Structural basis of chronic beryllium disease: linking allergic hypersensitivity and autoimmunity.

T-cell-mediated hypersensitivity to metal cations is common in humans. How the T cell antigen receptor (TCR) recognizes these cations bound to a major histocompatibility complex (MHC) protein and self-peptide is unknown. Individuals carrying the MHCII allele, HLA-DP2, are at risk for chronic beryllium disease (CBD), a debilitating inflammatory lung condition caused by the reaction of CD4 T cells to inhaled beryllium. Here, we show that the T cell ligand is created when a Be(2+) cation becomes buried in an HLA-DP2/peptide complex, where it is coordinated by both MHC and peptide acidic amino acids. Surprisingly, the TCR does not interact with the Be(2+) itself, but rather with surface changes induced by the firmly bound Be(2+) and an accompanying Na(+) cation. Thus, CBD, by creating a new antigen by indirectly modifying the structure of preexisting self MHC-peptide complex, lies on the border between allergic hypersensitivity and autoimmunity.

SARS-CoV-2-specific T cells associate with inflammation and reduced lung function in pulmonary post-acute sequalae of SARS-CoV-2.

As of January 2022, at least 60 million individuals are estimated to develop post-acute sequelae of SARS-CoV-2 (PASC) after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While elevated levels of SARS-CoV-2-specific T cells have been observed in non-specific PASC, little is known about their impact on pulmonary function which is compromised in the majority of these individuals. This study compares frequencies of SARS-CoV-2-specific T cells and inflammatory markers with lung function in participants with pulmonary PASC and resolved COVID-19 (RC). Compared to RC, participants with respiratory PASC had between 6- and 105-fold higher frequencies of IFN-γ- and TNF-α-producing SARS-CoV-2-specific CD4+ and CD8+ T cells in peripheral blood, and elevated levels of plasma CRP and IL-6. Importantly, in PASC participants the frequency of TNF-α-producing SARS-CoV-2-specific CD4+ and CD8+ T cells, which exhibited the highest levels of Ki67 indicating they were activity dividing, correlated positively with plasma IL-6 and negatively with measures of lung function, including forced expiratory volume in one second (FEV1), while increased frequencies of IFN-γ-producing SARS-CoV-2-specific T cells associated with prolonged dyspnea. Statistical analyses stratified by age, number of comorbidities and hospitalization status demonstrated that none of these factors affect differences in the frequency of SARS-CoV-2 T cells and plasma IL-6 levels measured between PASC and RC cohorts. Taken together, these findings demonstrate elevated frequencies of SARS-CoV-2-specific T cells in individuals with pulmonary PASC are associated with increased systemic inflammation and decreased lung function, suggesting that SARS-CoV-2-specific T cells contribute to lingering pulmonary symptoms. These findings also provide mechanistic insight on the pathophysiology of PASC that can inform development of potential treatments to reduce symptom burden.

Innate and Adaptive Immunity in Noninfectious Granulomatous Lung Disease.

Sarcoidosis and chronic beryllium disease are noninfectious lung diseases that are characterized by the presence of noncaseating granulomatous inflammation. Chronic beryllium disease is caused by occupational exposure to beryllium containing particles, whereas the etiology of sarcoidosis is not known. Genetic susceptibility for both diseases is associated with particular MHC class II alleles, and CD4+ T cells are implicated in their pathogenesis. The innate immune system plays a critical role in the initiation of pathogenic CD4+ T cell responses as well as the transition to active lung disease and disease progression. In this review, we highlight recent insights into Ag recognition in chronic beryllium disease and sarcoidosis. In addition, we discuss the current understanding of the dynamic interactions between the innate and adaptive immune systems and their impact on disease pathogenesis.

Shared αß TCR Usage in Lungs of Sarcoidosis Patients with Löfgren's Syndrome.

Sarcoidosis is a granulomatous disease that primarily affects the lungs and is characterized by an accumulation of CD4+ T cells in the bronchoalveolar lavage (BAL). Previous work has indicated that HLA-DRB1*03:01+ (DR3+) patients diagnosed with the acute form of the disease, Löfgren's syndrome (LS), have an accumulation of CD4+ T cells bearing TCRs using TRAV12-1 (formerly AV2S3). However, the importance of these α-chains in disease pathogenesis and the paired TCRß-chain remains unknown. This study aimed to identify expanded αßTCR pairs expressed on CD4+ T cells derived from the BAL of DR3+ LS patients. Using a deep-sequencing approach, we determined TCRα- and TCRß-chain usage, as well as αßTCR pairs expressed on BAL CD4+ T cells from LS patients. TRAV12-1 and TRBV2 (formerly BV22) were the most expanded V region gene segments in DR3+ LS patients relative to control subjects, and TRAV12-1 and TRBV2 CDR3 motifs were shared among multiple DR3+ LS patients. When assessing αßTCR pairing, TRAV12-1 preferentially paired with TRBV2, and these TRAV12-1/TRBV2 TCRs displayed CDR3 homology. These findings suggest that public CD4+ TCR repertoires exist among LS patients and that these T cells are recognizing the putative sarcoidosis-associated Ag(s) in the context of DR3.

Identification of shared TCR sequences from T cells in human breast cancer using emulsion RT-PCR.

Infiltration of T cells in breast tumors correlates with improved survival of patients with breast cancer, despite relatively few mutations in these tumors. To determine if T-cell specificity can be harnessed to augment immunotherapies of breast cancer, we sought to identify the alpha-beta paired T-cell receptors (TCRs) of tumor-infiltrating lymphocytes shared between multiple patients. Because TCRs function as heterodimeric proteins, we used an emulsion-based RT-PCR assay to link and amplify TCR pairs. Using this assay on engineered T-cell hybridomas, we observed ∼85% accurate pairing fidelity, although TCR recovery frequency varied. When we applied this technique to patient samples, we found that for any given TCR pair, the dominant alpha- or beta-binding partner comprised ∼90% of the total binding partners. Analysis of TCR sequences from primary tumors showed about fourfold more overlap in tumor-involved relative to tumor-free sentinel lymph nodes. Additionally, comparison of sequences from both tumors of a patient with bilateral breast cancer showed 10% overlap. Finally, we identified a panel of unique TCRs shared between patients' tumors and peripheral blood that were not found in the peripheral blood of controls. These TCRs encoded a range of V, J, and complementarity determining region 3 (CDR3) sequences on the alpha-chain, and displayed restricted V-beta use. The nucleotides encoding these shared TCR CDR3s varied, suggesting immune selection of this response. Harnessing these T cells may provide practical strategies to improve the shared antigen-specific response to breast cancer.

Beryllium-Induced Hypersensitivity: Genetic Susceptibility and Neoantigen Generation.

Chronic beryllium (Be) disease is a granulomatous lung disorder that results from Be exposure in a genetically susceptible host. The disease is characterized by the accumulation of Be-responsive CD4(+) T cells in the lung, and genetic susceptibility is primarily linked to HLA-DPB1 alleles possessing a glutamic acid at position 69 of the ß-chain. Recent structural analysis of a Be-specific TCR interacting with a Be-loaded HLA-DP2-peptide complex revealed that Be is coordinated by amino acid residues derived from the HLA-DP2 ß-chain and peptide and showed that the TCR does not directly interact with the Be(2+) cation. Rather, the TCR recognizes a modified HLA-DP2-peptide complex with charge and conformational changes. Collectively, these findings provide a structural basis for the development of this occupational lung disease through the ability of Be to induce posttranslational modifications in preexisting HLA-DP2-peptide complexes, resulting in the creation of neoantigens.

Regulatory T cells modulate granulomatous inflammation in an HLA-DP2 transgenic murine model of beryllium-induced disease.

Susceptibility to chronic beryllium disease (CBD) is linked to certain HLA-DP molecules, including HLA-DP2. To elucidate the molecular basis of this association, we exposed mice transgenic (Tg) for HLA-DP2 to beryllium oxide (BeO) via oropharyngeal aspiration. As opposed to WT mice, BeO-exposed HLA-DP2 Tg mice developed mononuclear infiltrates in a peribronchovascular distribution that were composed of CD4(+) T cells and included regulatory T (Treg) cells. Beryllium-responsive, HLA-DP2-restricted CD4(+) T cells expressing IFN-γ and IL-2 were present in BeO-exposed HLA-DP2 Tg mice and not in WT mice. Using Be-loaded HLA-DP2-peptide tetramers, we identified Be-specific CD4(+) T cells in the mouse lung that recognize identical ligands as CD4(+) T cells derived from the human lung. Importantly, a subset of HLA-DP2 tetramer-binding CD4(+) T cells expressed forkhead box P3, consistent with the expansion of antigen-specific Treg cells. Depletion of Treg cells in BeO-exposed HLA-DP2 Tg mice exacerbated lung inflammation and enhanced granuloma formation. These findings document, for the first time to our knowledge, the development of a Be-specific adaptive immune response in mice expressing HLA-DP2 and the ability of Treg cells to modulate the beryllium-induced granulomatous immune response.

Identification of multiple public TCR repertoires in chronic beryllium disease.

Chronic beryllium disease (CBD) is a granulomatous lung disease characterized by the accumulation of beryllium (Be)-specific CD4(+) T cells in bronchoalveolar lavage. These expanded CD4(+) T cells are composed of oligoclonal T cell subsets, suggesting their recruitment to the lung in response to conventional Ag. In the current study, we noted that all bronchoalveolar lavage-derived T cell lines from HLA-DP2-expressing CBD patients contained an expansion of Be-responsive Vß5.1(+) CD4(+) T cells. Using Be-loaded HLA-DP2-peptide tetramers, the majority of tetramer-binding T cells also expressed Vß5.1 with a highly conserved CDR3ß motif. Interestingly, Be-specific, Vß5.1-expressing CD4(+) T cells displayed differential HLA-DP2-peptide tetramer staining intensity, and sequence analysis of the distinct tetramer-binding subsets showed that the two populations differed by a single conserved amino acid in the CDR3ß motif. TCR Vα-chain analysis of purified Vß5.1(+) CD4(+) T cells based on differential tetramer-binding intensity showed differing TCR Vα-chain pairing requirements, with the high-affinity population having promiscuous Vα-chain pairing and the low-affinity subset requiring restricted Vα-chain usage. Importantly, disease severity, as measured by loss of lung function, was inversely correlated with the frequency of tetramer-binding CD4(+) T cells in the lung. Our findings suggest the presence of a dominant Be-specific, Vß5.1-expressing public T cell repertoire in the lungs of HLA-DP2-expressing CBD patients using promiscuous Vα-chain pairing to recognize an identical HLA-DP2-peptide/Be complex. Importantly, the inverse relationship between expansion of CD4(+) T cells expressing these public TCRs and disease severity suggests a pathogenic role for these T cells in CBD.

Mutagenesis of beryllium-specific TCRs suggests an unusual binding topology for antigen recognition.

Unconventional Ags, such as metals, stimulate T cells in a very specific manner. To delineate the binding landscape for metal-specific T cell recognition, alanine screens were performed on a set of Be-specific TCRs derived from the lung of a chronic beryllium disease patient. These TCRs are HLA-DP2-restricted and express nearly identical TCR Vß5.1 chains coupled with different TCR α-chains. Site-specific mutagenesis of all amino acids comprising the CDRs of the TCRA and TCRB genes showed a dominant role for Vß5.1 residues in Be recognition, with little contribution from the TCR α-chain. Solvent-exposed residues along the α-helices of the HLA-DP2 α- and ß-chains were also mutated to alanine. Two ß-chain residues, located near the proposed Be binding site of HLA-DP2, played a dominant role in T cell recognition with no contribution from the HLA-DP2 α-chain. These findings suggest that Be-specific T cells recognize Ag using an unconventional binding topology, with the majority of interactions contributed by TCR Vß5.1 residues and the HLA-DP2 ß1-chain. Thus, unusual docking topologies are not exclusively used by autoreactive T cells, but also for the recognition of unconventional metal Ags, such as Be.

Crystal structure of HLA-DP2 and implications for chronic beryllium disease.

Chronic beryllium disease (CBD) is a fibrotic lung disorder caused by beryllium (Be) exposure and is characterized by granulomatous inflammation and the accumulation of Be-responsive CD4(+) T cells in the lung. Genetic susceptibility to CBD has been associated with certain alleles of the MHCII molecule HLA-DP, especially HLA-DPB1*0201 and other alleles that contain a glutamic acid residue at position 69 of the beta-chain (betaGlu69). The HLA-DP alleles that can present Be to T cells match those implicated in the genetic susceptibility, suggesting that the HLA contribution to disease is based on the ability of those molecules to bind and present Be to T cells. The structure of HLA-DP2 and its interaction with Be are unknown. Here, we present the HLA-DP2 structure with its antigen-binding groove occupied by a self-peptide derived from the HLA-DR alpha-chain. The most striking feature of the structure is an unusual solvent exposed acidic pocket formed between the peptide backbone and the HLA-DP2 beta-chain alpha-helix and containing three glutamic acids from the beta-chain, including betaGlu69. In the crystal packing, this pocket has been filled with the guanidinium group of an arginine from a neighboring molecule. This positively charged moiety forms an extensive H-bond/salt bridge network with the three glutamic acids, offering a plausible model for how Be-containing complexes might occupy this site. This idea is strengthened by the demonstration that mutation of any of the three glutamic acids in this pocket results in loss of the ability of DP2 to present Be to T cells.

Defective leukocyte GM-CSF receptor (CD116) expression and function in inflammatory bowel disease.

BACKGROUND & AIMS: Inflammatory bowel disease (IBD) refers to 2 chronic inflammatory diseases of the intestine, ie, ulcerative colitis and Crohn's disease. IBD results from environmental factors (eg, bacterial antigens) triggering a dysregulated immune response in genetically predisposed hosts. Although the basis of IBD is incompletely understood, a number of recent studies have implicated defective innate immune responses in the pathogenesis of IBD. In this regard, there is much interest in therapies that activate innate immunity (eg, recombinant granulocyte-macrophage colony-stimulating factor). METHODS: In this study, we screened expression and function of circulating leukocyte granulocyte-macrophage colony-stimulating factor receptor (CD116) messenger RNA and surface protein in 52 IBD patients and 52 healthy controls. RESULTS: Our results show that both granulocyte and monocyte CD116 levels, but not CD114 or interleukin-3Rα, were significantly decreased in IBD compared to control (P<.001) and disease controls (irritable bowel syndrome; P<.001; rheumatoid arthritis; P<.025). IBD-associated CD116 repression was more prominent in patients with ulcerative colitis compared to Crohn's disease (P<.05), was independent of disease activity (P>.05), and was not influenced by current medications (P>.05). Receiver operating characteristic curve analysis revealed that leukocyte CD116 expression is a sensitive (85%) and specific (92%) biomarker for IBD. Moreover, granulocyte CD116-mediated function (phosphorylation of signal transducers and activators of transcription 3) paralleled decreased expression of CD116 in IBD granulocytes compared to control (P<.001). CONCLUSIONS: These studies identify defective expression and function of CD116 as a distinguishing feature of IBD and implicate an associated defect in innate immune responses toward granulocyte-macrophage colony-stimulating factor.

Beryllium-specific CD4+ T cells in blood as a biomarker of disease progression.

BACKGROUND: CD4(+) T cells are responsible for the progressive lung damage seen in patients with chronic beryllium disease (CBD), a granulomatous lung disorder in which antigen-specific, T(H)1-type, cytokine-secreting T cells have been characterized. Compared with those seen in beryllium (Be)-sensitized subjects, increased numbers of Be-responsive T cells are present in the blood of patients with CBD. OBJECTIVE: The aim of this study was to determine whether the number of Be-specific T cells in blood predicted the development of CBD in a cohort of Be-exposed subjects. METHODS: Using IFN-γ ELISpot and proliferation-based assays, we determined the frequency and proliferative capacity of Be-responsive T cells in blood. RESULTS: Compared with the Be lymphocyte proliferation test, which detected an abnormal Be-induced proliferative response in 11 (4.2%) of 260 workers from a Be-machining facility, the IFN-γ ELISpot detected a sensitization rate of 10% (χ(2) = 55.7, P < .0001). A significant positive correlation was also noted between the number of Be-responsive CD4(+) T cells in the blood and lung tissue of patients with CBD. Importantly, the transition from Be sensitization to CBD was associated with an increased number of antigen-specific T cells in blood. CONCLUSION: These findings have important implications for Be-induced disease and potentially other immune-mediated disorders, suggesting that the frequency of antigen-specific T cells in blood can serve as a noninvasive biomarker to predict disease development and severity of the Be-specific CD4(+) T-cell alveolitis.

Deficient and dysfunctional regulatory T cells in the lungs of chronic beryllium disease subjects.

RATIONALE: Chronic beryllium disease (CBD) is a CD4(+) T cell-mediated disorder characterized by persistent lung inflammation. Naturally occurring regulatory T (T(reg)) cells modulate adaptive immune responses. The role of this T-cell subset in beryllium-induced lung disease is unknown. OBJECTIVES: The aim of this study was to determine whether dysfunctional T(reg) cells in the lung contribute to the "unchecked" inflammatory response that characterizes CBD. METHODS: Using blood and bronchoalveolar lavage (BAL) cells from normal control subjects and individuals with beryllium-induced disease, we determined the frequency and function of naturally occurring T(reg) cells. MEASUREMENTS AND MAIN RESULTS: A significantly decreased percentage and expression of FoxP3 in BAL CD4(+) T cells from CBD patients compared with beryllium-sensitized subjects was seen, and the percentage of FoxP3-expressing CD4(+) T(reg) cells in BAL inversely correlated with disease severity. In contrast to blood T(reg) cells derived from beryllium-sensitized subjects and patients with CBD that completely suppressed blood responder T-cell proliferation, BAL FoxP3-expressing T(reg) cells from patients with CBD are unable to suppress anti-CD3-mediated BAL T-cell proliferation. Mixing studies showed that blood T(reg) cells are capable of suppressing autologous BAL responder T cells. Conversely, BAL CD4(+) T(reg) cells are incapable of suppressing blood T cells, confirming that the failure of BAL T(reg) cells to suppress T-cell proliferation is caused by a dysfunctional T(reg) cell subset and not by resistance of BAL effector T cells to suppression. CONCLUSIONS: These findings suggest that the deficient and dysfunctional T(reg) cells in the lung of patients with CBD contribute to the persistent inflammatory response in this disease.

Beryllium-specific CD4+ T cells induced by chemokine neoantigens perpetuate inflammation.

Discovering dominant epitopes for T cells, particularly CD4+ T cells, in human immune-mediated diseases remains a significant challenge. Here, we used bronchoalveolar lavage (BAL) cells from HLA-DP2-expressing patients with chronic beryllium disease (CBD), a debilitating granulomatous lung disorder characterized by accumulations of beryllium-specific (Be-specific) CD4+ T cells in the lung. We discovered lung-resident CD4+ T cells that expressed a disease-specific public CDR3ß T cell receptor motif and were specific to Be-modified self-peptides derived from C-C motif ligand 4 (CCL4) and CCL3. HLA-DP2-CCL/Be tetramer staining confirmed that these chemokine-derived peptides represented major antigenic targets in CBD. Furthermore, Be induced CCL3 and CCL4 secretion in the lungs of mice and humans. In a murine model of CBD, the addition of LPS to Be oxide exposure enhanced CCL4 and CCL3 secretion in the lung and significantly increased the number and percentage of CD4+ T cells specific for the HLA-DP2-CCL/Be epitope. Thus, we demonstrate a direct link between Be-induced innate production of chemokines and the development of a robust adaptive immune response to those same chemokines presented as Be-modified self-peptides, creating a cycle of innate and adaptive immune activation.

CD4+ T cells in the lungs of acute sarcoidosis patients recognize an Aspergillus nidulans epitope.

Löfgren's syndrome (LS) is an acute form of sarcoidosis characterized by a genetic association with HLA-DRB1*03 (HLA-DR3) and an accumulation of CD4+ T cells of unknown specificity in the bronchoalveolar lavage (BAL). Here, we screened related LS-specific TCRs for antigen specificity and identified a peptide derived from NAD-dependent histone deacetylase hst4 (NDPD) of Aspergillus nidulans that stimulated these CD4+ T cells in an HLA-DR3-restricted manner. Using ELISPOT analysis, a greater number of IFN-γ- and IL-2-secreting T cells in the BAL of DR3+ LS subjects compared with DR3+ control subjects was observed in response to the NDPD peptide. Finally, increased IgG antibody responses to A. nidulans NDPD were detected in the serum of DR3+ LS subjects. Thus, our findings identify a ligand for CD4+ T cells derived from the lungs of LS patients and suggest a role of A. nidulans in the etiology of LS.

T cell recognition of beryllium.

Chronic beryllium disease (CBD) is a granulomatous lung disorder caused by a hypersensitivity to beryllium and characterized by the accumulation of beryllium-specific CD4(+) T cells in the lung. Genetic susceptibility to beryllium-induced disease is strongly associated with HLA-DP alleles possessing a glutamic acid at the 69th position of the ß-chain (ßGlu69). The structure of HLA-DP2, the most prevalent ßGlu69-containing molecule, revealed a unique solvent-exposed acidic pocket that includes ßGlu69 and represents the putative beryllium-binding site. The delineation of mimotopes and endogenous self-peptides that complete the αßTCR ligand for beryllium-specific CD4(+) T cells suggests a unique role of these peptides in metal ion coordination and the generation of altered self-peptides, blurring the distinction between hypersensitivity and autoimmunity.

Identification of beryllium-dependent peptides recognized by CD4+ T cells in chronic beryllium disease.

Chronic beryllium disease (CBD) is a granulomatous disorder characterized by an influx of beryllium (Be)-specific CD4⁺ T cells into the lung. The vast majority of these T cells recognize Be in an HLA-DP­restricted manner, and peptide is required for T cell recognition. However, the peptides that stimulate Be-specific T cells are unknown. Using positional scanning libraries and fibroblasts expressing HLA-DP2, the most prevalent HLA-DP molecule linked to disease, we identified mimotopes and endogenous self-peptides that bind to MHCII and Be, forming a complex recognized by pathogenic CD4⁺ T cells in CBD. These peptides possess aspartic and glutamic acid residues at p4 and p7, respectively, that surround the putative Be-binding site and cooperate with HLA-DP2 in Be coordination. Endogenous plexin A peptides and proteins, which share the core motif and are expressed in lung, also stimulate these TCRs. Be-loaded HLA-DP2­mimotope and HLA-DP2­plexin A4 tetramers detected high frequencies of CD4⁺ T cells specific for these ligands in all HLADP2+ CBD patients tested. Thus, our findings identify the first ligand for a CD4⁺ T cell involved in metal-induced hypersensitivity and suggest a unique role of these peptides in metal ion coordination and the generation of a common antigen specificity in CBD.

Linking genetic susceptibility and T cell activation in beryllium-induced disease.

Chronic beryllium disease (CBD) is a granulomatous lung disorder caused by beryllium (Be) exposure in the workplace. It is characterized by the accumulation of Be-specific CD4(+) T cells in the lung as well as persistent lung inflammation, culminating in the development of lung fibrosis. CBD occurs in 2 to 16% of Be-exposed workers depending on the individuals' genetic susceptibility and the characteristics of the exposure. Genetic susceptibility to Be-induced disease has been linked to major histocompatibility complex class II molecules. In particular, HLA-DP alleles possessing a glutamic acid at the 69th position of the beta-chain (betaGlu69) are most strongly linked to disease susceptibility. The HLA-DP alleles that present Be to T cells match those implicated in the genetic susceptibility, suggesting that the HLA contribution to disease is based on the ability of those molecules to bind and present Be to T cells. However, the structural features of betaGlu69-containing HLA-DP molecules that explain the disease association remain unknown. We have recently crystallized HLA-DP2, which is the most prevalent of the betaGlu69-containing HLA-DP molecules. Its unique structure, which includes surface exposure of betaGlu69, provides an explanation of the genetic linkage between betaGlu69-containing HLA-DP alleles and Be-induced disease.

Oligoclonal expansions of CD4+ and CD8+ T-cells in the target organ of patients with biliary atresia.

BACKGROUND & AIMS: Biliary atresia is an inflammatory, fibrosclerosing neonatal cholangiopathy, characterized by a periductal infiltrate composed of CD4(+) and CD8(+) T cells. The pathogenesis of this disease has been proposed to involve a virus-induced, subsequent autoreactive T cell-mediated bile duct injury. Antigen-specific T-cell immunity involves clonal expansion of T cells expressing similar T-cell receptor (TCR) variable regions of the beta-chain (Vbeta). We hypothesized that the T cells in biliary atresia tissue expressed related TCRs, suggesting that the expansion was in direct response to antigenic stimulation. METHODS: The TCR Vbeta repertoire of T cells from the liver, extrahepatic bile duct remnants, and peripheral blood of biliary atresia and other cholestatic disease controls were characterized by fluorescent-activated cell sorter analysis, and TCR junctional region nucleotide sequencing was performed on expanded TCR Vbeta regions to confirm oligoclonality. RESULTS: FACS analysis revealed Vbeta subset expansions of CD4(+) and CD8(+) T cells from the liver or bile duct remnant in all patients with biliary atresia and only 1 control. The CD4(+) TCR expansions were limited to Vbeta3, -5, -9, and -12 T-cell subsets and the CD8(+) TCR Vbeta expansions were predominantly Vbeta20. Each Vbeta subset expansion was composed of oligoclonal populations of T cells. CONCLUSIONS: Biliary atresia is associated with oligoclonal expansions of CD4(+) and CD8(+) T cells within liver and extrahepatic bile duct remnant tissues, indicating the presence of activated T cells reacting to specific antigenic stimulation. Future studies entail identifying the specific antigen(s) responsible for T-cell activation and bile duct injury.

Class II major histocompatibility complex-peptide tetramer staining in relation to functional avidity and T cell receptor diversity in the mouse CD4(+) T cell response to a rheumatoid arthritis-associated antigen.

OBJECTIVE: Although studies have suggested that human cartilage (HC) gp-39 may be an antigen recognized by autoreactive CD4(+) T cells in rheumatoid arthritis, we previously failed to identify specific CD4(+) T cells in patients' synovial fluid or blood using a class II major histocompatibility complex-peptide tetramer composed of the immunodominant HC gp-39(263-275) epitope covalently linked to DR4. We undertook this study to better understand the parameters for specific binding of this tetramer. METHODS: DR4-transgenic mice were immunized with the HC gp-39 peptide, and a set of peptide-responsive hybridomas was derived. Hybridomas were stained with the DR4-gp-39 tetramer and cultured with increasing amounts of peptide in the presence of DR4-expressing antigen-presenting cells to determine functional avidity. RESULTS: Great variability was apparent in the ability of the tetramer to stain the hybridomas, and there was a strong correlation between the intensity of tetramer staining and functional avidity. Importantly, nearly 30% of the hybridomas did not stain with tetramer, and these cells exhibited relatively low functional avidity. Although the addition of an anti-T cell receptor (anti-TCR) monoclonal antibody during the staining procedure enhanced binding of the tetramer to a number of the hybridomas, a significant percentage remained unstainable. Analysis of TCR expression showed that >90% of the hybridomas expressed the same TCR beta-chain variable region (V(beta)10), and sequencing of the TCR junctional regions showed diversity in the third complementarity-determining region. CONCLUSION: These results suggest that immune responses dominated by relatively low-affinity TCR interactions, such as those that may occur in autoimmune disease, will be difficult to detect using standard tetramer techniques.