Functional profile of cytomegalovirus (CMV)-specific CD8+ T cells and kinetics of NKG2C+ NK cells associated with the resolution of CMV DNAemia in allogeneic stem cell transplant recipients

Immune mechanisms involved in control of cytomegalovirus (CMV) infection in the allogeneic stem cell transplantation setting have not been fully disclosed. CMV pp65 and IE-1-specific CD8(+) T cells expressing IFN-γ, TNF-α, and CD107a, alone or in combination, and NKG2C(+) NK cells were prospectively enumerated during 13 episodes of CMV DNAemia. The expansion of monofunctional and polyfunctional CD8(+) T cells was associated with CMV DNAemia clearance. The size and functional diversity of the expanding CD8(+) T-cell population was greater in self-resolved episodes than in episodes treated with antivirals. These differences were related to the magnitude of expansion of cognate antigen IFN-γ CD4(+) T cells. The resolution of CMV DNAemia was associated frequently with a marked expansion of both CD56(dim) /CD16(+) NK cells and NKG2C(+) CD56(bright) /CD16(-) NK cells. The data lend support to the role of polyfunctional CD8(+) T cells in controlling CMV replication in the allogeneic stem cell transplantation setting, and suggest that NKG2C(+) NK cells may be involved critically in the resolution of CMV DNAemia episodes.     

Evolution of diverse antiviral CD8+ T cell populations after murine cytomegalovirus infection

Cytomegalovirus (CMV) is a major human pathogen normally controlled by cellular immune responses. The infection can be modeled in the mouse using murine CMV (MCMV). During the latent phase of infection, two different patterns of CD8(+) T cell responses have been observed: some specificities show increasing frequencies over time ("memory inflation"), while others, which are present acutely, are barely detectable at later time points. This distinction is independent of initial immunodominance. We analyzed the extent to which such responses differ functionally and tracked both their population distribution and their evolution over time. We observed two clear patterns of memory development that diverged early after infection. Acutely, CD8(+) T cells directed against all epitopes showed similar activation, phenotype and distribution. Thereafter, one set of responses ("inflationary") increased in frequency over time, was found in high numbers in non-lymphoid organs and was associated with an activated (CD28(low) CD27(low)CD122(low)) phenotype. In contrast, CD8(+) T cells responses specific for other MCMV epitopes ("non-inflationary") showed a slow reversion to a classical "central" memory phenotype without enrichment in non-lymphoid organs. A simple model to describe the equilibrium state in MCMV is presented, which may point to previously unexplored antiviral populations present after human CMV infection.     

Effects of therapy with highly active anti-retroviral therapy (HAART) and IL-2 on CD4+ and CD8+ lymphocyte apoptosis in HIV+ patients

The kinetics and effects of in vivo spontaneous apoptosis and activation-induced cell death (AICD) upon CD4+ and CD8+ lymphocyte subsets and CD4 naive cell numbers were studied in HIV+ subjects with CD4 pretreatment values > 200/mm3, who were subsequently treated for 48 weeks with HAART alone or in combination with six cycles of subcutaneous IL-2. Irrespective of the type of treatment, patients showed a statistically significant increase in CD4 cell counts after 4 weeks, although the CD4 naive subset only increased significantly in the IL-2-treated subjects at the end of treatment. The percentage of CD4 cells undergoing spontaneous apoptosis and AICD was significantly reduced in all patients after 4 weeks and this reduction was maintained until the end of therapy; however, the level always remained significantly higher in comparison with healthy subjects. A statistically significant reduction in CD8 apoptosis levels required at least 24 weeks of therapy. Together these data suggest that a reduction in the level of apoptosis may contribute to the early rise in CD4 numbers measured after HAART, but that later on HAART is unable to improve further this biological parameter. Although the use of IL-2 had no additional effects on spontaneous apoptosis and AICD, it may be beneficial by stimulating a late increase in the numbers of CD4 naive cells in HIV-treated subjects.     

CD8+ T cell responses to human immunodeficiency viruses type 2 (HIV-2) and type 1 (HIV-1) gag proteins are distinguishable by magnitude and breadth but not cellular phenotype

The mechanisms underlying the relatively slow progression of human immunodeficiency virus type 2 (HIV-2) compared with HIV-1 infection are undefined and could be a result of more effective immune responses. We used HIV-2 and HIV-1 IFN-gamma enzyme-linked immunospot assays to evaluate CD8(+) T cell responses in antiretroviral-naive HIV-2- ('HIV-2(+)') and HIV-1-infected ('HIV-1(+)') individuals. Gag-specific responses were detected in the majority of HIV-2(+) and HIV-1(+) subjects. Overlapping gag peptide analysis indicated a significantly greater magnitude and breadth of responses in the HIV-1(+) cohort, and this difference was attributable to low responses in HIV-2(+) subjects with undetectable viral load (medians 2107 and 512 spot-forming units per 10(6) PBMC, respectively, p=0.007). We investigated the phenotype of viral epitope-specific CD8(+) T cells identified with HLA-B53- and HLA-B58-peptide tetramers (8 HIV-2(+), 11 HIV-1(+) subjects). HIV-2-specific CD8(+) T cells were predominantly CD27(+) CD45RA(-), and only a minority expressed perforin. The limited breadth and low frequency of CD8(+) T cell responses to HIV-2 gag in aviremic HIV-2(+) subjects suggests that these responses reflect antigen load in plasma, as is the case in HIV-1 infection. Immune control of HIV-2 does not appear to be related to the frequency of perforin-expressing virus-specific CD8(+) T cells.     

Interleukin-2 is essential for CD4+CD25+ regulatory T cell function

Constitutive expression of CD25, the IL-2 receptor alpha-chain, defines a distinct population of CD4+ T cells (Treg) with suppressive activity in vitro and in vivo. IL-2 has been implicated in the generation and maintenance of Treg, however, a functional contribution of the IL-2 receptor during suppression is thus far unknown. We show that IL-2 is required for Treg function in vitro, since suppression is completely abrogated by selective blocking of the IL-2 receptor on Treg during co-culture with responder T cells. We demonstrate that Treg, which do not produce IL-2, compete for IL-2 secreted by responder T cells. In accordance with the idea of competition being part of the suppressive mechanism, in vitro neutralization of IL-2 mimics all effects of Treg. Conversely, recombinant IL-2 abrogates inhibition of IL-2 production in responder T cells, the hallmark of Treg suppression. Finally, activation in the presence of IL-2 primes Treg to produce IL-10 upon secondary stimulation, indicating that IL-2 uptake is also required to induce additional suppressive factors that might be more relevant for suppression in vivo. We propose the parakrine uptake of soluble mediators as a flexible mechanism to adapt Treg activity to the strength of the responder T cell reaction.     

CD8 lymphocytosis in primary cytomegalovirus (CMV) infection of allograft recipients: expansion of an uncommon CD8+ CD57- subset and its progressive replacement by CD8+ CD57+ T cells.

Allograft recipients undergoing cytomegalovirus infection present increased proportions of circulating CD8+ lymphocytes. A longitudinal study of 11 kidney and five liver allograft recipients with primary CMV infection but no other etiological factor of graft dysfunction revealed selective imbalances of peripheral blood CD8+ T cell subsets. Initially, CMV viraemia is associated with elevated CD8+bright T cell numbers and T cell activation. Activation markers fall to normal when viral cultures become negative (before the end of the first month). During the second to sixth month, most (12/16) patients keep up high CD8+ T cell counts (1050-2900 CD8+ cells/mm3), comprising an uncommon CD8+ T cell subset, as 45-73% of CD8+bright lymphocytes were CD3+ and TCR alpha beta+, but were not stained by anti-CD28, CD11b, CD16, CD56, and CD57 antibody. Unexpectedly, CD8+CD57+ T cells, a hallmark of CMV infection, do not appear until the second to sixth month of primary CMV infection, and their numbers increase progressively thereafter. They become the predominant CD8+ T cell subset after 6 months of infection and their persistence for several (up to 4) years is strongly correlated (r = 0.87) with expansion of CD8+ cells. By analysis with MoAbs, there was no bias towards the use of particular TCR-V beta gene families at any time of primary CMV infection. Persistence of CD8 lymphocytosis is thus directly related to the rate of expansion of an uncommon CD8+CD57- subset and its progressive replacement by CD8+CD57+ T cells that are chronically elicited by CMV.     

医源性HIV感染者CD8+细胞非细胞毒性HIV抑制作用的研究

目的 观察医源性HIV感染者CD8+细胞非细胞毒性HIV抑制反应(CNAR),并比较CNAR与CD4细胞计数的关系.方法 免疫磁珠法分离HIV感染者的CD8+细胞,按2:1,1:1,0.5:1和0.25:1的比例,与体外急性感染的CD4+细胞混合培养,测定培养物上清中逆转录酶活性,与阴性对照比较计算病毒抑制率.结果 CNAR活性达到80%病毒抑制率时,CD4<300个/μl组的平均CD8与CD4比例为2.4:1,CD4>300个/μl组的平均CD8与CD4比例为1.3:1,两组间比较差异有统计学意义(P<0.05).结论 HIV感染者的CNAR活性与其CIM细胞计数相关,CD4>300的个体较CD4<300的个体有着更显著的抑制HIV复制的能力.     

Phenotypic characterization of CD8+ T cell populations in HIV disease and in anti-HIV immunity.

The CD8+ T cell population is believed to play an important role in the control of viral infection, both for suppression of viral replication and for cytotoxic activity against viral infected cells. Elevated numbers of CD8+ T cells have been demonstrated in HIV infection, and CD8+ cytotoxic T cell (CTL) activity is associated with the early, asymptomatic stage of disease. We investigated the phenotypic characteristics of the CD8 population, in whole blood, in HIV disease and determined the predominant CD8+ subpopulation involved in anti-HIV CTL activity. We found that CD8+ T cells co-expressing markers of activation (HLA-DR), memory (CD45RO, CD29), and cytotoxic activity (S6F1) were significantly elevated in the early stages of disease, while the numbers of naive (CD45RA) cells remained unchanged. Progression to AIDS resulted in an overall loss of absolute CD8+ T cells, though the percentages of CD8+ HLA-DR+ and CD8+ S6F1+ remained elevated. In contrast to patients in the late stages of disease, anti-HIVgag CTL activity, following in vitro stimulation, was present in most HIV+ asymptomatic subjects and was associated with an expansion of CD8+ HLA-DR+ and CD8+ CD45RO+ cells. The absence of CTL activity was associated with a reduced ability of these populations to expand in vitro and with a significant loss of peripheral CD4+ T cells, independent of clinical stage. We suggest that CD8+ expressing HLA-DR+ CD45RO+ and S6F1+ play an important role in anti-HIV cytotoxicity.     

Interleukin‐4 downregulates CD127 expression and activity on human thymocytes and mature CD8+ T cells

Signaling via the IL‐7 receptor complex (IL‐7Rα/CD127 and IL‐2Rγ/CD132) is required for T‐cell development and survival. Decreased CD127 expression has been associated with persistent viral infections (e.g. HIV, HCV) and cancer. Many IL‐2Rγ‐sharing (γ_C) cytokines decrease CD127 expression on CD4⁺ and CD8⁺ T cells in mice (IL‐2, IL‐4, IL‐7, IL‐15) and in humans (IL‐2, IL‐7), suggesting a common function. IL‐4 is of particular interest as it is upregulated in HIV infection and in thyroid and colon cancers. The role of IL‐4 in regulating CD127 expression and IL‐7 activity in human thymocytes and mature CD8⁺ T cells is unknown and was therefore investigated. IL‐4 decreased CD127 expression on all thymocyte subsets tested and only on naïve (CD45RA⁺) CD8⁺ T cells, without altering membrane‐bound CD127 mRNA expression. Pre‐treatment of thymocytes or CD8⁺ T cells with IL‐4 inhibited IL‐7‐mediated phosphorylation of STAT5 and decreased proliferation of CD8⁺ T cells. By downregulating CD127 expression and signaling on developing thymocytes and CD8⁺ T cells, IL‐4 is a potential contributor to impaired CD8⁺ T‐cell function in some anti‐viral and anti‐tumor responses. These findings are of particular consequence to diseases such as HIV, HCV, RSV, measles and cancer, in which CD127 expression is decreased, IL‐7 activity is impaired and IL‐4 concentrations are elevated.     

Interleukin-4 induced down-regulation of skin homing receptor expression by human viral-specific CD8 T cells may contribute to atopic risk of cutaneous infection

Factors controlling the expression of cutaneous lymphocyte-associated antigen (CLA) by T cells are poorly understood, but data from murine and human CD4(+) T cell systems have suggested that cytokines play an important role. However, there are no data examining the influence of cytokines on the expression of CLA by human antigen-specific CD8(+) T cells. Peripheral blood mononuclear cells (PBMC) were isolated from 10 HLA-A*0201-positive healthy individuals. Using HLA-peptide tetrameric complexes refolded with immunodominant peptides from Epstein-Barr virus (EBV), cytomegalovirus (CMV) and influenza A virus, we investigated the temporal associations of CLA expression by viral-specific CD8(+) T cells following stimulation with antigen. Ex vivo influenza matrix-specific CD8(+) T cells expressed significantly (P < 0.05) greater levels of CLA than EBV BMLF1 and CMV pp65-specific CD8(+) T cells (mean 9.7% influenza matrix versus 1.4% BMLF1 versus 1.1% pp65) and these differences were sustained on culture. However, regardless of viral specificity, interleukin (IL)-12 and IL-4 induced significant (P < 0.05) dose-dependent up-regulation and down-regulation of CLA expression, respectively, with IL-4 showing a dominant negative effect. In many cases, IL-4 resulted in complete abrogation of detectable CLA expression by the viral-specific CD8(+) T cells. Overall these data demonstrate that CLA expression by human viral-specific CD8(+) T cells is highly dynamic and that IL-4 causes significant down-regulation. Disorders associated with a type 2 cytokine shift may reduce the efficiency of skin homing by viral-specific CD8(+) T cells. Furthermore, the ability to modify the local and systemic microenvironment may offer novel therapeutic strategies that influence tissue-specific T cell homing.     

Dichotomy of two CD8+ lymphocyte subsets in HIV infection. Depletion of CD8+ CD3- and expansion of CD8+ CD3+ subsets: consequence on the CD4/CD8 ratio.

In order to highlight the underlying mechanism(s) of the CD8 lymphocyte expansion in the HIV infection, two distinct CD8 subsets were analysed: T CD8bright+ CD3+ with MHC-restricted activity, and non-T CD8dim+ CD3-, which performs natural killer (NK) activity. It consists of a cross-sectional study including 168 HIV-infected patients (74 CDC stage II, 48 CDC stage III and 46 CDC stage IV) compared among them and to 60 healthy individuals. We observed an expansion of CD8+ CD3+ cells which masks a depletion of CD8+ CD3-. The comparative study showed that the expansion of the CD8+ CD3+ is relatively higher than that of total CD8+ lymphocytes and that the depletion of the CD8+ CD3- subset is severe, begins early and remains constant through the HIV progression. The comparison of CD4/CD8 and CD4/CD8+ CD3+ ratios showed that the latter could possibly be a better indicator in the HIV infection. The mechanism of inverted CD4/CD8 ratio in healthy individuals was also clarified. The CD8+ CD3+, CD8+ CD3- and CD4/CD8+ CD3+ parameters would be more specific markers than total CD8 and CD4/CD8 ratio especially in therapy trials.     

Estimation of CD4+ and CD8+ T-lymphocytes in human immunodeficiency virus infection and acquired immunodeficiency syndrome patients in Manipur

Purpose: To estimate and stratify CD4⁺and CD8⁺T-lymphocyte levels in human immunodeficiency virus (HIV) infected (asymptomatic) and acquired immunodeficiency syndrome (AIDS) patients (symptomatic) and correlate the clinical features of the patients with CD4+ and CD8+ lymphocyte level. Methods: : Between April 2002 and September 2003, a total of 415 HIV seropositive adult patients (297 males and 118 females) attending Regional Institute of Medical Sciences (RIMS) hospitals were tested for CD4+ and CD8+ T-lymphocytes by fluorescent activated cell sorter (FACS) counter (Becton Dickinson). Symptomatic patients were diagnosed as per NACO clinical case definition. Results: Ranges of 0-50, 51-100, 101-200, 201-300, 301-400, 401-500 and above 500 CD4+ T-lymphocyte per microlitre were seen in 68, 52, 101, 73, 47, 31 and 43 patients respectively whereas CD8+ T-lymphocyte ranges of 0-300, 301-600, 601-900, 901-1500, 1501-2000, 2001-3500 per microlitre were seen in 29, 84, 92, 145, 40 and 25 patients respectively. One hundred and fifty patients were asymptomatic and 265 were symptomatic. CD4/CD8 ratio in asymptomatics and symptomatics were 0.13-1.69 and 0.01-0.93 respectively. Tuberculosis and candidiasis occurred in CD4+ T-lymphocyte categories between 0-400 cells per μL in symptomatics. However, cryptosporidiosis, toxoplasmosis, herpes zoster, cryptococcal meningitis, Pneumocystis carinii pneumonia, penicilliosis and cytomegalovirus retinitis were seen in patients having CD4+ T-lymphocyte less than 200 per μL. Conclusions: CD4+ T-lymphocyte was decreased in both asymptomatic and symptomatic HIV patients, The decrease was greater in symptomatics while CD8+ T-lymphocyte was increased in both except advanced stage symptomatics. CD4: CD8 ratio was reversed in both groups. Opportunistic infections correlated with different CD4+ T-lymphocyte categories.     

Proliferation and interleukin 5 production by CD8hi CD57+ T cells

CD8hi CD57+ T cells have previously been described as effector memory T cells with minimal expansion capacity and high susceptibility to activation-induced cell death. In contrast, we demonstrate here that CD8hi CD57+ T cells are capable of rapid expansion using multiple techniques including [(3)H]thymidine uptake, flow cytometric bead-based enumeration and standard haemocytometer counting. Previous reports can be explained by marked inhibition of activation-induced expansion and increased 7-amino-actinomycin D uptake by CD8hi CD57+ T cells following treatment with CFSE, a dye previously used to measure their proliferation, combined with specific media requirements for the growth of this cell subset. The ability of CD8hi CD57+ T cells to further differentiate is highlighted by a distinct cytokine profile late after activation that includes the unexpected release of high levels of interleukin 5. These data indicate that CD8hi CD57+ T cells should not be considered as "end-stage" effector T cells incapable of proliferation, but represent a highly differentiated subset capable of rapid division and exhibiting novel functions separate from their previously described cytotoxic and IFN-gamma responses.     

Kinetics of cytomegalovirus (CMV) pp65 and IE‐1‐specific IFNγ CD8+ and CD4+ T cells during episodes of viral DNAemia in allogeneic stem cell transplant recipients: Potential implications for the management of active CMV infection

The dynamics of CMV pp65 and IE‐1‐specific IFNγ‐producing CD8⁺ (IFNγ CD8⁺) and CD4⁺ (IFNγ CD4⁺) T cells and CMV DNAemia were assessed in 19 pre‐emptively treated episodes of active CMV infection. Peripheral counts of IFNγ CD8⁺ and IFNγ CD4⁺ T cells inversely correlated with CMV DNAemia levels (P = <0.001 and P = 0.003, respectively). A threshold value of 1.3 cells/µl predicting CMV DNAemia clearance was established for IFNγ CD8⁺ T cells (PPV, 100%; NPV, 93%) and for IFNγ CD4⁺ T cells (PPV, 100%; NPV, 75%). Undetectable T‐cell responses were usually observed at the time of initiation of pre‐emptive therapy. Either a rapid (within 7 days) or a delayed (median 31 days) expansion of both T‐cell populations concomitant with CMV DNAemia clearance was observed in 5 and 8 episodes, respectively. An inconsistent or a lack of expansion of both T‐cell subsets was related to a persistent CMV DNAemia. Robust and maintained CMV‐specific T‐cell responses after CMV DNAemia clearance and cessation of antiviral therapy were associated with a null incidence of relapsing infections at least during the following month. Data obtained in the present study may be helpful in the design of therapeutic strategies for the management of active CMV infections in the allo‐SCT recipient. J. Med. Virol. 82: 1208–1215, 2010. © 2010 Wiley‐Liss, Inc.     

The stromal cell antigen CD248 (endosialin) is expressed on naive CD8+ human T cells and regulates proliferation

CD248 (endosialin) is a transmembrane glycoprotein that is dynamically expressed on pericytes and fibroblasts during tissue development, tumour neovascularization and inflammation. Its role in tissue remodelling is associated with increased stromal cell proliferation and migration. We show that CD248 is also uniquely expressed by human, but not mouse (C57BL/6), CD8(+) naive T cells. CD248 is found only on CD8(+) CCR7(+) CD11a(low) naive T cells and on CD8 single-positive T cells in the thymus. Transfection of the CD248 negative T-cell line MOLT-4 with CD248 cDNA surprisingly reduced cell proliferation. Knock-down of CD248 on naive CD8 T cells increased cell proliferation. These data demonstrate opposing functions for CD248 on haematopoietic (CD8(+)) versus stromal cells and suggests that CD248 helps to maintain naive CD8(+) human T cells in a quiescent state.     

健康青年人HCMV特异性CD8+T细胞频率和表型分析

目的 利用负载pp65495.503抗原肽的HLA-A*0201四聚体染色结合流式细胞术,分析HLA-A2 健康青年供者外周血中HCMV pp65495-503特异性记忆CD8 T细胞的频率和表型.方法 以优化的四聚体染色方法对22例中国青年供者全血进行染色,用流式细胞仪对样品进行三色荧光分析.结果 健康中国青年人外周血中存在高频率的pp65495-503特异性CD8 T细胞,占CD8 T细胞的百分率为0.14～6.84%(均数2.45%);表型分析显示其CD28 细胞占四聚体阳性和四聚体阴性细胞的百分率分别为为32.5%(±21.7%)和58.58%(±10.4%)(P＜0.001);CD57 细胞占四聚体阳性和四聚体阴性细胞的百分率分别为55.8%(±18.4%)和27.4%(±8.3%)(P＜0.001).同时,对三例健康青年人CD8 T细胞上多种表面分子的详细分析显示,pp65495-503特异性记忆CD8 T细胞有不同比率的细胞表达CD62L、CD45RO、CD38和CD27,而且还有一定比例的细胞表达CD45RA,但不表达活化抗原CD69分子.结论 青年中国人外周血中存在高频率的HCMV特异性CD8 T细胞,这些细胞的表型存在高度异质性,可能是处于不同分化阶段的记忆和效应细胞群体组成.     

Chronic myelogenous leukemia maintains specific CD8+ T cells through IL‐7 signaling

Chronic myelogenous leukemia (CML) is a malignant myeloproliferative disease of hematopoietic stem cells. The disease progresses after several years from an initial chronic phase to a blast phase. Leukemia‐specific T cells are regularly detected in CML patients and may be involved in the immunological control of the disease. Here, we analyzed the role of leukemia‐specific CD8⁺ T cells in CML disease control and the mechanism that maintains CD8⁺ T‐cell immunosurveillance in a retroviral‐induced murine CML model. To study antigen‐specific immune responses, the glycoprotein of the lymphocytic choriomeningitis virus was used as model leukemia antigen. Leukemia‐specific CTL activity was detectable in vivo in CML mice and depletion of CD8⁺ T cells rapidly led to disease progression. CML‐specific CTL were characterized by the expression of the IL‐7 receptor α‐chain. In addition, leukemia cells produced IL‐7 that was crucial for the maintenance of leukemia‐specific CTL and for disease control. Therefore, CML cells maintain the specific CD8⁺ T‐cell‐mediated immune control by IL‐7 secretion. This results in prolonged control of disease and probably contributes to the characteristic chronic phase of the disease.     

Human cytomegalovirus infection and T cell immunosenescence: a mini review

The mammalian immune system defends the organism against pathogens, and possibly cancer, but is known to become dysregulated with increasing age. This results in greater morbidity and mortality due to infectious disease in old people. The most important changes occur in T cell immunity, manifested sometimes dramatically as altered clonal expansions of cells of limited antigen specificity and a marked shrinkage of the T cell antigen receptor repertoire. At the same time, it was independently reported that CMV seropositivity was associated with many of the same T cell changes that were being identified as biomarkers of immune ageing. It has now become clear that CMV is commonly the driving force behind the oligoclonal expansions and altered phenotypes and functions of CD8 cells seen in most old people. These changes are much less obvious in centenarians and most extreme in people whom longitudinal studies have shown to possess an "immune risk profile". This is a cluster of immunological parameters of which CMV seropositivity is one component and which predicts incipient mortality in an elderly population. Taken together, these findings suggest the hypothesis that persistence of CMV as a chronic antigenic stressor is a major contributor to immunosenescence and associated mortality.     

Expansion of regulatory CD8+ CD25+ T cells after neonatal alloimmunization

Transplantation tolerance induced by neonatal injection of semi-allogeneic spleen cells is associated with a pathological syndrome caused by T helper type 2 (Th2) differentiation of donor-specific CD4(+) T lymphocytes. We have shown previously that this Th2-biased response is inhibited by host CD8(+) T cells. Herein, we demonstrate that upon neonatal immunization with (A/J × BALB/c)F(1) spleen cells, BALB/c mice expand a population of CD8(+) T cells expressing both CD25 and forkhead box P3 (FoxP3) markers. In this setting, CD8(+) CD25(+) T cells predominantly produce interferon (IFN)-γ and interleukin (IL)-10 and are efficient in controlling IL-4, IL-5 and IL-13 production by donor-specific CD4(+) T cells in vitro. CD8(+) FoxP3(-) T cells are single producers of IFN-γ or IL-10, whereas CD8(+) FoxP3(+) T cells are double producers of IFN-γ and IL-10. We further demonstrate that IFN-γ and IL-10 are two major cytokines produced by CD8(+) T cells involved in the in vivo regulation of Th2-type pathology. In this setting, we conclude that neonatal alloimmunization induces the expansion of several regulatory CD8(+) T cells which may control Th2 activities via IFN-γ and IL-10.     

Frontline: An in-depth evaluation of the production of IL-2 by antigen-specific CD8 T cells in vivo

IL-2 is an important cytokine that is capable of inducing both proliferation and apoptosis of activated T cells. CD4 T cells are thought to be the major producers of IL-2, but CD8 T cells also produce copious amounts of this cytokine. However, our current understanding regarding the kinetics of IL-2 production by antigen-specific CD8 T cells, and the proportion of these cells that produce IL-2 in vivo, is extremely limited. We now demonstrate that virus-specific CD8 T cells initiate IL-2 production by 6 h post-infection and prior to cell division in vivo. Interestingly, peak levels of IL-2 production were achieved very early during the response and prior to the proliferative peak. We also show -- using transgenic mice expressing herpes simplex virus-1 thymidine kinase under the control of the IL-2 promoter -- that, unlike what has been reported for antigen-specific CD4 T cells, the majority of antigen-specific CD8 T cells produce IL-2 during primary as well as secondary immune responses in vivo.