Co-stimulatory pathways controlling activation and peripheral tolerance of human CD4+CD28- T cells

Peripheral blood and granuloma CD4(+)CD28(-) T cells are a major source of interferon-gamma and tumor necrosis factor-alpha in Wegener's granulomatosis

To elucidate whether the fraction of CD28(-) T cells within the CD4(+) T-cell population is a major source of Th1-like and proinflammatory cytokine production driving Wegener's granulomatosis (WG) granuloma formation, we analyzed the phenotype and functional characteristics of peripheral blood CD4(+)CD28(-) T cells and of T cells in granulomatous lesions of 12 patients with active WG. Surface markers and intracytoplasmic cytokine and perforin expression were assessed by flow cytometry. Cytokine secretion was measured by enzyme-linked immunosorbent assay. Immunohistological studies demonstrated interferon-gamma and tumor necrosis factor-alpha cytokine positivity attributable to CD4(+)CD28(-) T cells in granulomatous lesions. Peripheral blood CD4(+)CD28(-) T cells expressed CD57, also found on natural killer cells, and intracytoplasmic perforin. They were generally CD25 (interleukin-2 receptor)-negative. CD18 (adhesion molecule beta(2)-integrin) was strongly up-regulated on CD4(+)CD28(-) T cells, whereas only a minority of CD4(+)CD28(+) T cells expressed CD18. CD4(+)CD28(-) T cells appeared as a major source of interferon-gamma and tumor necrosis factor-alpha. In contrast, CD4(+)CD28(+) T cells were able to produce and secrete a wider variety of cytokines including interleukin-2. One-quarter of CD4(+)CD28(+) T cells expressed the activation marker CD25, but they lacked perforin. Thus, CD4(+)CD28(-) T cells appeared more differentiated than CD4(+)CD28(+) T cells. They displayed Th1-like cytokine production and features suggestive of the capability of CD4(+) T-cell-mediated cytotoxicity. CD4(+)CD28(-) T cells may be recruited into granulomatous lesions from the blood via CD18 interaction, and may subsequently promote monocyte accumulation and granuloma formation through their cytokine secretion in WG.

Formation of the killer Ig-like receptor repertoire on CD4+CD28null T cells

Killer Ig-like receptors (KIRs) are expressed on CD4(+)CD28(null) T cells, a highly oligoclonal subset of T cells that is expanded in patients with rheumatoid arthritis. It is unclear at what stage of development these T cells acquire KIR expression. To determine whether KIR expression is a consequence of clonal expansion and replicative senescence, multiple CD4(+)CD28(null) T cell clones expressing the in vivo dominant TCR beta-chain sequences were identified in three patients and analyzed for their KIR gene expression pattern. Based on sharing of TCR sequences, the clones were grouped into five clone families. The repertoire of KIRs was diverse, even within each clone family; however, the gene expression was not random. Three particular receptors, KIR2DS2, KIR2DL2, and KIR3DL2, had significant differences in gene expression frequencies between the clone families. These data suggest that KIRs are successively acquired after TCR rearrangement, with each clone family developing a dominant expression pattern. The patterns did not segregate with the individual from whom the clones were derived, indicating that peripheral selection in the host environment was not a major shaping force. Several models were examined using a computer algorithm that was designed to simulate the expression of KIRs at various times during T cell proliferation. The computer simulations favored a model in which KIR gene expression is inducible for a limited time during the initial stages of clonal expansion.

T-cell-mediated lysis of endothelial cells in acute coronary syndromes

BACKGROUND

CD4 T lymphocytes accumulate in unstable plaque. The direct and indirect involvement of these T cells in tissue injury and plaque instability is not understood.

METHODS AND RESULTS

Gene profiling identified perforin, CD161, and members of the killer-cell immunoglobulin-like receptors as being differentially expressed in CD4(+)CD28(null) T cells, a T-cell subset that preferentially infiltrates unstable plaque. Frequencies of CD161(+) and perforin-expressing CD4 T cells in peripheral blood were significantly increased in patients with unstable angina (UA). CD161 appeared on CD4(+)CD28(null) T cells after stimulation, suggesting spontaneous activation of circulating CD4 T cells in UA. Perforin-expressing CD4(+) T-cell clones from patients with UA exhibited cytotoxic activity against human umbilical vein endothelial cells (HUVECs) in redirected cytotoxicity assays after T-cell receptor triggering and also after stimulation of major histocompatibility complex class I-recognizing killer-cell immunoglobulin-like receptors. HUVEC cytolysis was dependent on granule exocytosis, as demonstrated by the paralyzing effect of pretreating CD4(+)CD28(null) T cells with strontium. Incubation of HUVECs with C-reactive protein (CRP) increased HUVEC lysis in a dose-dependent fashion.

CONCLUSIONS

In patients with UA, CD4 T cells undergo a change in functional profile and acquire cytotoxic capability. Cytotoxic CD4 T cells effectively kill endothelial cells; CRP sensitizes endothelial cells to the cytotoxic process. We propose that T-cell-mediated endothelial cell injury is a novel pathway of tissue damage that contributes to plaque destabilization. The sensitizing effect of CRP suggests synergy between dysregulated T-cell function and acute phase proteins in acute coronary syndromes.

Involvement of CD4+,CD57+ T cells in the disease activity of rheumatoid arthritis

OBJECTIVE

To evaluate the relationship between the frequency of peripheral CD57+ T cells and the physical status of rheumatoid arthritis (RA) patients, and to perform cytokine analysis of these CD57+ T cells.

METHODS

Four-color fluorescence-activated cell sorter analysis was performed to detect both cell surface antigens and intracellular cytokines in peripheral blood leukocytes, using monoclonal antibodies against CD3, CD4, CD8, CD57, interferon-gamma (IFNgamma), and interleukin-4 (IL-4). RA patients were clinically evaluated with a modified Health Assessment Questionnaire (M-HAQ), joint score, face scale, and visual analog scale (VAS) assessing pain and disease activity.

RESULTS

There was a significant correlation between the frequency of CD4+,CD57+ T cells and erythrocyte sedimentation rate (ESR), whereas a correlation was not found between the frequency of CD8+,CD57+ T cells and ESR. The frequency of CD4+,CD57+ T cells also showed a significant correlation with the mHAQ score, VAS, and face scale. Again, there was no significant correlation between the above-mentioned clinical scores and the frequency of CD8+,CD57+ T cells. Flow cytometric analysis of intracellular cytokines revealed that 14.5% of the CD57+ T cells produced IFNgamma, whereas only 2.8% of the CD57+ T cells produced IL-4 in RA patients.

CONCLUSION

Evidence showing that the frequency of CD4+,CD57+ T cells among CD3+ cells of RA patients had a significant correlation not only with ESR but also with the physical status of the patients, and that a large proportion of the CD4+,CD57+ T cells had the capacity to produce IFNgamma, strongly suggests that these CD4+,CD57+ T cells are involved in the immunopathogenesis of RA.

T-cell immunity in acute coronary syndromes

Acute coronary syndromes (ACS) are complications of atherosclerotic vascular disease that are triggered by the sudden rupture of an atheroma. Atherosclerotic plaque stability is determined by multiple factors, of which immune and inflammatory pathways are critical. Unstable plaque is characterized by an infiltrate of T cells and macrophages, thereby resembling a delayed hypersensitivity reaction. On activation, T cells secrete cytokines that regulate the activity of macrophages, or the T cells may differentiate into effector cells with tissue-damaging potential. Constitutive stimulation of T cells and macrophages in ACS is not limited to the vascular lesion but also involves peripheral immune cells, suggesting fundamental abnormalities in homeostatic mechanisms that control the assembly, turnover, and diversity of the immune system as a whole. This review gives particular attention to the emergence of a specialized T-cell subset, natural killer T cells, in patients with ACS. Natural killer T cells have proinflammatory properties and the capability of directly contributing to vascular injury.

Role of NFkappaB in antigen presentation and development of regulatory T cells elucidated by treatment of dendritic cells with the proteasome inhibitor PSI

Dendritic cells (DC) are the most potent antigen-presenting cells for naive T cells, due to their high expression of MHC and costimulatory molecules, but relatively little is known about the biochemical pathways that regulate this function. We used the proteasome inhibitor N-benzyloxycarbonyl-Ile-Glu(O-tert-butyl)-Ala-leucinal (PSI) to demonstrate that DC antigen presentation is NFkappaB dependent. As PSI is not a specific inhibitor of NFkappaB, we reproduced this finding using a very specific approach, namely adenoviral gene transfer of IkappaBalpha, the naturally occurring inhibitor of NFkappaB. The mechanism for this inhibition of DC antigen presentation involves at least three aspects of antigen presenting function: down-regulation of HLA class II, down-regulation of CD86, and inhibition of the immunostimulatory cytokines IL-12 and TNF-alpha. In the light of the marked down-regulation of antigen-presentation cell function, it was of interest to investigate what effects exposure to PSI-treated DC might have on T cell function. It was found that immunological tolerance was induced, as challenge of T cells previously exposed to PSI-treated DC, with normal DC from the same donor did not restore their response, despite the presence of viable T cells. There were also changes in T cell surface markers, with down-regulation of CD3 and CD25 expression, and inhibition of the production of Th1 cytokines like IL-2 and IFN-gamma. These results demonstrates that NFkappaB is an effective target for blocking DC antigen presentation and inhibiting T cell-dependent immune responses, and this has implications for the development of therapeutic agents for use in multiple conditions, including transplantation, allergy and autoimmune diseases.

Molecular fingerprint of interferon-gamma signaling in unstable angina

BACKGROUND

Activation of circulating monocytes in patients with acute coronary syndromes may reflect exposure to bacterial products or stimulation by cytokines such as IFN-gamma. IFN-gamma induces phosphorylation and nuclear translocation of transcription factor STAT-1, which initiates a specific program of gene induction. To explore whether monocyte activation is IFN-gamma driven, patients with unstable (UA) or stable angina (SA) were compared for nuclear translocation of STAT-1 complexes and upregulation of IFN-gamma-inducible genes CD64 and IP-10.

METHODS AND RESULTS

Peripheral blood mononuclear cells were stained for expression of CD64 on CD14(+) monocytes and analyzed by PCR for transcription of IP-10. Expression of CD64 was significantly increased in patients with UA. Monocytes from UA patients remained responsive to IFN-gamma in vitro, with accelerated transcriptional competency of CD64. IP-10-specific sequences were spontaneously detectable in 82% of the UA patients and 15% of SA patients (P<0.001). Most importantly, STAT-1 complexes were found in nuclear extracts prepared from freshly isolated monocytes of patients with UA, which provides compelling evidence for IFN-gamma signaling in vivo.

CONCLUSIONS

Monocytes from UA patients exhibit a molecular fingerprint of recent IFN-gamma triggering, such as nuclear translocation of STAT-1 complexes and upregulation of IFN-gamma-inducible genes CD64 and IP-10, which suggests that monocytes are activated, at least in part, by IFN-gamma. IFN-gamma may derive from stimulated T lymphocytes, which implicates specific immune responses in the pathogenesis of acute coronary syndromes.

Functional disruption of the CD28 gene transcriptional initiator in senescent T cells

We recently reported that aging is accompanied by the emergence of CD4(+)CD28(null) T cells, a functionally aberrant lymphocyte subset rarely seen in individuals younger than 40 years. Here, we directly examined whether the lack of CD28 expression is due to a defect at the level of transcriptional initiation. Molecular studies reveal that CD28 gene transcription is controlled by two sequence motifs, sites alpha and beta. In vitro transcription assays using initiator-dependent DNA templates revealed that reversed polarity or the deletion of either motif inhibited transcription, indicating that alpha/beta sequences constitute a composite initiator. Moreover, nuclear extracts from CD28(null) cells failed to activate transcription of alphabeta-initiator DNA templates. Transcription of such templates was, however, restored with the addition of extracts from CD28(+) cells. Although previously described initiator elements have been defined by a consensus sequence, the alphabeta-initiator has no homology to such sequence. These studies demonstrate that initiators have functions other than positioning elements for the basal transcription complex. Rather, initiators can have a direct role in regulating the expression of specific genes. The gain or loss of initiator activity can be an important determinant of cell phenotypes.

CD4+,CD28- T cells in rheumatoid arthritis patients combine features of the innate and adaptive immune systems

OBJECTIVE

To determine whether CD4+,CD28- T cells, which are expanded in patients with rheumatoid arthritis (RA), express receptors that typically regulate the function of natural killer (NK) cells.

METHODS

Expression of the NK cell surface molecules CD158, p70, CD94, CD161, and CD8alpha on T cell subsets was determined by multicolor flow cytometric analysis of peripheral blood mononuclear cells from 36 RA patients. Expression of CD161 on tissue-infiltrating CD4 T cells was determined by 2-color immunohistochemistry analysis of synovial tissue samples.

RESULTS

Killer cell-inhibitory receptors (KIR) and killer cell-activating receptors (KAR) were exclusively expressed on CD4+,CD28- T cells, with the CD158b molecule being the most frequently detected isoform. A coordinated mechanism inducing KIR/KAR expression was suggested by similarities in the expression of CD158b on CD4 and CD8 T cells. CD4+,CD28- T cells were also positive for CD8-alphaalpha homodimers, another characteristic shared with NK cells. Of the C-type lectin NK cell receptors (NK receptors), CD94 was consistently absent, but CD161 was found on a CD4 T cell population that is significantly expanded in RA patients (P = 0.01). Involvement in disease of NK receptor-expressing CD4 T cells was suggested by the presence of CD4+,CD161+ T cells in follicular microstructures typical of rheumatoid synovitis.

CONCLUSION

Patients with RA have an expanded and unusual subset of CD4 T cells that infiltrates the tissue lesions and is characterized by a deficiency of CD28, the expression of CD8-alphaalpha homodimers, and the expression of several types of HLA class I-recognizing NK receptors. CD4 T cells bearing NK receptors can bridge functions of the innate and adaptive immune systems, such as responsiveness to specific antigen, rapid release of interferon-gamma, cytotoxicity, independence from classic costimulatory pathways, and integration of multiple activating and inhibitory signals to control effector functions.

Clonality and longevity of CD4+CD28null T cells are associated with defects in apoptotic pathways

CD4(+)CD28(null) T cells are oligoclonal lymphocytes rarely found in healthy individuals younger than 40 yr, but are found in high frequencies in elderly individuals and in patients with chronic inflammatory diseases. Contrary to paradigm, they are functionally active and persist over many years. Such clonogenic potential and longevity suggest altered responses to apoptosis-inducing signals. In this study, we show that CD4(+)CD28(null) T cells are protected from undergoing activation-induced cell death. Whereas CD28(+) T cells underwent Fas-mediated apoptosis upon cross-linking of CD3, CD28(null) T cells were highly resistant. CD28(null) T cells were found to progress through the cell cycle, and cells at all stages of the cell cycle were resistant to apoptosis, unlike their CD28(+) counterparts. Neither the activation-induced up-regulation of the IL-2R alpha-chain (CD25) nor the addition of exogenous IL-2 renders them susceptible to Fas-mediated apoptosis. These properties of CD28(null) T cells were related to high levels of Fas-associated death domain-like IL-1-converting enzyme-like inhibitory protein, an inhibitor of Fas signaling that is normally degraded in T cells following activation in the presence of IL-2. Consistent with previous data showing protection of CD28(null) cells from spontaneous cell death, the present studies unequivocally show dysregulation of apoptotic pathways in CD4(+)CD28(null) T cells that favor their clonal outgrowth and maintenance in vivo.

Killer cell activating receptors function as costimulatory molecules on CD4+CD28null T cells clonally expanded in rheumatoid arthritis

Expansion of CD4+CD28null T cells is a characteristic finding in patients with rheumatoid arthritis. Despite lacking CD28 molecules, these unusual CD4 T cells undergo clonal proliferation and form large and long-lived clonal populations. They produce high levels of IFN-gamma, exhibit autoreactivity, and have cytolytic function. The mechanisms facilitating the expansion and longevity of CD4+CD28null T cell clones in vivo are unknown. Here, we report that CD4+CD28null, but not CD4+CD28+, T cells express MHC class I-recognizing receptors normally found on NK cells. CD4+CD28null T cells preferentially expressed killer cell activating receptors (KAR), often in the absence of killer cell inhibitory receptors. Cross-linking of KAR molecules enhanced the proliferative response to TCR-mediated stimulation, but not the cytolytic function of CD4+CD28null T cells, suggesting different signaling pathways in CD4 T cells and NK cells. Triggering of KAR signaling led to the phosphorylation of several cellular targets, although the pattern of phosphorylation differed from that induced by the TCR. Aberrant expression of KAR molecules in the absence of inhibitory receptors and in the appropriate HLA setting may lead to the clonal outgrowth of autoreactive CD4+CD28null T cells commonly seen in rheumatoid arthritis.

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.

Altered expression of costimulatory molecules in myasthenia gravis

To characterize the involvement of costimulatory pathways in the pathogenesis of myasthenia gravis (MG), a multiparameter flow cytometry assay was adopted to enumerate blood mononuclear cells (MNC) expressing CD28, CD80, CD86, CD40, and CD40L molecules in patients with MG and healthy subjects. Patients with MG had lower percentages of CD8(+)CD28(+) cells, augmented percentages of CD4(+)CD80(+), CD4(+)CD86(+), CD8(+)CD80(+), CD8(+)CD86(+), CD14(+)CD80(+), and CD14(+)CD86(+) cells, and similar levels of cells expressing CD40 and CD40L and of B cells expressing CD80 and CD86 compared to the controls. Patients with early onset of MG (<40 years) had lower percentages of CD3(+)CD86(+), CD4(+)CD86(+), CD8(+)CD86(+) T cells and CD20(+)CD86(+) B cells compared to those with late onset (>40 years). There was a positive correlation between the patients' age and percentages of CD86(+) cells. The data indicate that the CD28/CD80-CD86 costimulatory pathway is involved in MG. The high percentages of CD80 and CD86 positive T cells and monocytes may reflect persistent activation of T and B cells, whereas the low CD28 expression may be the result of chronic exposure to CD80 and CD86. These molecules could be the focus for new and improved immunomodulating therapies of MG.

Antineutrophil cytoplasmic antibodies (ANCA) and systemic vasculitis: update of assays, immunopathogenesis, controversies, and report of a novel de novo ANCA-associated vasculitis after kidney transplantation

OBJECTIVES

To characterize antineutrophil cytoplasmic antibodies (ANCA), their major autoantigens, disease associations, and pathophysiology in systemic vasculitides. To describe a patient with a novel de novo ANCA-associated vasculitis after kidney transplantation.

METHODS

We reviewed and compiled the literature on ANCA-related topics and systemic vasculitis. Laboratory and clinical data from a cadaveric kidney transplant patient who developed necrotizing vasculitis involving glomerular capillaries, with crescent formation associated with P-ANCA and myeloperoxidase, were analyzed.

RESULTS

Large-scale multi-center testing of patient and normal sera by the European ANCA Assay Standardization Project using immunofluorescence assays and enzyme immunoassays indicate the assays have good sensitivity and specificity, and diagnostic utility for ANCA-associated vasculitis. A few investigations covering basic and clinical research with ANCA remain controversial: whether endothelial cells do or do not express a 29-kd neutral serine protease termed proteinase-3 (PR-3), the target of ANCA in most individuals with Wegener's granulomatosis, and whether anti-myeloperoxidase (MPO) ANCAs recognize a restricted number of epitopes on MPO. This issue has relevance for using monoclonal antibodies to treat patients with vasculitis who have adverse effects from immunosuppressive drugs. The two allelic forms of FcgammaRIIa (H131/R131) and the two of FcgammaRIIlb (NA1/NA2) are discussed as possible inheritable genetic elements for vasculitic disorders and for signaling responses. Stimulatory and costimulatory molecules, and cytokine profiles of T lymphocytes are characterized to show that these cells are actively involved in the ANCA-associated vasculitides. The patient described had a de novo ANCA associated small vessel vasculitis which developed after renal transplantation.

CONCLUSIONS

There have been significant advances in the development of sensitive and specific ANCA assays. The immunopathogenetic mechanism of ANCA involves the constitutive FcgammaRs, ligands, and signaling responses to activate cytokine-primed neutrophils. This may lead to the generation of reactive oxygen intermediates, degranulation, and secretion of intracellular granule contents, and ultimately inflammation and vasculitis.

Central role of thrombospondin-1 in the activation and clonal expansion of inflammatory T cells

Thrombospondin-1 (TSP) is a transiently expressed matricellular protein known to promote chemotaxis of leukocytes to inflammatory sites. However, TSP and its receptor CD36 are abundantly expressed in chronically inflamed tissues such as the rheumatoid synovium. Here, we show that TSP provides the costimulatory signal that is necessary for the activation of autoreactive T cells. Data presented reveal that TSP-mediated costimulation is achieved through its independent interaction with CD36 on APCs and with CD47 on T cells. We propose that a CD47-TSP-CD36 trimolecular complex is a novel costimulatory pathway that significantly decreases the threshold of T cell activation. Consistent with the paradigm that lesions in rheumatoid synovitis are sites of antigenic recognition, the characteristic focal expression of TSP on APCs such as macrophages and fibroblast-like synoviocytes suggest a central role of TSP in the expansion of tissue-infiltrating T cells.

Association of MHC and rheumatoid arthritis. HLA polymorphisms in phenotypic variants of rheumatoid arthritis

Genes in the human leukocyte antigen (HLA) region remain the most powerful disease risk genes in rheumatoid arthritis (RA). Several allelic variants of HLA-DRB1 genes have been associated with RA, supporting a role for T-cell receptor-HLA-antigen interactions in the pathologic process. Disease-associated HLA-DRB1 alleles are similar but not identical and certain allelic variants are preferentially enriched in patient populations with defined clinical characteristics. Also, a gene dosing effect of HLA-DRB1 alleles has been suggested by the accumulation of patients with two RA-associated alleles, especially in patient subsets with a severe disease course. Therefore, polymorphisms in HLA genes are being explored as tools to dissect the clinical heterogeneity of the rheumatoid syndrome. Besides HLA polymorphisms, other risk genes will be helpful in defining genotypic profiles correlating with disease phenotypes. One such phenotype is the type of synovial lesion generated by the patient. HLA genes in conjunction with other genetic determinants may predispose patients to a certain pathway of synovial inflammation. Also, patients may or may not develop extraarticular manifestations, which are critical in determining morbidity and mortality. HLA genes, complemented by other RA risk genes, are likely involved in shaping the T-cell repertoire, including the emergence of an unusual T-cell population characterized by the potential of vascular injury, such as seen in extraarticular RA.

HLA polymorphisms and T cells in rheumatoid arthritis

A dense infiltrate of activated T cells, macrophages, and B cells in the synovial membrane is the cardinal pathological feature of rheumatoid arthritis (RA). Frequently, tissue infiltrating cells acquire a morphological organization reminiscent of secondary lymphoid tissue. The composition of the inflammatory lesions, the production of autoantibodies, and the association of disease risk with genes related to the HLA-D region have all been cited as evidence for a critical role of T cells in disease pathogenesis. Investigations on the precise role of HLA genes in RA have confirmed the importance of this genetic risk factor and have identified a consensus sequence within the HLA-DRBI genes. The observation that HLA polymorphisms are mostly associated with disease progression and severity and that a gene dose effect for HLA-DR genes is operational has challenged the simple model that HLA molecules select and present an arthritogenic antigen. Studies analyzing the repertoire of tissue infiltrating T cells have not been able to identify a dominant and common disease relevant T cell. The infiltrate is diverse in terms of T cell receptor gene usage but consistently includes clonally expanded populations. Recent evidence indicates that RA patients carry expanded CD4 clonotypes which are characterized by deficient CD28 expression and autoreactivity. These autoreactive CD4 T cells are not restricted to the joint, raising the possibility that rheumatoid synovitis is a manifestation of a systemic autoimmune disease. Support for this model has come from studies in T cell receptor (TCR) transgenic animals which develop inflammation of the synovial membrane stimulated by a T cell response to ubiquitously expressed self-MHC molecules. Antigens driving the chronic persistent immune response in RA may not be restricted to the joint but rather may be widely distributed, providing an explanation for the difficulties in identifying arthritogenic antigens directly or indirectly through the selection of joint infiltrating T cells.

Impaired expression of CD28 on T cells in hairy cell leukemia

T cells from patients with active hairy cell leukemia (HCL), a chronic B cell malignancy, show poor proliferation in response to allogeneic peripheral blood mononuclear cells (PBMC). In order to study the T cell dysfunction, the expression of several adhesion and costimulatory molecules was analyzed by flow cytometry. Circulating T cells from HCL patients showed increased percentages of CD28(-) in all T cell subsets. In some patients the percentage of CD28(-) T cells within the CD4(+) subset was increased up to 80%. These CD4(+)CD28(-) T cells did not proliferate in a mixed lymphocyte culture (MLC) against allogeneic PBMC. After enrichment for CD4(+)CD28(+) T cells, the proliferative response in the MLC was recovered, but this response was still lower than the proliferative response from control T cells. In conclusion, lack of CD28 on T cells and a restricted T cell repertoire may contribute to immune deficiency in patients with HCL.

Perturbation of the T-cell repertoire in patients with unstable angina

BACKGROUND

Monocytes are constitutively activated in unstable angina (UA), resulting in the production of IL-6 and the upregulation of acute phase proteins. Underlying mechanisms are not understood. To explore whether the production of the potent monocyte activator IFN-gamma is altered in UA, we compared cytokine production by T lymphocytes in patients with UA (Braunwald's class IIIB) and with stable angina (SA).

METHODS AND RESULTS

Peripheral blood lymphocytes were collected at the time of hospitalization and after 2 and 12 weeks. Cytokine-producing CD4(+) and CD8(+) T cells were quantified by 3-color flow cytometry after stimulation with phorbol myristate acetate and ionomycin. UA was associated with an increased number of CD4(+) and CD8(+) T cells producing IFN-gamma, whereas patients with SA had higher frequencies of IL-2(+) and IL-4(+) CD4(+) T cells. Expansion of the IFN-gamma( +) T-cell population in UA persisted for at least 3 months. Increased production of IFN-gamma in UA could be attributed to the expansion of an unusual subset of T cells, CD4(+)CD28(null) T cells.

CONCLUSIONS

Patients with UA are characterized by a perturbation of the functional T-cell repertoire with a bias toward IFN-gamma production, suggesting that monocyte activation and acute phase responses are consequences of T-cell activation. IFN-gamma is produced by CD4(+)CD28(null) T cells, which are expanded in UA and distinctly low in SA and controls. The emergence of CD4(+)CD28(null) T cells may result from persistent antigenic stimulation.

Intracellular analysis of interleukin-2 induction provides direct evidence at the single cell level of differential coactivation requirements for CD45RA+ and CD45RO+ T cell subsets

Through measurements of intracellular cytokine production, evidence is provided at the single cell level that triggering different cell surface molecules preferentially activates discrete human peripheral blood (PB) T cell subsets. T cell costimulation due to cross-linking a variety of individual molecules (beta1, beta2, and beta7 integrins, CD26, CD43, or CD44), in conjunction with the CD3/TCR complex, preferentially activated CD45RO+ PB T lymphocytes. CD28, however, costimulated interleukin-2 (IL-2) production in both CD45RO+ and CD45RA+ subpopulations. The amount of soluble IL-2 produced by CD28 coactivation was 15-30-fold higher than that due to integrin or CD26-dependent coactivation, although even the lowest amount of soluble IL-2 produced was in the range of the high-affinity IL-2 receptor. The overall proliferative responses were similar among all costimulatory settings. This was in part due to the uniform upregulation of IL-2 receptor-alpha (IL-2R alpha) (CD25) expression on the entire T cell population activated under each of the different costimulatory conditions. The data provide direct evidence on a single cell level that activation of human CD45RA+ (naive) T cells is stringently controlled and, in these studies, limited to CD28 costimulation for induction of IL-2 production. In contrast, coactivation of CD45RO+ (memory) T lymphocytes can proceed by a variety of different PB T cell surface molecules.

Modulation of CD28 Expression: Distinct Regulatory Pathways During Activation and Replicative Senescence

The costimulatory molecule CD28 has a restricted tissue distribution and is expressed on T cells and some plasmacytoma cells. Although CD28 is constitutively expressed, its expression is transiently down-regulated following T cell activation and declines progressively with in vitro senescence. In vivo, CD8+ T cells and, less frequently, CD4+ T cells may completely lose CD28 surface expression during chronic infections and with aging. This correlates with changes of nuclear protein-binding activities to two motifs, site α and β, within the CD28 minimal promoter. Both α- and β-bound complexes are found only in lymphoid tissues, in CD28+ T cells, and in some transformed B cells. These complexes are coordinately expressed except during replicative senescence, which is characterized by the down-modulation of site β- but not site α-binding activities. In contrast, T cell activation induces a parallel decline in both site α- and β-binding activities. CD4+ and CD8+ T cells differ in their β-binding profiles, which may explain the more pronounced down-regulation of CD28 in senescent CD8+ T cells. In vivo expanded CD4+CD28null and CD8+CD28null T cells uniformly lack α- and β-bound complexes, resembling the pattern seen in chronically activated cells and not of senescent cells.

T cell receptor repertoire in rheumatoid arthritis

CD4+ T cells are a major component of the inflammatory infiltrate in rheumatoid synovitis. Within synovial lesions, clonal CD4+ T cell populations are detectable, supporting the notion of an antigen specific recognition even in the joint. In general, the clonal size of individual T cell clones is small and does not lead to a marked distortion of the synovial T cell receptor (TCR) repertoire. Comparison of TCR sequences derived from different patients has not provided evidence for common sequences. Either multiple antigens are recognized or the TCR repertoire is sufficiently plastic with a multitude of different TCR structures responding to the same antigen(s). However, within one individual, the repertoire of clonal T cell populations is restricted. Identical T cell clones can be identified in different joints and at different timepoints of the disease, emphasizing that the spectrum of antigens recognized is conserved over time and that the T cell response pattern is not subject to evolution. Characterization of antigens involved in the latter stages of the disease may thus provide critical information on disease-initiating events. Recent data have led to the new concept that the role of T cells in rheumatoid arthritis (RA) is not limited to synovial inflammation. Evidence has been provided that the premorbid TCR repertoires of RA patients and normal controls can be distinguished. The T cell repertoire in RA patients is prone to recognize certain microbial products and autoantigens. The selection of this response pattern can only partially be attributed to the disease associated HLA-DRB1 alleles. Additional factors common in RA patients but not in HLA-DR matched control individuals seem to be important in shaping the TCR repertoire. Furthermore, the repertoire of mature T cells in RA patients is characterized by oligoclonality which involves T cells in the peripheral blood compartment. Possibly, these clonal T cell populations react to widespread autoantigens, raising the possibility that RA patients have a defect in controlling peripheral tolerance and an anomaly of lymphoproliferation. In contrast to joint residing CD4+ T cells, expanded clonotypes isolated from the blood of different patients have been described to share TCR beta chain structures. How these characteristic features of the global TCR repertoire in RA patients translate into mechanisms of disease remains to be elucidated.

Heterogeneity of rheumatoid arthritis: from phenotypes to genotypes

Rheumatoid arthritis (RA) is now recognized as a multigene disorder with a number of genetic polymorphisms contributing to disease pathogenesis. Here, we propose that the diagnostic category of RA includes multiple subtypes of disease and that the different phenotypes of RA correlate to different genotypes. Support for this concept has come from a reappraisal of the clinical heterogeneity of RA and the observation that HLA-DRB1 polymorphisms are useful in describing genetic heterogeneity of RA phenotypes. A series of HLA-DRB1 genes has been identified as RA associated, and in recent years emphasis has been put on the sequence similarities of these alleles. An alternative view focuses on the amino acid variations found in RA-associated HLA-DRB1 alleles with different alleles being enriched in distinct subtypes of RA. Rheumatoid factor-positive destructive joint disease is predominantly associated with the HLA-DRB1*0401 allele, while HLA-DRB1*0404 and B1*0101 predispose for milder and often seronegative disease. Expression of disease-associated alleles on both haplotypes carries a high risk for extra-articular manifestations. In particular, patients homozygous for HLA-DRB1*0401 frequently develop rheumatoid vasculities on follow-up. Besides HLA gene polymorphisms, abnormalities in the generation and function of CD4 T cells and in inflammatory pathways established in synovial lesions can be used to dissect patient subsets with different variants of RA. Emergence of CD28-deficient CD4 T cells identifies RA patients with extra-articular manifestations. These cells undergo clonal expansion in vivo, produce high amounts of IFN-gamma, and exhibit autoreactivity. Concordance of monozygotic twins for the expression of CD4+ CD28- T cells suggests a role for genetic factors in the generation of these unusual T cells. Evidence for heterogeneity of the synovial component of RA comes from studies describing three distinct patterns of lymphoid organization in the synovium. Based upon the topography of tissue-infiltrating mononuclear cells, diffuse, follicular, and granulomatous variants of rheumatoid synovitis can be distinguished. Each pattern of lymphoid organization correlates with a unique profile of tissue cytokines, demonstrating that several pathways of immune deviation modulate disease expression in RA. A dissection of RA variants would have major implications on how the disease is studied, treated, and managed. Identifying combinations of RA risk genes that correlate with disease variants could, therefore, become an important diagnostic tool.

Functional subsets of CD4 T cells in rheumatoid synovitis

OBJECTIVE

To identify the functional properties of CD4+ CD28- T cells, which accumulate and clonally expand in patients with rheumatoid arthritis (RA).

METHODS

The gene expression of molecules involved in T cell effector functions was compared in CD4+ CD28- and CD4+ CD28+ T cell clones. The expression of differentially up-regulated genes was confirmed by flow cytometry of T cells and by 2-color immunohistochemistry of rheumatoid synovial tissue. Cytotoxicity of CD4+ CD28- T cells was tested by anti-CD3 redirected lysis of Fc receptor-positive target cells.

RESULTS

CD4+ CD28- T cell clones lacked messenger RNA for the CD40 ligand (CD40L) but transcribed the perforin gene. Perforin was also found in freshly isolated CD4+ CD28- peripheral blood lymphocytes from RA patients. CD4+ CD28-, but not CD4+ CD28+, T cell clones lysed Fc receptor-bearing target cells. CD4+ perforin-positive T cells were present in the synovial tissue, where their frequency correlated with the expansion of the CD4+ CD28- compartment in the periphery. Among tissue-infiltrating CD4+ T cells, only the CD40L-negative subset expressed perforin transcripts.

CONCLUSION

Clonally expanded CD4+ CD28- T cells are functionally specialized for killing, while they lack the ability to provide B cell help. Tissue-infiltrating CD4+ T cells can be subdivided phenotypically and functionally into at least 2 distinct subsets based on their expression of perforin and CD40L. Because the expansion of CD4+ CD28- T cells is associated with extraarticular RA, T cell-mediated cytotoxicity may be particularly important in these most severe complications of RA.

Perturbation of the T cell repertoire in rheumatoid arthritis

Aberrations in the T cell repertoire with the emergence of oligoclonal populations have been described in patients with rheumatoid arthritis (RA). However, the extent of the repertoire perturbations as well as the underlying mechanisms are not known. We now have examined the diversity of the peripheral CD4 T cell repertoire by determining the frequencies of arbitrarily selected T cell receptor (TCR) beta-chain sequences. Healthy individuals displayed a highly diverse repertoire, with a median frequency of individual TCR beta-chain sequences of 1 in 2.4 x 10(7) CD4 T cells. In RA patients, the median TCR beta-chain frequency was increased 10-fold, indicating marked contraction of the repertoire (P < 0.001). The loss in TCR diversity was not limited to CD4 memory T cells but also involved the compartment of naive T cells, suggesting that it reflected an abnormality in T cell repertoire formation and not a consequence of antigen recognition in the synovium. Also, control patients with chronic inflammatory disease such as hepatitis C expressed a diverse repertoire indistinguishable from that of normals. Telomere length studies indicated an increased replicative history of peripheral CD4 T cells in RA patients, suggesting an enhanced turnover within the CD4 compartment. Compared with age-matched controls, terminal restriction fragment sizes were 1.7 kilobases shorter (P < 0.001). These data demonstrate an altered CD4 T cell homeostasis in RA that may contribute to the autoimmune response as well as to the immunodeficiency in these patients.

Costimulatory molecules in Wegener's granulomatosis (WG): lack of expression of CD28 and preferential up-regulation of its ligands B7-1 (CD80) and B7-2 (CD86) on T cells

T cells are most likely to play an important role in the pathogenesis of WG, and recently a predominant Th1 pattern of immune response has been demonstrated in granulomatous inflammation. Since the expression of costimulatory molecules has a significant impact on the cytokine profile and proliferation response of T cells, the goal of this study was to characterize the expression of costimulatory molecules (CD28, CTLA-4 (CD152), B7-1 (CD80), B7-2 (CD86)) on T cells, monocytes and B cells in WG, and to correlate the findings with clinical parameters such as disease activity, extent and therapy. WG patients (n = 24) and healthy controls (HC; n = 17) were examined for the expression of costimulatory molecules by fluorescence-activated cell sorter analysis, both in whole peripheral blood and after in vitro activation of T cells and antigen-presenting cells. Results were correlated with clinical data. The expression of CD28 on CD4+ and CD8+ cells was significantly lower in WG than in HC (CD28+ 81.4% in WG versus 97.9% of CD4+ cells (P < 0.0001); CD28+ 44.6% in WG versus 68.5% of CD8+ cells (P < 0.00001)), both in peripheral blood and after in vitro activation. A lower percentage of monocytes was B7-2+ in WG than in HC in peripheral blood, whereas no significant differences in the expression of B7-1 and B7-2 were observed after in vitro stimulation of monocytes and B cells. After in vitro activation a significantly higher percentage of B7-1+ and B7-2+ T cells was seen in WG. There was no significant difference in the CTLA-4 expression pattern between WG and HC. The percentage of CD28+ lymphocytes correlated negatively with the Disease Extent Index cumulated over the course of disease (r = -0.46, P = 0.03), indicating a more severe manifestation in patients with lower CD28 expression. Correlations with other clinical parameters such as activity or therapy were not seen. WG patients show a lack of CD28 expression on T cells and an unusual up-regulation of its ligands B7-1 and B7-2 on T cells after in vitro activation as well as a lower expression of B7-2 on freshly isolated monocytes compared with HC. These features might promote the Th1 cytokine pattern and thereby contribute to persistently high levels of immune activation in WG.

Resistance to Apoptosis and Elevated Expression of Bcl-2 in Clonally Expanded CD4+CD28− T Cells from Rheumatoid Arthritis Patients

Patients with rheumatoid arthritis have a subset of CD4+ T lymphocytes that are characterized by a defect in CD28 expression. CD4+CD28− T cells frequently undergo clonal expansion in vivo. These clonotypes include autoreactive cells and persist over many years. The clonogenic potential and longevity of these T cells could be related to an altered response to apoptosis-inducing signals. To explore this possibility, CD4+CD28− T cell lines and clones were examined for their response pattern to stimuli inducing physiologic cell death. CD4+CD28− T cells were found to be resistant to apoptosis upon withdrawal of the growth factor, IL-2. To examine whether the altered sensitivity to this apoptotic signal was correlated with the expression of proteins of the bcl-2 family, the expression of bcl-2, bcl-x, and bax proteins was determined. CD28+ and CD28−CD4+ T cells could not be distinguished by the levels of bax or bcl-xL protein; however, CD4+CD28− T cells expressed higher amounts of bcl-2 protein than did CD4+CD28+ T cells. The increased bcl-2 expression in CD4+CD28− T cells was relatively independent of signals provided by exogenous IL-2. In CD28-deficient CD4+ T cells, bcl-2 was not significantly up-regulated by the addition of exogenous IL-2 and was maintained despite IL-2 withdrawal, as opposed to CD28-expressing CD4+ T cells. We propose that CD4+CD28− T cells are characterized by a dysregulation of the survival protein, bcl-2, which may favor the clonal outgrowth of autoreactive T cells and thus contribute to the pathogenesis of rheumatoid arthritis.

Functional properties of CD4+ CD28- T cells in the aging immune system

The aging immune system is characterized by a progressive decline in the responsiveness to exogenous antigens and tumors in combination with a paradoxical increase in autoimmunity. From a clinical viewpoint, deficiencies in antibody responses to exogenous antigens, such as vaccines, have a major impact and may reflect intrinsic B cell defects or altered performance of helper T cells. Here we describe that aging is associated with the emergence of an unusual CD4 T cell subset characterized by the loss of CD28 expression. CD28 is the major costimulatory molecule required to complement signaling through the antigen receptor for complete T cell activation. CD4+ CD28- T cells are long-lived, typically undergo clonal expansion in vivo, and react to autoantigens in vitro. Despite the deficiency of CD28, these unusual T cells remain functionally active and produce high concentrations of interferon-gamma (IFN-gamma) and interleukin-2 (IL-2). The loss of CD28 expression is correlated with a lack of CD40 ligand expression rendering these CD4 T cells incapable of promoting B cell differentiation and immunoglobulin secretion. Aging-related accumulation of CD4+ CD28- T cells should result in an immune compartment skewed towards autoreactive responses and away from the generation of high-affinity B cell responses against exogenous antigens. We propose that the emergence of CD28-deficient CD4 T cells in the elderly can partially explain age-specific aberrations in immune responsiveness.

Aging-related deficiency of CD28 expression in CD4+ T cells is associated with the loss of gene-specific nuclear factor binding activity

Changes in T cell populations and concomitant perturbation of T cell effector functions have been postulated to account for many aging-related immune dysfunctions. Here, we report that high frequencies of CD28(null) CD4+ T cells were found in elderly individuals. Because deviations in the function of these unusual CD4+ T cells might be directly related to CD28 deficiency, we examined the molecular basis for the loss of CD28 expression in CD4+ T cells. In reporter gene bioassays, the minimal promoter of the CD28 gene was mapped to the proximal 400 base pairs (bp) of the 5' untranslated region. CD28 deficiency was associated with the loss of two noncompeting binding activities within a 67-bp segment of the minimal promoter. These binding activities were not competed by consensus Ets, Elk, or AP3 motifs that were found within the sequence stretch. The DNA-protein complexes were also not recognized by antibodies to Ets-related transcription factors. Furthermore, introduction of mutations into the 67-bp segment at positions corresponding to the two DNA-protein interaction sites, i.e. nucleotides spanning -206 to -179 and -171 to -148, resulted in the loss of specific nuclear factor binding activities and the abrogation of promoter activity. These observations implicate at least two regulatory motifs in the constitutive expression of CD28. The loss of binding activity of trans-acting factors specific for these sequences may contribute to the accumulation CD4+CD28(null) T cells during aging.