Differentiation of human dendritic cell subsets for immune tolerance induction.

OBJECTIVES: Since no further progress was achieved, in order to improve the long-term organ transplantation outcome, the immune tolerance appears as an interesting therapeutic goal. Dendritic cells (DCs) are specialized cells participating in the homeostasis of the immune response. Moreover, subsets of DCs, identified in humans, appear to have their respective competences in immune response modulation. Our objective is to purify from PBMC or to differentiate DC subsets from monocytes using several strategies and evaluate their IL10 secretion. METHODS: CD14+ cells were purified from peripheral blood mononuclear cell (PBMC) by affinity beads and cultured with cytokines up to 7 days. The pDCs were purified with anti-BDCA-2 beads from PBMC fraction enriched by Percoll® gradient. The moDCs, pDCs and moLCs subsets were analyzed by phenotype labelling and FACS analyses and IL10 secretion measured by ELISA. RESULTS: The moDCs were characterized by the CD209 expression and a lower expression of CD1a markers. Expression of CD207 and CD1a markers characterized moLCs and CD123+/BDCA-2+ pDCs. Variable IL-10 secretions were shown between the three DC subsets, both at basal and activated levels. CONCLUSIONS: As the several DC populations studied have different capacities of IL-10 synthesis, they might play, among others, distinct roles in the induction of immune tolerance.

Impact of a polymorphism in the IL-12p40 gene on the outcome of kidney transplantation.

A number of factors interfere with the outcome of renal transplantation. Revealing genetic factors that impact on graft outcome may have consequences for clinical practice. Interleukin-12 (IL-12), by stimulating interferon gamma (IFNgamma) production, plays a crucial role in immune responses against both graft and viral agents. An A-to-C single nucleotide polymorphism (SNP) within the 3'-untranslated region (3'UTR) of the IL-12p40 gene has been reported to be both functionally and clinically relevant. Since the impact of this SNP on kidney graft outcome has never been reported, we investigated the impact of the 3'UTR polymorphism on clinical events after transplantation among 253 kidney recipients transplanted between 1995 and 2003. The polymorphism was genotyped using the restriction fragment length polymorphism method. Our results showed that the 3'UTR polymorphism affected neither graft survival (P = .768) nor the occurrence of delayed graft function (DGF; P = .498). C allele carriers in our study displayed more acute rejections in the first year than patients with the A/A genotype, but it did not reach statistical significance (P = .108). In contrast, the C allele appeared to be a significant risk factor for cytomegalovirus infection (odds ratio = 1.77; P = .027). In conclusion, IL12B 3'UTR polymorphism did not affect graft survival, DGF, or acute rejection episodes, but had an impact on the occurrence of cytomegalovirus infection.

Anti-CD25 antibodies decrease the ability of human dendritic cells to prime allogeneic CD4 T cells.

Anti-CD25 monoclonal antibodies are largely used in clinical transplantation to prevent acute allograft rejection episodes. Although their effects on T lymphocytes have been extensively studied, their impact on human dendritic cells (DCs) has been less reported. Furthermore, the role of the interleukin-2 in DC functions has not yet been fully elucidated. In this study, we observed that stimulation of human monocyte-derived DCs with lipopolysa ccharide or CD40L strongly induced the expression of CD25. We showed that pretreatment of DC with anti-CD25 diminished their ability to prime T-helper cells. In contrast, humanized anti-CD25 monoclonal antibodies did not affect the up-regulation of CD86, CD80, CD83, HLA-DR, or CD40 induced by lipopolysaccharide stimulation. This study supported previously unrecognized effects of anti-CD25 monoclonal antibodies on DCs that may contribute to their clinical efficacy.

Mycophenolic Acid Inhibits p38 Mitogen-Activated Protein Kinase in Human Monocyte-Derived Dendritic Cells Stimulated by Lipopolysaccharide.

Dendritic cell (DC) maturation, a crucial stage in the immune response, can be induced by various stimuli, such as lipopolysaccharide (LPS). Maturation signals trigger up-regulation of costimulatory molecule expression, increasing the ability of DCs to prime T helper cells. We and others have previously reported that mycophenolic acid (MPA) inhibits DC maturation and activation. However, the mechanisms remain unknown. The primary effect of MPA is inhibition of inosine monophosphate dehydrogenase (IMPDH), an enzyme involved in the de novo synthesis of guanosine nucleotide. The process of DC maturation is highly dependent on mitogen-activated protein kinase (MAPK) phosphorylation, especially p38MAPK. We therefore decided to study whether MPA affects these processes. Human monocyte-derived DCs were activated by LPS in the presence or absence of MPA. To assess whether the depletion of guanine affected p38MAPK phosphorylation, increasing doses of exogenous guanosine were added before stimulation. The results by flow cytometry showed that MPA inhibited p38MAPK phosphorylation by 25%. Interestingly, exogenous guanosine did not reverse the MPA inhibition. Our results suggested that MPA inhibits p38MAPK activity independent of IMPDH in human DCs. This effect of MPA may explain its capacity to inhibit maturation marker expression on DCs.

Induction of porcine regulatory cells by mycophenolic Acid-treated dendritic cells.

Tolerance induction in murine allogeneic transplantation is relatively easy, often by induction of regulatory T cells (Treg). Unfortunately, the implementation of these models in clinical situations has not yielded reliable protocols of tolerance induction in humans. Our project sought to create a preclinical model of tolerance induction in large animals. Our current efforts seek to induce and characterize porcine Treg, obtaining dendritic cells (DC) able to preferentially stimulate them. DCs were differentiated from blood monocytes with porcine recombinant interleukin-4 (IL-4) and granulocyte-macrophage colony-stimulating factor (GM-CSF) for 6 days. These DCs were then stimulated by human CD40 ligand-transfected L cells with or without mycophenolic acid (MPA) for 48 hours. We analyzed surface marker expression, cytokine synthesis, and ability to stimulate allogeneic peripheral blood mononuclear cells (PBMC). The porcine lymphocytes underwent 4 rounds of 1-week stimulation with allogeneic DC treated or not with MPA. At the end of this coculture we analyzed their capacity to suppress allogeneic PBMC proliferation induced by mature DC. Our results showed that porcine DCs pretreated with MPA display a low expression of B7 costimulatory molecules, produce low levels of IL-12, and induce weak proliferation of allogeneic lymphocytes. Moreover, after 4 rounds of stimulation with MPA-treated DCs, PBMCs were able to inhibit an alloreactive response. These preliminary results suggested induction of a regulatory T-cell population that we are currently seeking to characterize.

Anti-CD25 antibodies affect cytokine synthesis pattern of human dendritic cells and decrease their ability to prime allogeneic CD4+ T cells.

Anti-CD25 monoclonal antibodies are widely used in clinical transplantation to prevent acute allograft rejection. Although their effects on T lymphocytes have been extensively studied, their impact on human dendritic cells (DC) has never been reported. Furthermore, the role of the IL-2 in DC functions has not yet been fully elucidated. In this study, we confirm that the stimulation of human monocyte-derived DC with LPS strongly induced the expression of CD25 and that LPS-matured DC also expressed the beta and gamma chain of the IL-2R. We also showed that adding anti-CD25 monoclonal antibodies to LPS induced a decrease in IL-12, IL-1, TNF-alpha, IL-6, and IFN-gamma production and an increase in IL-10 synthesis by DC compared with stimulation with LPS alone. Furthermore, we showed that these modifications diminished the T helper priming ability of DC and polarized the alloimmune response toward TH2. In contrast, humanized anti-CD25 monoclonal antibodies did not affect the up-regulation of CD86, CD80, CD83, HLADR, or CD40 induced upon LPS stimulation. Taken together, this study discloses some previously unrecognized effects of anti-CD25 monoclonal antibodies on DC that may contribute to their clinical efficacy. In addition, this study also shed some light on the role of the IL-2 in human DC activation.

Prospects for a human Toxoplasma vaccine.

Human toxoplasmosis is usually benign, but may occasionally lead to severe or lethal damages when combined with immunosuppressive states or when transmitted to the fetus during pregnancy. Only a vaccine could prevent these harmful effects. The oral route is the natural portal of entry of T. gondii. A protective immune response at the mucosal level is required to kill the parasite as soon as it penetrates the intestinal barrier thus preventing toxoplasma from invading the host and settling into tissues. The probable major roles played by both CD8 T cells and antibodies, specially IgA, suggest that the best strategy would be to stimulate both the cellular and humoral arms of the mucosal immune system. Mucosal dendritic cells have been shown to induce good protection against oral toxoplasma challenge. Our hypothesis is that an acceptable and effective human vaccine would have to carry the optimized synthetic vaccine (subunit, DNA or replicon) plus an appropriate adjuvant and to target the mucosal dendritic cells by means of an inert delivery system such as polymer microparticles, which can be endocytosed by M cells of the gut or nasal-associated lymphoid tissues.

Anti-SAG1 peptide antibodies inhibit the penetration of Toxoplasma gondii tachyzoites into enterocyte cell lines.

The initial attachment of Toxoplasma tachyzoites to the target host cell is an important event in the life-cycle of the parasite and a critical stage in infection. Previous studies have shown that polyclonal antibodies directed against the major surface antigen of Toxoplasma gondii (SAG1) inhibit the infection of enterocyte cell lines. Here, we demonstrate that antibodies raised against a central peptide (V41T) of SAG1 and the SAGI protein itself are able to inhibit the infection of various cell lines by the tachyzoites. Antibodies directed against SAG1 peptides were used to define a site on the SAGI antigen that interacts with the host cell. The epitope carried by V41T was identified on the tachyzoite surface by immunofluorescence. The peptide sequence seems to be conserved in all the members of the SAGI Related Sequence family (SRS). Using undifferentiated and differentiated Caco-2 cells, we found that tachyzoites enter preferentially via the basolateral side of the cell. These findings highlight the role of the SRS family members in the mediation of host cell invasion.

Intranasal immunization with SAG1 and nontoxic mutant heat-labile enterotoxins protects mice against Toxoplasma gondii.

Effective protection against intestinal pathogens requires both mucosal and systemic immune responses. Intranasal administration of antigens induces these responses but generally fails to trigger a strong protective immunity. Mucosal adjuvants can significantly enhance the immunogenicities of intranasally administered antigens. Cholera toxin (CT) and heat-labile enterotoxin (LT) are strong mucosal adjuvants with a variety of antigens. Moreover, the toxicities of CT and LT do not permit their use in humans. Two nontoxic mutant LTs, LTR72 and LTK63, were tested with Toxoplasma gondii SAG1 protein in intranasal vaccination of CBA/J mice. Vaccination with SAG1 plus LTR72 or LTK63 induced strong systemic (immunoglobulin G [IgG]) and mucosal (IgA) humoral responses. Splenocytes and mesenteric lymph node cells from mice immunized with LTR72 plus SAG1, but not those from mice immunized with LTK63 plus SAG1, responded to restimulation with a T. gondii lysate antigen in vitro. Gamma interferon and interleukin 2 (IL-2) production by splenocytes and IL-2 production by mesenteric lymph node cells were observed in vitro after antigen restimulation, underlying a Th1-like response. High-level protection as assessed by the decreased load of cerebral cysts after a challenge with the 76K strain of T. gondii was obtained in the group immunized with LTR72 plus SAG1 and LTK63 plus SAG1. They were as well protected as the mice immunized with the antigen plus native toxins. This is the first report showing protection against a parasite by using combinations of nontoxic mutant LTs and SAG1 antigen. These nontoxic mutant LTs are now attractive candidates for the development of mucosally delivered vaccines.

Intranasal immunization with Toxoplasma gondii SAG1 induces protective cells into both NALT and GALT compartments.

Intranasal (i.n.) immunization with the SAG1 protein of Toxoplasma gondii plus cholera toxin (CT) provides protective immunity. The aim of this study was to analyze the cellular activation of several mucosal compartments after i.n. immunization. Cervical and mesenteric lymph node (CLN and MLN, respectively) lymphoid cell and intraepithelial lymphocyte (IEL) passive transfer experiments were performed with CBA/J mice immunized i.n. with SAG1 plus CT. CLN and MLN cells and IEL isolated 42 days after immunization conferred protective immunity on naive recipient mice challenged with strain 76K T. gondii, as assessed by the reduction in the number of brain cysts. There were proliferative specific responses in nose-associated lymphoid tissue and the CLN and MLN cells from mice immunized with SAG1 plus CT, but no cytokine was detectable. Thus, protective immunity is associated with a specific cellular response in the nasal and mesenteric compartments after i.n. immunization.

Molecular mechanisms of the adsorption of a model protein (human serum albumin) on poly(methylidene malonate 2.1.2) nanoparticles.

PURPOSE: To understand the molecular mechanisms involved in protein-methylidene malonate 2.1.2 polymer interactions. METHODS: To assess the importance of electrostatic forces in polymer-protein interactions use was made of HSA and its derivatives, which were anionized by succinylation and aconitylation. Surface plasmon resonance measurements, using the three HSA molecules as immobilized ligands and polymer nanoparticles as analytes in the liquid phase, allowed the determination of initial kinetic constants and affinity constants at equilibrium at two different temperatures. RESULTS: Saturation of binding for the three proteins occurred at approximately 900 protein molecules/nanoparticle. The apparent affinity decreased with increasing electronegativity of the proteins. Surface plasmon resonance measurement of proteins, covalently linked to the chip matrix, showed a high affinity for the nanoparticles (K(A) approximately 10(10) M(-1) and confirmed the moderate decrease of affinity with increasing electronegativity of the modified albumins. Measurements at 25 and 37 degrees C showed no significant increase in the albumin-nanoparticle interactions. Dissociation of the proteins from the nanoparticles could only be realized with chaotropic salt solutions. CONCLUSIONS: These results suggest the molecular forces initiating the protein-nanoparticle interactions are mainly of electrostatic nature followed by stabilization by hydrophobic forces. The high affinity confirms the nanoparticles as excellent carriers for protein delivery.

Differences in immunological response to a T. gondii protein (SAG1) derived peptide between two strains of mice: effect on protection in T. gondii infection.

This study presents the analysis of the immunogenicity, antigenicity and protective effects of a peptide derived from the major surface antigen of Toxoplasma gondii, SAG1. This synthetic peptide carrying three predicted H-2k restricted T cell epitopes was used to immunize mice. The protective effect of the peptide was evaluated in CBA/J and C57BL/6 mice using the decrease in brain cyst load as evidence of protection. Immunization of C57BL/6 mice yielded high antibody titres but had no protective effect after oral challenge. Immunized CBA/J, mice which responded with a lower titre, showed a 35% reduction in cyst burden after oral challenge. Both strains yielded antibodies which recognized the cognate SAG1 protein on immunoblot assay. Using the BIAcore, system, it was shown that at lower titres the CBA/J mouse sera recognized the native SAG1 protein more effectively than the C57BL/6 mouse sera, yielding much higher anti-peptide titres. Lymphoproliferation assays using the peptide experimentally confirmed the predicted T-cell epitopes and showed that they were also recognized by cells of T. gondii infected mice. The anti-peptide subclass analysis suggested a Th1 orientation in CBA/J mice, whereas a Th2 orientation was observed in C57BL/6 mice. Finally, fine analysis of sequences recognized under MHC class I indicated the existence of a T-cell epitope in the H-2k haplotype (CBA/J mice) but not in the H-2b haplotype (C57BL/6 mice). This study provides a structural basis to the understanding of the vaccination response to one of the T. gondii antigens in different strains of mice.

Alternative splicing determines the binding of platelet-derived growth factor (PDGF-AA) to glycosaminoglycans.

We have shown previously that the platelet-derived growth factor (PDGF) and a synthetic oligopeptide, corresponding to the basic carboxyl-terminal amino acid extension of the long PDGF-A isoform, bind to heparin. Here, we have expressed the long (rA125) and the short (rA109) variants of PDGF A-chains in Escherichia coli and produced the functional homodimers. Surface plasmon resonance analyses showed that while the dimeric rA125 bound with high affinity to low molecular weight heparin, the rA109, lacking the basic extension, did not. This strongly indicated that high affinity binding is due to the carboxyl-terminal extension. Investigations of kinetics and thermodynamics suggested an allosteric binding mechanism. Thus, dimeric rA125 contains two equivalent binding sites. Following low affinity binding of heparin to one binding site, the dimer undergoes a conformational change, increasing the affinity for heparin about 40 times. This positive cooperativity requires the basic amino acid extension in both monomers of the dimeric PDGF molecule. Thermodynamics of the reaction, showing an entropy-driven endothermic process, suggest the involvement of hydrophobic interactions in this rearrangement. Three amino acids in the basic carboxyl-terminal extension were essential for the interaction: the basic residues Arg111 and Lys116, and the polar Thr125. We also found that other glycosaminoglycan species, corresponding to those produced by human arterial smooth muscle cells, bound to dimeric rA125 and that heparan sulfate showed the highest affinity.

Immunochemical characterization of antibody-coated nanoparticles.

A new method using surface plasmon resonance (SPR) through the BIAcore was used to demonstrate the specific interaction between an anti-CD4 monoclonal antibody (IOT4a), adsorbed on poly(methylidene malonate 2.1.2) (PMM 2.1.2) nanoparticles, and the CD4 molecule. The results obtained were compared with the interaction of the same immunonanoparticles with rabbit anti-mouse Fc antibodies. The molar ratio (Fc)/(Fab) was 1, suggesting that the same number of epitopes on the Fc and the Fab fragments were accessible after IOT4a adsorption onto nanoparticles. Comparing the observed association rates of free antibody and antibody adsorbed on nanoparticles, the number of molecules of IOT4a antibody on PMM 2.1.2 nanoparticles was estimated as between 2.6 and 3 per nanoparticle. The properties of the antibody-coated nanoparticles are compatible with their use as antibody-targeted pharmacophores.

Analysis of human CD4-antibody interaction using the BIAcore system.

Interaction between CD4 cell surface protein and HIV-bearing gp120 has been described as the initial step for HIV entry into host cells. Some anti-CD4 antibodies were shown to inhibit this interaction. Biosensor studies using the BIAcore were performed to determine kinetic and thermodynamic parameters of the interaction of one of these antibodies (i.e. IOT4a, clone 13B8-2) with immobilized recombinant soluble CD4 (rsCD4). A non-linear regression method was used to analyze the sensorgrams, showing the existence of a double exponential time curve. A KA of 5.2 x 10(7) M-1 was calculated at 25 degrees C. The complex formation was exothermic (-4.5 kcal.mol-1( and entropically positive (+20 cal.mol-1.K-1). The reaction rate (0.234 x 10(5) M-1.s-1 at 25 degrees C) as well as the enthalpy change of the activated complex (+9.7 kcal.mol-1) are not compatible with a diffusion controlled reaction. The thermodynamic values calculated from equilibrium data corresponded to those calculated from kinetic data confirming the validity of the theoretical approach. As for most antigen-antibody interactions, complex formation was enthalpy driven. The overall positive entropy contribution to the stabilization of the complex is in contrast to that observed for the lysozyme-anti-lysozyme model and is probably due to electrostatic interaction between the epitope and the antibody combining site.

Epitopic analysis of the Toxoplasma gondii major surface antigen SAG1.

T and B cell epitopes of the major Toxoplasma gondii surface antigen SAG1 were studied following CNBr fragmentation. Three fragments, F1, F2 and F3, were obtained, of 19, 16.5 and 14 kDa, respectively. The positions of F1 F2 and F3 within the SAG1 protein were identified by N-terminal sequence determination. The F1 fragment located on residues 125-269 contains the C-terminus, and the fragment F2 (residues 1-124) is located at the N-terminal region. F3 is a C-terminal peptide about 40 amino acids shorter than the F1 fragment (residues 165-269). Polyclonal antibodies obtained from infected animals or humans and a monoclonal anti-SAG1 antibody did not recognize either the reduced protein or the reduced fragments on immunoblotting. The monoclonal antibody 1E5 did not recognize fragment F1. Mouse IgA and IgG antibodies from infected mouse sera and intestinal secretions, as well as human IgG antibodies, only recognized the whole protein and the F1 fragment. These results suggest that the fragment F1 encompasses all B cell epitopes recognized on the SAG1 protein after infection with the parasite and that the sequence 125-165 is essential for the structural integrity of these B cell epitopes. Murine anti-SAG1 T cell proliferation was observed in SAG1 immunized CBA/J mice (H-2k) and BALB/c mice (H-2d), but not in C57BL/6 mice (H-2b). The three fragments F1, F2 and F3 were able to induce specific proliferation of anti-SAG1 T cells from CBA/J mice, while only the F1 and F2 fragments induced specific blastogenesis of anti-SAG1 T cells from BALB/c mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Mucosal and systemic cellular immune responses induced by Toxoplasma gondii antigens in cyst orally infected mice.

This study was performed to determine the T-cellular immune responses following Toxoplasma gondii oral infection and to assess further toxoplasma antigens on their ability to stimulate in vitro mucosal and systemic T-cell immunity. Parasite-specific cellular immune responses in Peyer's patches (PP), in mesenteric lymph nodes (MLN) and in spleen (SPL) were investigated using a lymphoblastic transformation test following oral infection of mice with strain 76K cysts of T. gondii. An early toxoplasma sonicate-induced mucosal T-cell proliferation occurred in MLN and PP with a peak responsiveness on day 6 post-infection (PI) and rapidly reached background levels on day 7 PI in PP and on day 8 PI in mesenteric lymph nodes. A later splenic cellular blastogenesis was observed from day 28 PI and persisted throughout the experiment (day 91). At the time of T-cell proliferation, FACS analyses revealed a decrease in the relative percentages of CD4+ and CD8+ T cells with a predominance of CD8+ lymphocytes which leads to an inversion of the CD4/CD8 ratios. We found that CBA/J is a high responder mouse strain in the induction of mesenteric and splenic T-lymphocyte blastogenesis compared to the intermediate responder BALB/c and low responder C57BL/6. Toxoplasma gondii antigens SAG1 (30,000 MW) and GRA4 (40,000-41,000 MW), which are known to induce locally IgA antibodies, are shown to stimulate primed mucosal T lymphocytes from CBA/J and BALB/c mice whereas no proliferation was demonstrated with C57BL/6 T cells. 229-242 peptide, derived from the deduced amino acid sequence of GRA4, only induces detectable proliferation of primed-CBA/J T lymphocytes. Following oral experimental infection, the in vitro mesenteric response to a toxoplasma sonicate is dominated by a Th2-type cytokine pattern whereas a predominant Th1 cytokine response is observed in the spleen. Finally, in vitro stimulation of mesenteric T cells with the three defined toxoplasma antigens resulted in secretion of interleukin-5 (IL-5) and IL-6 (except for SAG1) and interferon-gamma (IFN-gamma) whereas no detectable IL-2 or IL-4 was observed.