRB3 subtypes were determined by standard PCR-genotyping.

RESULTS

The primary associations with the DRB3*0101--DRB1*0301--DQA1*0501--DQB1*0201 and DRB1*1301--DQA1*0103--DQB1*0603 haplotypes were confirmed (O.R. = 2.69, p < 0.0000025 and O.R. = 3.8, p < 0.0005). In addition the strong protective influence of the DRB1*04--DQB1*0302 haplotype was reaffirmed (O.R. = 0.26, p < 0.000025) and a previously unreported negative (i.e. protective) association with the DRB1*0701--DQB1*0303 haplotype was also demonstrated (O.R. = 0.15, p < 0.005). Further analysis suggested that susceptibility/resistance encoded by the second and third susceptibility haplotypes and by the two resistance haplotypes may be determined by specific amino acids at DQbeta-87 and DQbeta-55, respectively.

HLA-DR4 molecules in neuroendocrine epithelial cells associate to a heterogeneous repertoire of cytoplasmic and surface self peptides

Expression of MHC class II genes by epithelial cells is induced in inflammatory conditions such as autoimmunity and organ transplantation. Class II ligands generated by the epithelial cell processing mechanisms are unknown, although some unique epitopes have been described in epithelial cells that B cells could not generate. Epithelial cells are the targets of autoreactive T cell responses in autoimmune diseases and of transplant rejection processes, which may involve recognition of cell type-specific epitopes. In the present report, we have compared the DR4-associated repertoire and the intracellular distribution of class II, invariant chain (Ii), and DM molecules between a human DR4-, Ii-, and DM-transfected rat neuroendocrine epithelial cell line and a homozygous DR4 (DRB1*0401) lymphoblastoid B cell line, by mass spectrometry sequencing techniques, and immunoelectron microscopy. The epithelial cells chosen for transfection, RINm5F, are rat insular cells widely used for human studies of autoimmune diabetes. The results revealed a remarkably heterogeneous pool of self protein-derived peptides from the cell surface and various intracellular compartments, including the cytosol and secretory vesicles in epithelial cells, compared with a very restricted homogeneous repertoire in lymphoblastoid B cell lines, where few epitopes from surface molecules were predominant. The generation of distinct DR4-associated peptide repertoires in these two cell types could be due to the effect of several factors including differences in subcellular location of Ii and DM molecules, differential DO expression, and cell type-specific mechanisms of class II ligand generation. This is specially relevant to processes involving epithelial T cell interactions such as organ-specific autoimmunity and transplant rejection.

Evidence for preferred MHC class II-TCR recognition independent of the source of bound peptide

The interaction between TCR and peptide-MHC is well described in terms of the recognition of the peptide, but the recognition of the MHC is less well understood. At issue is whether particular V gene products may have higher affinity for some MHC over others and to what extent the bound peptide influences V gene selection. We examined this issue by developing T cell lines in which the presenting MHC class II molecule has a constant TCR contact region, while the presented peptides vary. If there is an affinity between particular V genes and the specific MHC used, only a subset of the V genes will be associated with the response. Indeed, in all the cell lines analyzed, there was a reproducible usage of a limited number of Vbeta genes, regardless of the bound peptides. This Vbeta-gene constraint was independent of the CDR3 sequence, compatible with the lack of involvement of specific peptides. Our results support the hypothesis that certain V gene products may have a preference for interacting with a particular MHC molecule, and this could have an impact in selectively controlling immune responses.

The influence of HLA-DR4 (0401) on the immune response to type II collagen and the development of collagen induced arthritis in mice

Rheumatoid arthritis (RA) is an autoimmune disease that is genetically associated with the MHC class II molecule HLA-DRbeta1*0401 (DR4). In order to determine if this MHC can influence the immune response to the candidate autoantigen type II collagen (CII), we have studied collagen induced arthritis (CIA) resistant C57BL/6 mice, made transgenic (Tg) for human DR4. These DR4 Tg mice exhibited a strong T cell proliferative response to CII and its DR4 restricted peptide p261-273 after immunization with these antigens that was not seen in the C57BL/6 wild type mice. DR4 Tg mice also exhibited an increase in IFN-gamma production in response to CII, indicating the activation of Th1 cells. While these Tg mice produced IgM anti-CII antibodies, they failed to produce a detectable level of IgG2a (Th1 type) anti-bCII antibody and did not develop CIA. This study shows that a Th1 type T cell response to CII can be established in CIA non-susceptible mice by introducing the human transgene, DR4. This T cell response, however, is not sufficient to induce an antibody isotype switch to IgG2a, nor is it sufficient for the induction of CIA. These results may help to explain why many individuals expressing HLA-DRbeta1*0401 do not develop RA.

HLA-DR1 (DRB1*0101) and DR4 (DRB1*0401) use the same anchor residues for binding an immunodominant peptide derived from human type II collagen

Rheumatoid arthritis is an autoimmune disease in which susceptibility is strongly associated with the expression of specific HLA-DR haplotypes, including DR1 (DRB1*0101) and DR4 (DRB1*0401). As transgenes, both of these class II molecules mediate susceptibility to an autoimmune arthritis induced by immunization with human type II collagen (hCII). The dominant T cell response of both the DR1 and DR4 transgenic mice to hCII is focused on the same determinant core, CII(263-270). Peptide binding studies revealed that the affinity of DR1 and DR4 for CII(263-270) was at least 10 times less than that of the model Ag HA(307-319), and that the affinity of DR4 for the CII peptide is 3-fold less than that of DR1. As predicted based on the crystal structures, the majority of the CII-peptide binding affinity for DR1 and DR4 is controlled by the Phe(263); however, unexpectedly the adjacent Lys(264) also contributed significantly to the binding affinity of the peptide. Only these two CII amino acids were found to provide binding anchors. Amino acid substitutions at the remaining positions had either no effect or significantly increased the affinity of the hCII peptide. Affinity-enhancing substitutions frequently involved replacement of a negative charge, or Gly or Pro, hallmark amino acids of CII structure. These data indicate that DR1 and DR4 bind this CII peptide in a nearly identical manner and that the primary structure of CII may dictate a different binding motif for DR1 and DR4 than has been described for other peptides that bind to these alleles.

Rheumatoid arthritis (RA)-associated HLA-DR alleles form less stable complexes with class II-associated invariant chain peptide than non-RA-associated HLA-DR alleles

Certain HLA-DR alleles confer strong susceptibility to the autoimmune disease rheumatoid arthritis (RA). We compared RA-associated alleles, HLA-DR*0401, HLA-DR*0404, and HLA-DR*0405, with closely related, non-RA-associated alleles, HLA-DR*0402 and HLA-DR*0403, to determine whether they differ in their interactions with the class II chaperone, invariant chain (Ii). Ii binds to class II molecules in the endoplasmic reticulum, inhibits binding of other ligands, and directs class II-Ii complexes to endosomes, where Ii is degraded to class II-associated Ii peptide (CLIP). To evaluate the interaction of Ii and CLIP with these DR4 alleles, we introduced HLA-DR*0401, *0402, and *0404 alleles into a human B cell line that lacked endogenous HLA-DR or HLA-DM molecules. In a similar experiment, we introduced HLA-DR*0403 and *0405 into an HLA-DM-expressing B cell line, 8.1.6, and its DM-negative derivative, 9.5.3. Surface abundance of DR4-CLIP peptide complexes and their susceptibility to SDS-induced denaturation suggested that the different DR4-CLIP complexes had different stabilities. Pulse-chase experiments showed CLIP dissociated more rapidly from RA-associated DR molecules in B cell lines. In vitro assays using soluble rDR4 molecules showed that DR-CLIP complexes of DR*0401 and DR*0404 were less stable than complexes of DR*0402. Using CLIP peptide variants, we mapped the reduced CLIP interaction of RA-associated alleles to the shared epitope region. The reduced interaction of RA-associated HLA-DR4 molecules with CLIP may contribute to the pathophysiology of autoimmunity in RA.

gp100/pmel17 and tyrosinase encode multiple epitopes recognized by Th1-type CD4+T cells

CD4+ T cells modulate the magnitude and durability of CTL responses in vivo, and may serve as effector cells in the tumour microenvironment. In order to identify the tumour epitopes recognized by tumour-reactive human CD4+ T cells, we combined the use of an HLA-DR4/peptide binding algorithm with an IFN-gamma ELISPOT assay. Two known and three novel CD4+ T cell epitopes derived from the gp 100/pmel17 and tyrosinase melanocyte-associated antigens were confirmed or identified. Of major interest, we determined that freshly-isolated PBMC frequencies of Th1-type CD4+ T recognizing these peptides are frequently elevated in HLA-DR4+ melanoma patients (but not normal donors) that are currently disease-free as a result of therapeutic intervention. Epitope-specific CD4+ T cells from normal DR4+ donors could be induced, however, after in vitro stimulation with autologous dendritic cell pulsed with antigens (peptides or antigen-positive melanoma lysates) or infected with recombinant vaccinia virus encoding the relevant antigen. Peptide-reactive CD4+ T cells also recognized HLA-DR4+ melanoma cell lines that constitutively express the relevant antigen. Based on these data, these epitopes may serve as potent vaccine components to promote clinically-relevant Th1-type CD4+ T cell effector function in situ.

pH stability of HLA-DR4 complexes with antigenic peptides

Complexes between antigenic peptides and class II proteins of the major histocompatibility complex (MHC) trigger cellular immune responses. These complexes usually dissociate more rapidly at mildly acidic pH, where they are formed intracellularly, as compared to neutral pH, where they function at the cell surface. This paper describes the pH dependence of the dissociation kinetics of complexes between MHC proteins and antigenic peptides containing aspartic and glutamic acid residues. Some of these complexes show an unusual pH dependence, dissociating much more rapidly at pH 7 than at pH 5.3. This occurs when the carboxylate group of the aspartic or glutamic acid residue is located in a neutral pocket of the protein. In contrast, solvent-exposed carboxylate groups or carboxylate groups buried in pockets where they form salt bridges with the protein do not show this unusual pH dependence. The kinetic data having the unusual pH dependence conform closely to a model in which there is a rapid reversible equilibration between a less stable deprotonated complex and a more stable protonated complex. In this model, the pK(a) of the protonation reaction for the partially buried peptide carboxylate group ranges from 7.7 to 8.3, reflecting the strongly basic conditions required for deprotonation. One of the few peptide/MHC complexes demonstrated to play a role in autoimmunity in humans contains a buried peptide carboxylate and shows this unusual pH dependence. The relevance of this finding to understanding the chemical basis of autoimmunity is briefly discussed.

Identification of T cell ligands in a library of peptides covalently attached to HLA-DR4

While T cells have been clearly implicated in a number of disease processes including autoimmunity, graft rejection, and atypical immune responses, the precise Ags recognized by the pathogenic T cells have often been difficult to identify. This has particularly been true for MHC class II-restricted CD4+ T cells. Although such cells can be demonstrated to have undergone clonal expansion at sites of pathology, they are frequently difficult to establish as stable T cell clones. Furthermore, in general, larger peptides in higher concentrations are required to stimulate CD4+ T cells than CD8+ T cells, which makes some of the techniques developed to identify CD8+ T cell Ags impractical. To circumvent some of these problems, we developed a model system consisting of two parts. The first part involves the construction of an indicator T cell hybridoma expressing a chimeric TCR comprised of murine constant regions and human variable regions specific for influenza hemagglutinin 307-319 presented by DR4. The second part consists of a library of fibroblasts each expressing multiple peptides as amino terminal covalent extensions of the beta-chain of HLA-DR4 (DRA1*0101, DRB1*0401). Using this model system, we screened approximately 100, 000 peptides and identified three novel peptides stimulatory for the HA1.7 TCR. While there is some convergence at residues known to be important for T cell recognition, all three peptides differ markedly from each other and bear little resemblance to wild-type hemagglutinin 307-319.