Targeting neonatal ischemic brain injury with a pentapeptide-based irreversible caspase inhibitor

Brain protection of the newborn remains a challenging priority and represents a totally unmet medical need. Pharmacological inhibition of caspases appears as a promising strategy for neuroprotection. In a translational perspective, we have developed a pentapeptide-based group II caspase inhibitor, TRP601/ORPHA133563, which reaches the brain, and inhibits caspases activation, mitochondrial release of cytochrome c, and apoptosis in vivo. Single administration of TRP601 protects newborn rodent brain against excitotoxicity, hypoxia-ischemia, and perinatal arterial stroke with a 6-h therapeutic time window, and has no adverse effects on physiological parameters. Safety pharmacology investigations, and toxicology studies in rodent and canine neonates, suggest that TRP601 is a lead compound for further drug development to treat ischemic brain damage in human newborns.

Targeted Vpr-derived peptides reach mitochondria to induce apoptosis of alphaVbeta3-expressing endothelial cells

The HIV-1 encoded apoptogenic protein Vpr induces mitochondrial membrane permeabilization (MMP) via interactions with the voltage-dependent anion channel (VDAC) and the adenine nucleotide translocator (ANT). We have designed a peptide, TEAM-VP, composed of two functional domains, one a tumor blood vessel RGD-like 'homing' motif and the other an MMP-inducing sequence derived from Vpr. When added to isolated mitochondria, TEAM-VP interacts with ANT and VDAC, reduces oxygen consumption and overcomes Bcl-2 protection to cause inner and outer MMP. TEAM-VP specifically recognizes cell-surface expressed alpha(V)beta(3) integrins, internalizes, temporarily localizes to lysosomes and progressively co-distributes with the mitochondrial compartment with no sign of lysosomal membrane permeabilization. Finally TEAM-VP reaches mitochondria of angiogenic endothelial cells to induce mitochondrial fission, dissipation of the mitochondrial transmembrane potential (DeltaPsi(m)), cytochrome c release and apoptosis hallmarks. Hence, this chimeric peptide constitutes the first example of a virus-derived mitochondriotoxic compound as a candidate to kill selectively tumor neo-endothelia.

Structural basis of the cross-reaction between an antibody to the Trypanosoma cruzi ribosomal P2beta protein and the human beta1 adrenergic receptor

Antibodies from patients with Chagas heart disease and monoclonal antibodies (or mAb) to the carboxy-terminal end (B cell epitope R13) of the ribosomal P2beta protein of Trypanosoma cruzi (TcP2beta) cross-react with the beta1 adrenergic receptor (beta1-AR). Two single-chain Fv fragments (scFv) C5 and B7 derived from the variable regions of the anti-R13 mAb 17.2 were expressed. scFv C5 was a dimer and bound to TcP2beta with an affinity of K(d) = 8 nM, whereas scFv B7 was monomeric and had less affinity than scFv C5 for TcP2beta, K(d) = 46 nM. The affinity constant of scFv C5 to the second extracellular loop of the human beta1-AR was of 10 microM. Moreover, scFv C5 induced an increase in cAMP levels of CHO-K cells transfected with the human beta1-AR; scFv B7 had no effect but blocked isoproterenol stimulation. The agonist-like activity of scFv C5 and the antagonist activity of scFv B7 were both confirmed in vivo on heart beating frequency after their passive transfer to mice. Molecular modeling of the variable region of mAb 17.2 indicated which amino acids were likely to be involved in recognizing both peptide EDDDMGFGLF, derived from the R13 epitope of TcP2beta, and peptide ESDEARRCYN from the second extracellular loop of the human beta1-AR. It is plausible that the recently described cross-reaction of mAb 17.2 with rhodopsin can also be explained by this model. The physiological effects of this type of anti-T. cruzi antibodies may increase the liability of patients with Chagas disease.

The N-terminus of HIV-1 Tat protein is essential for Tat-TAR RNA interaction

The human HIV transactivator protein Tat is essential for efficient viral transcription that occurs by a complex mechanism involving interaction of Tat with the TAR RNA element. This interaction appears to require the mediation of a cellular protein, cyclin T1. However, the possibility that Tat and TAR associate in a binary Tat-TAR complex has been little investigated. Using a chemically synthesized active Tat protein, the kinetic and equilibrium parameters of its interaction with TAR were determined by surface plasmon resonance technology. Independently of partner and method of immobilization onto the sensor chip, the association (k(a) = 5-9 x 10(5) M(-1) s(-1)) and dissociation rate constants (k(d) = 1.7-4.3 x 10(-3) s(-1)) yielded similar equilibrium dissociation constants (K(d) = 2-8 nM). A truncated peptide encompassing residues 30-86 of Tat did not bind to TAR at all. We conclude that Tat can form a high-affinity complex with TAR in the absence of cyclin T1 and that the N-terminal domain of Tat is essential for this interaction, suggesting a conformational link between this domain and the basic domain of Tat. These results are important in our quest for developing therapeutic compounds that impair viral replication.

Structural and functional complexity of the humoral response against the Trypanosoma cruzi ribosomal P2 beta protein in patients with chronic Chagas' heart disease

High levels of antibodies against the C-terminus of the Trypanosoma cruzi TcP2 beta ribosomal protein, defined by the peptide EEEDDDMGFGLFD, named R13, have been measured in sera from patients with chronic Chagas' Heart Disease (cChHD). These antibodies also recognize an epitope on the second extracellular loop of the beta 1-adrenergic receptor, inducing a functional response on cardiomyocytes. The aim of this study was to gain novel insights into the structural basis of this cross-reactivity as well as to evaluate the origin of anti-M2- cholinergic receptor antibodies, which are also commonly found in cChHD patients. To address these questions we immunopurified anti-R13 antibodies and studied the structural requirements of epitope recognition. Results showed that the immunopurified antibodies recognized a conformation of R13 in which the third Glu residue was essential for binding, explaining their low affinity for the mammalian homologue (peptide H13: EESDDDMGFGLFD). Alanine mutation scanning showed individual variations in epitope recognition in each of the studied patients. The importance of a negatively charged residue at position 3 for the recognition of anti-R13 antibodies was further confirmed by competition experiments using a Ser3-phosphorylated H13 analogue, which had 10 times more affinity for the anti-R13 antibody than the native H13 peptide. Moreover, anti-R13 antibodies stimulated either the beta 1-adrenergic or the M2-cholinergic receptor, in strict agreement with the functional properties of the IgG fractions from which they derived, demonstrating that the same parasite antigen may generate antibody specificities with different functional properties. This may be a clue to explain the high variability of electrophysiological disturbances found in cChHD.

Immunogenicity of polymerizable synthetic peptides derived from a vaccine candidate against schistosomiasis: the asparaginyl endopeptidase (Sm32)

The asparaginyl endopeptidase (Sm32) is expressed in the gastrodermal cells of the schistosome gut and in the head glands of the cercariae. Possibly, Sm32 hydrolyzes pro-proteins involved in the degradation of host hemoglobin [Parasitol. Today 12 (1996) 125]. Preliminary evidences using an Sj32/Sm32 murine vaccine have shown a profound effect on oviposition and worm burden [Chin. J. Schist. Control. 7 (1995) 72; Bull. Human Med. Univ. 24 (1999) 225; Vaccine 20 (2002) 439]. The importance of Sm32 as a novel vaccine candidate is based on the possibility of preventing the maturation of other cathepsins and/or preventing schistosome skin invasion. We studied the immunogenicity of polymerizable peptides derived from Sm32 to select potential protective epitopes. Sm32 prediction of T and B epitopes and homology studies with human legumain were performed. Among the variety of factors that influence the antibody response, we specifically examined the effect of: (i) genetic background of mouse strain, inbred (C57BL/6) versus outbred (Swiss) mice; and (ii) vaccination with a single peptide versus pool of peptides. Swiss mice raised antibodies to three different regions of the Sm32, as tested by the Multiple Antigen Blot Assay (MABA): 182-215 (peptides IMT-70 and 72), 244-273 (IMT-64) and 336-355 (IMT-66). None of these regions were immunogenic for C57BL/6. On the contrary, other peptides, IMT-4 (21-40), IMT-12 (101-120) and IMT-26 (292-313) were highly immunogenic for this inbred strain. Only Swiss mice immunized with a single peptide (IMT-64 and 72) or with three different pools of IMT-peptides (Pool A-II: 14, 16, 18, 70, 72, 89; pool A-III: 22, 64, 24, 26, 28 and pool A-V: 64, 66, 28, 70, 72) recognized the original protein in a crude extract of the worm antigen by Western blot. Peptides IMT-64, 14 and 26 were responsible for this recognition. In general, the vaccination with pool of peptides was more immunogenic for both mouse strains. Predicted B cell epitopes, with hydrophilicity scores over +10 (IMT-12, 64, 26) were always immunogenic after either single or combined peptide vaccination. Sm32 sequences 41-80 (IMT-6 and 8), 141-160 (IMT-16) and 182-215 (IMT-70 and 72) were nearly identical to the corresponding human legumain regions and should be excluded from the human vaccine. We can conclude that the regions of Sm32 that were recognized by antibodies of mice immunized with polymerizable peptides depended on the mice strain and on the hydrophilicity score of the peptides.

A novel retro-inverso gonadotropin-releasing hormone (GnRH) immunogen elicits antibodies that neutralize the activity of native GnRH

GnRH vaccines have been successfully used for the inhibition of gonadotropin secretion and gonadal function. As an alternative to native GnRH, retro-inverso (RI) GnRH might be an improved immunogen. The RI peptides are composed of D-amino acids assembled in the reverse order (C to N terminus) in relation to the parent L peptide. These peptides are immunogenic and can produce high titers of antibodies that bind the parent peptide with high affinity and specificity. We show that RI-GnRH peptides conjugated to ovalbumin as well as unconjugated RI-GnRH elicit high titers of anti-GnRH antibodies in rabbits and mice. Antibodies were affinity purified and shown by ELISA to be selective for mammalian GnRH compared with GnRH II and [Gln(8)]GnRH. The binding kinetics of antibody-peptide interactions was determined using biosensor technology (BIACORE). The purified anti-GnRH antibodies inhibited GnRH-stimulated signal transduction in COS-1 cells expressing the human GnRH receptor. Immunization of mice with unconjugated and conjugated RI-GnRH peptide, in the absence of complete Freund's adjuvant, produced antisera that cross-reacted with mammalian GnRH. As RI peptides are resistant to cleavage by proteolytic enzymes, they are potentially orally active. The ability of RI-GnRH peptides to produce antibodies to GnRH without conjugation and without Freund's complete adjuvant constitutes a novel vaccine with improved properties of potential application in animal management and sex hormone-dependent cancers.

Agonist-like activity of antibodies directed against the second extracellular loop of the human cardiac serotonin 5-HT4(e) receptor in transfected COS-7 cells

We have previously reported that antipeptide antibodies directed against the second extracellular loop of the cardiac h5-HT4 receptor could block the activation of the L-type Ca channel in human atrial cardiomyocytes. In this paper we investigate the immunological and physiological activity of these antibodies, in a cell system expressing a larger amount of receptors than the atrial cells. The recombinant receptor was expressed at the surface of COS-7 cells under an active form (serotonin, EC50 = 1.81 x 10(-7) M), at a high level (375 +/- 25 fmol receptor/mg total protein) and was able to bind a specific ligand (GR113808) with a high affinity (Kd = 0.28 +/- 0.05 nM). In this system, the same anti-peptide antibodies used for the cardiac cells induced an "agonist-like" effect on the recombinant h5-HT4 receptor. These results are in line with those shown for others G-protein coupled receptors, as adrenoreceptors. In addition, this work showed that the effect of the antibodies is not only dependent on the epitopic region recognised but also on the molecular density and/or the cellular environment of the target receptors. Finally, our results support the hypothesis that the h5-HT4 receptor could be a new target for autoantibodies in patients with atrial arrhythmia.

Immunomodulatory properties of cystatins

Cystatins are natural tight-binding reversible inhibitors of cysteine proteases. Because these cysteine proteases exist in all living organisms and because they are involved in various biological and pathological processes, the control of these protease functions by cystatins is of cardinal importance. Cystatins are found in mammals but cystatin-like molecules are also present in mammals and parasites. In the immune system, cystatins modulate cathepsin activities and antigen presentation. They also induce tumor necrosis factor alpha and interleukin 10 synthesis, and they stimulate nitric oxide production by interferon gamma-activated murine macrophages. In turn, nitric oxide has inhibitory activity on cysteine proteases, especially those from parasitic protozoa. Cystatins isolated from parasitic nematodes also have immunomodulatory activities that are distinguishable from those induced by lipopolysacharide-like molecules from endosymbiotic bacteria. On the whole, cystatins and cystatin-like molecules belong to a new category of immunomodulatory molecules. Doubtless increasing data will improve our knowledge of this property, leading to practical applications in immunotherapy.

Differential recognition of epitopes present on monomeric and oligomeric forms of gp160 glycoprotein of human immunodeficiency virus type 1 by human monoclonal antibodies

The mechanism of infectivity neutralization of human immunodeficiency virus type 1 (HIV-1) by Ig is poorly understood. Three human monoclonal antibodies (mAbs 1b12, 2G12 and 2F5) that are able to neutralize primary isolates of HIV-1 in vitro have been shown to act synergistically. In the present study this synergy was analyzed by measuring the epitope accessibility and binding kinetics for these three mAbs with respect to monomeric and oligomeric env protein gp160 IIIB using surface plasmon resonance. The results indicate that oligomerization of gp160 affects the accessibility of some of the epitopes recognized by the mAbs and provide some insight into the mechanism of synergy between different anti-(HIV-1) mAbs.

Immunogenicity of synthetic peptides from the Sm31 antigen (cathepsin B) of the Schistosoma mansoni adult worms

The chemical synthesis of peptides may simplify the production of molecules for diagnosis of Schistosoma mansoni. Seventeen polymeric, 20-amino acids long, peptides comprising the entire Sm31 molecule of the adult worm, were synthesized under the t-boc strategy and their immunogenicity was evaluated. Of these, 10 peptides were immunogenic in rabbits. The peptides containing the sequence Gly74-Ser93 (peptide IMT-172) and the sequence Val154-Ala173 (peptide IMT-180) were responsible for the recognition of the Sm31 molecule by Western blot. This was confirmed by the specific inhibition of recognition of each molecule with the homologous peptide. Additionally, antibodies against these peptides strongly fixed to the adult worm gut. The present results, together with the strong immunogenicity shown for the adult worm 31 kDa antigen, establish the basis for the development of an immunodiagnostic method using synthetic peptides.

cGMP-mediated inhibition of cardiac L-type Ca(2+) current by a monoclonal antibody against the M(2) ACh receptor

The effects of a monoclonal antibody (B8E5) directed against the second extracellular loop of the muscarinic M(2) receptor were studied on the L-type Ca(2+) currents (I(Ca,L)) of guinea pig ventricular myocytes using the whole cell patch-clamp technique. Similar to carbachol, B8E5 reduced the isoproterenol (ISO)-stimulated I(Ca,L) but did not significantly affect basal I(Ca,L). Atropine blocked the inhibitory effect of B8E5. The electrophysiological parameters of ISO-stimulated I(Ca,L) were not modified in presence of B8E5. Inhibition of I(Ca,L) by B8E5 was still observed when intracellular cAMP was either enhanced by forskolin or maintained constant by using a hydrolysis-resistant cAMP analog (8-bromoadenosine 3',5'-cyclic monophosphate) or by applying the phosphodiesterase inhibitor IBMX. The effect of B8E5 was mimicked by 8-bromoguanosine 3',5'-cyclic monophosphate, a potent stimulator of cGMP-dependent protein kinase, and prevented by a selective inhibitor of nitric oxide-sensitive guanylyl cyclase [1H-(1,2,4)oxadiazolo[4,3-a]quinoxaline-1-one]. These results indicate that the antibody B8E5 inhibits the beta-adrenergic-stimulated I(Ca,L) through activation of the M(2) muscarinic receptor and further suggest that the antibody acts not via the classical pathway of decreasing intracellular cAMP, but rather by increasing cGMP.

A monoclonal antibody against the immunodominant epitope of the ribosomal P2beta protein of Trypanosoma cruzi interacts with the human beta 1-adrenergic receptor

Monoclonal antibodies were raised against a recombinant ribosomal P2beta protein of Trypanosoma cruzi. One of these reacted with the C terminus of this protein (peptide R13, EEEDDDMGFGLFD) and epitope mapping confirmed that this epitope was the same as the one defined by the serum of immunized mice, and similar to the previously described chronic Chagas' heart disease (cChHD) anti-P epitope. Western blotting showed that the monoclonal antibody recognized the parasite ribosomal P proteins, as well as the human ribosomal P proteins. Electron microscopy showed that it stained different structures in parasite and human cells. Interestingly, surface plasmon resonance measurements indicated that the affinity for the parasite ribosomal P protein epitope (R13) was five times higher than for its human counterpart (peptide H13, EESDDDMGFGLFD). Since the human epitope contained an acidic region (EESDD) similar to the AESDE peptide recognized by cChHD patients in the second extra-cellular loop of the human beta1-adrenergic receptor, the biological activity of the antibody was assessed on neonatal rat cardiomyocytes in culture. The monoclonal antibody had an agonist-like effect. These results, together with the fact that the monoclonal reacted in Western blots with the different isoforms of the heart beta1-adrenergic receptor, confirm the possible pathogenic role of antibodies against the parasite ribosomal P protein based on their cross-reaction with the human beta1-adrenergic receptor.

Heuristic Statistical Analysis of Fluorescence Fluctuation Data with Bright Spikes: Application to Ligand Binding to the Human Serotonin Receptor Expressed in Escherichia coli Cells

A statistical method for the analysis of fluorescence fluctuation amplitudes including bright spikes is presented. This situation arises e. g. when fluorescent ligands interact with receptors carrying multiple binding sites. The technique gives information on the amount of bound ligand in solution, making it a complementary technique to fluorescence correlation spectroscopy analysis, which cannot be applied in this situation. Two simple statistical tests are proposed that can discriminate between fluorescence intensities originating from free ligands or complexes. The performance of the two tests is evaluated and compared on mixtures of a fluorophore and fluorophore coated beads that mimic the behaviour of multiliganded complexes. An application to ligand binding to the serotonin receptor, expressed on Escherichia coli cells, is also provided. Specific binding of a fluorophore to this receptor, as well as competition with several ligands, is assessed.

Inhibitory activity of antibodies against the human atrial 5-HT(4)receptor

Antibodies directed against the second extracellular loop of G protein-coupled receptors have been shown to exert "agonist-like" activities. In order to test the hypothesis that this is a general phenomenon, antibodies were raised in rabbits against a synthetic peptide corresponding to the second extracellular loop of the newly sequenced human cardiac 5-HT(4)receptor. The antibodies were affinity-purified and shown to recognize the 5-HT(4)receptor in immunoblots of Chinese hamster ovary (CHO) cells expressing the receptor. The antibodies had no intrinsic effect but could depress the activation of L -type calcium channel induced by serotonin in human atrial cells. This antagonist-like effect was exerted both by intact IgG and by Fab fragments. These results are physiologically important since it has been shown that the 5-HT(4)receptor could be a target for autoantibodies in mothers at risk of giving birth to children with neonatal atrio-ventricular block.

Control of mitochondrial membrane permeabilization by adenine nucleotide translocator interacting with HIV-1 viral protein rR and Bcl-2

Viral protein R (Vpr), an apoptogenic accessory protein encoded by HIV-1, induces mitochondrial membrane permeabilization (MMP) via a specific interaction with the permeability transition pore complex, which comprises the voltage-dependent anion channel (VDAC) in the outer membrane (OM) and the adenine nucleotide translocator (ANT) in the inner membrane. Here, we demonstrate that a synthetic Vpr-derived peptide (Vpr52-96) specifically binds to the intermembrane face of the ANT with an affinity in the nanomolar range. Taking advantage of this specific interaction, we determined the role of ANT in the control of MMP. In planar lipid bilayers, Vpr52-96 and purified ANT cooperatively form large conductance channels. This cooperative channel formation relies on a direct protein-protein interaction since it is abolished by the addition of a peptide corresponding to the Vpr binding site of ANT. When added to isolated mitochondria, Vpr52-96 uncouples the respiratory chain and induces a rapid inner MMP to protons and NADH. This inner MMP precedes outer MMP to cytochrome c. Vpr52-96-induced matrix swelling and inner MMP both are prevented by preincubation of purified mitochondria with recombinant Bcl-2 protein. In contrast to König's polyanion (PA10), a specific inhibitor of the VDAC, Bcl-2 fails to prevent Vpr52-96 from crossing the mitochondrial OM. Rather, Bcl-2 reduces the ANT-Vpr interaction, as determined by affinity purification and plasmon resonance studies. Concomitantly, Bcl-2 suppresses channel formation by the ANT-Vpr complex in synthetic membranes. In conclusion, both Vpr and Bcl-2 modulate MMP through a direct interaction with ANT.

Induction of neonatal lupus in pups of mice immunized with synthetic peptides derived from amino acid sequences of the serotoninergic 5-HT4 receptor

We have previously suggested that the recognition of a cross-reactive epitope on the 5-HT4 receptor and the 52-kDa SSA/Ro protein by serotonin-antagonizing autoantibodies could explain the electrophysiological symptoms of congenital heart block in neonatal lupus. To confirm this hypothesis, we immunized female mice with four synthetic peptides corresponding to the recognized epitopes. All mice developed anti-peptide antibodies, which cross-reacted with the Ro52 and 5-HT4 receptor peptides and recognized both cognate proteins. Peptide-immune mice were mated. The pups from mice immunized with the Ro52 peptides had no symptoms of neonatal lupus apart from bradycardia. However, pups from mice immunized with the 5-HT4 receptor peptides and bradycardia, atrioventricular block of type I or II, longer QT intervals, skin rashes and neuromotor problems. The 5-HT4 receptor was detectable in the different fetal tissues affected (heart, skin and brain) by immunohistochemistry. Hearts from diseased pups were less developed and showed disorganized myocardial hyperplasia, compared to the normal littermates. These results demonstrate that the serotoninergic 5-HT4 receptor is the antigenic target of physiopathological autoantibodies in neonatal lupus.

Design of folic acid-conjugated nanoparticles for drug targeting

The new concept developed in this study is the design of poly(ethylene glycol) (PEG)-coated biodegradable nanoparticles coupled to folic acid to target the folate-binding protein; this molecule is the soluble form of the folate receptor that is overexpressed on the surface of many tumoral cells. For this purpose, a novel copolymer, the poly[aminopoly(ethylene glycol)cyanoacrylate-co-hexadecyl cyanoacrylate] [poly(H(2)NPEGCA-co-HDCA)] was synthesized and characterized. Then nanoparticles were prepared by nanoprecipitation of the obtained copolymer, and their size, zeta potential, and surface hydrophobicity were investigated. Nanoparticles were then conjugated to the activated folic acid via PEG terminal amino groups and purified from unreacted products. Finally, the specific interaction between the conjugate folate-nanoparticles and the folate-binding protein was evaluated by surface plasmon resonance. This analysis confirmed a specific binding of the folate-nanoparticles to the folate-binding protein. This interaction did not occur with nonconjugated nanoparticles used as control. Thus, folate-linked nanoparticles represent a potential new drug carrier for tumor cell-selective targeting.

Design of folic acid-conjugated nanoparticles for drug targeting

The new concept developed in this study is the design of poly(ethylene glycol) (PEG)-coated biodegradable nanoparticles coupled to folic acid to target the folate-binding protein; this molecule is the soluble form of the folate receptor that is overexpressed on the surface of many tumoral cells. For this purpose, a novel copolymer, the poly[aminopoly(ethylene glycol)cyanoacrylate-co-hexadecyl cyanoacrylate] [poly(H(2)NPEGCA-co-HDCA)] was synthesized and characterized. Then nanoparticles were prepared by nanoprecipitation of the obtained copolymer, and their size, zeta potential, and surface hydrophobicity were investigated. Nanoparticles were then conjugated to the activated folic acid via PEG terminal amino groups and purified from unreacted products. Finally, the specific interaction between the conjugate folate-nanoparticles and the folate-binding protein was evaluated by surface plasmon resonance. This analysis confirmed a specific binding of the folate-nanoparticles to the folate-binding protein. This interaction did not occur with nonconjugated nanoparticles used as control. Thus, folate-linked nanoparticles represent a potential new drug carrier for tumor cell-selective targeting.

Melanoma peptide MART-1(27-35) analogues with enhanced binding capacity to the human class I histocompatibility molecule HLA-A2 by introduction of a beta-amino acid residue: implications for recognition by tumor-infiltrating lymphocytes

The design of heteroclytic antigens with high MHC binding capacity is of particular interest to overcome the weak immunogenicity of peptide epitopes derived from tissue antigens expressed by tumors. In the present study, double-substituted peptide analogues of the tumor-associated antigen MART-1(27-35) incorporating a substitution at a primary anchor residue and a beta-amino acid residue at different positions in the sequence were synthesized and evaluated for binding to the human histocompatibility class I molecule HLA-A2 and for recognition by tumor-infiltrating lymphocytes. Interestingly, by combining a Leu for Ala substitution at P2 (which alone is deleterious for antigenic activity) with a beta-amino acid substitution at a putative TCR contact residue, recognition by tumor-infiltrating lymphocytes was partially restored. The analogue [Leu(28),beta-HIle(30)]MART-1(27-35) displays both a higher affinity to HLA-A2 and a more prolonged complex stability compared to [Leu(28)]MART-1(27-35). Overall, these results suggest that double-substitution strategies and beta-amino acid replacements at putative TCR contact residues might prove useful for the design of epitope mimics with high MHC binding capacity.

Enzyme activities in Schistosoma mansoni soluble egg antigen

Schistosoma mansoni egg antigens are mostly responsible for the granulomatous pathology in human intestinal schistosomiasis. Several previous studies have indicated that the induction of an immune response against some parasite enzymes may protect against pathology. The present work was designed to identify enzyme activities present in a standard soluble egg antigen (SEA) preparation. Simple colorimetric analyses were performed incubating SEA with 2-naphthyl, 2-naphthylamide (2NA), or p-nitrophenyl substrates at different pHs in the absence of added effectors. Results showed prominent acid phosphatase (pH 5.4), alkaline phosphatase (pH 8.5), and N-acetyl-beta-glucosaminidase (pH 5.4) activities. Relevant peptidase activities were also detected at pH 6.5-7.5 against 2NA derivatives of (1) aliphatic (alpha-Ala > beta-Ala > Leu > Met > S-benzyl-Cys), polar (Ser > Gln), basic (Arg > Lys > ornithine), and acidic (Glu) amino acids; (2) dipeptides: X-Ala (X = Gly > Leu > Lys > Asp), X-Arg (X = Ala > Arg > Phe > Gly > Pro > Asp), Ser-Met, and Phe-Pro; and (3) tripeptides (Ala-Phe-Pro > Phe-Pro-Ala). The data demonstrated that S. mansoni SEA contains a rich set of hydrolases with different specificities that might play a role in the egg physiology and possibly also in the host-parasite relationships.

Anti-SSA/Ro52 autoantibodies blocking the cardiac 5-HT4 serotoninergic receptor could explain neonatal lupus congenital heart block

The 52-kDa SSA/Ro (Ro52) ribonucleoprotein is an antigenic target strongly associated with the autoimmune response in mothers whose children develop neonatal lupus and congenital heart block. When sera from patients with systemic lupus erythematosus were used as autoimmune controls in an enzyme immunoassay to screen for antibodies against the human serotoninergic 5-HT4-receptor, a high correlation was found between the presence of anti-Ro52 protein antibodies in such sera and antibodies reacting with a synthetic peptide, corresponding to the second extracellular loop of the human 5-HT4 receptor (amino acid residues 165-185). Homology scanning between the 5-HT4 peptide and the sequence of the Ro52 protein indicated two potential common epitopes located between residues 365 and 396 of the Ro52 protein. Cross-reactivity was found between the peptide derived from the 5-HT4 receptor, and a peptide corresponding to residues 365-382 of the Ro52 protein. Autoantibodies, affinity-purified on the 5-HT4 receptor peptide, specifically recognized both the Ro52 protein and the 5-HT4 receptor protein in immunoblots. The affinity-purified antibodies antagonized the serotonin-induced L-type Ca channel activation on human atrial cells. This effect could explain the electrophysiological abnormalities in neonatal lupus.

From agonist to antagonist: Fab fragments of an agonist-like monoclonal anti-beta(2)-adrenoceptor antibody behave as antagonists

We previously demonstrated that the monoclonal antibody Mab6H8 raised against the second extracellular loop of the beta(2)-adrenoceptor (beta(2)-AR) had an agonist-like activity, mediated by the activation of L-type Ca(2+) channels by protein kinase A through the adenylyl cyclase pathway. We suggested that this Mab acts by stabilizing an active dimeric conformation of the beta(2)-AR. To substantiate this hypothesis, we prepared monomeric Fab fragments of Mab6H8. Comparison of the physicochemical parameters of antigen interaction with both the Mab and its Fab fragments were determined by surface plasmon resonance, showing a 5- to 10-fold lower affinity of the fragments compared with the bivalent antibody. We determined the biological activity of antibody and Fab fragments in two systems: spontaneous beating neonatal rat cardiomyocytes to study the chronotropic effects and isolated guinea pig cardiomyocytes to study L-type Ca(2+) channel activation. Fab fragments as such had no "agonist-like" effects in both systems but inhibited receptor activation with the beta(2)-specific agonist clenbuterol. Addition of a cross-linking rabbit anti-mouse IgG restored the agonist-like effect of the Fab fragments. These results suggest that Fab fragments induce a conformational change in the receptor, inhibiting the accessibility of the pharmacophore pocket to clenbuterol. Dimerization of this receptor conformation induces an agonist-like effect. Antireceptor antibodies can thus act both as agonist in the dimeric state and as antagonist in the monomeric state.

Autoantibodies against the angiotensin receptor (AT1) in patients with hypertension

Sera from patients with malignant essential hypertension (n = 14), malignant secondary hypertension mainly attributable to renovascular diseases (n = 12) and renovascular diseases without malignant hypertension (n = 11) and from normotensive healthy blood donors (n = 35) were studied for the presence of autoantibodies against G-protein-coupled cardiovascular receptors. Autoantibodies against the angiotensin II receptor (AT1) were detected in 14, 33, 18 and 14% of patients with malignant essential hypertension, malignant secondary hypertension, renovascular diseases and control patients, respectively. Sensitivity of the enzyme immunoassay was assessed as 5 microg/ml IgG. Patients did not show antibodies against bradykinin (B2) or angiotensin II subtype 2 (AT2) receptors. Autoantibodies affinity-purified from positive patients localized AT receptors in Chinese hamster ovary transfected cells, and displayed a positive chronotropic effect on cultured neonatal rat cardiomyocytes. These results demonstrate the existence of autoantibodies against a functional extracellular domain of human AT1 receptors in patients with malignant hypertension, and suggest that these autoantibodies might be involved in the pathogenesis of malignant hypertension.

Targeted macrophage cytotoxicity using a nonreplicative live vector expressing a tumor-specific single-chain variable region fragment

Antigen-specific recognition and subsequent destruction of tumor cells is the goal of vaccine-based immunotherapy of cancer. Often, however, tumor antigen-specific cytotoxic T lymphocytes (CTLs) are either not available or in a state of anergy. In addition, MHCI expression on tumor cells is often downregulated. Either or both of these situations can allow tumor growth to proceed unchecked by CTL control. We have shown previously that tumor antigen-specific monoclonal antibodies can be expressed in vaccinia virus and that activated macrophages infected with this virus acquire the ability to kill tumor cells expressing that antigen. Here we show that a membrane-anchored form of the scFv portion of the MUC1 tumor antigen-specific monoclonal antibody, SM3, can be expressed on activated macrophages with the highly attenuated poxvirus, modified vaccinia Ankara (MVA), as a gene transfer vector. Cells infected with the MVA-scFv construct were shown to express the membrane-bound scFv by Western blot and FACS analysis. That cells expressing the membrane-anchored scFv specifically bind antigen was shown by FACS and by BIAcore analysis. GM-CSF-activated macrophages were infected with the construct and shown to recognize specifically MUC1-expressing tumor cells as measured by IL-12 release. Furthermore, activated macrophages expressing the membrane-bound scFv specifically lyse target cells expressing the MUC1 antigen but not cells that do not express MUC1.

Myocardial hypertrophy in transgenic mice overexpressing the bovine growth hormone (bGH) gene

OBJECTIVES

The main purpose of the present study was to characterize cardiac muscle hypertrophy using both qualitative and quantitative microscopy in mice overexpressing the bovine growth hormone.

RESULTS

Measurements of 30 fibres from each group revealed that fibre diameter in transgenic hearts was significantly larger than in control hearts. There was a significant decrease in interfibrillar space in transgenic hearts as compared with control hearts. The enlarged transgenic hearts displayed unchanged organelles such as normal myofibrils and mitochondria in a normal pattern, suggesting balanced growth. Myelin structures were occasionally observed between normal myofibrils. Moreover, myocardial beta-adrenergic receptors and muscarinic receptors in the hearts of transgenic mice overproducing GH were studied to see whether they are involved in the hypertrophic process. It was shown that the density of muscarinic receptors had decreased and the super-high affinity of muscarinic receptors was lost, without any significant changes in either the density or the affinity of beta-adrenergic receptors, as compared with controls.

CONCLUSIONS

These results demonstrate that a GH excess was able to induce significant myocardial hypertrophy and that there was a downregulation of muscarinic receptors.

A monoclonal antibody directed against an autoimmune epitope on the human beta1-adrenergic receptor recognized in idiopathic dilated cardiomyopathy

A monoclonal antibody (MAb M16) was obtained by immunizing Balb/C mice with free peptide H26R, corresponding to the second extracellular loop of the human beta1-adrenergic receptor (beta1AR), against which functional autoantibodies have been detected in patients with idiopathic dilated cardiomyopathy. The MAb was found to be of IgG2b type and directed against a conformational epitope, encompassing the sequence recognized by the human autoantibodies. BIAcore measurements yielded an equilibrium constant of 6.5 X 10(7) M1 with an association rate constant (kon) of 6.5 X 10(4) M(-1) sec(-1) and a dissociation rate constant (koff) of 1.0 X 10(-3) sec(-1). It immunoprecipitated only poorly the solubilized beta1AR of Sf9 cell membranes. Functionally, the MAb was capable of not only reducing the number of the maximal binding sites to the beta1-adrenergic receptor of transfected Sf9 cell membranes, but also of displaying a positive chronotropic effect on cultured neonatal rat cardiomyocytes. These properties, which the MAb shares with the human autoantibodies, makes it an interesting tool for passive transfer studies in mice.

Chicken cystatin stimulates nitric oxide release from interferon-gamma-activated mouse peritoneal macrophages via cytokine synthesis

Cystatins are natural tight-binding, reversible inhibitors of cysteine proteases. We have shown that cystatins also stimulate nitric oxide (NO) production by interferon-gamma-activated mouse peritoneal macrophages [Verdot, L., Lalmanach, G., Vercruysse, V., Hartman, S., Lucius, R., Hoebeke, J., Gauthier F. & Vray, B. (1996) J. Biol. Chem. 271, 28077-28081]. The present study was undertaken to further document this new function. Macrophages activated with interferon-gamma and then stimulated with interferon-gamma plus chicken cystatin generated increased amounts of NO in comparison with macrophages only activated with interferon-gamma. Interferon-gamma-activated macrophages must be incubated with chicken cystatin for at least 8 h to upregulate NO production. NO induction was due to increased inducible nitric oxide synthase protein synthesis. Macrophages incubated with chicken cystatin alone or with interferon-gamma plus chicken cystatin produced increased amounts of both tumor necrosis factor alpha and interleukin 10. The addition of recombinant murine tumor necrosis factor alpha alone or in combination with recombinant murine interleukin-10 mimicked the effect of chicken cystatin. The addition of neutralizing anti-(tumor necrosis factor alpha) antibodies reduced sharply NO production by chicken cystatin/interferon-gamma-activated mouse peritoneal macrophages. Taken together, these data suggest that chicken cystatin induces the synthesis of tumor necrosis factor alpha and interleukin 10. In turn, these two cytokines stimulate the production of NO by interferon-gamma-activated macrophages. The findings point to a new relationship between cystatins, cytokines, inflammation and the immune response.

Probing the immunological properties of the extracellular domains of the human beta(1)-adrenoceptor

The human beta(1)-adrenoceptor is an immune target for autoantibodies with functional activity in cardiovascular diseases. Different epitopes on the extracellular domains of the receptor are involved. To study the immunological and pharmacological properties of these epitopes, rabbits were immunized with peptides corresponding to a large domain in the N-terminal part of the receptor and to its first and second extracellular loops. In contrast to the two other peptides, the first extracellular loop did not have immunogenic properties but acted as a hapten. Antibodies affinity-purified with the three synthetic peptides were able to significantly immunoprecipitate the solubilized receptor, confirming that they recognized the target receptor. While antibodies against the N-terminal domain did not inhibit the binding of a radiolabelled antagonist to the receptor, those against the first and second extracellular loop showed non-competitive inhibition. Similarly, only the two latter antibodies exerted a specific agonist-like effect on the receptor, as assessed on neonatal rat cardiomyocytes in culture. Our results are in accordance with those found for human anti-receptor autoantibodies with functional effects. We conclude that not all extracellular epitopes give rise to functional autoantibodies with potential physiopathological relevance in cardiac diseases with an autoimmune component.

Catalytic activity of antibodies against factor VIII in patients with hemophilia A

Hemophilia A is an X chromosome-linked recessive disorder resulting in defective or deficient factor VIII (FVIII) molecules, which, in its severe form, is a life-threatening and crippling hemorrhagic disease. Infusion of homologous FVIII to patients with severe hemophilia A results, in 25% of patients, in the emergence of alloantibodies against FVIII (inhibitors)( ref. 1) that inhibit FVIII procoagulant activity by steric hindrance of the interaction of FVIII either with stabilizing molecules, with molecules essential for its activity or with activating molecules. Here, we report on the proteolysis of FVIII by alloantibodies of two patients with severe hemophilia A, demonstrating a previously unknown mechanism by which FVIII inhibitors may prevent the pro-coagulant function of FVIII. The kinetic parameters of FVIII hydrolysis indicate a functional role for the catalytic immune response in the inactivation of FVIII in vivo. The characterization of alloantibodies against FVIII as site-specific proteases may provide new approaches to the treatment of FVIII inhibitors.

Purification and characterization of two alpha-amylases from Toxoplasma gondii

Two distinct alpha-amylases have been identified in Toxoplasma gondii. They were purified close to homogeneity from cytoplasmic and membrane fractions. The apparent molecular weight of the cytoplasmic amylase was 22,300 Da and that of the membrane enzyme was 39,600 Da by gel filtration, and 25,000 and 41,000 Da by SDS gel electrophoresis, respectively. The physicochemical and catalytic properties of both enzymes showed them to be very different. Cytoplasmic alpha-amylase had an acid isoelectric point and its optimum pH was pH 5.0; its activity was unaffected by NaCl, Ca2+, or EDTA. The membrane alpha-amylase had an isoelectric point of 7.7 and an optimum pH of 8.0. It was affected by Ca2+, inhibited by EDTA, and activated eight-fold by NaCl. Both amylases were inactivated by temperatures above 65 degrees C, but cytoplasmic amylase was more resistant to thermal denaturation.

Salbutamol as an adjuvant for nasal vaccination

Salbutamol, a beta-adrenergic agonist, which transiently increases cAMP levels, was tested for its potential adjuvant activity in nasal vaccination. SAG1, the major surface protein of Toxoplasma gondii was used as vaccinating protein to protect CBA mice from a challenge with the parasite. Mice, vaccinated with SAG1 in the presence of salbutamol, showed a highly significant decrease in cerebral cysts, compared to non-vaccinated mice or mice receiving the vaccinating protein alone. Lymph node cells from BALB/c mice, receiving in the footpads a dendritic cell line pulsed with the antigen in the presence of salbutamol, showed a proliferative response in the presence of SAG1. The adjuvant properties of salbutamol are thus partially mediated by its effect on antigen presenting cells.

Processing of PDGF gene products determines interactions with glycosaminoglycans

The platelet derived growth factor (PDGF), a mitogen for mesenchymal cells, may be bound to and inhibited by heparin and other glycosaminoglycans. PDGF is a homo- or heterodimer of A- and B-chains. They occur as short (A109 and B110) and long (A125 and B160) isoforms. The latter contain basic carboxyl-terminal extensions. Dimeric A125 binds to heparin through its basic extension in a two-step reaction. The mechanism involves a conformational change and is consistent with a Monod-Wyman-Changeux allosteric model. Previous indirect experiments suggested that three critical amino acids (basic R111, K116 and polar T125) might be involved. Here, direct binding experiments using dimeric full-length mutants in surface plasmon resonanse analysis showed that all three critical amino acids in an R(X)4K(X)8T-motif contributed in a concerted manner to the high affinity binding. Mutations of these amino acids to alanine resulted in large thermodynamic changes, loss of the allosteric mechanism and order(s) of magnitude lower binding affinity. The binding mechanism and affinity of long dimeric rB were similar to the mutants. Short dimeric rA109 and rB110 showed 100 times lower binding affinity than rA125. Consequently, interactions with glycosaminoglycans in tissues varies between PDGF isoforms and may influence their local accumulation and activity.

Immunohistochemical localization of angiotensin II receptors (AT1) in the heart with anti-peptide antibodies showing a positive chronotropic effect

Antibodies were produced against a synthetic peptide corresponding to amino acids (165-191) of the second extracellular loop of the human angiotensin II receptor subtype 1 (AT1) in rabbits. The purified antibodies had an apparent affinity of about 1 nM and were monospecific for the AT1-receptor peptide. Chemical modification of the carboxyl groups (glu at positions 173 and 185) and the sulfhydryl group (cys at position 180) of the AT1-receptor peptide did not alter the relative affinity of the coated AT1-receptor peptide to antibodies. The antibodies specifically stained CHO cells expressing the rat AT1a receptor. Immunoblots on rat kidney revealed that the antibody recognized a protein band of 59 +/- 3 kDa in a dose-dependent manner and this band was no longer detected after preincubating the antibodies with AT1-receptor peptide. Using electron microscopic and immunofluorescence immunocytochemistry techniques, angiotensin II receptors were detected in (1) the sarcolemma, T-tubules and nuclei of rat cardiomyocytes, (2) the transluminal side of endothelial cells and (3) fibroblast cells. These localizations are specific, as the immunostaining did not appear when preimmune rabbit serum was used and was blocked after preincubating antibodies with antigenic peptide. Functionally, these antibodies did not affect the ligand binding properties of the receptors but displayed agonist-like activity as shown by dose-dependent increases in beating frequency in cultured neonatal cardiomyocytes. These results suggest that the antibodies against the second extracellular loop of human AT1 receptors were able to specifically recognize AT1 receptors. In addition, they extend the observation that the second extracellular loop of the G-protein coupled membrane receptors is a specific target for antibodies with agonist-like activity.

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.

Functionally active cardiac antibodies in chronic Chagas' disease are specifically blocked by Trypanosoma cruzi antigens

Antibodies of chronic chagasic patients have been shown to interfere with electric and mechanical activities of cardiac embryonic myocytes in culture and with whole mammalian hearts. A mechanism proposed for this effect involves interaction of the antibodies with G-protein-linked membrane receptors, thus leading to activation of beta adrenergic and muscarinic receptors; more specifically, IgG of chagasic patients would interact with the negatively charged regions of the second extracellular loop of these receptors. We performed competition experiments to test this hypothesis. We evaluated the effect of sera/IgG from patients previously known to depress electrogenesis and/or atrioventricular conduction in isolated rabbit hearts after incubation with live and lysed parasites, the peptide corresponding to the second extracellular loop (O2) of the M2 receptor, and different peptides derived from two ribosomal proteins of T. cruzi: P0 and P2beta. Our results indicate that 1) the antigenic factor inducing the functionally active IgGs in the chagasic patients is probably an intracellular T. cruzi antigen; 2) IgG/serum is interacting with the O2 region of the M2 receptor in the rabbit heart; and 3) the negative charges present in the ribosomal proteins of T. cruzi are important in mediating the interaction between the patients' serum/IgG and the receptor.

A partially modified retro-inverso pseudopeptide modulates the cytokine profile of CTL specific for an influenza virus epitope

There is considerable evidence that peptides corresponding to MHC class I-restricted epitopes can be used as immunogens or immunomodulators. Pseudopeptides containing isosteric replacements of the amide bond provide more stable analogues, which may even have enhanced biologic activity. But there have been very few studies on the use of pseudopeptides to initiate or modulate the cellular immune response. This study describes the immunogenicity of a partially modified retro-inverso pseudopeptide of an influenza virus epitope and shows that this pseudopeptide modulates the cytokine profile expressed by CD8+ CTL generated from primed precursors. Moreover, the pseudopeptide is much more efficient at low concentration than the wild-type epitope to stimulate IFN-gamma secretion by CD8+ T effector cells. These results are analyzed with reference to changes in the conformation of the MHC molecule/peptide complex deduced from molecular modeling. The findings support the idea that partially modified retro-inverso analogues can be used as altered peptide ligands to enhance the stimulation of natural epitope-specific CTL and to modify their functional properties. Hence, pseudopeptide ligands might be promising tools for use in immunotherapy.

An agonist-like monoclonal antibody against the human beta2-adrenoceptor

Monoclonal antibodies were produced against a peptide corresponding to the second extracellular loop of the human beta2-adrenoceptor. One of these monoclonals, inducing an agonist-like effect in neonatal rat cardiomyocytes, was used to define the structural and physiological basis of this activity. The epitope recognized by the antibody corresponds to the sequence Trp-Tyr-Arg-Ala-Thr-His-Gln-Glu as determined by peptide scanning. Analysis by alanine modification of the peptide epitope showed the importance of the Trp, and Glu residues in antibody recognition The apparent affinity of the antibody assessed either by surface plasmon resonance or by functional titration on its agonist-like activity showed a similar value (10(8) M(-1)). The antibody recognized the receptor in its native form as shown by immunofluorescence experiments on A431 cells but not in its denatured form as shown by its absence of staining in immunoblots. The positive chronotropic effect in vitro was specifically blocked by both the antigenic peptide and the specific beta2-antagonist (+/-)-1-[2,3-(Dihydro-7-methyl1H-inden-4-yl)oxy]-3-[(1-methy lethyl)amino]-2-butanol hydrochloride (ICI1118,551). This activity was mediated through activation of Ca2+ L-type channels as assessed in guinea pig cardiomyocytes. These results suggest that the epitope is located in an extracellular alpha-helix, whose recognition by the antibody could stabilize the receptor in its 'active' conformation.

A new quantitative fluorimetric assay for phagocytosis of bacteria

We describe a new quantitative fluorimetric assay for phagocytosis of bacteria. A suspension of fluorescein-labelled bacteria (Micrococcus lysodeikticus) is mixed and incubated with phagocytes. After fixation with paraformaldehyde, the excess non-phagocytosed and adsorbed bacteria are lysed with a solution of lysozyme in phosphate-buffered saline. After washing of the phagocytes, the fluorescence of those that have ingested the labelled bacteria is measured with a spectrofluorimeter. We report results obtained with different types of phagocytes which show that this method allows sensitivity, saturation and kinetic studies and the calculation of a phagocytic index.

Immunochemical and functional characterization of an agonist-like monoclonal antibody against the M2 acetylcholine receptor

Monoclonal antibodies were raised against a peptide corresponding to the second extracellular loop of the M2 acetylcholine receptor. One of the monoclonal antibodies, B8E5, was selected for further characterization on the basis of its high yield, its isotype (IgG2a), its dissociation kinetics and its agonist-like activity. The epitope recognized by B8E5 corresponded to the N-terminal part of the second extracellular loop of the receptor (V-R-T-V-E-) as determined by competition immunoassays and epitope scanning. The KA of B8E5 for the target peptide was assessed by surface plasmon resonance (SPR) to be 6.5x10(7) M(-1) by equilibrium and 3.7x10(7) M(-1) by kinetic analysis. B8E5 recognized the M2 acetylcholine receptor on rat cardiac tissue. It only recognized the non-reduced receptor in immunoblots. The antibody had no effect on antagonist binding but decreased the affinity for the agonist carbachol. B8E5 decreased the beating frequency of neonatal rat cardiomyocytes. The effect was specific since it was blocked by the target peptide and the antagonist atropine. The EC50 of the antibody corresponded to the KA measured by surface plasmon resonance. The physiological effect of the antibody did not lead to desensitization. The Fab fragments had no physiological effect; subsequent addition of anti-mouse IgG however restored the physiological effect. These results confirm that the N-terminus of the second extracellular loop is a functional target for antibodies against the M2 acetylcholine receptor. They suggest that the functional epitope is only accessible in the non-reduced receptor. The antibodies act through a functional dimerization of the receptor.

Immunoreactivity of sera to a peptide derived from the serotonin 5-HT1A receptor in a group of children with developmental disorders: possible role in non-autistic epilepsy

The presence of autoantibodies against the serotoninergic 5-HT1A receptor has been reported in serum from an autistic child using radioligand binding studies. It is now well established that, in cardiovascular diseases with an autoimmune component, patients present in their sera autoantibodies directed against the second extracellular loop of some G-protein coupled membrane receptors. We thus investigated by an enzyme-immunoassay method the presence of anti-5-HT1A receptor antibodies in sera of children with developmental disorders using synthetic peptides corresponding to the first and the second extracellular loops of this receptor. The population of children with developmental disorders was divided in autistic children with or without EEG abnormalities, and in non-autistic children with or without EEG abnormalities. We found that 6 out of 10 sera of non-autistic children with an abnormal EEG recognized the second extracellular loop of the 5-HT1A receptor. This is significantly higher than the other groups of children with developmental disorders or a healthy control group. These observations support the existence of an autoimmune component in epilepsy.

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.

Antibodies to ribosomal P proteins of Trypanosoma cruzi in Chagas disease possess functional autoreactivity with heart tissue and differ from anti-P autoantibodies in lupus

Anti-P antibodies present in sera from patients with chronic Chagas heart disease (cChHD) recognize peptide R13, EEEDDDMGFGLFD, which encompasses the C-terminal region of the Trypanosoma cruzi ribosomal P1 and P2 proteins. This peptide shares homology with the C-terminal region (peptide H13 EESDDDMGFGLFD) of the human ribosomal P proteins, which is in turn the target of anti-P autoantibodies in systemic lupus erythematosus (SLE), and with the acidic epitope, AESDE, of the second extracellular loop of the beta1-adrenergic receptor. Anti-P antibodies from chagasic patients showed a marked preference for recombinant parasite ribosomal P proteins and peptides, whereas anti-P autoantibodies from SLE reacted with human and parasite ribosomal P proteins and peptides to the same extent. A semi-quantitative estimation of the binding of cChHD anti-P antibodies to R13 and H13 using biosensor technology indicated that the average affinity constant was about 5 times higher for R13 than for H13. Competitive enzyme immunoassays demonstrated that cChHD anti-P antibodies bind to the acidic portions of peptide H13, as well as to peptide H26R, encompassing the second extracellular loop of the beta1 adrenoreceptor. Anti-P antibodies isolated from cChHD patients exert a positive chronotropic effect in vitro on cardiomyocytes from neonatal rats, which resembles closely that of anti-beta1 receptor antibodies isolated from the same patient. In contrast, SLE anti-P autoantibodies have no functional effect. Our results suggest that the adrenergic-stimulating activity of anti-P antibodies may be implicated in the induction of functional myocardial impairments observed in cChHD.