Functional Competence of Peritoneal Macrophages in Murine Lyme Borreliosis

In mice infected with the Lyme disease spirochete, Borrelia burgdorferi, spirochetes can be cultured from the uninflamed peritoneal cavity despite their proximity to resident macrophages. Here we have evaluated the phagocytic and killing capacity of peritoneal macrophages ex vivo from such mice, and compared them to cells from uninfected controls. We noted no significant differences in the numbers of cells recovered from lavage fluid nor in the proportion of lymphocytes in that fluid or their type or state of activation; B cells vs. T cells, CD4 vs. CD8, T cell receptor display (TCR vs. TCR), or B cell activation markers (CD24 vs. CD44). In addition, in studies conducted with coded samples, macrophages from infected animals were similar to controls in their ability (i) to bind and ingest spirochetes as shown by immunofluorescent kinetic studies imaged by confocal microscopy, (ii) to kill spirochetes as detected by acridine orange vital staining in live confocal microscopy, and (iii) to generate H₂O₂, a measure of their activation. Finally, we observed no difference in the ability of cells isolated from infected mice to kill the parasite, Toxoplasma gondii, a sensitive functional measure of the activation of killing capacity. Thus, despite the failure of immune clearance that results in persistent or chronic disease in vivo, there does not appear to be a global impairment of macrophage function in the infected host. It remains to be determined whether specific sites of inflammation, e.g., skin, joints, heart, are associated with a downregulation of phagocyte function locally.     

CD28/B7 regulation of autoimmune diabetes

The initiation and progression of autoimmune diseases, such as insulin-dependent diabetes mellitus (IDDM), are complex processes that depend on autoantigen exposure, genetic susceptibility, and secondary events that promote autoaggression. T-cell costimulation, largely mediated by CD28/B7 interactions, is a major regulatory pathway in the activation and differentiation of T-cells that cause IDDM in murine models. In this article, we summarize our results in two models of IDDM: the nonobese diabetic (NOD) mouse and diabetes induced with multiple low doses of streptozotocin (MDSDM). In both of these models, blockade of CD28/B7 costimulation regulates the development of disease. The effects of blockade vary with the intensity of cognate signal delivered to the T-cells, the timing of the costimulatory signal, and perhaps even the CD28 ligand expressed on antigen-presenting cells (APCs). Our results suggest that targeting CD28/B7 signals is a feasible approach for treatment and prevention of recurrence of autoimmune diabetes. However, the dynamic nature of these interactions highlights the importance of a clear understanding of their role in regulation of the disease.     

Modulation of experimental blood stage malaria through blockade of the B7/CD28 T-cell costimulatory pathway

Recent studies have implicated cytokines associated with CD4+ T lymphocytes of both T helper (Th)1 and Th2 subsets in resistance to experimental blood stage malaria. As the B7/CD28 costimulatory pathway has been shown to influence the differentiation of Th cell subsets, we investigated the contribution of the B7 molecules CD80 and CD86 to Th1/Th2 cytokine and immunoglobulin isotype profiles and to the development of a protective immune response to malaria in NIH mice infected with Plasmodium chabaudi. Effective blockade of CD86/CD28 interaction was demonstrated by elimination of interleukin (IL)-4 and up-regulation of interferon (IFN)-gamma responses by P. chabaudi-specific T cells and by reduction of P. chabaudi-specific immunoglobulin G1 (IgG1). The shift towards a Th1 cytokine pattern corresponded with efficient control of acute parasitaemia but an inability to resolve chronic infection. Moreover, combined CD80/CD86 blockade by using anti-CD80 and anti-CD86 monoclonal antibodies raised IFN-gamma production over that seen with CD86 blockade alone, with augmentation of this Th1-associated cytokine reducing levels of peak primary parasitaemia. These results demonstrate that IL-4 production by T cells in P. chabaudi-infected NIH mice is dependent upon CD86/CD28 interaction and that IL-4 and IFN-gamma contribute significantly, at different times of infection, to host resistance to blood stage malaria. In addition, combined CD80/CD86 blockade resulted in preferential expansion of IFN-gamma-producing T cells during P. chabaudi infection, suggesting that costimulatory pathways other than B7/CD28 may contribute to T-cell activation during continuous antigen stimulation. This study indicates a role for B7/CD28 costimulation in modulating the CD4+ T-cell response during malaria, and further suggests involvement of this pathway in other infectious and autoimmune diseases in which the Th cell immune response is also skewed.     

Immunotherapy Targeting the CD40/CD154 Costimulatory Pathway for Treatment of Autoimmune Disease

The CD154–CD40 ligand pair interaction plays a central role in both induction of the immune response and in immune effector functions. Indeed, many animal disease models and human autoimmune diseases have demonstrated a central role for CD154 expression. The expression of CD154 is very tightly regulated by the immune system through a number of non-redundant overlapping mechanisms that ensure its limited initial induction, along with its temporal maintenance and rapid elimination from the cell surface, and its functional neutralization by the release of soluble CD40. In this review, we discuss the current state of understanding of CD154 regulation during the activation of the immune system and describe numerous strategic mechanisms by which modulation of CD154–CD40 interactions may be applied to treat autoimmune disease.     

The Caspase 1 Inflammasome Is Not Required for Control of Murine Lyme Borreliosis

The contribution of the inflammasome to the development of immune responses and disease during infection with the Lyme disease spirochete, Borrelia burgdorferi, is not well defined. Host defense against the spirochete is severely impaired in mice deficient in the adaptor molecule myeloid differentiation antigen 88 (MyD88), which is required not only for Toll-like receptor-mediated responses but also for the production of the proforms of interleukin 1β (IL-1β) and IL-18. These cytokines are released in active forms after cleavage by the inflammasome-associated enzyme caspase 1. To investigate the contribution of the inflammasome to host defense against B. burgdorferi, we examined Lyme borreliosis in mice deficient in either caspase 1 or apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC), a molecule upstream of caspase 1 in the inflammasome signaling cascade. We found that caspase 1-deficient mice had a mild transient elevation in pathogen burden and a trend toward an increase in the prevalence of arthritis early in infection, but these differences resolved by day 14 postinfection. Caspase 1 deficiency had no effect on B. burgdorferi-induced humoral immunity, T-cell responses, or the abilities of macrophages to ingest and degrade spirochetes. The absence of the ASC protein had no effect on the control of the spirochete or the development of immune responses and disease. These findings reveal that the caspase 1 inflammasome is not critical to host defense against the extracellular pathogen Borrelia burgdorferi.Infection of humans with the Lyme disease spirochete, Borrelia burgdorferi, results in a characteristic pattern of skin lesions, arthritis, carditis, and neurologic abnormalities that reflect the immune response to the spirochete as it invades and disseminates in the mammalian host (7). In the murine model of Lyme borreliosis, spirochetes inoculated into the skin disseminate within days to infect all organ systems, but disease is primarily manifested in the joints and heart (4). Disease in the animal model is due largely to the innate immune response to spirochetes because histopathology reveals mainly neutrophils and macrophages within inflamed joints and hearts, respectively (5, 28, 36, 43), and occurs in the absence of adaptive (T- and B-cell-mediated) immunity (8, 28, 43).Recent studies have further defined the role of innate immunity in Lyme borreliosis. B. burgdorferi lipoproteins activate innate immune cells through the pattern recognition molecule Toll-like receptor 2 (TLR2), which is required for innate but not adaptive immune responses to the spirochete (2, 19, 49). Spirochete components also stimulate murine cells through TLR5 and TLR9 (44). The TLR cytosolic domains contain a Toll/interleukin 1 (IL-1) receptor domain (TIR) that interacts with myeloid differentiation antigen 88 (MyD88) and results in the activation of NF-κB and the production of proinflammatory cytokines, chemokines, and costimulatory molecules that are important for host defense (6, 12, 14). We and others have previously shown that B. burgdorferi-infected MyD88-deficient (MyD88^−/−) mice have significantly elevated pathogen burdens that persist through 90 days of infection despite the presence of high titers of anti-B. burgdorferi antibodies (9, 25). The elevated level of pathogen DNA in tissues was explained in part by our finding that MyD88^−/− peritoneal macrophages ingested spirochetes at the same rate as wild-type (WT) cells, but the kinetics of degradation was slower, with internalized spirochetes remaining in an elongated form for a longer period. Others have found that bone marrow-derived MyD88^−/− macrophages do not efficiently ingest spirochetes (44). The MyD88^−/− mice developed carditis and arthritis similar to the disease in WT mice analyzed at its peak (days 14 and 28) and during regression (day 45) (9, 25). Together, these results showed that MyD88-dependent signaling pathways are not required for B. burgdorferi-induced inflammation or disease regression but are necessary for efficient control of the pathogen burden by phagocytes. These studies did not distinguish whether interruption of MyD88-dependent TLR signaling pathways was solely responsible for the impaired control of the pathogen or whether other MyD88-dependent pathways also play a role.In addition to being a crucial signaling molecule for TLRs involved in B. burgdorferi recognition, MyD88 is required for IL-1 receptor (IL-1R)- and IL-18R-associated kinase signaling. TLR activation is a key inducer of the proforms of IL-1β and IL-18, and the secreted forms of these two cytokines require MyD88 for their receptors to mediate their effects (1, 34, 38). Behera et al. (6) have shown that IL-18 alone does not significantly contribute to host immunity in Lyme borreliosis because IL-18^−/− mice exhibit no defects in pathogen clearance or the development of disease. IL-1β, however, may play a role because human peripheral blood mononuclear cells secrete IL-1β after ingestion of live B. burgdorferi spirochetes (15). In support of this hypothesis, serum levels of IL-1β were reported to be elevated in Lyme disease patients, and the levels decreased significantly after doxycycline treatment (35). IL-1β mRNA levels in erythema migrans lesions were also shown to be elevated (31).To further delineate the role of MyD88-dependent signaling pathways in host defense against B. burgdorferi, we examined the course of Lyme borreliosis in mice deficient in either the intracellular cysteine protease caspase 1 or apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC). Caspase 1 plays a key role in inflammatory responses by cleaving pro-IL-1β and pro-IL-18 into their active secreted forms (16, 22). These cytokines are matured in a large caspase 1-containing protein complex called the inflammasome (37). ASC, a component of the inflammasome, is required for eliciting the enzymatic activity of caspase 1. Caspase 1 contains an N-terminal caspase recruitment domain (CARD) shown to be involved in the assembly of protein platforms that promote proteolytic activation of recruited caspases in the context of apoptosis and inflammation (14). In addition to cleaving pro-IL-1 and pro-IL-18, caspase 1 is also involved in other proinflammatory pathways, including NF-κB signaling pathways associated with innate and adaptive immune responses (21, 23, 41). In contrast, ASC is essential only for the secretion of IL-1β/IL-18 but dispensable for caspase 1-mediated IL-6 and tumor necrosis factor alpha secretion and NF-κB and p38 activation (40). Thus, although both caspase 1^−/− mice and ASC^−/− mice have defects in the production of IL-1β/IL-18, caspase 1^−/− mice have additional defects in the activation of NF-κB.Several published reports have established that the inflammasome is important for immunity to intracellular bacteria and viruses, but much less is known about the contribution of the inflammasome to host defense against extracellular pathogens that elicit cytokines activated by caspase 1 (27, 29, 30, 32, 38, 42, 48). Thus, we sought to determine whether the inflammasome is also important during infection with the B. burgdorferi spirochete as representative of a subset of extracellular pathogens. We found that while B. burgdorferi can elicit IL-1β in a caspase 1-dependent fashion from mouse macrophages in vitro, the caspase 1-dependent inflammasome is not essential for the ultimate control of B. burgdorferi infection and disease.     

The B7/CD28 costimulatory family in autoimmunity

Summary: Host defense is dependent on the appropriate induction of immune responses. A central concept in immunology is the ability of the immune system to differentiate foreign from self‐antigens. The failure of the immune response to recognize foreign pathogens can result in infection and disease in the host. The inappropriate response of the immune system to self‐antigens is equally problematic, leading to autoimmune disease. Central and peripheral tolerance mechanisms control self‐reactive T‐cell responses and protect peripheral tissues from autoimmune attack. This review examines the roles of B7/CD28 family members, which can augment or antagonize T‐cell receptor signaling, in the regulation of central and peripheral T‐cell tolerance. We also discuss how B7/CD28 pathways influence both T‐cell‐intrinsic and ‐extrinsic mechanisms of regulation.     

Interaction Between B.7 and CD28 Costimulatory Molecules is Essential for the Activation of Effector Function Mediating Spontaneous Tumour Regression

The spontaneous regression of a rat histiocytoma, AK-5, is mediated by activated natural killer cells through antibody-dependent cellular cytotoxicity. In addition to the Fc-FcR interaction between the target and the effector cells demonstrated previously, we show the participation of costimulatory molecules B7 and CD28 in the efficient killing of the tumour cell. Blockade of the costimulatory interaction in vivo using anti-CD28 led to increased tumour growth and a suppressed cytokine response. Anti-CD28 antibody administration in vivo also diminished the cytotoxic potential of NK cells against AK-5 cells in vitro. Our studies also demonstrate the expression of B7.1 and B7.2 antigen on AK-5 tumour cells. The cytotoxic activity of natural killer cells was significantly inhibited when the effector/target cells were cultured in the presence of antibodies raised against B7.1, B7.2 and CD28. Administration of anti-CD28 in vivo also affected the efficiency of the formation of effector/target conjugates in vitro. Similarly, anti-CD28 injections affected expression of the adhesion molecules LFA 1 and ICAM 1 by splenocytes. Administration of anti-B7.1 and B7. 2 antibodies in AK-5 tumour-bearing animals showed a differential response. The cytotoxicity of natural killer cells was significantly inhibited after anti-B7.2 administration, suggesting the preferential participation of B7.2 molecules in vivo. These observations suggest an important role for B7-CD28 interaction in AK-5 tumour regression.     

The B7 and CD28 receptor families

Current evidence suggests that T-cell receptor (TCR) recognition of antigen bound to the major histocompatibility complex (Ag-MHC) is insufficient to lead to T-cell proliferation or effector function. For a helper T cell to produce sufficient interleukin 2 (IL-2) to allow autocrine-driven clonal expansion, there is a requirement for so-called ‘co-stimulatory’ or ‘accessory’ signals in addition to TCR ligation by Ag-MHC. The interaction of the CD28 receptor on T cells with B7 on antigen-presenting cells (APCs) supplies one such co-stimulatory signal. However, the recent discovery that CD28 and B7 are each members of larger gene families suggests that the regulation of co-stimulation is more complex than previously imagined. Here, Carl June and colleagues highlight recent advances in the understanding of the CD28 and B7 receptor families.     

CD28/B7-1与儿童肾病综合征

CD28/B7-1是一对参与机体特异性免疫应答极其重要作用的分子.CD28主要存在于T淋巴细胞表面,而B7-1为CD28的配体之一,可表达于肾脏足突细胞.初步研究显示,B7-1分子参与了足突细胞病变的发生发展,而肾脏足突细胞参与了肾病综合征病理免疫反应过程,尤其在微小病变型肾病综合征中起主导作用.国内外学者已经着手相关动物实验及少量临床试验的研究,并取得一定成果.通过阻断CD28/B7-1信号而抑制肾病综合征的发生发展过程,将为儿童肾病综合征的临床治疗提供新的思路.     

Role of CD28/B7 costimulation in the dexamethasone-induced suppression of IFN-gamma.

In vitro exposure of peripheral blood mononuclear cells (PBMC) to glucocorticoids (GC), at concentrations observed during psychologic stress, induces a shift in the human type 1/type 2 cytokine balance toward a type 2 cytokine response. The mechanisms involved in these cytokine alterations are unknown but likely include modulation of regulatory cytokines or the interaction between the antigen-presenting cell (APC) and T lymphocyte or both. The CD28/B7 costimulation pathway has been reported to modulate the type 1/type 2 cytokine balance and may contribute to the GC-associated cytokine alterations. Therefore, we sought to determine the effect of dexamethasone (Dex) on the expression and function of the human CD28/B7 costimulatory pathway and whether these alterations contribute to the Dex-induced type 1/type 2 cytokine alterations. Dex inhibited the expression of both CD80 and CD86 on THP-1 cells, a human acute monocytic leukemia cell line, as determined by flow cytometry. Dex also inhibited the expression of CD28 and CTLA-4 on phytohemagglutinin (PHA)-stimulated CD3+ T lymphocytes, which was attenuated by the addition of interleukin-12 (IL-12). Lastly, activation of CD28 with anti-CD28 antibody attenuated the Dex-induced decrease in interferon-gamma (IFN-gamma) production by anti-CD3 antibody-stimulated PBMC. These data suggest that Dex induces a modulation of the CD28/B7 costimulatory pathway that contributes to the shift in the type 1/type 2 cytokine balance toward a predominant type 2 cytokine response.     

Expression of Costimulatory Molecules CD80 and/or CD86 by a Kaposi's Sarcoma Tumor Cell Line Induces Differential T-Cell Activation and Proliferation

During physiological stimulation of resting T-cells, at least two activation signals by antigen presenting cells are required. Besides the first antigen-specific signal, the second costimulatory signal involves CD80 and CD86 expressed by the antigen presenting cell. These costimulatory molecules have been suggested to be of clinical relevance in many different autoimmune and malignant disease processes. We previously observed that tumor cells in Kaposi's sarcoma (a common AIDS-related cutaneous neoplasm) completely lack both CD80 and CD86, and these tumor cells fail to stimulate T-cell proliferation. In this study, using a Kaposi's sarcoma tumor cell line designated SLK, various stable transfected cell lines were produced. Tumor cells that were either singly positive for either CD80 or CD86, as well as a double-positive cell line, were examined for their ability to induce T-cell activation, T-cell proliferation, and cytokine production profiles. Compared to the parental double-negative tumor cell line, the CD80-positive cells, but not the CD86-positive tumor cells, induced significant T-cell activation and proliferation. Tumor cells expressing both CD80 and CD86 also induced T-cell activation. After stimulation by the transfected tumor cells, T-cells produced a Th-1 type cytokine production profile with increased IL-2 and IFN-gamma levels. These results demonstrate that Kaposi's sarcoma tumor cells lacking co-stimulatory molecules cannot induce T-cell activation; however, if they express CD80, they can induce peripheral blood T-cell proliferation, and there is a differential response as expression of CD86 did not have the same immunostimulatory effect.     

CTLA-4与超抗原对SEA诱导T细胞无能的关联研究

在建立超抗原SEA诱导T细胞无能的体外模型基础上 ,观察了无能T细胞受SEA刺激时共刺激分子CD2 8和CTLA 4的表达。结果发现 ,与活化组相比 ,在SEA加入后的不同时相点无能T细胞上CD2 8的表达都是正常的 ,而CTLA 4分子在SEA加入的第 60小时细胞表面有高水平的表达。这些结果表明 ,超抗原SEA诱导的这种无能状态与CTLA 4所介导的抑制作用增强有关     

A novel role for CD28 in thymic selection: elimination of CD28/B7 interactions increases positive selection

While the importance of the CD28/B7 costimulation pathway is well established for mature T cells, the role of CD28 in thymocyte selection is less well defined. The role of CD28 in both negative and positive selection was assessed using H-Y-specific TCR-transgenic (Tg) RAG-2-deficient (H-Yrag) mice. Negative selection in male H-Yrag mice was not affected by deficiency in CD28 or B7. Surprisingly, absence of CD28 or B7 in H-Yrag females resulted in increased numbers of CD8 single-positive (SP) thymocytes. The CD8 SP thymocytes found in these females were mature and functionally competent. Furthermore, double-positive (DP) thymocytes from CD28-knockout (CD28KO) or B7.1/B7.2 double-KO (B7DKO) females had higher levels of both CD5 and TCR than those from WT females, consistent with a stronger selecting signal. CD28KO H-Yrag fetal thymic organ cultures also had elevated numbers of thymic CD8 SP cells, reflecting increased thymic differentiation and not recirculation of peripheral T cells. Finally, increased selection of mature CD4 and CD8 SP T cells was observed in non-TCR-Tg CD28KO and B7DKO mice, indicating that this function of CD28-B7 interaction is not unique to a TCR-Tg model. Together these findings demonstrate a novel negative regulatory role for CD28 in inhibiting differentiation of SP thymocytes, probably through inhibition of thymic selection.     

CD28/CTLA-4/B7 and CD40/CD40L costimulation and activation of regulatory T cells

Costimulatory signals are crucial for T cell activation. Attempts to block costimulatory pathways have been effective in preventing unwanted immune reactions. In particular, blocking the CD28/cytotoxic T lymphocyte antigen(CTLA)-4/B7 interaction(using CTLA-4Ig) and the CD40/CD40 L interaction(using anti-CD40 L antibodies) prevents T cell mediated autoimmune diseases, transplant rejection and graft vs host disease in experimental models. Moreover, CTLA-4Ig is in clinical use to treat rheumatoid arthritis(abatacept) and to prevent rejection of renal transplants(belatacept). Under certain experimental conditions, this treatment can even result in tolerance. Surprisingly, the underlying mechanisms of immune modulation are still not completely understood. We here discuss the evidence that costimulation blockade differentially affects effector T cells(Teff) and regulatory T cells(Treg). The latter are required to control inappropriate and unwanted immune responses, and their activity often contributes to tolerance induction and maintenance. Unfortunately, our knowledge on the costimulatory requirements of Treg cells is very limited. We therefore summarize the current understanding ofthe costimulatory requirements of Treg cells, and elaborate on the effect of anti-CD40 L antibody and CTLA-4Ig treatment on Treg cell activity. In this context, we point out that the outcome of a treatment aiming at blocking the CD28/CTLA-4/B7 costimulatory interaction can vary with dosing, timing and underlying immunopathology.     

CD28 Function: A Balance of Costimulatory and Regulatory Signals

Both the recognition of MHC/antigen complex by the T-cell receptor and engagement of costimulatory molecules are necessary for efficient T-cell activation. CD28 has been widely recognized as the major costimulation pathway for naive T-cell activation, and the CD28/B7 pathway plays a central role in immune responses against pathogens, autoimmune diseases, and graft rejection. In this review, we will summarize evidence that CD28 is also prominent in the regulation of immune responses and the maintenance of peripheral tolerance. Indeed, CD28 engagement increases the expression of the down-modulatory molecule CTLA-4, induces the differentiation of Th2 cells that have a protective function in autoimmunity, and has an obligatory role in the homeostasis of regulatory T cells. Therefore, CD28/B7 interactions induce a balance of costimulatory and regulatory signals that have opposite outcomes on immune responses. This new perspective on CD28 function suggests that caution should be taken in the development of immunotherapies targeting costimulatory pathways.     

Comparison of thymocyte development and cytokine production in CD7-deficient, CD28-deficient and CD7/CD28 double-deficient mice

CD7 and CD28 are Ig superfamily molecules expressed on thymocytes and mature T cells that share common signaling 0mechanisms and are co-mitogens for T cell activation. CD7-deficient mice are resistant to lipopolysaccharide (LPS)-induced shock syndrome, and have diminished in vivo LPS-triggered IFN-gamma and tumor necrosis factor (TNF)-alpha production. CD28-deficient mice have decreased serum Ig levels, defective IgG isotype switching, decreased T cell IL-2 production and are resistant to Staphylococcus aureus enterotoxin-induced shock. To determine synergistic roles CD7 and CD28 might play in thymocyte development and function, we have generated and characterized CD7/CD28 double-deficient mice. CD7/CD28-deficient mice were healthy, reproduced normally, had normal numbers of thymocyte subsets and had normal thymus histology. Anti-CD3 mAb induced similar levels of apoptosis in CD7-deficient, CD28-deficient and CD7/CD28 double-deficient thymocytes as in control C57BL/6 mice (P = NS). Similarly, thymocyte viability, apoptosis and necrosis following ionomycin or dexamethasone treatment were the same in control, CD7-deficient, CD28-deficient and CD7/CD28-deficient mice. CD28-deficient and CD7/CD28-deficient thymocytes had decreased [3H]thymidine incorporation responses to concanavalin A (Con A) stimulation compared to control mice (P < or = 0.01 and P < or = 0.05 respectively). CD7/CD28 double-deficient mice had significantly reduced numbers of B7-1/B7-2 double-positive cells compared to freshly isolated wild-type, CD7-deficient and CD28-deficient thymocytes. Con A-stimulated CD4/CD8 double-negative (DN) thymocytes from CD7/CD28 double-deficient mice expressed significantly lower levels of CD25 when compared to CD4/CD8 DN thymocytes from wild-type, CD7-deficient and CD28-deficient mice (P < 0.05). Anti-CD3-triggered CD7/CD28-deficient thymocytes also had decreased IFN-gamma and TNF-alpha production compared to C57BL/6 control, CD7-deficient and CD28-deficient mice (P < or = 0.05). Thus, CD7 and CD28 deficiencies combined to produce abnormalities in the absolute number of B7-1/B7-2-expressing cells in the thymus, thymocyte IL-2 receptor expression and CD3-triggered cytokine production.     

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.