The life cycle of a T cell after vaccination - where does immune ageing strike?

Vaccination is the optimal intervention to prevent the increased morbidity and mortality from infection in older individuals and to maintain immune health during ageing. To optimize benefits from vaccination, strategies have to be developed that overcome the defects in an adaptive immune response that occur with immune ageing. Most current approaches are concentrated on activating the innate immune system by adjuvants to improve the induction of a T cell response. This review will focus upon T cell-intrinsic mechanisms that control how a T cell is activated, expands rapidly to differentiate into short-lived effector cells and into memory precursor cells, with short-lived effector T cells then mainly undergoing apoptosis and memory precursor cells surviving as long-lived memory T cells. Insights into each step of this longitudinal course of a T cell response that takes place over a period of several weeks is beginning to allow identifying interventions that can improve this process of T cell memory generation and specifically target defects that occur with ageing.

Activated human T cells express alternative mRNA transcripts encoding a secreted form of RANKL.

Receptor activator of nuclear factor-kappaB-ligand (RANKL), encoded by the gene TNFSF11, is required for osteoclastogenesis, and its expression is upregulated in pathologic bone loss. Transcript variants of TNFSF11 messenger RNA (mRNA) have been described that encode a membrane-bound and a putative secreted form of RANKL. We identify a TNFSF11 transcript variant that extends the originally identified transcript encoding secreted RANKL. We demonstrate that this TNFSF11 transcript variant is expressed by the human osteosarcoma cell line, Saos-2, and by both primary human T cells and Jurkat T cells. Of relevance to the production of RANKL in pathologic bone loss, expression of this secreted TNFSF11 transcript is upregulated in Jurkat T cells and primary human T cells upon activation. Furthermore, this transcript can be translated and secreted in Jurkat T cells in vitro and is able to support osteoclast differentiation. Our data highlight the complexity of the TNFSF11 genomic locus, and demonstrate the potential for the expression of alternate mRNA transcripts encoding membrane-bound and secreted forms of RANKL. Implications of alternate mRNA transcripts encoding different RANKL protein isoforms should be carefully considered and specifically examined in future studies, particularly those implicating RANKL in pathologic bone loss.

Long-term humoral unresponsiveness in vivo, induced by treatment with monoclonal antibody against L3T4.

mAbs directed against the L3T4 molecule administered in vivo caused a severe and long lasting helper cell depletion in mice. Regeneration of the L3T4+ subpopulation occurred gradually (2-3 mo) after a single antibody treatment. Experiments were designed to examine the humoral immunocompetence of such anti-L3T4-treated animals during and after regeneration of the L3T4+ T cell subset. The animals were injected with anti-L3T4, immunized with soluble antigen, and challenged with antigen every 2 wk. Antibody responses to two antigens, sperm whale myoglobin (SpWMb) and KLH, which differ with regard to their immunogenicity, were compared. The lack of humoral immune responsiveness to either of these two antigens shorty after anti-L3T4 treatment responsiveness to either of these two antigens shortly after anti-L3T4 treatment was probably due to clonal depletion. The anti-L3T4-induced immunosuppressive effect on antibody production seemed to be determined in part by the preexisting T cell repertoire, as was suggested by the recovery of responsiveness to the highly immunogenic antigen KLH and the transient inhibitory effect of anti-L3T4 treatment in primed animals. The regenerating L3T4+ T cell subpopulation was relatively incompetent in initiating B cell responses. More than 40% of the L3T4+ T cell compartment had to recover to provide help for the production of anti-KLH antibodies, whereas elimination of 90% of the L3T4+ helper cells did not inhibit a primary anti-KLH response. Evidence for a heterogeneous composition of the L3T4+ subset came from experiments using rIL-2 in vivo. The addition of rIL-2 during early helper cell depletion improved the recovery of the humoral responsiveness without apparently affecting the kinetics of the regeneration of L3T4+ T cells. Interestingly, humoral unresponsiveness to the weakly immunogenic antigen SpWMb persisted for at least 120 d. This long lasting unresponsiveness could not be explained by clonal depletion, and suggested as one possibility that the presence of antigen during regeneration of the L3T4+ helper cell population may have influenced the ultimate T cell repertoire.

Administration of recombinant interleukin 2 in vivo induces a polyclonal IgM response.

We studied the potential immunoenhancing effects of high doses of rIL-2 on murine T and B cell functions in vivo. Injection of rIL-2 caused a threefold or more increase in the frequencies of antigen-specific proliferative T cells, suggesting that rIL-2 initiated a polyclonal T cell response. In primary and secondary humoral immune responses, administration of rIL-2 in vivo selectively enhanced the production of IgM antibodies, whereas the IgG response was unaffected. Coadministration of rIL-2 with antigen failed to induce an isotype switch from IgM to IgG in genetically low-responding mice. Interestingly, in mice treated with rIL-2 alone (in the absence of exogenous antigen), polyclonal IgM production was induced. Polyclonal IgM production of lesser magnitude was found when mice were immunized with specific antigen in the absence of exogenous rIL-2, suggesting that local IL-2 concentrations in a primary immune response might be sufficient to elicit a polyclonal IgM response.

Distinct vascular lesions in giant cell arteritis share identical T cell clonotypes.

Giant cell arteritis (GCA) is a spontaneous vasculitic syndrome that specifically targets the walls of medium and large arteries. Vascular lesions are characterized by patchy granulomatous infiltrates composed of T cells, macrophages, histiocytes, and giant cells. To test the hypothesis that a locally residing antigen recruits T cells into the vessel walls, we have analyzed T cell receptor (TCR) molecules of tissue infiltrating T cells. A total of 638 CD4+ T cell clones were isolated from temporal artery specimens of three patients with GCA. Analysis of TCR molecules for the usage of V beta 1-V beta 20 revealed that all TCR V beta elements were represented, demonstrating that interleukin 2 (IL-2)-responsive T cells infiltrating the tissue are highly diverse. To detect expanded T cell specificities, we made use of the patchy character of the inflammatory disease and compared the TCR repertoire of T cells established from independent vasculitic foci of the same artery. Sequence analysis of TCR V beta chains documented that individual TCR specificities were present in multiple copies, indicating clonal expansion. T cells with identical beta chains were isolated from distinct inflammatory foci of the same patient. These specificities represented only a small fraction of tissue-infiltrating T cells and involved the V beta 5.3 gene segment in the two patients sharing the HLA-DRB1*0401 allele. The third complementarity determining region of clonally expanded TCR beta chains was characterized by a cluster of negatively and positively charged residues, suggesting that the juxtaposed antigenic peptide is charged. The sharing of identical T cell specificities by distinct and independent regions of the granulomatous inflammation suggests that these T cells are disease relevant and that their repertoire is strongly restricted. These data suggest that an antigen residing in the arterial wall is recognized by a small fraction of CD4+ T cells in the inflammatory process characteristic for GCA.

Major histocompatibility complex class I-recognizing receptors are disease risk genes in rheumatoid arthritis.

Rheumatoid arthritis (RA) is a heterogeneous syndrome of which a subset of patients develops vascular inflammation. The genetic determinants that confer risk for rheumatoid vasculitis are not known, but patients with vascular complications are known to have an expansion of CD4(+)CD28(null) T cells, a cell population potentially involved in endothelial damage. CD4(+)CD28(null) T cell clones isolated from RA patients with vasculitis were found to express killer cell immunoglobulin-like receptors (KIRs) with the stimulatory KIR2DS2 often present in the absence of opposing inhibitory receptors with related specificities. To test the hypothesis that the KIR2DS2 gene is involved in the development of vasculitis, association studies were performed. The KIR2DS2 gene was significantly enriched among patients with rheumatoid vasculitis compared with normal individuals (odds ratio 5.56, P = 0.001) and patients with RA but no vasculitis (odds ratio 7.96, P = 0.001). Also, the distribution of human histocompatibility leukocyte antigen (HLA)-C, the putative ligand for KIRs, was significantly different in patients with rheumatoid vasculitis in comparison with the control populations. These data suggest that HLA class I-recognizing receptors and HLA class I genes are genetic risk determinants that modulate the pattern of RA expression. Specifically, KIR2DS2 in conjunction with the appropriate HLA-C ligand may have a role in vascular damage by regulating CD4(+)CD28(null) T cells.

[Pathogenesis of medium- and large-vessel vasculitis]. / Pathogenese der Vaskulitis mittlerer und grosser Gefässe.

Giant cell arteritis (GCA), is a systemic vasculitis which preferentially targets large and medium branches of the upper-body aorta. Typical clinical manifestations result from arterial stenosis/occlusion causing blindness, stroke and aortic arch syndrome. Aortic involvement leads to dissection and aneurysm. On the cellular and molecular level, GCA is a sequel of abnormal innate and adaptive immune responses that occur in the specialized tissue niche of the arterial wall. Based on recent pathogenic studies, a novel disease model for GCA is emerging. It is now understood that the series of pathogenic events begins with dendritic cells (DC) indigenous to the artery's outer wall, leading to inflammatory vasculopathy. Placed close to the vasa vasorum, vascular DC are highly sensitive in recognizing pathogen-associated motifs assigning immune monitoring functions to blood vessels. Thus the large vessels are actively involved in immune monitoring. Each vascular territory expresses a unique profile of pathogen-sensing receptors, emphasizing functional diversity amongst structurally similar arteries. Innate immune stimulators can transform vascular DC into efficient antigen-presenting cells, attracting, activating, and instructing T lymphocytes to acquire tissue-invasive features. Macrophages provide critical tissue-damaging effector functions, directly injuring wall-residing cells and promoting a remodeling process that leads to intimal hyperplasia and luminal occlusion. Novel diagnostic and therapeutic approaches to GCA need to focus on the key position of vascular DC and the signals that break the immunoprivileged state of the vessel wall.

Disease-associated human histocompatibility leukocyte antigen determinants in patients with seropositive rheumatoid arthritis. Functional role in antigen-specific and allogeneic T cell recognition.

The susceptibility to develop seropositive rheumatoid arthritis (RA) has been linked to specific genomic polymorphisms within the HLA complex. Two different haplotypes have been associated with the disease, HLA-DR1 and HLA-DR4. To investigate the link between such phenotypic disease associations and potential immune mechanisms we used alloreactive and antigen-specific human T cell clones. Here we describe a panel of alloreactive T cell clones directed to polymorphic determinants encoded by the third hypervariable region (hvr) of the HLA-DR beta 1-chain. T cell determinants defined by these clones are shared among HLA-DR1, HLA-Dw4, HLA-Dw13, HLA-Dw14, and HLA-Dw15, and are frequent in a population of RA patients. To study the role of such disease-associated epitopes in antigen-restricted T cell recognition we generated T cell clones from RA patients specific for mycobacterial antigens, Epstein-Barr virus antigens, and tetanus toxoid. In all three antigenic systems T cell clones were restricted to either HLA-DR1 or HLA-DR4. These data suggest that the polymorphisms within the first and second hvr of the HLA-DR beta 1-chain that are distinct in HLA-DR1 and HLA-DR4 and not associated with the disease are crucially involved in the recognition of antigens. Polymorphic determinants encoded by the third hvr are shared among disease-associated haplotypes and may function to mediate the interaction of alloreactive T cell receptor molecules with the HLA complex.

CD4+ CD7- CD28- T cells are expanded in rheumatoid arthritis and are characterized by autoreactivity.

Clonal expansion of CD4+ T cells is a characteristic finding in patients with RA and is only infrequently found in patients with psoriatic arthritis and healthy controls. Expanded CD4+ clonotypes are present in the blood, infiltrate into the joint, and persist over years. We have not addressed the question of whether the expanded clonotypes have unique functional and phenotypic properties which may explain the preferential in vivo expansion in RA. In contrast to most CD4+ T cells, expanded clonotypes lacked the expression of the CD28 and CD7 cell surface molecules. Accordingly, the subsets of CD4+ CD28- (9.7 vs 1.7, P = 0.00002) and CD4+ CD7- T cells (21.5 vs 12.26, P = 0.018) were increased in RA patients compared with age-matched normal individuals. Despite the lack of CD28 expression, clonally expanded CD4+ T cells were not anergic but proliferated in response to immobilized anti-CD3 and could be maintained in tissue culture. In vivo expanded CD4+ T cells were autoreactive to ubiquitously distributed autoantigens. They responded in an autologous mixed lymphocyte reaction, and T cell clones isolated from selected patients proliferated to autologous peripheral blood adherent cells. These data suggest that in RA patients selected CD4+ T cells which share the CD7- CD28- phenotype escape from peripheral tolerance.

Functional profile of tissue-infiltrating and circulating CD68+ cells in giant cell arteritis. Evidence for two components of the disease.

Macrophages represent a critical component in the inflammatory lesions of giant cell arteritis. By combining immunohistochemistry and in situ hybridization, we have analyzed the functional heterogeneity of tissue-infiltrating macrophages in patients with untreated vasculitis. 20% of macrophages in temporal artery tissue synthesized IL-6-specific mRNA and produced IL-6 and IL-1 beta proteins. IL-6 and IL-1 beta production was not limited to CD68+ cells in the lymphoid aggregates but was a feature of CD68+ cells dispersed throughout the tissue. 50% of tissue-infiltrating CD68+ cells synthesized 72-kD type IV collagenase. Only a small subset of CD68+ cells produced cytokines as well as collagenase, indicating functional specialization or distinct differentiation stages of CD68+ cells in the inflamed tissue. Activation of CD68+ cells was not restricted to tissue-infiltrating cells. Expression of IL-6 and IL-1 beta was found in 60-80% of circulating monocytes of patients with untreated giant cell arteritis, whereas collagenase production was restricted to tissue macrophages. IL-6 and IL-1 beta production by the majority of circulating monocytes was a shared feature of patients with giant cell arteritis and polymyalgia rheumatica but was not found in rheumatoid arthritis. These data suggest that giant cell arteritis has two components of disease, an inflammatory reaction in vessel walls and a systemic activation of monocytes. Systemic monocyte activation can manifest independently without vasculitis as exemplified in patients with polymyalgia rheumatica.

Correlation between disease phenotype and genetic heterogeneity in rheumatoid arthritis.

RA is a heterogeneous group of disorders characterized by variations in clinical manifestations, disease course, and probably response to therapeutic interventions. We have addressed the question whether genetically and potentially etiologically more homogeneous subgroups of RA patients can be defined based upon the expression of the RA-linked sequence motif in the third hypervariable region of the HLA-DRB1 gene. Genetic comparison of patients classified upon clinical manifestation and disease course demonstrated that patients with mild disease were genetically distinct from those progressing to severe and destructive disease. Specifically, rheumatoid factor (RF) negative patients preferentially expressed RA-linked HLA-DRB1 alleles with an arginine substitution in position 71, whereas the alleles with a lysine substitution in position 71 accumulated in RF+ patients. RF- patients were further subdivided based on clinical markers (time of onset of erosive disease and requirement for aggressive therapy). Clinical heterogeneity correlated with genetic heterogeneity. Patients with early erosive disease and patients requiring aggressive therapy frequently typed HLA-DRB1*04+. Patients with late erosive/nonerosive disease or a benign disease course manageable with nonaggressive treatment preferentially expressed HLA-DRB1*01 or lacked an RA-linked haplotype. These data indicate that the heterogeneity of RA reflects genetic differences. Sequence variations within the disease-linked sequence motif, as well as polymorphisms surrounding the candidate genetic element, affect pattern, course, and treatment response of RA. Amino acid position 71 in the HLA-DRB1 gene has a unique role, the understanding of which may provide important clues to disease etiology.

Homozygosity for the HLA-DRB1 allele selects for extraarticular manifestations in rheumatoid arthritis.

Seropositive rheumatoid arthritis is genetically linked to a group of HLA-DRB1 alleles sharing a sequence motif within the third hypervariable region. Controversy exists over the role of the distinct allelic variants in affecting not only the risk to develop disease, but also in modifying the expression of the disease. We have stratified 81 patients according to their patterns of disease manifestations and identified the HLA-DRB1 alleles by polymerase chain reaction amplification and subsequent oligonucleotide hybridization. To identify precisely the allelic combinations at the HLA-DRB1 locus, homozygosity was confirmed by locus-specific cDNA amplification and subsequent sequencing. Our study demonstrated a high correlation of allelic combinations of disease-associated HLA-DRB1 alleles with the clinical manifestations. Characteristic genotypes were identified for patients who had progressed toward nodular disease and patients who had developed major organ involvement. Rheumatoid nodules were highly associated with a heterozygosity for two disease associated HLA-DRB1 alleles. Homozygosity for the HLA-DRB1*0401 allele was a characteristic finding for RA patients with major organ involvement. Our data suggest a role of the disease-associated sequence motif in determining severity of the disease. The finding of a codominant function of HLA-DRB1 alleles suggests that the biological function of HLA-DR molecules in thymic selection might be important in the pathogenesis of RA.

Shared T cell recognition sites on human histocompatibility leukocyte antigen class II molecules of patients with seropositive rheumatoid arthritis.

Seropositive rheumatoid arthritis (RA) in adult and juvenile patients is associated with the serologic marker HLA-DR4. This association is incomplete; about one-third of the patients lack the disease-associated HLA-DR4 haplotype. The main biological function of class II molecules is to restrict the recognition of antigen by T lymphocytes. We therefore tested the hypothesis that patients with seropositive RA share T cell recognition sites for an unknown antigen and that such T cell "epitopes" are not identified by conventional serologic typing. We generated alloreactive human T cell clones by stimulating peripheral blood lymphocytes of normal donors against a lymphoblastoid cell line from a juvenile patient with seropositive RA. A panel of clones that recognized only HLA-Dw14 cells on a panel of homozygous typing cells was used to analyze class II molecules of adult patients with seropositive RA. By inhibition studies using monoclonal antibodies, the epitopes recognized by the different clones could be further characterized and assigned either to DR- or to DQ-encoded cell surface products. By using four different clones, it was possible to identify Dw14-associated T cell epitopes on all seropositive rheumatoid patients tested who typed HLA-DR4-positive and also on all eight DR4-negative patients tested. Approximately one-half of nonrheumatoid DR4-positive donors carried one or more determinants recognized by these clones; the expression of these allodeterminants in DR4-negative nonrheumatoid patients was rare (less than 10%). Thus, alloreactive human T cell clones are powerful tools to define T cell recognition sites on class II molecules that are not identified by conventional typing. Using T cell clones with specificities for determinants expressed on Dw14 homozygous typing lines, we were able to demonstrate shared epitopes on cells of all patients tested with seropositive RA irrespective of their HLA-D or HLA-DR type. These data suggest that major histocompatibility complex class II antigens of RA patients might be much more homogeneous than demonstrated by the incomplete HLA-DR4 association.

Induction of B cell apoptosis by TH0, but not TH2, CD4+ T cells.

Engagement of the T cell receptor molecules with MHC-antigen complexes presented by B cells ascertains antigen specificity in T cell-dependent help. Ligation of MHC molecules on the surface of B cells, however, has not only been implicated in antigen-specific T-B cell interaction, but has also been linked to the induction of B cell apoptosis. To examine the role of T helper cells in either induction of immunoglobulin synthesis or B cell apoptotic death, we have facilitated T cell receptor-MHC interaction through a bacterial superantigen. CD4+ T cell clones could be categorized into two clearly distinct subsets based upon their ability to promote B cell help in the presence of superantigen. One subset of T cell clones supported immunoglobulin synthesis, and thus functioned as effective helper cells. B cells interacting with the second subset of T cells did not differentiate into antibody-secreting cells, but underwent apoptosis. Both types of helper cells were able to provide contact help after anti-CD3 stimulation. Induction of apoptosis was a dominant phenomenon; the addition of the superantigen suppressed immunoglobulin production in B cells activated by anti-CD3-stimulated helper T cells, indicating that the T cells delivered an apoptotic signal to the B cell. T cell clones providing effective MHC restrictive B cell help could be distinguished from T cells facilitating B cell apoptosis based on their lymphokine secretion profile. Induction of B cell apoptosis was a feature of T cells with a TH0 lymphokine pattern. Promotion of MHC-restricted B cell help was associated with a TH2 lymphokine profile. TH1-derived cytokines alone could not substitute for apoptosis-inducing T cells.

The HLA-DRB1 locus as a genetic component in giant cell arteritis. Mapping of a disease-linked sequence motif to the antigen binding site of the HLA-DR molecule.

Giant cell arteritis (GCA) is a granulomatous vasculitis affecting persons over 50 years of age. The inflammatory infiltrate, which is targeted at the aorta and its proximal branches, includes activated CD4+ helper T cells, histiocytes, and giant cells. To investigate whether the genetic polymorphism of the HLA-DRB1 genes contributes to the local accumulation of activated T cells, we have analyzed both HLA-DRB1 alleles in a cohort of 42 patients with biopsy-proven GCA. The majority of patients (60%) expressed the B1*0401 or B1*0404/8 variant of the HLA-DR4 haplotype, both of which also represent the major genetic factors underlying the disease association in RA. GCA patients negative for the disease-linked HLA-DR4 alleles were characterized by a nonrandom distribution of HLA-DRB1 alleles. Sequence comparison among the allelic products identified in the GCA cohort demonstrated heterogeneity for the sequence polymorphism of the third hypervariable region (HVR), but homology for the polymorphic residues within the HVR2 of the HLA-DRB1 gene. The GCA patients shared a sequence motif spanning amino acid positions 28-31 of the HLA-DR beta 1 chain. In the structural model for HLA-DR molecules, this sequence motif can be mapped to the antigen-binding site of the HLA complex, suggesting a crucial role of antigen selection and presentation in GCA. In contrast, the sequence polymorphism linked to RA has been mapped to the HVR3 of the HLA-DRB1 gene and translates into a distinct domain of the HLA-DR molecule, the alpha-helical loop surrounding the antigen-binding groove. A consecutive case series study demonstrated that GCA and RA rarely co-occurred, supporting the interpretation that distinct functional domains of the HLA-DR molecule are implicated in the pathomechanisms of these two autoimmune diseases.

Correlation of the topographical arrangement and the functional pattern of tissue-infiltrating macrophages in giant cell arteritis.

End organ ischemia, fragmentation of elastic membranes, and aneurysm formation in patients with giant cell vasculitis results from an inflammation destroying the mural layers of large and medium sized arteries. Although the inflammatory infiltrate extends through all layers of the affected blood vessel, the most pronounced changes involve the intima and the internal elastic lamina. Analysis of the functional profile of tissue infiltrating CD68+ cells demonstrates that different subsets of macrophages can be distinguished. TGFbeta1-expressing CD68+ cells coproduce IL-1beta and IL-6, are negative for inducible nitric oxide synthase (iNOS), and exhibit a strong preference for localization in the adventitia. The adventitial homing of TGFbeta1+ CD68+ cells places them in the vicinity of IFN-gamma secreting CD4+ T cells which also accumulate in the exterior layer of the artery. Conversely, iNOS expressing CD68+ cells are negative for TGFbeta and are almost exclusively found in the intimal layer of the inflamed artery. The intimal-medial junction is the preferred site for 72-kD collagenase expressing CD68+ cells. Thus, TGFbeta1-producing macrophages colocalize with activated CD4+ T cells and home to an area of inflammation which is distant from the site of tissue damage but critical in regulating cellular influx, suggesting that TGFbeta1 functions as a proinflammatory mediator in this disease. iNOS- and 72-kD collagenase-producing macrophages accumulate at the center of pathology implying a role of these products in tissue destruction. These data indicate that the microenvironment controls the topographical arrangement as well as the functional commitment of macrophages.

Dominant clonotypes in the repertoire of peripheral CD4+ T cells in rheumatoid arthritis.

Clonal expansion of T cell specificities in the synovial fluid of patients has been taken as evidence for a local stimulation of T cells. By studying the T cell receptor (TCR) repertoire of CD4+ T cells in the synovial and peripheral blood compartments of patients with early rheumatoid arthritis (RA), we have identified clonally expanded CD4+ populations. Expanded clonotypes were present in the peripheral blood and the synovial fluid but were not preferentially accumulated in the joint. Dominant single clonotypes could not be isolated from CD4+ cells of HLA-DRB1*04+ normal individuals. Clonal expansion involved several distinct clonotypes with a preference for V beta 3+, V beta 14+, and V beta 17+CD4+ T cells. A fraction of clonally related T cells expressed IL-2 receptors, indicating recent activation. The frequencies of clonally expanded V beta 17+CD4+ T cells fluctuated widely over a period of one year. Independent variations in the frequencies of two distinct clonotypes in the same patient indicated that different mechanisms, and not stimulation by a single arthritogenic antigen, were involved in clonal proliferation. These data support the concept that RA patients have a grossly imbalanced TCR repertoire. Clonal expansion may result from intrinsic defects in T cell generation and regulation. The dominance of expanded clonotypes in the periphery emphasizes the systemic nature of RA and suggests that T cell proliferation occurs outside of the joint.

Glucocorticoid-mediated repression of cytokine gene transcription in human arteritis-SCID chimeras.

Giant cell arteritis (GCA) is a vasculitic syndrome that preferentially affects medium and large-sized arteries. Glucocorticoid therapy resolves clinical symptoms within hours to days, but therapy has to be continued over several years to prevent disease relapses. It is not known whether and how glucocorticoids affect the function of the inflammatory infiltrate or why the disease persists subclinically despite chronic treatment. GCA is self-sustained in temporal arteries engrafted into SCID mice, providing a model in which the mechanisms of action and limitations of glucocorticoid therapy can be examined in vivo. Administration of dexamethasone to temporal artery-SCID chimeras for 1 wk induced a partial suppression of T cell and macrophage function as indicated by the reduced tissue concentrations of IL-2, IL-1beta, and IL-6 mRNA, and by the diminished expression of inducible NO synthase. In contrast, synthesis of IFN-gamma mRNA was only slightly decreased, and expression of TGF-beta1 was unaffected. These findings correlated with activation of the IkappaBalpha gene and blockade of the nuclear translocation of NFkappaB in the xenotransplanted tissue. Dose-response experiments suggested that steroid doses currently used in clinical medicine are suboptimal in repressing NFkappaB-mediated cytokine production in the inflammatory lesions. Chronic steroid therapy was able to deplete the T cell products IL-2 and IFN-gamma, whereas the activation of tissue-infiltrating macrophages was only partially affected. IL-1beta transcription was abrogated; in contrast, TGF-beta1 mRNA synthesis was steroid resistant. The persistence of TGF-beta1-transcribing macrophages, despite paralysis of T cell function, may provide an explanation for the chronicity of the disease, and may identify a novel therapeutic target in this inflammatory vasculopathy.

Aldose reductase functions as a detoxification system for lipid peroxidation products in vasculitis.

Giant cell arteritis (GCA) is a systemic vasculitis preferentially affecting large and medium-sized arteries. Inflammatory infiltrates in the arterial wall induce luminal occlusion with subsequent ischemia and degradation of the elastic membranes, allowing aneurysm formation. To identify pathways relevant to the disease process, differential display-PCR was used. The enzyme aldose reductase (AR), which is implicated in the regulation of tissue osmolarity, was found to be upregulated in the arteritic lesions. Upregulated AR expression was limited to areas of tissue destruction in inflamed arteries, where it was detected in T cells, macrophages, and smooth muscle cells. The production of AR was highly correlated with the presence of 4-hydroxynonenal (HNE), a toxic aldehyde and downstream product of lipid peroxidation. In vitro exposure of mononuclear cells to HNE was sufficient to induce AR production. The in vivo relationship of AR and HNE was explored by treating human GCA temporal artery-severe combined immunodeficiency (SCID) mouse chimeras with the AR inhibitors Sorbinil and Zopolrestat. Inhibition of AR increased HNE adducts twofold and the number of apoptotic cells in the arterial wall threefold. These data demonstrate that AR has a tissue-protective function by preventing damage from lipid peroxidation. We propose that AR is an oxidative defense mechanism able to neutralize the toxic effects of lipid peroxidation and has a role in limiting the arterial wall injury mediated by reactive oxygen species.

Monoclonal T-cell proliferation and plaque instability in acute coronary syndromes.

BACKGROUND: Unstable angina (UA) is associated with systemic inflammation and with expansion of interferon-gamma-producing T lymphocytes. The cause of T-cell activation and the precise role of activated T cells in plaque instability are not understood. METHODS AND RESULTS: Peripheral blood T cells from 34 patients with stable angina and 34 patients with UA were compared for the distribution of functional T-cell subsets by flow cytometric analysis. Clonality within the T-cell compartment was identified by T-cell receptor spectrotyping and subsequent sequencing. Tissue-infiltrating T cells were examined in extracts from coronary arteries containing stable or unstable plaque. The subset of CD4(+)CD28(null) T cells was expanded in patients with UA and infrequent in patients with stable angina (median frequencies: 10.8% versus 1.5%, P<0.001). CD4(+)CD28(null) T cells included a large monoclonal population, with 59 clonotypes isolated from 20 UA patients. T-cell clonotypes from different UA patients used antigen receptors with similar sequences. T-cell receptor sequences derived from monoclonal T-cell populations were detected in the culprit but not in the nonculprit lesion of a patient with fatal myocardial infarction. CONCLUSIONS: UA is associated with the emergence of monoclonal T-cell populations, analogous to monoclonal gammopathy of unknown significance. Shared T-cell receptor sequences in clonotypes of different patients implicate chronic stimulation by a common antigen, for example, persistent infection. The unstable plaque but not the stable plaque is invaded by clonally expanded T cells, suggesting a direct involvement of these lymphocytes in plaque disruption.