Differential expression of the cytokine receptors for human interleukin (IL)-12 and IL-18 on lymphocytes of both CD45RA and CD45RO phenotype from tonsils, cord and adult peripheral blood

Defining CD4 T cell memory by the epigenetic landscape of CpG DNA methylation

Memory T cells are primed for rapid responses to Ag; however, the molecular mechanisms responsible for priming remain incompletely defined. CpG methylation in promoters is an epigenetic modification, which regulates gene transcription. Using targeted bisulfite sequencing, we examined methylation of 2100 genes (56,000 CpGs) mapped by deep sequencing of T cell activation in human naive and memory CD4 T cells. Four hundred sixty-six CpGs (132 genes) displayed differential methylation between naive and memory cells. Twenty-one genes exhibited both differential methylation and gene expression before activation, linking promoter DNA methylation states to gene regulation; 6 of 21 genes encode proteins closely studied in T cells, whereas 15 genes represent novel targets for further study. Eighty-four genes demonstrated differential methylation between memory and naive cells that correlated to differential gene expression following activation, of which 39 exhibited reduced methylation in memory cells coupled with increased gene expression upon activation compared with naive cells. These reveal a class of primed genes more rapidly expressed in memory compared with naive cells and putatively regulated by DNA methylation. These findings define a DNA methylation signature unique to memory CD4 T cells that correlates with activation-induced gene expression.

BTLA exhibits immune memory for αβ T cells in patients with active pulmonary tuberculosis

Despite past extensive studies, the role of B and T lymphocyte attenuator (BTLA) in αβ T cells in patients with active pulmonary tuberculosis (ATB) remains poorly understood. Here we demonstrate that BTLA expression on αβ T cells is decreased in patients with M. tuberculosis (Mtb) infection. Particularly, BTLA expression levels are likely critical for αβ T cells to manifest and maintain an active central memory phenotype with high capacity for secretion of IFN-γ and perforin, which are important for immune memory against TB infection. BTLA(high) αβ T cells also exhibited higher capacity in response to Mtb peptide stimulation. In contrast to the role of BTLA played for negative regulation of immune responses, our data in the current studies suggest that BTLA expression on αβ T cells is likely associated with protective immune memory against Mtb infection in the setting of patients with active pulmonary tuberculosis. This previous unappreciated role for BTLA may have implications for prevention and treatment of patients with Mtb infection.

Enveloped virus but not bacteria block IL-13 responses in human cord blood T cells in vitro

Infections that occur early in life may have a beneficial effect on the immune system and thereby reduce the risk of allergen sensitization and/or allergic disease. It is not yet clear to what extent specific virus and/or bacteria can mediate this effect. The purpose of this study was to assess the role of virus and bacteria in CD4⁺ T cell‐derived cytokine production in newborns. We compared the effects of five bacteria (Staphlococcus aureus, Escherichia coli, Clostridium difficile, Lactobacillus rhamnosus and Bifidobacterium bifidus) and seven virus (adenovirus, coronavirus, cytomegalovirus, herpes simplex virus, influenza virus, morbillivirus and poliovirus) on the Th1/Th2 cytokine production in mixed lymphocyte reactions using CD4⁺ T cells from cord blood cocultured with allogenic myeloid or plasmacytoid dendritic cells. When comparing the baseline cytokine production prior to microbial stimulation, we observed that cord plasmacytoid DC were stronger inducers of Th2 cytokines (IL‐5 and IL‐13) compared with cord myeloid DC and to adult DC. When adding microbes to these cultures, bacteria and virus differed in two major respects; Firstly, all enveloped viruses, but none of the bacteria, blocked Th2 (IL‐13) production by cord CD4⁺ cells. Secondly, all Gram‐positive bacteria, but none of the virus, induced IL‐12p40 responses, but the IL‐12p40 responses did not affect Th1 cytokine production (IFN‐γ). Instead, Th1 responses were correlated with the capacity to induce IFN‐α secretion, which in cord cells were induced by S. aureus and influenza virus alone. These data imply that enveloped virus can deviate Th2 responses in human cord T cells.

Antigen-independent IFN-γ production by human naïve CD4 T cells activated by IL-12 plus IL-18

The role of T cells in innate immunity is not well defined. In this report, we show that a subset of human peripheral blood CD4⁺ T cells responds to IL-12 plus IL-18, but not to IL-12 or IL-18 alone, by producing IFN-γ in the absence of any antigenic stimulation or cell proliferation. Intracellular staining reveals a small percentage of resting CD4⁺ T cells (0.5 to 1.5%) capable of producing IFN-γ in response to IL-12 plus IL-18. Interestingly, both naïve (CD45RA⁺) and memory (CD45RO⁺) CD4⁺ populations were responsive to IL-12 plus IL-18 stimulation in producing IFN-γ. The expression of IFN-γinduced by IL-12 and IL-18 is sensitive to rapamycin and SB203580, indicating the possible involvement of mTOR and p38 MAP kinase, respectively, in this synergistic pathway. While p38MAP kinase is involved in transcription, mTOR is involved in message stabilization. We have also shown that NFκB family member, cRel, but not GADD45β and GADD45γ, plays an important role in IL-12 plus IL-18-induced IFN-γ transcription. Thus, the present study suggests that naïve CD4⁺ T cells may participate in innate immunity or amplify adaptive immune responses through cytokine-induced antigen-independent cytokine production.

Bystander T cells in human immune responses to dengue antigens

BACKGROUND

Previous studies of T cell activation in dengue infection have focused on restriction of specific T cell receptors (TCRs) and classical MHC molecules. However, bystander T cell activation, which is TCR independent, occurs via cytokines in other viral infections, both in vitro and in vivo, and enables T cells to bypass certain control checkpoints. Moreover, clinical and pathological evidence has pointed to cytokines as the mediators of dengue disease severity. Therefore, we investigated bystander T cell induction by dengue viral antigen.

RESULTS

Whole blood samples from 55 Thai schoolchildren aged 13-14 years were assayed for in vitro interferon-gamma (IFN-γ) induction in response to inactivated dengue serotype 2 antigen (Den2). The contribution of TCR-dependent and independent pathways was tested by treatment with cyclosporin A (CsA), which inhibits TCR-dependent activation of T cells. ELISA results revealed that approximately 72% of IFN-γ production occurred via the TCR-dependent pathway. The major IFN-γ sources were natural killer (NK) (mean ± SE = 55.2 ± 3.3), CD4+T (24.5 ± 3.3) and CD8+T cells (17.9 ± 1.5), respectively, as demonstrated by four-color flow cytometry. Interestingly, in addition to these cells, we found CsA-resistant IFN-γ producing T cells (CD4+T = 26.9 ± 3.6% and CD8+T = 20.3 ± 2.1%) implying the existence of activated bystander T cells in response to dengue antigen in vitro. These bystander CD4+ and CD8+T cells had similar kinetics to NK cells, appeared after 12 h and were inhibited by anti-IL-12 neutralization indicating cytokine involvement.

CONCLUSIONS

This study described immune cell profiles and highlighted bystander T cell activation in response to dengue viral antigens of healthy people in an endemic area. Further studies on bystander T cell activation in dengue viral infection may reveal the immune mechanisms that protect or enhance pathogenesis of secondary dengue infection.

Cytokine-induced human IFN-gamma-secreting effector-memory Th cells in chronic autoimmune inflammation

T-helper (Th) cells activated by cytokines in the absence of T-cell receptor ligation are suspected to participate in inflammatory processes by production of interferon-gamma (IFN-gamma). Still, the relevance of such a mechanism has not been addressed in humans. Here we demonstrate that a subset of human effector-memory Th cells expressing functional interleukin-12R (IL-12R), IL-18Ralpha, and CCR5 ex vivo can be induced to secrete IFN-gamma by cytokines signaling via the IL-2R common gamma-chain in combination with IL-12 and IL-18. Cytokine-driven IFN-gamma production depends on JAK3- and p38 mitogen-activated kinase signals and is sensitive to suppression by CD25(++) regulatory T cells. Contrary to IFN-gamma(+) Th cells induced upon antigen-specific stimulation, their cytokine-activated counterparts characteristically lack expression of costimulator 4-1BB (CD137). Strikingly, the majority of Th cells infiltrating inflamed joints of rheumatoid arthritis patients is equipped with receptors prerequisite for cytokine-induced IFN-gamma secretion. Among these cells, we detected a substantial fraction that secretes IFN-gamma directly ex vivo but lacks 4-1BB expression, indicating that cytokine-induced IFN-gamma(+) Th cells operate in autoimmune inflammation. Our data provide a rationale for how human effector-memory Thcells can participate in perpetuating inflammatory processes in autoimmunity even in the absence of T-cell receptor ligation.

Macrophage and T-cell gene expression in a model of early infection with the protozoan Leishmania chagasi

Visceral leishmaniasis is a potentially fatal infectious disease caused by the protozoan parasite Leishmania infantum/chagasi in the New World, or by L. donovani or L. infantum/chagasi in the Old World. Infection leads to a variety of outcomes ranging from asymptomatic infection to active disease, characterized by fevers, cachexia, hepatosplenomegaly and suppressed immune responses. We reasoned that events occurring during the initial few hours when the parasite encounters cells of the innate and adaptive immune systems are likely to influence the eventual immune response that develops. Therefore, we performed gene expression analysis using Affymetrix U133Plus2 microarray chips to investigate a model of early infection with human monocyte-derived macrophages (MDMs) challenged with wild-type L. chagasi parasites, with or without subsequent co-culture with Leishmania-naïve, autologous T-cells. Microarray data generated from total RNA were analyzed with software from the Bioconductor Project and functional clustering and pathway analysis were performed with DAVID and Gene Set Enrichment Analysis (GSEA), respectively. Many transcripts were down-regulated by infection in cultures containing macrophages alone, and the pattern indicated a lack of a classically activated phenotype. By contrast, the addition of autologous Leishmania-naïve T cells to infected macrophages resulted in a pattern of gene expression including many markers of type 1 immune cytokine activation (IFN-γ, IL-6, IL-1α, IL-1β). There was simultaneous up-regulation of a few markers of immune modulation (IL-10 cytokine accumulation; TGF-β Signaling Pathway). We suggest that the initial encounter between L. chagasi and cells of the innate and adaptive immune system stimulates primarily type 1 immune cytokine responses, despite a lack of classical macrophage activation. This local microenvironment at the site of parasite inoculation may determine the initial course of immune T-cell development.

Visceral leishmaniasis (VL) is a potentially fatal vector-borne infectious disease that leads to a variety of outcomes ranging from asymptomatic infection to symptomatic disease. In northeast Brazil, the etiological agent of VL is the protozoan Leishmania chagasi/infantum. Active VL is characterized by fevers, weight loss, hepatosplenomegaly and eventually immune suppression. Without treatment, most symptomatic patients die from secondary bacterial or viral super-infection. We hypothesized that a unique immune response to L. chagasi is initiated early during the initial interactions between the immune system cells that first encounter the parasite. These include macrophages and T-cells, elements of the innate and adaptive immune systems, respectively. We studied an in vitro model of these interactions in which human monocyte-derived macrophages were challenged with L. chagasi, and subsequently cultured with Leishmania-naïve, autologous T cells. Using microarray chips, we examined changes in global gene expression induced by these early interactions. Infection did not elicit a classical inflammatory program in macrophages. However, co-culture of infected macrophages and autologous T cells exhibited a pattern of gene expression, including many markers of acute inflammation or a type 1 immune response. These data suggest that early changes at the site of parasite infection would be conducive to the development of a protective type 1 response, followed by modulation of this same response.

Initial steroid bolus injection promotes vigorous CD8+ alloreactive responses toward early graft acceptance immediately after liver transplantation in humans

We have found that steroid bolus withdrawal prior to graft reperfusion increased the incidence of acute cellular rejection (ACR). This study aims to clarify how initial steroid bolus (ISB) injection at reperfusion influences the kinetics of CD8(+) alloreactive immune responses immediately after living donor liver transplantation (LDLT). A total of 49 hepatitis C virus (HCV)-infected recipients were classified into 3 groups according to hierarchical clustering by preoperative CD8(+)CD45 isoforms. The naive T cell proportion was considerably higher in Group I than in Groups II and III, whereas Group II recipients had the highest effector memory (EM) T cells and Group III the highest effector T cells. The frequency of ACR was significantly higher in recipients without ISB than in those with ISB. In particular, the ACR rates were the highest in Group II without ISB. Following ISB, the proportion of effector T cells was promptly upregulated within 6 hours after graft reperfusion, simultaneously with the upregulation of CD27(-)CD28(-) subsets, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha and perforin expression, which significantly correlated with increasing interleukin (IL)-12 receptor beta 1 cells. These were then downregulated to below preoperative levels by tacrolimus (Tac) administered at 24 hours. These changes did not occur in the absence of ISB. In Group II without ISB, the downregulation of IL-12Rbeta1(+) cells was the greatest, consistent with the highest rates of ACR and mortality (60%). In conclusion, ISB must be done in place, especially in Group II with preexisting high EM T cells, to enable the development of early allograft acceptance.

Profound enhancement of the IL-12/IL-18 pathway of IFN-gamma secretion in human CD8+ memory T cell subsets via IL-15

Human memory CD8(+) T cell subsets, termed central memory and effector memory T cells, can be identified by expression of CD45RA, CD62 ligand (CD62L), and CCR7. Accordingly, functional differences have been described for each subset, reflecting unique roles in immunological memory. The common gamma-chain cytokines IL-15 and IL-7 have been shown to induce proliferation and differentiation of human CD8(+) T cell subsets, as well as increased effector functions (i.e., cytokines, cytotoxicity). In this study, we observed that addition of IL-15 or IL-7 to cultures of human CD8(+) T cells profoundly enhanced the IL-12-IL-18 pathway of IFN-gamma production. Importantly, IL-15 and IL-7 lowered the threshold concentrations of IL-12 and IL-18 required for induction of IFN-gamma by 100-fold. Comparison of IL-15 and IL-7 demonstrated that IL-15 was superior in its ability to enhance IL-12-IL-18-induced IFN-gamma, without evidence of a synergistic effect between IL-15 and IL-7. We also observed that IL-15- and IL-7-mediated enhancement of IL-12-IL-18-induced IFN-gamma production was a functional property of effector memory CD8(+) T cells. Despite a lack of association between cell division and acquisition of IL-12-IL-18-induced IFN-gamma, down-regulation of CD62L expression correlated well with increased IL-12-IL-18-induced IFN-gamma. Purified central memory T cells stimulated with IL-15 and IL-7 down-regulated CD62L and acquired potent IL-12-IL-18-induced IFN-gamma similar to effector memory T cells. Thus, in addition to its known role in development of T cell memory, IL-15 may amplify memory CD8(+) T cell effector functions by increasing sensitivity to proinflammatory cytokine stimulation.

Primary alloproliferative TH1 response induced by immature plasmacytoid dendritic cells in collaboration with myeloid DCs

The role played by dendritic cell (DC) subsets in the immune response to alloantigens is not well defined. In vitro experiments have extensively shown that freshly isolated myeloid (M)DCs induce a strong T lymphocyte proliferation whereas plasmacytoid (P)DCs do not, unless activated by CD40 ligation. The aim of these studies was to explore whether the interplay among PDCs, MDCs and T cells modulates alloresponse. Freshly isolated MDCs and PDCs were merged in different proportions and used as antigen presenting cells (APCs) in mixed lymphocyte cultures (MLC). As described, isolated PDCs only induced a mild alloresponse, while MDCs were potent inducers of alloproliferation. Unexpectedly, when PDCs were merged with even low numbers of MDCs (down to 100 cells) and used as APCs, a potent Th1 cell proliferation was detected. Survival and maturation of PDCs was increased in these MLC conditions, which could partially explain the magnitude of the T-cell response. Interestingly, the proportion of IFNgamma-producing cells generated in such cultures was higher compared to MDC-stimulated cultures. These data suggest that the interaction between both DC subsets is determinant to generate a potent Th1 response, at least in an allogeneic situation, and may be relevant to the outcome of allogeneic stem cell transplantation.