Expansion of rare CD8+ CD28- CD11b- T cells with impaired effector functions in HIV-1-infected patients

The decline in the number of CD4+ T cells in HIV-1-infected patients is known to be related to the increased number of CD8+CD28- T cells. In this paper, we show that CD8+CD28- T cells from HIV-positive patients have an impaired capability to interact with human endothelial cells. This is due to the dramatic expansion, within this subset, of rare CD11b- cells lacking cell-cell adhesion functions. In 50 HIV-positive patients, 19.5% +/- 6.5% of all T cells were CD8+CD28-CD11b-, whereas only 0.8% +/- 0.4% of all T cells from healthy donors showed this uncommon phenotype. The percentage of circulating CD8+CD28-CD11b- T cells was strongly related to the percentage of CD4+ T cells (r = -0.82). This population is peculiar in terms of HIV infection and was found to possess some characteristics associated with effector functions but its cytotoxic properties were impaired. The percentage of target cells lysed by CD8+CD28-CD11b- was significantly lower than that of cells lysed by its CD11b- counterpart (p <.05) both at low (5:1) or at relatively high (20:1) effector/target ratios. CD8+CD28-CD11b- T cells, which lack the ability to interact with endothelial cells, are likely to accumulate and persist in circulation. The biologic properties of CD8+CD28-CD11b- T cells suggest that these cells might be endstage or aberrant differentiated effector cells. Lack of cell-cell adhesion and impaired cytolytic functions favor the hypothesis of a role for CD8+CD28-CD11b- T cells in the development of immunodeficiency.     

Endobronchial eosinophils preferentially stimulate T helper cell type 2 responses

BACKGROUND: Antigen-loaded eosinophils instilled intratracheally into mice were capable of migrating into local lymph nodes and localize to the T cell-rich paracortical zones where they stimulated antigen-specific proliferation of CD4+ T cells. The aim of the present study was to evaluate whether eosinophils within the tracheobronchial lumen can stimulate Th2 cell expansion by presenting antigen both in vitro and in vivo. METHODS: Airway eosinophils were recovered from ovalbumin-sensitized and -challenged BALB/c mice, these eosinophils were then co-cultured with sensitized CD4+ cells in the absence or presence of anti-CD80 or/and -CD86 monoclonal antibodies. Airway eosinophils were instilled into the trachea of sensitized mice. At 3 days thereafter, the draining paratracheal lymph nodes were removed and teased into cell suspensions for culture. Cell-free culture supernatants were collected for detection of cytokines. RESULTS: Our data showed that airway eosinophils functioned as CD80- and CD86-dependent antigen-presenting cells (APCs) to stimulate sensitized CD4+ lymphocytes to produce interleukin (IL)-4, IL-5, and IL-13, but not interferon (IFN)-gamma in in vitro assay. When instilled intratracheally in sensitized recipient mice, airway eosinophils migrated into draining paratracheal lymph nodes primed Th2 cells in vivo for IL-4, IL-5, and IL-13, but not IFN-gamma, production during the in vitro culture that was also CD80- and CD86-dependent. CONCLUSION: Eosinophils within the lumina of airways could process inhaled antigen function in vitro and in vivo as APCs to promote expansion of Th2 cells. This investigation highlights the potential of eosinophils to not only act as terminal effector cells but also to actively modulate immune responses by amplifying Th2 cell responses.     

Distinct in vivo roles of CD80 and CD86 in the effector T-cell responses inducing antigen-induced arthritis

CD80 and CD86 play a critical role in the initiation of T-cell responses. However, their role in the in vivo effector CD4+ T-cell responses has been less extensively investigated. The current studies have examined the functional relevance of CD80 and CD86 in the effector CD4+ T-cell responses inducing antigen-induced arthritis. Arthritis was induced in C57BL/6 mice by sensitization to methylated bovine serum albumin (mBSA) on day 0, booster immunization (day 7) and intra-articular injection of mBSA (day 21). Control or anti-CD80 and/or anti-CD86 monoclonal antibodies were administered from day 21 to day 28. Arthritis severity and immune responses were assessed on day 28. The development of arthritis was significantly suppressed by inhibition of CD80 or CD86. Blockade of both CD80 and CD86 caused a trend towards reduced disease severity compared to control antibody-treated mice. Neutralization of CD80 attenuated accumulation of CD4+ T cells in joints and enhanced splenocyte production and circulating levels of interleukin-4. Inhibition of CD86 or both CD80 and CD86 reduced T-cell accumulation in joints without affecting T helper type 1/type 2 (Th1/Th2) differentiation or antibody levels. Blockade of CD86, and not CD80, significantly suppressed splenocyte interleukin-17 (IL-17) production. These results provide further in vivo evidence that CD80 and CD86 play important pathogenic roles in effector T-cell responses. CD80 exacerbates arthritis by downregulating systemic levels of IL-4 and increasing T-cell accumulation in joints without affecting IL-17 production. CD86 enhances disease severity by upregulating IL-17 production and increasing the accumulation of effector T cells in joints without affecting Th1/Th2 development.     

Activation requirements for the induction of CD4+CD25+ T cell suppressor function

The in vivo differentiation/survival of CD4(+)CD25(+) T suppressor cells is dependent on IL-2 and CD28-mediated costimulatory signals. To determine the cytokine and costimulatory requirements for CD25(+) T cells in vitro, we established a two-stage culture system where CD25(+) T cells were activated in a primary culture. In the subsequent culture, activated CD4(+)CD25(+) cells were then mixed with responders in order to assess their suppressor function. Pre-culture of CD25(+) T cells with anti-CD3 alone resulted in poor survival and minimal induction of suppressor activity. Pre-culture in the presence of anti-CD3 and IL-2 or IL-4, but not IL-6, IL-7, IL-9, IL-10 or IL-15, resulted in proliferation of the CD25(+) cells and induction of potent suppressor function. Inhibition of the interaction of CD28 or cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) with CD80/CD86 in the pre-culture of CD4(+)CD25(+) cells did not prevent the induction of suppressor function. Furthermore, the inhibition of costimulatory signals did not inhibit the ability of fresh CD25(+) T cells to inhibit CD8(+) responders under conditions where activation of the responders was independent of CD80/CD86. These studies support the view that activation of CD25(+) T cells requires IL-2/IL-4 for their survival/differentiation into effector cells, but is independent of CD28/CTLA-4-mediated costimulation.     

CD4+ T cell help and innate-derived IL-27 induce Blimp-1-dependent IL-10 production by antiviral CTLs

Interleukin (IL)-10 is an important regulatory cytokine that can modulate excessive immune mediated injury. Several distinct cell types have been demonstrated to produce IL-10, including most recently CD8+ cytotoxic T lymphocytes (CTLs) responding to respiratory virus infection. Here we report that CD4+ T cell help in the form of IL-2 is required for IL-10 production by CTLs, but not for the induction of CTL effector cytokines. We show that IL-2 derived from CD4+ helper T cells cooperates with innate immune cell-derived IL-27 to amplify IL-10 production by CTLs through a Blimp-1-dependent mechanism. These findings reveal a previously unrecognized pathway that coordinates signals derived from innate and helper T cells to control the production of a regulatory cytokine by CTLs during acute viral infection.     

Modulation of cell cycle progression by CTLA4-CD80/CD86 interactions on CD4+ T cells depends on strength of the CD3 signal: critical role for IL-2

Cytotoxic T-lymphocyte antigen 4 (CTLA4) is a well-studied T cell costimulatory receptor that is known to inhibit T cell activation. In this study, the relationship between strength of the first signal and costimulatory interactions on primary mouse CD4(+) T cells was investigated. CTLA4-CD80/CD86 interactions differentially modulate T cell cycling based on the mode of CD3 signal: Activation with plate-bound (pb) anti-CD3 generates a strong signal compared with a weak signal with soluble (sol) anti-CD3, resulting in approximately sevenfold higher amounts of interleukin (IL)-2 and an increase in cell cycling. Activation of T cells with sol anti-CD3 (weak signal) together with CTLA4-CD80/CD86 blockade lowers IL-2 production and cell cycling, demonstrating an enhancing role for these interactions. Conversely, blockade of CTLA4-CD80/CD86 interactions on T cells activated with pb anti-CD3 (strong signal) increases proliferation, which is consistent with CTLA4 as a negative regulator. Also, coculture of T cells with Chinese hamster ovary cells expressing CD80 or CD86 demonstrates that the strength of the primary signal plays an important role. It is important that modulation of IL-2 amounts leads to distinct alterations in the functional effects of CTLA4-CD80/CD86 interactions. On increasing IL-2 amounts, activation of T cells stimulated with sol anti-CD3 (weak signal) and CTLA4-CD80/CD86 blockade is greater compared with control. Concurrently, neutralization of IL-2 greatly reduces activation of T cells stimulated with pb anti-CD3 (strong signal) and CTLA4-CD80/CD86 blockade compared with control. These results underscore the importance of strength of first signal, CTLA4-CD80/CD86 interactions, and IL-2 amounts in modulating primary CD4(+) T cell responses.     

Role of CD80, CD86, and CTLA4 on mouse CD4(+) T lymphocytes in enhancing cell-cycle progression and survival after activation with PMA and ionomycin

Cell surface interactions between the T cell costimulatory receptors, CD28 and cytotoxic T-lymphocyte antigen-4 (CTLA4), with their cognate ligands, CD80 and CD86, on antigen-presenting cells play an important role in T cell activation. Although CD80 and CD86 are induced on T cells after activation, not much is known about their role in modulating T cell function. We show that CD80, CD86, and CTLA4 are induced on purified CD4(+) T cells after in vitro activation with phorbol 12-myristate 13-acetate (PMA) and ionomycin, and they play an essential role for proliferation and survival. Blockade of CTLA4-CD80/CD86 interactions greatly reduces PMA and ionomycin-mediated mouse CD4(+) T cell activation. The three key features of this inhibition of activation are: First, late events in T cell activation (after 18 h) are affected; second, these cells do not undergo anergy; and third, CD4(+)CD25(+) regulatory T cells are not responsible. Activation of T cells with PMA and ionomycin together with CTLA4-CD80/CD86 blockade results in decreased induction of CD25 and Bcl-X(L), reduced interleukin (IL)-2, and enhanced transforming growth factor-beta (TGF-beta) production. Furthermore, extended CTLA4-CD80/CD86 blockade results in decreased cell-cycle progression and enhanced apoptosis in a large proportion of cells. This inhibition of T cell proliferation can be rescued completely with anti-CD28 or IL-2 and partially with TGF-beta antagonists. This study reveals a functional role for CD80, CD86, and CTLA4 on CD4(+) T lymphocytes and sheds light on the mechanisms by which these molecules enhance activation and survival with PMA and ionomycin.     

Interleukin-12 can replace CD28-dependent T-cell costimulation during nonspecific cytotoxic T lymphocyte induction by anti-CD3 antibody

Cytotoxic T lymphocyte (CTL) development is regulated closely by an intricate series of signals provided by the T-cell receptor/CD3 complex, cytokines, and costimulatory ligand/receptor systems. In this study, we have explored the role of interleukin (IL)-12 and CD28 in mouse CTL development. Activation of T cells with anti-CD3 monoclonal antibody (mAb) in the presence of anti-CD86 mAb, which prevents CD28-CD86 interaction, led to decreased production of type 1 (IL-2, interferon-gamma) and type 2 (IL-4, IL-6, IL-10) cytokines, as well as diminished expression of granzyme B (Gzm B) and reduced cytotoxic effector function. Cytolytic activity in T-cell cultures that were activated in the presence of anti-CD86-blocking mAb alone or in combination with anti-CD80 mAb could be restored by the addition of exogenous IL-12 at initiation of culture. The ability of IL-12 to substitute for CD28-costimulatory signaling during CTL development was found to be dependent on the presence of IL-2 rather than interferon-gamma. IL-2 is required for IL-12Rbeta2 expression by T cells activated in the presence of anti-CD86 mAb. Moreover, IL-12Rbeta2 expression by T cells activated in the presence of anti-CD86 mAb is enhanced by IL-12. We, therefore, conclude that the ability of IL-12 to substitute for CD28-costimulatory signaling during CTL development is a result of the interaction of IL-12 with IL-12Rbeta2 induced by low levels of IL-2 synthesized by T cells activated in a CD28-independent manner.     

HIV-1 transgenic rat CD4+ T cells develop decreased CD28 responsiveness and suboptimal Lck tyrosine dephosphorylation following activation

Impaired CD4+ T cell responses, resulting in dysregulated T-helper 1 (Th1) effector and memory responses, are a common result of HIV-1 infection. These defects are often preceded by decreased expression and function of the alpha/beta T cell receptor (TCR)-CD3 complex and of co-stimulatory molecules including CD28, resulting in altered T cell proliferation, cytokine secretion and cell survival. We have previously shown that HIV Tg rats have defective development of T cell effector function and generation of specific effector/memory T cell subsets. Here we identify abnormalities in activated HIV-1 Tg rat CD4+ T cells that include decreased pY505 dephosphorylation of Lck (required for Lck activation), decreased CD28 function, reduced expression of the anti-apoptotic molecule Bcl-xL, decreased secretion of the mitogenic lympokine interleukin-2 (IL-2) and increased activation induced apoptosis. These events likely lead to defects in antigen-specific signaling and may help explain the disruption of Th1 responses and the generation of specific effector/memory subsets in transgenic CD4+ T cells.     

Induction of interleukin-12 production in mouse macrophages by berberine,a benzodioxoloquinolizine alkaloid,deviates CD4+ T cells from a Th2 to a Th1 response

In this study we investigated whether berberine-mediated induction of interleukin-12 (IL-12) production in antigen-presenting cells could regulate a cytokine profile of antigen-primed CD4+ T helper (Th) cells. Pretreatment with berberine induced IL-12 production in both macrophages and dendritic cells, and significantly increased the levels of IL-12 production in lipopolysaccharide-stimulated macrophages and in CD40 ligand-stimulated dendritic cells. Importantly, berberine pretreatment of macrophages increased their ability to induce interferon-gamma (IFN-gamma) and reduced their ability to induce IL-4 in antigen-primed CD4+ T cells. Berberine did not influence the macrophage cell surface expression of the class II major histocompatibility complex molecule, the co-stimulatory molecules CD80 and CD86, and intracellular adhesion molecule-1. Addition of neutralizing anti-IL-12p40 monoclonal antibody to cultures of berberine-pretreated macrophages and CD4+ T cells restored IL-4 production in antigen-primed CD4+ T cells. The in vivo administration of berberine resulted in the enhanced induction of IL-12 production by macrophages when stimulated in vitro with lipopolysaccharide or heat-killed Listeria monocytogenes, leading to the inhibition of the Th type 2 cytokine profile (decreased IL-4 and increased IFN-gamma production) in antigen-primed CD4+ T cells. These findings may point to a possible therapeutic use of berberine or medicinal plants containing berberine in the Th type 2 cell-mediated immune diseases such as allergic diseases.     

CD4+CD25+ regulatory T cells down-regulate co-stimulatory molecules on antigen-presenting cells

CD4+CD25+ T cells have been shown to inhibit experimentally induced organ-specific autoimmune disease and depletion of these regulatory T cells from normal mice results in development of such conditions. Furthermore, CD4+CD25+ T cells suppress the IL-2 production and thereby the proliferation of polyclonally activated CD4+CD25- T cells in vitro. The suppression in vitro is independent of secreted factors but requires interactions between CD4+CD25- and CD4+CD25+ T cells and antigen-presenting cells (APC). We have now further investigated the function of CD4+CD25+ T cells in vitro and have focused on their interactions with APC. We found that CD4+CD25+ T cells down-regulated the expression of the co-stimulatory molecules CD80 and CD86 on dendritic cells. The steady-state level of CD80 mRNA was also decreased, while the steady-state level of CD86 mRNA was not, suggesting that distinct mechanisms regulate the expression of these molecules. The down-regulation occurred even in the presence of stimuli that would normally increase the expression of CD80 and CD86 molecules. Thus, down-regulation of co-stimulatory molecules may be an additional effector function of these regulatory T cells.     

IL-15 induces unspecific effector functions in human peptide-specific CD8+ T-cell cultures

Antigen (Ag)-specific CD8+ T cells are a major host defence against viral infections. In the present study, we generated human CD8+ T-cell lines specific towards influenza matrix peptide (IMP)-pulsed Ag-presenting cells. We compared the effect of interleukin-2 (IL-2) and IL-15 on the proliferation and cytotoxic activity of primary and secondary IMP-specific cytotoxic T lymphocyte (CTL) culture. In primary CTL cultures, IL-15-induced cell expansion was considerably reduced as compared with IL-2-induced cell expansion, and IL-15 favoured the outgrowth of CTLs without peptide specificity in these cultures. Secondary IMP-specific CD8+ T cells were generated by the addition of IL-2 during two cycles of restimulation. From the third restimulation, identical CTL cultures were expanded with either IL-2 or IL-15 in parallel. Cell expansion as well as Ag specificity was considerably reduced after a 5 day culture period in the presence of IL-15. No or low CD69 expression was observed in IL-15-cultured CTLs, whereas IL-2-cultured CTLs contained high fractions of CD69+ cells. Furthermore, a high fraction of these latter cells coexpressed the cytotoxic marker CD56. However, IL-15-cultured CTLs exhibited cytotoxic activity without detectable expression of CD56, suggesting that CD56 is not essential for cytotoxic activity. Thus, the results presented suggest that IL-15 favours the outgrowth of unspecific cytotoxic effector T cells.     

CD80, but not CD86 were up-regulated on the spleen-derived dendritic cells from OVA-sensitized and challenged BALB/c mice

Allergen-specific CD4+ T-helper (Th) 2 cells are involved in the induction and effector phase of allergic asthma. It is well established that T cells activation requires interaction of T cell receptor (TCR) and MHC-peptide complex, as well as costimulatory signal delivered by antigen presenting cells (APCs). There is increasing evidence that CD80 (B7.1) and CD86 (B7.2), as the most important costimulatory molecules, are involved in the allergic immune responses. In the present study, we investigated the CD80 and CD86 expression of spleen-derived dendritic cells (DCs) in a murine model of allergic asthma. We first established a murine model of ovalbumin (OVA)-allergic asthma that showed unique histological characteristic of allergic inflammation in the lung, high serum OVA-specific IgE level, high numbers of eosinophils in the bronchoalveolar lavage (BAL) and high production of Type 2 cytokines in the splenic T cells. In this model, we found that CD80 were significantly upregulated on the spleen-derived DCs from OVA-sensitized and challenged mice compared with that from PBS-treated or non-treated mice, while CD86 is not different among three groups. Furthermore, we demonstrated that Th2 immune responses were elicited by these DCs with high expression of CD80, even to nai;ve T cells from non-treated mice. Our results suggest that DCs in the spleen of allergic mice, via upregulation of CD80 might play a pivotal role in the maintenance and amplification of allergic immune response, namely Th2 immune response.     

Importance of CD80/CD86-CD28 interactions in the recognition of target cells by CD8+CD122+ regulatory T cells

CD8+CD122+ regulatory T cells are a newly identified, naturally occurring type of regulatory T cell that produce interleukin-10 (IL-10) and effectively suppress interferon-gamma (IFN-gamma) production from both CD8+ and CD4+ target cells. Molecular mechanisms responsible for the recognition of target cells by CD8+CD122+ regulatory T cells were investigated in this study by using an in vitro culture system that reconstitutes the regulatory action of these cells. CD8+CD122( regulatory T cells did not produce IL-10 and did not suppress the IFN-gamma production of allogeneic target T cells when they were stimulated by immobilized anti-CD3 antibody alone, but they clearly produced IL-10 and suppressed the IFN-gamma production of target cells when stimulated by anti-CD3 plus anti-CD28-coated beads. IFN-gamma production by major histocompatibility complex-class I-deficient T cells was also suppressed by CD8+CD122+ regulatory T cells stimulated with anti-CD3 plus anti-CD28 antibody but was not suppressed by cells stimulated by anti-CD3 alone. Experiments examining the blockade of cell surface molecules expressed on either the regulatory cells or the target cells by adding specific neutralizing antibodies in the culture indicated that CD80, CD86, and CD28 molecules were involved in the regulatory action, but cytotoxic T lymphocyte antigen-4, inducible costimulatory molecule (ICOS) and programmed death-1 (PD-1) molecules were not. Finally, CD8+CD122+ cells isolated from CD28-knockout (CD28-/-) mice showed no regulatory activity. These results indicate that CD8+CD122(+) regulatory T cells recognize target T cells via the interaction of CD80/CD86-CD28 molecules to become active regulatory cells that produce suppressive factors such as IL-10.     

Intracellular concentrations of Ca(2+) modulate the strength of signal and alter the outcomes of cytotoxic T-lymphocyte antigen-4 (CD152)-CD80/CD86 interactions in CD4(+) T lymphocytes

The costimulatory receptors CD28 and cytotoxic T-lymphocyte antigen (CTLA)-4 and their ligands, CD80 and CD86, are expressed on T lymphocytes; however, their functional roles during T cell-T cell interactions are not well known. The consequences of blocking CTLA-4-CD80/CD86 interactions on purified mouse CD4(+) T cells were studied in the context of the strength of signal (SOS). CD4(+) T cells were activated with phorbol 12-myristate 13-acetate (PMA) and different concentrations of a Ca(2+) ionophore, Ionomycin (I), or a sarcoplasmic Ca(2+) ATPase inhibitor, Thapsigargin (TG). Increasing concentrations of I or TG increased the amount of interleukin (IL)-2, reflecting the conversion of a low to a high SOS. During activation with PMA and low amounts of I, intracellular concentrations of calcium ([Ca(2+)](i)) were greatly reduced upon CTLA-4-CD80/CD86 blockade. Further experiments demonstrated that CTLA-4-CD80/CD86 interactions reduced cell cycling upon activation with PMA and high amounts of I or TG (high SOS) but the opposite occurred with PMA and low amounts of I or TG (low SOS). These results were confirmed by surface T-cell receptor (TCR)-CD3 signalling using a low SOS, for example soluble anti-CD3, or a high SOS, for example plate-bound anti-CD3. Also, CTLA-4-CD80/CD86 interactions enhanced the generation of reactive oxygen species (ROS). Studies with catalase revealed that H(2)O(2) was required for IL-2 production and cell cycle progression during activation with a low SOS. However, the high amounts of ROS produced during activation with a high SOS reduced cell cycle progression. Taken together, these results indicate that [Ca(2+)](i) and ROS play important roles in the modulation of T-cell responses by CTLA-4-CD80/CD86 interactions.     

Predominance of Th2-promoting dendritic cells in early human pregnancy decidua

Dendritic cells (DCs) are specialized antigen-presenting cells required for the priming and activation of T cells and promote the differentiation of na?ve CD4+ T cells toward the T helper cell type 1 (Th1) or Th2 phenotype. Here, we describe the characterization of CD45+CD3-CD14-CD16-CD19-CD20-CD56-HLA-DRbright DCs from early human pregnancy decidua by flow cytometry. The percentage of DCs to mononuclear cells (leukocytes) in the decidua was significantly higher than that in the peripheral blood. Moreover, decidual DCs expressed costimulatory molecules such as CD80 and CD86 and a mature marker such as CD83 on their surface. The percentage of CD11c+CD123- myeloid DCs in the decidua was significantly higher than that in the peripheral blood. Conversely, the ratio of CD11c-CD123+ lymphoid DCs in the decidua was significantly lower than that in the peripheral blood. The number of interleukin (IL)-12-producing cells in the total DC population and the myeloid DCs in the decidua was significantly lower than that in the peripheral blood. IL-12 secretion by activated decidual myeloid DCs was significantly lower than that by peripheral DCs. Na?ve CD4+ T cells primed with decidual myeloid DCs led to a higher percentage of Th2 cells in comparison with that with peripheral myeloid DCs. This finding was abolished by exogenous IL-12 administration with decidual myeloid DCs. Thus, the DCs in the decidua could regulate the Th1/Th2 balance to maintain a Th2-dominant state, leading to maintenance of pregnancy.     

Requirement of CD28-CD86 co-stimulation in the interaction between antigen-primed T helper type 2 and B cells

The interaction between CD28 and its ligands, CD80 and CD86, is crucial for an optimal activation of antigen-specific T cells. However, the requirement of CD80 or CD86 co-stimulation in Th2 cell differentiation and activation is controversial. Freshly isolated murine CD4+ and CD8+ T cells were incubated with P815 transfectants expressing a similar level of either CD80 or CD86 in the presence of anti-CD3 mAb. Both CD80 and CD86 co-stimulated the proliferation of CD4+ and CD8+ T cells at comparable time-kinetics and magnitude, but CD86 alone was able to co- stimulate IL-4 and especially IL-10 production in CD4+ T cells. In typical Th2-dependent immune responses elicited by Nippostrongylus brasillensis infection, the anti-CD86 mAb treatment but not the anti- CD80 mAb treatment efficiently inhibited antigen-specific IgE and IgG1 production, which was accompanied with the reduced IL-4 production. Our results suggest that CD86 co-stimulation plays a dominant role not only in the primary activation of Th2 cells but also in the secondary interaction between antigen-primed Th2 cells and B cells.      

CTLA4-CD80/CD86 interactions on primary mouse CD4+ T cells integrate signal-strength information to modulate activation with Concanavalin A

The mechanisms by which concanavalin A (Con A), a lectin, activates T cells are poorly studied. A low dose of Con A is stimulatory for T cells, whereas a high dose of Con A results in suppression of proliferation and enhanced T cell death. The expression and functional roles of costimulatory receptors, CD28 and cytotoxic T-lymphocyte antigen 4 (CTLA4), and their ligands, CD80 and CD86, on primary mouse CD4(+) T cells after activation with different doses of Con A were studied. CTLA4-CD80/CD86 interactions in this T:T cell activation model demonstrate distinct outcomes depending on the dose of Con A. CTLA4-CD80/CD86 interactions inhibit CD4(+) T cell cycling and survival after activation with a suppressive dose of Con A by increasing oxidative stress and decreasing levels of BclX(L). The enhanced CD4(+) T cell death with a suppressive dose of Con A is dependent on excess H(2)O(2) and nitric oxide but is independent of Fas and caspase activity. It is surprising that the increased proliferation of CD4(+) T cells with a suppressive dose of Con A on blocking CTLA4-CD80/CD86 interactions is largely interleukin (IL)-2-independent but is cyclosporine A-sensitive. On activation with a stimulatory dose of Con A, CTLA4-CD80/CD86 interactions enhance T cell activation and survival by reducing the production of reactive oxygen species, increasing IL-2 and BclX(L) levels. Here IL-10 but not transforming growth factor-beta plays a functional role. In summary, CTLA4-CD80/CD86 interactions on T cells integrate signal strength, based on the dose of Con A, to enhance or inhibit primary mouse CD4(+) T cell cycling and survival.