Role of monocytes in the up-regulation of the early activation marker CD69 on B and T murine lymphocytes induced by microbial mitogens

Mild Cognitive Impairment Is Associated with Enhanced Activation of Th17 Lymphocytes in Non-Alcoholic Fatty Liver Disease

Patients with nonalcoholic fatty liver disease (NAFLD) may show mild cognitive impairment (MCI). The mechanisms involved remain unclear. The plasma concentrations of several cytokines and chemokines were measured in 71 NAFLD patients (20 with and 51 without MCI) and 61 controls. Characterization and activation of leukocyte populations and CD4⁺ sub-populations were carried out and analyzed by flow cytometry. We analyzed the cytokines released from CD4⁺ cell cultures and the mRNA expression of transcription factors and receptors in peripheral blood mononuclear cells. The appearance of MCI in NAFLD patients was associated with increased activation of CD4⁺ T lymphocytes, mainly of the Th17 subtype, increased plasma levels of pro-inflammatory and anti-inflammatory cytokines such as IL-17A, IL-23, IL-21, IL-22, IL-6, INF-γ, and IL-13, and higher expression of the CCR2 receptor. Constitutive expression of IL-17 was found in cultures of CD4⁺ cells from MCI patients, reflecting Th17 activation. High IL-13 plasma levels were predictive of MCI and could reflect a compensatory anti-inflammatory response to the increased expression of pro-inflammatory cytokines. This study identified some specific alterations of the immune system associated with the appearance of neurological alterations in MCI patients with NAFLD that could be the basis to improve and restore cognitive functions and quality of life in these patients.

Oxidative burst and Dectin-1-triggered phagocytosis affected by norepinephrine and endocannabinoids: implications for fungal clearance under stress

A prolonged stress burden is known to hamper the efficiency of both the innate and the adaptive immune systems and to attenuate the stress responses by the catecholaminergic and endocannabinoid (EC) systems. Key mechanisms of innate immunity are the eradication of pathogens through phagocytosis and the respiratory burst. We tested the concentration-dependent, spontaneous and stimulated (via TNFα and N-formylmethionine-leucyl-phenylalanine) release of reactive oxygen species (ROS) by human polymorphonuclear leukocytes (PMNs) in vitro in response to norepinephrine (NE) and AM1241, a pharmacological ligand for the EC receptor CB2. We evaluated phagocytosis of Dectin-1 ligating zymosan particles and tested the cytokine response against Candida antigen in an in vitro cytokine release assay. Increasing concentrations of NE did not affect phagocytosis, yet stimulated ROS release was attenuated gradually reaching maximum suppression at 500 nM. Adrenergic receptor (AR) mechanisms using non-AR-selective (labetalol) as well as specific α-(prazosin) and β-(propranolol) receptor antagonists were tested. Results show that only labetalol and propranolol were able to recuperate cytotoxicity in the presence of NE, evidencing a β-receptor-mediated effect. The CB2 agonist, AM1241, inhibited phagocytosis at 10 µM and spontaneous peroxide release by PMNs. Use of the inverse CB2 receptor agonist SR144528 led to partial recuperation of ROS production, confirming the functional role of CB2. Additionally, AM1241 delayed early activation of monocytes and induced suppression of IL-2 and IL-6 levels in response to Candida via lower activity of mammalian target of rapamycin (mTOR). These findings provide new insights into key mechanisms of innate immunity under stressful conditions where ligands to the sympatho-adrenergic and EC system are released.

Minimal hepatic encephalopathy is associated with expansion and activation of CD4+CD28-, Th22 and Tfh and B lymphocytes

Peripheral inflammation acts synergistically with hyperammonemia in inducing neurological alterations in cirrhotic patients with minimal hepatic encephalopathy (MHE). We hypothesized that appearance of MHE would be associated to some specific qualitative change in peripheral inflammation. The aim of this work was to characterize the changes in peripheral inflammation associated to appearance of MHE. We analyzed it by immunophenotyping and cytokine profile analysis, in cirrhotic patients without or with MHE and controls. The main alterations associated specifically with MHE are: 1) increased activation of all subtypes of CD4⁺ T-lymphocytes, with the increased expression of CD69; 2) increased amount of CD4⁺CD28⁻ T lymphocytes, associated with increased levels of CX3CL1 and of IL-15; 3) increased differentiation of CD4⁺ T lymphocytes to Th follicular and Th22; 4) increased activation of B lymphocytes and serum IgG. This study has identified some specific alterations of the immune system associated with appearance of the neurological alterations in MHE patients.

Full activation of CD4+ T cells early during sepsis requires specific antigen

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During sepsis, CD4⁺ T cells express activation markers within the first 24 h. In the present study, the mechanisms of T-cell activation and its consequences were addressed in an acute peritonitis model in mice. The response of CD4⁺ T cells to sepsis induction was compared between OTII mice, characterized by ovalbumin-specific T-cell receptor–transgenic T cells, and C57BL/6 controls (wild type [WT] mice). Because ovalbumin was absent during peritonitis, the OTII CD4⁺ T cells could not be activated by canonical antigen recognition. In both OTII and WT control mice, CD4⁺ T effector cells and CD4⁺ Foxp3⁺ regulatory T cells (Tregs) expressed the activation marker CD69 early after sepsis onset. However, full activation with upregulation of CD25 and proliferation took place only in the presence of the antigen. Besides this, the fraction of Tregs was lower in OTII than that in WT mice. Sepsis mortality was increased in OTII mice. Our data show that, in sepsis, partial activation of CD4⁺ T cells is induced by a T-cell receptor–independent pathway, whereas full stimulation and proliferation require a specific antigen. Antigen-dependent T-cell effector functions as well as Treg activity may contribute to sepsis survival.

Soluble β-1,3/1,6-glucan in seaweed from the southern hemisphere and its immunomodulatory effect

Five types of macroalgae from the southern hemisphere were analysed for the presence of β-1,3/1,6-glucan and its immunostimulant properties. We were able to extract soluble β-1,3/1,6-D-glucan from Durvillaea antarctica (Chamisso) Hariot (DA). The morphology of the brown algae influenced extraction, and the highest percentage of β-glucan was found in the fronds. The content of β-glucan in the stipes and holdfast was on average 33% and <5%, respectively, of that in the fronds. A simple laboratory extraction process was developed. A highly pure water-soluble polysaccharide, mainly composed of glucose residues, was obtained with a dominant average molecular weight of 6.9 kDa. NMR spectroscopy confirmed the polysaccharide structure to be of β-1,3/1,6-glucan type, comprising a β-1,3-glucan backbone and 21% degree of branching of β-1,6-glucan side chains. Mouse cells were exposed to four DA extract concentrations in water (50, 100, 250 and 500 μg/mL) and no adverse effects on survival were noted. Remarkably, the β-glucan induced a 16.9% increase in activated CD19+ B lymphocytes compared with the control sample. The optimal concentration for maximum activity was 100 μg DA extract/mL.

The presence of CD8+ invariant NKT cells in mice

Invariant natural killer T (iNKT) cells develop in the thymus upon recognition of CD1d expressed on developing thymocytes. Although CD4 and CD8 coreceptors are not directly involved in the interaction between CD1d and the T cell receptors (TCRs) of iNKT cells, a conspicuous lack of CD8(+) iNKT cells in mice raised the question of whether CD8(+) iNKT cells are excluded due to negative selection during their thymic development, or if there is no lineage commitment for the development of murine CD8(+) iNKT cells. To address this question, we analyzed iNKT cell-specific TCR V alpha 14(+) transgenic mice, where the V alpha 14 transgene forces the generation of iNKT cells. This allows detailed study of the iNKT cell repertoire. We were able to identify CD8(+) iNKT cells which respond to the NKT cell-specific glycolipid ligand alpha-galactosylceramide. Unlike conventional iNKT cells, CD8(+) iNKT cells produce predominantly IFN-gamma but not IL-4 upon antigen stimulation. We also confirmed the presence of CD8(+) iNKT cells in wild type mice. Our results suggest that CD8(+) NKT cells do exist in mice, although their population size is quite small. Their Th1-skewed phenotype might explain why the population size of this subtype needs to be controlled tightly.

Chronic mouse model of TMA-induced contact hypersensitivity

Due to the steadily increasing incidence of atopic dermatitis (AD), especially in children, there is a high medical need for new therapies and improved animal models. In mice, trimellitic anhydride (TMA) is routinely used to trigger T-cell-dependent contact hypersensitivity (CHS) reactions. In this study, we compared the standard acute TMA-induced CHS in Balb/c mice with subacute and chronic models of TMA-induced ear inflammation. Compared to the acute model, the chronic CHS model more closely reflects characteristics of AD, such as typical morphological changes of the inflamed skin, strong infiltration with T cells, major histocompatibility complex II-positive cells, eosinophils, and mast cells, a T-helper cell-type (Th) 2 cytokine profile and a strong increase of serum IgE levels. Moreover, a strong lymph node involvement with T-helper cell dominance and a mixed Th1/Th2 T-cell differentiation and activation pattern was demonstrated. Importantly, as demonstrated by successful therapy with prednisolone, the chronic TMA-induced CHS model, in contrast to acute and subacute models, made prolonged therapeutic treatment of a pre-established skin inflammation possible. Altogether, we present an improved model of mouse T-cell-dependent skin inflammation for AD. We hope this model will enhance the predictive value of animal models for therapeutic treatment of atopic eczema.

Acute depletion and recovery of peritoneal B-1 lymphocytes in BALB/c mice after a single injection of mercury chloride

The acute toxicity of mercury (Hg) to B cells was studied in the peritoneal cavity of BALB/c mice, a coelomic space where both B-1 and B-2 subsets of B lymphocytes are present. Up to 24 hr after a single in situ Hg injection, the peritoneal cavity became virtually devoid of lymphocytes, particularly of the B-1 subset. Lymphocyte depletion was more severe for B than T cells. This depletion was associated with partial lymphocyte activation (CD69(+)) at 6 hr of treatment and it was due to apoptosis rather than to necrosis. Partial recovery of both B and T cells was observed in the peritoneal cavity 48 hr after the Hg injection. The phenomenon was followed by a second decrease in peritoneal lymphocytes 72 hr after Hg. Neutrophils that entered the peritoneal cavity because of the Hg injection were resistant to apoptosis. No significant changes in lymphocyte number or subpopulation were found in the spleen and thymus of the mice up to 72 hr after the Hg treatment. We concluded that B lymphocytes were severely affected by the toxic effects of Hg. Our data suggest that Hg-induced unbalance in the repertoire of B cells, of the B-1 subset in particular, may result later in the secretion of the high titres of pathogenic autoantibodies that are found in the Hg-induced lupus disorder of BALB/c mice.

Neisserial outer membrane vesicles bind the coinhibitory receptor carcinoembryonic antigen-related cellular adhesion molecule 1 and suppress CD4+ T lymphocyte function

Pathogenic Neisseria bacteria naturally liberate outer membrane "blebs," which are presumed to contribute to pathology, and the detergent-extracted outer membrane vesicles (OMVs) from Neisseria meningitidis are currently employed as meningococcal vaccines in humans. While the composition of these vesicles reflects the bacteria from which they are derived, the functions of many of their constituent proteins remain unexplored. The neisserial colony opacity-associated Opa proteins function as adhesins, the majority of which mediate bacterial attachment to human carcinoembryonic antigen-related cellular adhesion molecules (CEACAMs). Herein, we demonstrate that the Opa proteins within OMV preparations retain the capacity to bind the immunoreceptor tyrosine-based inhibitory motif-containing coinhibitory receptor CEACAM1. When CD4(+) T lymphocytes were exposed to OMVs from Opa-expressing bacteria, their activation and proliferation in response to a variety of stimuli were effectively halted. This potent immunosuppressive effect suggests that localized infection will generate a "zone of inhibition" resulting from the diffusion of membrane blebs into the surrounding tissues. Moreover, it demonstrates that OMV-based vaccines must be developed from strains that lack CEACAM1-binding Opa variants.

Toll-like receptor 4 (TLR4)-dependent proinflammatory and immunomodulatory properties of the glycoinositolphospholipid (GIPL) from Trypanosoma cruzi

We have demonstrated recently that the glycoinositolphospholipid (GIPL) molecule from the protozoan Trypanosoma cruzi is a TLR4 agonist with proinflammatory effects. Here, we show that GIPL-induced neutrophil recruitment into the peritoneal cavity is mediated by at least two pathways: one, where IL-1beta acts downstream of TNF-alpha, and a second, which is IL-1beta- and TNFRI-independent. Moreover, NKT cells participate in this proinflammatory cascade, as in GIPL-treated CD1d(-/-) mice, TNF-alpha and MIP-2 levels are reduced significantly. As a consequence of this inflammatory response, spleen and lymph nodes of GIPL-treated mice have an increase in the percentage of T and B cells expressing the CD69 activation marker. Cell-transfer experiments demonstrate that T and B cell activation by GIPL is an indirect effect, which relies on the expression of TLR4 by other cell types. Moreover, although signaling through TNFRI contributes to the activation of B and gammadelta+ T cells, it is not required for increasing CD69 expression on alphabeta+ T lymphocytes. It is interesting that T cells are also functionally affected by GIPL treatment, as spleen cells from GIPL-injected mice show enhanced production of IL-4 following in vitro stimulation by anti-CD3. Together, these results contribute to the understanding of the inflammatory properties of the GIPL molecule, pointing to its potential role as a parasite-derived modulator of the immune response during T. cruzi infection.

Human immunodeficiency virus-like particles activate multiple types of immune cells

The rapid spread of human immunodeficiency virus (HIV) worldwide makes it a high priority to develop an effective vaccine. Since live attenuated or inactivated HIV is not likely to be approved as a vaccine due to safety concerns, HIV virus like particles (VLPs) offer an attractive alternative because they are safe due to the lack of a viral genome. Although HIV VLPs have been shown to induce humoral and cellular immune responses, it is important to understand the mechanisms by which they induce such responses and to improve their immunogenicity. We generated HIV VLPs, and VLPs containing Flt3 ligand (FL), a dendritic cell growth factor, to target VLPs to dendritic cells, and investigated the roles of these VLPs in the initiation of adaptive immune responses in vitro and in vivo. We found that HIV-1 VLPs induced maturation of dendritic cells and monocyte/macrophage populations in vitro and in vivo, with enhanced expression of maturation markers and cytokines. Dendritic cells pulsed with VLPs induced activation of splenocytes resulting in increased production of cytokines. VLPs containing FL were found to increase dendritic cells and monocyte/macrophage populations in the spleen when administered to mice. Administration of VLPs induced acute activation of multiple types of cells including T and B cells as indicated by enhanced expression of the early activation marker CD69 and down-regulation of the homing receptor CD62L. VLPs containing FL were an effective form of antigen in activating immune cells via dendritic cells, and immunization with HIV VLPs containing FL resulted in enhanced T helper type 2-like immune responses.

Characterization of the B-cell immune response elicited in BALB/c mice challenged with Neospora caninum tachyzoites

Activation of B cells occurring in hosts infected with protozoan parasites has been implicated either in protective or parasite-evasion immune-mediated mechanisms. Intraperitoneal inoculation of Neospora caninum tachyzoites into BALB/c mice induces an acute response characterized by a rapid increase in the numbers of CD69-expressing peritoneal and splenic B cells. This early B-cell stimulatory effect preceded an increase in the numbers of total and immunoglobulin-secreting splenic B cells and a rise in serum levels of N. caninum-specific immunoglobulins, predominantly of the immunoglobulin G2a (IgG2a) and IgM isotypes. Increased numbers of B cells expressing the costimulatory molecules CD80 and CD86 were also observed in the N. caninum-infected mice. The B-cell stimulatory effect observed in mice challenged with N. caninum tachyzoites was reduced in mice challenged with gamma-irradiated parasites. Contrasting with the peripheral B-cell expansion, a depletion of B-lineage cells was observed in the bone-marrow of the N. caninum-infected mice. Intradermal immunization of BALB/c mice with diverse N. caninum antigenic preparations although inducing the production of parasite-specific antibodies nevertheless impaired interferon-gamma (IFN-gamma) mRNA expression and caused lethal susceptibility to infection in mice inoculated with a non-lethal parasitic inoculum. This increased susceptibility to N. caninum was not observed in naïve mice passively transferred with anti-N. caninum antibodies. Taken together, these results show that N. caninum induces in BALB/c mice a parasite-specific, non-polyclonal, B-cell response, reinforce previous observations made by others showing that immunization with N. caninum whole structural antigens increases susceptibility to murine neosporosis and further stress the role of IFN-gamma in the host protective immune mechanisms against this parasite.

Expression and function of Toll-like receptor on T cells

Toll is the founder of a group of pattern recognition receptors, which play a critical role in the innate immunity in Drosophila. At least 13 distinct Toll-like receptors (TLRs), recognising pathogen-associated molecular pattern (PAMPs), have now been identified in humans. Most investigations on TLRs have focused on cells of the innate system. We report here that naïve human T cells expressed high levels of cell surface TLR2 after activation by anti-T cell receptor (TCR) antibody and interferon-alpha. Activated cells produced elevated levels of cytokines in response to the TLR2 ligand, bacterial lipopeptide (BLP). Furthermore, CD4(+)CD45RO(+) memory T cells from peripheral blood constitutively expressed TLR2 and produced IFNgamma in response to BLP. BLP also markedly enhanced the proliferation and IFNgamma production by CD45RO(+) T cells in the presence of IL-2 or IL-15. Thus, TLR2 serves as a co-stimulatory receptor for antigen-specific T cell development and participates in the maintenance of T cell memory. This suggests that pathogens, via their PAMPs, may contribute directly to the perpetuation and activation of long term T cell memory in both antigen dependent and independent manner.

Protection against systemic candidiasis in mice immunized with secreted aspartic proteinase 2

Secreted aspartic proteinases (Sap) have been described as virulence factors implicated in the mechanisms of host colonization by the yeast Candida albicans in different types of candidiasis. Intraperitoneal inoculation of C. albicans into BALB/c mice rapidly leads to systemic candidiasis, with significant colonization of the kidneys measurable in the following week. In this study we assessed the potential of vaccination with C. albicans secreted aspartic proteinase 2 (Sap2) in preventing systemic candidiasis in BALB/c mice. Intradermal injection of highly purified native Sap2 protein incorporated in alum adjuvant provided efficient immune protection, as indicated by a 20-fold decrease in the colonization of kidneys. The protective effect of Sap2 immunization with alum adjuvant was also observed in mice infected with a lethal inoculum of C. albicans. Immunization with the native Sap2 alone, as well as with a denatured recombinant form of the protein, also conferred protection, albeit to a lesser level. In all cases, protection correlated with an increase in serum antibodies to Sap2. Moreover, passive transfer of anti-Sap2 immunoglobulin G (IgG) significantly decreased the yeast burden in kidneys of C. albicans-infected mice. This result shows that immune protection against systemic candidiasis in mice immunized with Sap2 is antibody-mediated. Taken together, these analyses demonstrate that Sap2 can be successfully used as a vaccination target in systemic candidiasis and reveals the potential immunomodulatory role of Sap2 on C. albicans infection.

TLR2 is expressed on activated T cells as a costimulatory receptor

Toll is the founder of a group of pattern recognition receptors that play a critical role in the innate immunity in Drosophila. At least 10 distinct Toll-like receptors (TLRs), recognizing pathogen-associated molecular patterns, have now been identified in humans. Most investigations on TLRs have focused on cells of the innate system. We report here that naïve human T cells expressed high levels of cell-surface TLR2 after activation by anti-T cell receptor antibody and IFN-alpha. Activated cells produced elevated levels of cytokines in response to the TLR2 ligand, bacterial lipopeptide. Furthermore, CD4(+)CD45RO(+) memory T cells from peripheral blood constitutively expressed TLR2 and produced IFN-gamma in response to bacterial lipopeptide, which also markedly enhanced the proliferation and IFN-gamma production by CD45RO(+) T cells in the presence of IL-2 or IL-15. Thus, TLR2 serves as a costimulatory receptor for antigen-specific T cell development and participates in the maintenance of T cell memory. This suggests that pathogens, via their pathogen-associated molecular patterns, may contribute directly to the perpetuation and activation of long-term T cell memory in both antigen-dependent and independent manner.

Regulatory T cells selectively express toll-like receptors and are activated by lipopolysaccharide

Regulatory CD4 T cells (Treg) control inflammatory reactions to commensal bacteria and opportunist pathogens. Activation of Treg functions during these processes might be mediated by host-derived proinflammatory molecules or directly by bacterial products. We tested the hypothesis that engagement of germline-encoded receptors expressed by Treg participate in the triggering of their function. We report that the subset of CD4 cells known to exert regulatory functions in vivo (CD45RB(low) CD25(+)) selectively express Toll-like receptors (TLR)-4, -5, -7, and -8. Exposure of CD4(+) CD25(+) cells to the TLR-4 ligand lipopolysaccharide (LPS) induces up-regulation of several activation markers and enhances their survival/proliferation. This proliferative response does not require antigen-presenting cells and is augmented by T cell receptor triggering and interleukin 2 stimulation. Most importantly, LPS treatment increases CD4(+) CD25(+) cell suppressor efficiency by 10-fold and reveals suppressive activity in the CD4(+) CD45RB(low) CD25(-) subset that when tested ex-vivo, scores negative. Moreover, LPS-activated Treg efficiently control naive CD4 T cell-dependent wasting disease. These findings provide the first evidence that Treg respond directly to proinflammatory bacterial products, a mechanism that likely contributes to the control of inflammatory responses.

Neisserial binding to CEACAM1 arrests the activation and proliferation of CD4+ T lymphocytes

Infection with Neisseria gonorrhoeae can trigger an intense inflammatory response, yet there is little specific immune response or development of immune memory. In addition, gonorrhea typically correlates with a transient reduction in T lymphocyte counts in blood, and these populations recover when gonococcal infection is resolved. Such observations suggest that the gonococci have a suppressive effect on the host immune response. We report here that N. gonorrhoeae Opa proteins were able to bind CEACAM1 expressed by primary CD4+ T lymphocytes and suppress their activation and proliferation. CEACAM1 bound by gonococcal Opa52 associated with the tyrosine phosphatases SHP-1 and SHP-2, which implicates the receptor's ITIM (immunoreceptor tyrosine-based inhibitory motif) in this effect.

Rudimentary TCR signaling triggers default IL-10 secretion by human Th1 cells

Understanding the process of inducing T cell activation has been hampered by the complex interactions between APC and inflammatory Th1 cells. To dissociate Ag-specific signaling through the TCR from costimulatory signaling, rTCR ligands (RTL) containing the alpha1 and beta1 domains of HLA-DR2b (DRA*0101:DRB1*1501) covalently linked with either the myelin basic protein peptide 85-99 (RTL303) or CABL-b3a2 (RTL311) peptides were constructed to provide a minimal ligand for peptide-specific TCRs. When incubated with peptide-specific Th1 cell clones in the absence of APC or costimulatory molecules, only the cognate RTL induced partial activation through the TCR. This partial activation included rapid TCR zeta-chain phosphorylation, calcium mobilization, and reduced extracellular signal-related kinase activity, as well as IL-10 production, but not proliferation or other obvious phenotypic changes. On restimulation with APC/peptide, the RTL-pretreated Th1 clones had reduced proliferation and secreted less IFN-gamma; IL-10 production persisted. These findings reveal for the first time the rudimentary signaling pattern delivered by initial engagement of the external TCR interface, which is further supplemented by coactivation molecules. Activation with RTLs provides a novel strategy for generating autoantigen-specific bystander suppression useful for treatment of complex autoimmune diseases.

Endotoxin and muramyl dipeptide modulate surface receptor expression on human mononuclear cells

Endotoxin (lipopolysaccharide (LPS), 100 ng/ml) and muramyl dipeptide (MDP 100 ng/ml), two immunomodulatory bacterial cell wall products, were incubated with human whole blood, and the expression of receptors involved in antigen presentation, costimulation, and cell activation was investigated by use of flow cytometry. On monocytes, LPS and MDP increased surface expression of human leukocyte antigen-DR (HLA-DR), CD18, CD54 (intercellular adhesion molecule-1, ICAM-1), and CD86 (B7-2). On lymphocytes, LPS but not MDP increased HLA-DR expression after 18 h. The expression of CD28, CD49d/CD29, and CD106 (vascular cell adhesion molecule-1, VCAM-1) remained unchanged on both monocytes and lymphocytes. The early increase (1-6 h) of CD18 and ICAM-1 expression led us to hypothesize that CD18-dependent costimulatory signals were involved in the later (6 h) increase of monocyte HLA-DR expression. However, blocking studies using monoclonal antibodies against CD18 (IB4, 15 microg/ml) demonstrated that the LPS- and MDP-induced increase of HLA-DR and ICAM-1 expression on monocytes was not mediated through CD18. LPS induced the expression of the early activation marker CD69 by a CD14-dependent but CD18-independent mechanism, whereas MDP did not induce CD69 expression. Analysis of leukocyte subsets demonstrated that CD4(+) T-cells, CD8(+) T-cell, CD19(+) B-cells, CD56(+) natural killer (NK)-cells, and CD14(+) monocytes increased the expression of CD69 after stimulation with LPS. Collectively, these data demonstrate a stronger immunomodulatory effect of LPS compared with MDP which may, in part, explain the established difference of toxicity between these two bacterial cell wall products.

Pegylated alpha interferon is an effective treatment for virulent venezuelan equine encephalitis virus and has profound effects on the host immune response to infection

Venezuelan equine encephalitis virus (VEEV) is a highly infectious alphavirus endemic in parts of Central and South America. The disease is transmitted by mosquitoes, and the natural reservoir is the small rodent population, with epidemics occurring in horses and occasionally humans. Following infection, VEEV replicates in lymphoid tissues prior to invasion of the central nervous system. Treatment of VEEV-infected BALB/c mice with polyethylene glycol-conjugated alpha interferon (PEG IFN-alpha) results in a greatly enhanced survival from either a subcutaneous or an aerosol infection. Virus is undetectable within PEG IFN-alpha-treated individuals by day 30 postinfection (p.i.). Treatment results in a number of changes to the immune response characteristics normally associated with VEEV infection. Increased macrophage activation occurs in PEG IFN-alpha-treated BALB/c mice infected with VEEV. The rapid activation of splenic CD4, CD8, and B cells by day 2 p.i. normally associated with VEEV infection is absent in PEG IFN-alpha-treated mice. The high tumor necrosis factor alpha production by macrophages from untreated mice is greatly diminished in PEG IFN-alpha-treated mice. These results suggest key immunological mechanisms targeted by this lethal alphavirus that can be modulated by prolonged exposure to IFN-alpha.

alpha-galactosylceramide induces early B-cell activation through IL-4 production by NKT cells

alpha-Galactosylceramide (alpha-GalCer), a glycolipid antigen, specifically activates natural killer T (NKT) cells by a CD1d-restricted mechanism. In this work, we found that in vivo administration of alpha-GalCer resulted in the activation of B cells in addition to NKT cells, namely, alpha-GalCer administration caused upregulation of the early activation marker, CD69, on both NKT and B cells. In addition, expression of B7.2 and I-A(b) on B cells was greatly upregulated by alpha-GalCer. However, serum levels of IgE, IgG1, and IgG2a were not significantly changed within 48 h. In the present experiments, it was also demonstrated that the upregulation of CD69 expression by alpha-GalCer was strongly blocked by anti-IL-4 monoclonal antibody. Moreover, B-cell activation by alpha-GalCer was not observed in NKT-deficient mice. These results suggested that antigen-stimulated NKT cells might play a critical role not only in early defense mechanisms but also in early B-cell activation through IL-4 production.

Human hematopoietic stem/progenitor cells generate CD5+ B lymphoid cells in NOD/SCID mice

The nonobese diabetic/severe combined immunodeficient (NOD/SCID) xenotransplantation model is increasingly utilized to study both human lymphohematopoietic stem/progenitor cells and committed cell types. Human B lymphoid cells develop and proliferate in this model. We found high numbers of CD19+CD5+ B lymphoid cells in the bone marrows and spleens of NOD/SCID mice transplanted with human CD34+ stem/progenitor cells. The CD5+ cells accounted for a particularly large percentage of the B lymphoid cells in the spleens of chimeras analyzed three months after transplantation. CD19+CD5+ cells from all the analyzed chimeras coexpressed HLA-DR, surface IgM, CD20, CD38, CD43, and CD45. However, CD19+CD5+ cells were negative for kappa light chain, CD10, CD11a, CD11b, CD15, CD21, CD22, CD23, CD25, CD34, CD35, CD44, CD62L, CD69, and CD71. Cell surface expression of the lambda light chain, surface IgD, CD9, and CD40 antigens was detected in some but not all chimeras. Thus, the CD19+CD5+ cell population detected in our study has the phenotype of previously described CD5+ B lymphoid cells in humans and other species. The origin and role of the B lymphoid cells which express CD5 cell surface glycoprotein are poorly understood. The malignant cells in B lymphoid chronic lymphocytic leukemia express CD5, and the numbers of CD5+ B lymphoid cells are elevated in several autoimmune conditions. The human-NOD/SCID chimera system may provide an in vivo model to investigate the maturation and development of this cryptic human CD5+ B lymphoid cell subpopulation.

The biological effects induced in mice by p36, a proteinaceous factor of virulence produced by African swine fever virus, are mediated by interleukin-4 and also to a lesser extent by interleukin-10

We have previously presented indirect evidence that both specific immunosuppression and lymphocyte mitogenicity induced in mice by p36, a proteinaceous factor of virulence produced by porcine monocytes infected by African swine fever virus, were consistent with a Th2-driven response. Here we show: (1) Interleukin-4 (IL-4) and interleukin-10 (IL-10) mRNA expression in the spleen and thymus of C57BL/6 mice were displayed early after p36 inoculation. The expression of thymic IL-10 mRNA occurred, however, later than that of IL-4 mRNA. (2) Increased serum levels of these two cytokines were also soon detected after the protein inoculation. (3) Both immunosuppressive and mitogenic effects of p36 were absent in IL-4 gene-targeted mice and partially abrogated in mice depleted of IL-4 by neutralizing monoclonal antibodies. (4) IL-10 depletion abrogated the immunosuppressive but not the p36 lymphocyte mitogenic biological effects. (5) The increase in the serum concentrations of both IL-4 and IL-10 were lower in thymectomized than in non-thymectomized mice. (6) The expression of interferon-gamma (IFN-gamma) mRNA was weakly or not at all induced in p36-treated mice. Taken together, these results are in agreement with the promotion of a Th2 immune response induced by p36.

Kinetics of cytokine release and expression of lymphocyte cell-surface activation markers after in vitro stimulation of human peripheral blood mononuclear cells with Streptococcus pneumoniae

The aim of this study was to describe the kinetics of the cytokine release and the expression of activation markers on lymphocytes after stimulation of peripheral blood mononuclear cells (PBMC) with whole killed Streptococcus pneumoniae. The cytokine release and the expression of CD25 and HLA-DR on T cells, and CD69 on T cells, B cells and NK cells, were measured at different times. Our results show that tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-10 and IL-12 reached maximal levels at 24 h, while IL-6, IL-8, TNF-beta and interferon (IFN)-gamma increased throughout the 1-week test period. The strains tested gave an increased expression of CD69 on all cell types, as well as an increase of CD25 and HLA-DR expression on T cells. The maximal CD69 expression was seen after 24 h on T cells and NK cells, while the B-cell expression of CD69 reached a plateau at the same time. All the cells still expressed CD69 on their surfaces after 1 week. In conclusion the results indicate that there was probably an early activation of monocytes leading to a polyclonal activation of lymphocytes.

Early Preferential Stimulation of γδ T Cells by TNF-α

Although recent findings indicate that γδ T cells influence both early innate and Ag-specific adaptive host responses, it has remained unclear what triggers γδ T cell reactivity. Investigating very early T cell activation in mouse and human models of bacterial infection, we measured CD69 expression as an indicator of early cellular activation. Both murine αβ and γδ T cells responded polyclonally to systemic bacterial infections, and to LPS. However, γδ T cells responded more strongly to the bacteria and to LPS. In vitro LPS-stimulated human T cells showed a similar differential response pattern. We identified TNF-α as mediator of the early differential T cell activation, and of differential proliferative responses. The stronger response of γδ T cells to TNF-α was correlated with higher inducible expression levels of TNF-Rp75. Among unstimulated splenocytes, more γδ T cells than αβ T cells expressed CD44 at high levels. The data suggest that TNF-Rp75 determines the differential T cell reactivity, and that most γδ T cells in the normal spleen are present in a presensitized state. As TNF-α stimulates activated T cells, it may early preferentially connect γδ T cell functions with those of cells that produce this cytokine, including activated innate effector cells and Ag-stimulated T lymphocytes.

Administration to mouse of endotoxin from gram-negative bacteria leads to activation and apoptosis of T lymphocytes

Lipopolysaccharide (LPS) from gramnegative bacteria is a well-known T cell-independent B lymphocyte mitogen and macrophage/monocyte activator. While the conventional view holds that LPS is ignored by T cells, we report here that administration of LPS to mice activates all B cells, but also engages most CD4 and CD8 T cells, as measured by the expression of the activation markers CD69 and CD25 and by size increase. T cells recruited in endotoxin-treated mice showed, following in vitro stimulation by concanavalin A, altered patterns of cytokine production. In vivo, massive T cell apoptosis was evidenced in the days following LPS exposure. The present observation may contribute novel insights into the mechanisms of endotoxin shock and of the immunological consequences of gram-negative infections.

Effects of the murine genotype on T cell activation and cytokine production in murine mercury-induced autoimmunity

Mercury induces a systemic autoimmune condition characterized by auto-antibodies to the nucleolar protein fibrillarin (AFA) and systemic immune-complex (IC) deposits in genetically susceptible mouse strains. This study examines T cell activation and cytokine production following mercury exposure in genetically susceptible and resistant strains. Mercury injected s.c., according to the protocol for induction of autoimmunity, caused an early T cell activation, measured as an increase of IL-2-producing cells, and increased expression of the IL-2-receptor proteins CD25 and CD122 and of the proliferation marker CD71 on days 2-4 in the susceptible A.SW and A. TH strains. This was followed by a long-lasting increase in the number of T cells, dominated by CD4(+) cells. Mice of the susceptible A.SW strain showed a modest increase of TNF-alpha-, IFN-gamma-, and IL-4-producing cells after 4-6 days, and a very distinct increase of IL-4-producing cells on days 8-10. The susceptible SJL strain (H-2(s)), severely deficient in Th2-promoting CD4(+), NK1.1(+) T cells, showed no increase of IL-4(+) cells on days 8-10. Instead, the number of IFN-gamma-producing cells was increased. Susceptible mice developed an increase of Ig-producing cells, AFA, and systemic IC-deposits. Genetically mercury-resistant A.TL mice showed a minimal increase of T cells, but no increase in cytokine-producing cells. We conclude that autoimmunogenic doses of HgCl2 induce an activation and proliferation of T cells in genetically susceptible mouse strains, as well as a broad increase of cytokine-producing cells, followed by a late predominance of the Th2-associated IL-4. One strain, severely deficient in Th2-promoting CD4(+), NK1.1(+) T cells, lacked the increase in IL-4(+) cells, indicating that a predominantly Th2-response is not necessary for induction of autoimmunity by mercury. However, a Th2-dominated response led to a faster and stronger B cell activation.

Essential roles of the Fas ligand in the development of hepatitis

The Fas ligand (FasL) is expressed in activated T cells and induces apoptosis in Fas-bearing cells. A cytotoxic T lymphocyte (CTL) clone specific for hepatitis B surface antigen (HBsAg) causes an acute liver disease in HBsAg transgenic mice. Here we observed that the CTL clone killed hepatocytes expressing HBsAg in a Fas-dependent manner. Administration of the soluble form of Fas into HBsAg transgenic mice prevented the CTL-induced liver disease. In the second model, mice were primed with Propionibacterium acnes. A subsequent challenge with lipopolysaccharide (LPS) killed the mice by inducing liver injury. Neutralization of FasL rescued the mice from LPS-induced mortality, and Fas-null mice were resistant to LPS-induced mortality. These results suggest that FasL has an essential role in the development of hepatitis.