CD8+ T cells and not CD4+ T cells are hyporesponsive to CD28- and CD40L-mediated activation in HIV-infected subjects

T cell dysfunction in HIV-infected subjects could be the consequence of altered sensitivity of CD4⁺ or CD8⁺ T cells to various costimulatory signals. Therefore, we studied proliferation and cytokine production in highly purified CD8⁺ and CD4⁺ T cells from HIV-infected and HIV⁻ subjects, induced by co-activation via cell-bound CD80, CD86 and CD40 or by allo-activation. Regardless of the nature of the first and the costimulatory signal, CD8⁺ T cells from patients proliferated consistently less than controls, while responses from CD4⁺ T cells were similar in patients and controls. This phenomenon was observed after ligation of CD28 combined with anti-CD3 or phorbol myristate acetate (PMA), but also after allogeneic stimulation and after activation by CD40 and anti-CD3. Anti-CD3 combined with CD80 or CD86 induced a mixed Th1/Th2-type cytokine profile in both CD4⁺ and CD8⁺ T cells from controls, whereas anti-CD3 plus CD40 induced only low levels of Th2-type cytokines and no interferon-gamma (IFN-γ) in CD4⁺ T cells. Compared with controls, CD4⁺ T cells from patients produced slightly lower levels of IL-10 but equal amounts of IFN-γ, IL-4 and IL-5, while CD8⁺ T cells from patients produced less of all cytokines tested. In conclusion, responses of purified CD4⁺ T cells from HIV⁺ subjects to various costimulatory pathways are relatively intact, whereas CD8⁺ T cells are hyporesponsive at the level of proliferation and cytokine production. A generalized intrinsic CD8⁺ T cell failure might contribute to viral and neoplastic complications of HIV infection.     

Antigen processing and CD24 expression determine antigen presentation by splenic CD4+ and CD8+ dendritic cells

To examine heterogeneity in dendritic cell (DC) antigen presentation function, murine splenic DCs were separated into CD4⁺ and CD8⁺ populations and assessed for the ability to process and present particulate antigen to CD4⁺ and CD8⁺ T cells. CD4⁺ and CD8⁺ DCs both processed exogenous particulate antigen, but CD8⁺ DCs were much more efficient than CD4⁺ DCs for both major histocompatibility complex (MHC) class II antigen presentation and MHC class I cross-presentation. While antigen processing efficiency contributed to the superior antigen presentation function of CD8⁺ DCs, our studies also revealed an important contribution of CD24. CD8⁺ DCs were also more efficient than CD4⁺ DCs in inducing naïve T cells to acquire certain effector T-cell functions, for example generation of cytotoxic CD8⁺ T cells and interferon (IFN)-γ-producing CD4⁺ T cells. In summary, CD8⁺ DCs are particularly potent antigen-presenting cells that express critical costimulators and efficiently process exogenous antigen for presentation by both MHC class I and II molecules.     

CD8+ MAIT cells infiltrate into the CNS and alterations in their blood frequencies correlate with IL‐18 serum levels in multiple sclerosis

Recent findings indicate a pathogenic involvement of IL‐17‐producing CD8⁺ T cells in multiple sclerosis (MS). IL‐17 production has been attributed to a subset of CD8⁺ T cells that belong to the mucosal‐associated invariant T (MAIT) cell population. Here, we report a reduction of CD8⁺ MAIT cells in the blood of MS patients compared with healthy individuals, which significantly correlated with IL‐18 serum levels in MS patients. In vitro stimulation of peripheral blood mononuclear cells from healthy individuals and MS patients with IL‐18 specifically activated CD8⁺ MAIT cells. Moreover, IL‐18 together with T‐cell receptor stimulation induced, specifically on CD8⁺ MAIT cells, an upregulation of the integrin very late antigen‐4 that is essential for the infiltration of CD8⁺ T cells into the CNS. Notably, we were able to identify CD8⁺ MAIT cells in MS brain lesions by immunohistochemistry while they were almost absent in the cerebrospinal fluid (CSF). In summary, our findings indicate that an IL‐18–driven activation of CD8⁺ MAIT cells contributes to their CNS infiltration in MS, in turn leading to reduced CD8⁺ MAIT‐cell frequencies in the blood. Therefore, CD8⁺ MAIT cells seem to play a role in the innate arm of immunopathology in MS.     

IL‐12‐mediated STAT4 signaling and TCR signal strength cooperate in the induction of CD40L in human and mouse CD8+ T cells

CD40L is one of the key molecules bridging the activation of specific T cells and the maturation of professional and nonprofessional antigen‐presenting cells including B cells. CD4⁺ T cells have been regarded as the major T‐cell subset that expresses CD40L upon cognate activation; however, we demonstrate here that a putative CD8⁺ helper T‐cell subset expressing CD40L is induced in human and murine CD8⁺ T cells in vitro and in mice immunized with antigen‐pulsed dendritic cells. IL‐12 and STAT4‐mediated signaling was the major instructive cytokine signal boosting the ability of CD8⁺ T cells to express CD40L both in vitro and in vivo. Additionally, TCR signaling strength modulated CD40L expression in CD8⁺ T cells after primary differentiation in vitro as well as in vivo. The induction of CD40L in CD8⁺ T cells regulated by IL‐12 and TCR signaling may enable CD8⁺ T cells to respond autonomously of CD4⁺ T cells. Thus, we propose that under proinflammatory conditions, a self‐sustaining positive feedback loop could facilitate the efficient priming of T cells stimulated by high affinity peptide displaying APCs.     

A subset of CD8+ T cells from allergic patients produce IL-4 and stimulate IgE production in vitro

Background and Objective A subset of IL-4 producing CD8⁺ T cells was recently identified in HIV patients. Based on these findings we examined whether IL-4 producing CD8⁺ T cells would also be present in allergic patients and what would be the functional relevance of this T-cell population. Methods We investigated the role of CD8⁺ T cells in IgE production of allergic diseases by analysing the cytokine profile of individual CD4⁺ and CD8⁺ T cells. Results In allergic patients about twice as many CD4⁺ T cells and six times as many CD8⁺ T cells produced IL-4 as in non-allergic controls. In contrast the frequency of IFNγ⁺ T-cell subsets did not significantly differ between the allergic and non-allergic individuals. The frequency of 1L4⁺CD8⁺ T cells correlated with the level of serum IgE. Coculture experiments with T cells or purified CD8⁺ T cells together with autologous B cells indicated that CD8⁺ T cells enhanced IgE in vitro, but not IgM production, even when they were physically separated from B cells. This effect could be partially blocked by addition of an IL-4 binding protein, a soluble IL-4 receptor indicating that lL-4 is involved in CD8⁺ T-cell mediated IgE production. Conclusions These data indicate a positive role of IL-4 secreting CD8⁺ T cells in IgE regulation in allergic patients.     

Circulating CD137+CD8+ T cells accumulate along with increased functional regulatory T cells and thoracic tumour burden in lung cancer patients

CD137 is a promising target for immunostimulation strategies against cancer. Previous studies showed that CD137⁺CD8⁺ T cells are enriched in antitumour effector T cells in both preclinical tumour models and cancer patients, but to date, such T cells in the blood of lung cancer patients have not been sufficiently investigated. In this study, circulating antigen‐activated CD8⁺ T cell subsets, identified as CD137⁺CD8⁺ or PD‐1⁺ (programmed cell death protein 1) CD8⁺, and regulatory T cells (Treg), identified as CD4⁺CD25⁺CD127^low/?, in 40 untreated lung cancer patients and in 49 age‐ and sex‐matched healthy controls (HCs) were assessed by flow cytometry. Results were evaluated for associations with lung cancer patient clinical characteristics. Correlations between antigen‐activated CD8⁺ T cells and effector Treg (CTLA‐4⁺ [cytotoxic T‐lymphocyte antigen 4] CD4⁺CD25⁺CD127^low/?) were also investigated. Higher percentages of PD‐1⁺, CD137⁺ and PD‐1⁺CD137⁺ amongst CD8⁺ T cells were observed in lung cancer patients compared with HCs. The percentages of CD137⁺CD8⁺ and PD‐1⁺CD137⁺CD8⁺ T cell subsets amongst CD8⁺ T cells were positively correlated with thoracic tumour burden and were strongly positively correlated with the percentage of effector Treg subset. Smoking patients harboured higher percentages of the PD‐1⁺CD8⁺ T cell subset compared with non‐smoking patients. This study demonstrated that circulating antigen‐activated CD8⁺ T cells accumulated in lung cancer patients along with increased effector Treg and thoracic tumour burden. These findings aid a better understanding of immune‐host interactions in lung cancer patients using peripheral blood, and further support immunotherapeutic intervention strategies using combination therapy for differential control of Treg and activation of tumour‐specific effector T cells.     

Prognostic significance of resident CD103+CD8+T cells in human colorectal cancer tissues

The prognostic significance and clinical implications of resident CD103⁺CD8⁺T cells in human colorectal cancer tissues still remains largely unexplored. In our present study, we aimed to characterize the resident CD8⁺T cells in human colorectal cancer tissues by using double staining of CD103 and CD8, and further evaluated the prognostic significance of resident CD8⁺T cells in colorectal cancer. We found that the OS rate of the colorectal cancer patients with higher infiltration of CD8⁺T cells, or with higher numbers of resident CD103⁺CD8⁺T cells, or with higher ratio of CD103⁺CD8⁺T cells over total CD8⁺T cells in cancer tissues was significantly better than that of the patients with lower infiltration of CD8⁺T cells, or with lower numbers of resident CD103⁺CD8⁺T cells, or with higher ratio of CD103⁺CD8⁺T cells over total CD8⁺T cells in cancer tissues, respectively. Moreover, higher infiltration of CD8⁺T cells in colorectal cancer tissues was significantly and inversely correlated with advanced TNM stage. Higher numbers of resident CD103⁺CD8⁺T cells in colorectal cancer tissues were significantly and inversely correlated with distant metastasis status. Higher ratio of CD103⁺CD8⁺T cells over total CD8⁺T cells in colorectal cancer tissues was significantly and inversely correlated with age status. The COX model analysis demonstrated that higher infiltration of CD8⁺T cells, higher numbers of resident CD103⁺CD8⁺T cells, or higher ratio of CD103⁺CD8⁺T cells over total CD8⁺T cells in colorectal cancer tissues, could serve as independent prognostic predictors for colorectal cancer patients. Taken together, our present study demonstrated the density of tumor infiltrating CD8⁺T cells or the numbers of resident CD103⁺CD8⁺T cells in colorectal tissues could be used as an important prognostic predictor for this malignancy.     

Phenotypic differences of CD4+ T cells in response to red blood cell immunization in transfused sickle cell disease patients

Alloimmunization against red blood cells (RBCs) is the main immunological risk associated with transfusion in patients with sickle cell disease (SCD). However, about 50–70% of SCD patients never get immunized despite frequent transfusion. In murine models, CD4⁺ T cells play a key role in RBC alloimmunization. We therefore explored and compared the CD4⁺ T‐cell phenotypes and functions between a group of SCD patients (n = 11) who never became immunized despite a high transfusion regimen and a group of SCD patients (n = 10) who had become immunized (at least against Kidd antigen b) after a low transfusion regimen. We studied markers of CD4⁺ T‐cell function, including TLR, that directly control lymphocyte function, and their spontaneous cytokine production. We also tested responders for the cytokine profile in response to Kidd antigen b peptides. Low TLR2/TLR3 expression and, unexpectedly, strong expression of CD40 on CD4⁺ T cells were associated with the nonresponder status, whereas spontaneous expression of IL‐10 by CD4⁺ T cells and weak Tbet expression were associated with the responder status. A Th17 profile was predominant in responders when stimulated by Jb^k. These findings implicate CD4⁺ T cells in alloimmunization in humans and suggest that they may be exploited to differentiate responders from nonresponders.     

Diversion of CD4+ T cell development from regulatory T helper to effector T helper cells alters the contact hypersensitivity response

Cutaneous sensitization to reactive haptens and subsequent challenge results in a T cell-mediated response, contact hypersensitivity (CHS). Recent results from this laboratory have indicated that hapten sensitization induces two populations of reactive T cells: CD8⁺ T cells producing interferon (IFN)-γ which mediate the response and CD4⁺ T cells producing interleukin (IL)-4 and IL-10 which negatively regulate the magnitude and duration of the response. Since CD4⁺ T cell development to either IFN-γ- (Th1) or IL-4/IL-10- (Th2)-producing cells is dependent upon the cytokine environment during antigen priming, we hypothesized that CD4⁺ T cell induction in a Th1-promoting environment would not only alter the CD4⁺ T cell cytokine-producing phenotype but also the course of the CHS response. Administration of the Th1-promoting cytokine IL-12 during hapten sensitization resulted in a CHS response of greater magnitude following challenge and extended the duration of the response. In hapten-sensitized mice depleted of CD8⁺ T cells, treatment with IL-12 induced effector CD4⁺ T cells. Histological examination of challenged ear tissue from these mice indicated minimal edema and an acute mononuclear cell infiltration more typical of classical delayed-type hypersensitivity than CHS. Hapten-primed CD4⁺ T cells from IL-12 treated, sensitized mice produced IFN-γ, but not IL-4 in response to T cell receptor-mediated stimulation. Use of neutralizing anti-IFN-γ antibody indicated that IL-12 not only directly promoted Th1 development but also indirectly inhibited Th2 development through stimulation of IFN-γ production at the time of hapten sensitization. Overall, these results demonstrate that diversion of CD4⁺ T cell development to Th1 effector cells rather than to Th2 cells alters the efferent nature of CHS and removes a primary regulatory mechanism of the immune response.     

CD8+ lymphocyte phenotype and cytokine production in long-term non-progressor and in progressor patients with HIV-1 infection

In most HIV-1-infected patients, clinical and immunological progression develops within a few years. Few infected people, termed long-term non-progressors (LTNP), remain healthy and immunologically stable for a long time. The factors governing the maintenance of this condition are not well known, but it is conceivable that CD8⁺ lymphocytes, cells that play a central role in controlling in vitro HIV replication, may have a part in vivo in this process. The aim of this study was to characterize the phenotypic profile and the cytokine production of CD8⁺ cells in a group of LTNP patients who had stable CD4⁺ cell counts (>500/mm³) for at least 7 years. Their CD8⁺ absolute numbers were similar to a control group composed of HIV-1⁺ patients who have a progressive decline of their CD4⁺ cell counts. However, our multiparameter immunofluorescence studies show that a clinical and immunologically stable condition is associated with the presence of a CD28⁺, CD95 strongly positive CD8⁺ population, while disease progression is marked by the CD28⁻CD95⁺CD8⁺ subset. Purified CD8⁺ cells from LTNP retain their ability to produce IL-2, interferon-gamma (IFN-γ) and, to a lesser degree, to produce IL-10 and IL-4. In contrast, CD8⁺ cells from progressors are unable to secrete IL-2 and IL-10. Although CD8⁺ cytokine profile does not fit with the proposed T helper (Th)1/Th2 switch in progressive HIV infection, LTNP CD8⁺ T cells maintain their capacity to produce IL-2 and IL-10 (Th0-like), a pattern very similar to that observed in normal HIV healthy controls. We suggest that CD8⁺ cells expressing CD28, CD95 and having a Th0-like profile may be considered to be associated with long-term survival.     

Rapid identification and sorting of viable virus-reactive CD4(+) and CD8(+) T cells based on antigen-triggered CD137 expression

Current methods for the detection and isolation of antigen-specific CD4⁺ and CD8⁺ T cells require the availability of peptide/MHC multimers or are restricted to cells that produce cytokines after antigen contact. Here we show that de novo cell surface expression of the TNF-receptor family member CD137 (4-1BB) identifies recently activated, but not resting, human CD4⁺ and CD8⁺ memory T cells. Maximum CD137 expression level is uniformly observed in both T-cell subsets at 24h after stimulation with antigen. In experiments with CMV and EBV-reactive T cells, we confirmed the specificity of CD137 expression by co-staining with peptide/HLA tetramers. Substantial proportions of CD137⁺ T cells did not produce IFN-γ, suggesting that CD137 detects a broader repertoire of antigen-specific T cells. Activated CD137⁺ T cells could be easily purified by MACS and expanded in vitro thereafter. This CD137-based enrichment method was capable of isolating 2-fold higher numbers of anti-viral CD4⁺ and CD8⁺ T cells compared to the IFN-γ secretion assay. In conclusion, antigen-triggered CD137 expression allows the rapid detection and sorting of virus-reactive CD4⁺ and CD8⁺ T cells. The CD137 assay is most attractive for the simultaneous targeting of anti-viral T helper and effector cells in monitoring studies and adoptive immunotherapy trials.     

Circulating CD4+CD8+ T lymphocytes in patients with Kawasaki disease

We serially monitored cell surface antigen expression on mononuclear cells in peripheral blood isolated from patients with Kawasaki disease (KD), and found, for the first time, that a markedly increased number of CD4⁺CD8⁺ T lymphocytes was present in some of the patients (11 of the 24 cases). The cases of five of these 11 patients were complicated with coronary artery lesion (CAL); the 13 patients with normal numbers of CD4⁺CD8⁺ T lymphocytes did not have CAL. The patients' age, sex and grade of systemic inflammation evaluated by peripheral leucocyte count and serum C-reactive protein levels were not correlated to the number of CD4⁺CD8⁺ T lymphocytes. Other cell surface antigen characteristics of the CD4⁺CD8⁺ T lymphocytes included CD3⁺, CD45RA⁺, CD45RO⁺, CD16^?, and HLA-DR⁺. These results indicate that the surface antigen characteristics of the KD peripheral blood examined were the same as those of Epstein–Barr virus infection without CD45RA⁺. These findings provide useful information for the analysis of the pathogenesis of KD.     

Tumor‐specific CD4+ T cells maintain effector and memory tumor‐specific CD8+ T cells

Immunotherapies that augment antitumor T cells have had recent success for treating patients with cancer. Here we examined whether tumor‐specific CD4⁺ T cells enhance CD8⁺ T‐cell adoptive immunotherapy in a lymphopenic environment. Our model employed physiological doses of tyrosinase‐related protein 1‐specific CD4⁺ transgenic T cells‐CD4⁺ T cells and pmel‐CD8⁺ T cells that when transferred individually were subtherapeutic; however, when transferred together provided significant (p ≤ 0.001) therapeutic efficacy. Therapeutic efficacy correlated with increased numbers of effector and memory CD8⁺ T cells with tumor‐specific cytokine expression. When combined with CD4⁺ T cells, transfer of total (naïve and effector) or effector CD8⁺ T cells were highly effective, suggesting CD4⁺ T cells can help mediate therapeutic effects by maintaining function of activated CD8⁺ T cells. In addition, CD4⁺ T cells had a pronounced effect in the early posttransfer period, as their elimination within the first 3 days significantly (p < 0.001) reduced therapeutic efficacy. The CD8⁺ T cells recovered from mice treated with both CD8⁺ and CD4⁺ T cells had decreased expression of PD‐1 and PD‐1‐blockade enhanced the therapeutic efficacy of pmel‐CD8 alone, suggesting that CD4⁺ T cells help reduce CD8⁺ T‐cell exhaustion. These data support combining immunotherapies that elicit both tumor‐specific CD4⁺ and CD8⁺ T cells for treatment of patients with cancer.     

CD4 T cells inhibit in vivo the CD8-mediated immune response against murine colon carcinoma cells transduced with interleukin-12 genes

Retroviral-mediated cytokine gene transfer into tumor cells is a highly effective way of inducing tumor inhibition and immunity. We analyzed the tumorigenicity of C-26 murine colon carcinoma cells transduced with genes encoding the two subunits of murine interleukin-12 (IL-12) in a polycistronic retroviral vector and selected for resistance to G418 and for IL-12 production (30–80 pg/ml). BALB/c mice injected s.c., i.v. and intrasplenically with C-26/IL-12 cells from three different IL-12-producing clones showed delayed tumor onset as compared with mice injected with control Neo^R-transduced or parental tumor cells. Although C-26/IL-12 tumor-bearing mice eventually died of lung metastasis, their survival time was twice as long as that of mice injected with control cells. In experiments with mice selectively depleted of natural killer (NK) cells before tumor cell injection, the time of tumor onset and survival of mice injected with C-26/IL-12 s.c. and i.v., respectively, was reduced. CD8⁺ T cell depletion had no effect on latency or survival, whereas removal of CD4⁺ T cells led to C-26/IL-12 tumor regression in about 40% of mice. Histological and immunocytochemical characterization of leukocytes infiltrating C-26/IL-12 tumors showed only slight infiltration with few T cells in non-depleted mice but abundant infiltration by CD8⁺ T cells and asialo-GM1+ NK cells in tumors of mice depleted of CD4⁺ T cells. The lack of CD8⁺ T cell infiltration is not due to a CD4-mediated suppression of their activation because irradiated C-26/IL-12 cells primed for the induction of a strong cytotoxic T lymphocyte response against C-26 parental cells and induced CD8⁺ effector cells that protected against C-26/IL-12 in a Winn assay. Rather, the results suggest that, although C-26/IL-12 cells injected in vivo stimulate both NK and CD8⁺ T cells, tumor infiltration by the latter is inhibited by CD4⁺ T cells.     

Mapping of the lingual immune system reveals the presence of both regulatory and effector CD4+ T cells

Background Sublingual immunotherapy (SLIT) is safe and reduces both symptoms and medication requirements in patients with type I respiratory allergies. Nonetheless, immune mechanisms underlying SLIT need to be further documented. Objective A detailed characterization of the lingual immune system was undertaken in mice, to investigate the presence of tolerogenic and pro‐inflammatory mechanisms. Methods Immune cells were characterized in lingual tissues from BALB/c mice using immunohistology and flow cytometry. Resident CD4⁺ T cells were sorted and toll‐like receptor (TLR) expression profiles as well as functional characterization were assessed by RT‐PCR, T cell suppressive assays and cytokine gene expression, respectively. Results Eosinophils and mast cells were only detected in submucosal tissues. No NK, NK‐T, γ/δ, CD8⁺ T cells, nor B‐lymphocytes were detected. Potential antigen presenting cells include various subsets of dendritic cells (CD207⁺ Langerhans cells, CD11b⁺CD11c⁺ myeloid cells and 120G8⁺ plasmacytoid DCs) together with F4/80⁺ macrophages. Noteworthy, both CD103^? and CD103⁺ CD4⁺ T cells expressing TLR2 and TLR4 receptors are present along the lamina propria, in vicinity of myeloid CD11b⁺CD11c^± dendritic cells. Such resident lingual CD4⁺ T lymphocytes comprise both suppressive T cells as well as cells with memory/effector functions (i.e. expressing IFNγ, IL4, IL10 and IL17 genes following stimulation), irrespective of the presence of the mucosal addressing marker CD103. Conclusion The sublingual route is pertinent to induce antigen‐specific tolerance, due to (i) limited numbers of pro‐inflammatory cells, rather located in submucosal tissues, (ii) co‐localization of APCs and resident CD4⁺ T cells with regulatory functions. Since the oral immune system can also elicit pro‐inflammatory effector responses, the cytokine milieu in which allergens are presented by sublingual APCs needs to be controlled during immunotherapy (e.g. with adjuvants) in order to favour tolerance over inflammation.     

DC‐induced CD8+ T‐cell response is inhibited by MHC class II‐dependent DX5+CD4+ Treg

CD4⁺ T cells are important for CD8⁺ T‐cell priming by providing cognate signals for DC maturation. We analyzed the capacity of CD4⁺ T cells to influence CD8⁺ T‐cell responses induced by activated DC. Surprisingly, mice depleted for CD4⁺ cells were able to generate stronger antigen‐specific CD8⁺ T‐cell responses after DC vaccination than non‐depleted mice. The same observation was made when mice were vaccinated with MHC class II^?/? DC, indicating the presence of a MHC class II‐dependent CD4⁺ T‐cell population inhibiting CD8⁺ T‐cell responses. Recently we described the expansion of DX5⁺CD4⁺ T cells, a T‐cell population displaying immune regulatory properties, upon vaccination with DC. Intriguingly, we now observe an inverse correlation between CD8⁺ T‐cell induction and expansion of DX5⁺CD4⁺ T cells as the latter cells did not expand after vaccination with MHC class II^?/? DC. In vitro, DX5⁺CD4⁺ T cells were able to limit proliferation, modulate cytokine production and induce Foxp3⁺ expression in OVA‐specific CD8⁺ T cells. Together, our data show an inhibitory role of CD4⁺ T cells on the induction of CD8⁺ T‐cell responses by activated DC and indicate the involvement of DX5⁺CD4⁺, but not CD4⁺CD25⁺, T cells in this process.     

Intravenous immunoglobulin modulates the expansion and cytotoxicity of CD8+ T cells

Intravenous immunoglobulin (IVIg) is successfully used in the treatment of autoimmune diseases involving self‐reactive CD8⁺ T cells. However, its direct influence on the cytotoxic response remains unknown. Using an antigen cross‐presentation assay and a mouse model of ovalbumin (OVA) immunization, we showed that IVIg decreases the in vitro activation, proliferation and cytokine secretion of OVA‐specific CD8⁺ T cells (OT‐I), as well as the in vivo generation of OVA‐specific CD8⁺ T cells. In addition, IVIg significantly decreases the proportion of perforin‐ and CD107a‐expressing CD8⁺ T cells, and inhibits the cytotoxic activity of OVA‐activated OT‐I cells. The interference of IVIg with the CD8⁺ T‐cell response is associated with T‐cell receptor blockade, therefore reducing the interaction between effector and target cells. A similar blockade is observed on human CD8⁺ T cells, suggesting that the observations reported here could apply to the IVIg‐mediated improvement of CD8⁺ T‐cell‐mediated autoimmune conditions in human patients.     

Decreased expression of 20-kD homologous restriction factor (HRF20, CD59) on T lymphocytes in Epstein–Barr virus (EBV)-induced infectious mononucleosis

HRF20 (CD59) is one of the membrane-associated complement regulatory proteins. The characteristic function of CD59 is to prevent membrane attack complex (MAC) formation on the cell surface and to protect the cell from complement-mediated cell lysis. We examined the expression of CD59 antigen on T cell subpopulations in patients with acute infectious mononucleosis (IM) and analysed the relationship between the amount of CD59 expression and activation-induced cell death of mature T cells with apoptosis. Decreased expression of CD59 on CD8⁺ T cells, especially on CD45RO⁺ and HLA-DR⁺ activated T cells, was marked in acute IM patients. In contrast, activated CD4⁺ T cells from IM patients expressed as much CD59 antigen as CD4⁺ T cells from healthy volunteers. After incubation-induced cell death, viable CD8⁺ T cells showed normal amounts of CD59 antigen on their surface. CD59^dim CD8⁺ T cells were more susceptible to apoptosis than CD59^bright CD8⁺ T cells. These findings suggest that decreased expression of CD59 on CD8⁺ T cells may discriminate the susceptibility of activated CD8⁺ T cells to activation-induced cell death in IM.     

Depletion of CD4+CD25+CD127lo regulatory T cells does not increase allergen‐driven T cell activation

Background It has been suggested that allergic diseases are caused by defective suppression of allergen‐specific Th2 cells by CD4⁺CD25⁺ regulatory T cells. However, such studies have been hampered by the difficulty in distinguishing regulatory T cells from CD25‐expressing activated T cells. Recently, it was shown that conventional T cells expressed high levels of CD127, whereas regulatory T cells were CD127^lo, allowing discrimination between these distinct T cell subpopulations. Objective The aim of this study was to study whether the putative regulatory subset defined as CD4⁺CD25⁺CD127^lo was involved in grass pollen‐reactive T cell responses. Methods Peripheral blood mononuclear cells (PBMCs) were obtained from allergic donors and non‐atopic controls out of season. Grass pollen‐induced cytokine production and proliferation were compared in cultures of undepleted cells and cells depleted of CD4⁺CD25⁺, CD4⁺CD25⁺CD127^hi or CD4⁺CD25⁺CD127^lo T cells. Results Undepleted cell cultures from allergic patients showed significantly increased proliferation and Th2 cytokine production compared with non‐atopic controls. Depletion of all CD25⁺ T cells did not increase cytokine production or proliferation, and more importantly, no increase in Th2 cytokine production or proliferation was observed in cell cultures depleted of CD4⁺CD25⁺CD127^lo cells (putative regulatory T cells) compared with undepleted PBMCs in both the allergic and the non‐atopic group. Conclusion Our study showed that T cells from grass pollen‐allergic patients and non‐atopic controls responded very differently to grass pollen extract, but this difference could not be explained by differences in regulatory T cell function. Further studies are needed to understand the importance of regulatory T cells in allergy.     

Signals required for programming effector and memory development by CD8+ T cells

Summary: Stimulation of naïve CD8⁺ T cells with antigen and costimulation results in proliferation and weak clonal expansion, but the cells fail to develop effector functions and are tolerant long term. Initiation of the program leading to the strong expansion and development of effector functions and memory requires a third signal that can be provided by interleukin‐12 (IL‐12) or interferon‐α (IFN‐α). CD4⁺ T cells condition dendritic cells (DCs) to effectively present antigen to CD8⁺ T cells, and this conditioning involves, at least in part, CD40‐dependent upregulation of the production of these signal 3 cytokines by the DCs. Upon being fully activated, the cytotoxic T lymphocytes develop activation‐induced non‐responsiveness (AINR), a form of split anergy characterized by an inability to produce IL‐2 to support continued expansion. If antigen remains present, IL‐2 provided by CD4⁺ T cells can reverse AINR to allow further expansion of the effector population and conversion to responsive memory cells following antigen clearance. If IL‐2 or potentially other proliferative signals are not available, persistent antigen holds cells in the AINR state and prevents the development of a responsive memory population. Thus, in addition to antigen and costimulation, CD8⁺ T cells require cytokine signals at distinct stages of the response to be programmed for optimal generation of effector and memory populations.