Adenosine plasma level correlates with homocysteine and uric acid concentrations in patients with coronary artery disease.

The role of hyperhomocysteinemia in coronary artery disease (CAD) patients remains unclear. The present study evaluated the relationship between homocysteine (HCys), adenosine plasma concentration (APC), plasma uric acid, and CAD severity evaluated using the SYNTAX score. We also evaluated in vitro the influence of adenosine on HCys production by hepatoma cultured cells (HuH7). Seventy-eight patients (mean age ± SD: 66.3 ± 11.3; mean SYNTAX score: 19.9 ± 12.3) and 30 healthy subjects (mean age: 61 ± 13) were included. We incubated HuH7 cells with increasing concentrations of adenosine and addressed the effect on HCys level in cell culture supernatant. Patients vs. controls had higher APC (0.82 ± 0.5 µmol/L vs 0.53 ± 0.14 µmol/L; p < 0.01), HCys (15 ± 7.6 µmol/L vs 6.8 ± 3 µmol/L, p < 0.0001), and uric acid (242.6 ± 97 vs 202 ± 59, p < 0.05) levels. APC was correlated with HCys and uric acid concentrations in patients (Pearson's R = 0.65 and 0.52; p < 0.0001, respectively). The SYNTAX score was correlated with HCys concentration. Adenosine induced a time- and dose-dependent increase in HCys in cell culture. Our data suggest that high APC is associated with HCys and uric acid concentrations in CAD patients. Whether the increased APC participates in atherosclerosis or, conversely, is part of a protective regulation process needs further investigations.

A2A adenosine receptor function in patients with vasovagal syncope.

AIMS: Adenosine is a possible mediator in vasovagal syncope (VVS) via the activation of its receptors. High expression of adenosine A2A receptors (A2AR) has been reported in VVS. The function of these over-expressed receptors in this population has never been evaluated. METHODS AND RESULTS: We used Adonis, a specific-made antibody with A2AR agonist properties, to evaluate binding parameters (i.e. dissociation constant KD) and cAMP production (i.e. EC50) by peripheral blood mononuclear cells of 16 VVS patients. Eight healthy volunteers served as controls. A2AR expression was higher in patients than controls; mean: 11.5 ± 1.2 vs. 7.7 ± 0.8 AU, P = 0.04. Also, KD values were higher in patients than controls: 2.1 ± 0.02 × 10(-7) vs. 5 ± 1 × 10(-8) M, P < 0.01 In controls, KD values were lower than EC50 (5 ± 1.7 × 10(-8) vs. 2.8 ± 0.4 10(-7) M, P < 0.01), but in patients, KD values did not differ from EC50: 2. ± 0.2 × 10(-7) vs. 2.5 ± 0.4 × 10(-7) M, P > 0.05. However, four patients had lower EC50 (3.5 ± 0.3 × 10(-8) M) than KD (2.9 ± 1.2 × 10(-7) M; KD/EC50 = 9.6), suggesting the presence of spare receptors. CONCLUSION: The function of A2AR of patients with VVS was preserved since their stimulation by Adonis led to cAMP production with an EC50 comparable with those in controls. However, their affinity was lower than those of controls. Our results suggest that A2AR are implicated in the physiopathology of VVS.

Role of N-linked glycans in the interaction between the envelope glycoprotein of human immunodeficiency virus and its CD4 cellular receptor. Structural enzymatic analysis.

gp120 and CD4 are two glycoproteins that are considered to interact together to allow the binding of HIV to CD4+ cells. We have utilized enzymatic digestion by endoglycosidases in order to analyze N-linked carbohydrate chains of these proteins and their possible role in the interaction of gp120 or gp160 with CD4. SDS denaturation was not necessary to obtain optimal deglycosylation of either molecule, but deglycosylation of CD4, nonetheless, depended on the presence of 1% Triton X-100. Endo H and Endo F that cleave high mannose type and biantennary glycans diminish the molecular mass of the glycoproteins from 120 or 160 Kd to 90 or 130 Kd, respectively; but these enzymes had no action on CD4 glycans. Endo F N-glycanase mixture, which acts on all glycan species, including triantennary chains, led to complete deglycosylation of gp120/160 and of CD4. Therefore, probably half of the glycan moieties of gp120/160 are composed of high mannose and biantennary chains, the other half being triantennary species. The carbohydrate structures of CD4 seems to be triantennary chains. To analyze the binding of gp120/160 to CD4, we used a molecular assay in which an mAb (110-4) coupled to Sepharose CL4B allowed the attachment of soluble gp120/160 to the beads; 125I-sCD4 was then added to measure the binding of CD4 to different amounts of gp120/160. Binding to gp160 was not modified when using completely deglycosylated 125I-sCD4, while deglycosylation of gp120 or of gp160 resulted in the decrease of the binding to native CD4 by two- and fivefold, respectively. Native and deglycosylated gp120/160 bound to CD4+ cells with comparable affinities. In addition, deglycosylated gp120 displaced 125I-gp160 binding to CD4+ cells and inhibited fusion of fresh Molt-T4 cells with CEM HIV1- or HIV2-infected cells to the same extent. Taken together, these results indicate that carbohydrates of CD4 and of gp120/160 do not play a significant role in the in vitro interaction between these two molecules.

Functions of HIV envelope glycans.

The unusually highly glycosylated state of the major envelope glycoprotein (gp160) of the human immunodeficiency virus has offered a challenge to both glycobiologists and virologists. What is the functional significance of such a mass of glycans and how might they be manipulated to disadvantage virus pathogenesis? Some answers to each of these questions have already been obtained: N-linked glycans are necessary for the creation, but not the maintenance, of a bioactive conformation, and drug-induced alteration of the glycosylation pattern can lead to impaired virus infectivity. As a model for studying glycan function and as a target for antiviral therapy, gp160 represents a unique candidate.

Detection of anti-CD4 autoantibodies in the sera of HIV-infected patients using recombinant soluble CD4 molecules.

The use of purified recombinant soluble CD4 (sT4) allowed the detection of high titers of anti-CD4 immunoglobulins in the sera of three out of 33 HIV-infected patients. Binding of these antibodies to sT4 was first detected by enzyme-linked immunosorbent assay (ELISA), and their reactivity in the assay was blocked in a dose-dependent manner by preincubation with sT4. The antibodies could also immunoprecipitate iodinated sT4, but they failed to recognize CD4 expressed on the surface of CD4+ lymphocytes or cell lines. An ELISA which used as an antigen a truncated soluble CD4 molecule containing only the first two amino-terminal domains of the CD4 molecule did not react with these sera in ELISA, nor did it block antibody binding to sT4. Both these human sera and Leu3a, a mouse monoclonal antibody (mAb) which recognizes an epitope of CD4 close to the HIV binding site, failed to compete with one another for binding to sT4. Because these antibodies did not recognize epitope(s) of the CD4 molecule close to the HIV binding site, they are not likely to be anti-idiotypic antibodies directed against anti-HIV envelope antibodies. The exact location of the recognized epitope(s), as well as the role, if any, of these antibodies in the pathophysiology of HIV infection remains to be determined.

Use of synthetic peptides for the detection of antibodies against the nef regulating protein in sera of HIV-infected patients.

Human sera were tested for the presence of anti-nef antibodies by radioimmunoassay (RIA), with recombinant radiolabelled nef expressed in E. coli. Of the 300 HIV-positive sera tested by RIA, 70 +/- 5.3% were found to be anti-nef positive. Anti-nef antibodies bound to nef with a high affinity (K 0.5 = 2.2 x 10(-9) M). In 31 of the sera, the specificity of anti-nef antibodies was further analysed by enzyme-linked immunosorbent assay (ELISA) with large synthetic peptides ranging from 31 to 66 amino acid residues and spanning the total sequence of nef from HIV-1. The results obtained showed that the immunodominant antigenic sites of nef were located close to the N- and C-terminal regions of the molecule.

Early and specific diagnosis of seropositivity to HIVs by an enzyme-linked immunosorbent assay using env-derived synthetic peptides.

We describe and evaluate the sensitivity and specificity of an enzyme-linked immunosorbent assay (ELISA) using a 22-amino-acid peptide corresponding to the carboxy-terminal end of HIV-1 gp120 and two 30-amino-acid long cyclic peptides including the two vicinal cysteines present on HIV-1 gp41 and on HIV-2 gp36. This test was evaluated. Data obtained with the Western blot (WB) and the peptide-based ELISA on a first panel composed of sera from 547 patients attending a specialized outpatient clinic (high-risk population) are in perfect agreement; moreover, 39 samples that had falsely been found positive with a viral lysate-based ELISA were not detected by peptide-based ELISA. The second panel was composed of 309 sera which were difficult to resolve using both WB and viral lysate-based ELISA. Using the peptide-based ELISA, 134 were found clearly positive and 173 clearly negative; only two were falsely positive. Finally, sera from 16 individuals examined at the time of seroconversion gave high absorbancy readings even if they were weakly reactive by WB (weak gp160 band). This test is thus highly sensitive and specific, and capable of detecting early seroconversion. It is also instrumental in clearly defining samples that are found indeterminate in the WB, and consequently it avoids the unnecessary follow-up required when a false-positive result is obtained using viral lysate-based ELISA.

Polymorphism of prolactin secreted by human prolactinoma cells: immunological, receptor binding, and biological properties of the glycosylated and nonglycosylated forms.

Multiple forms of PRL differing in their physicochemical and biological characteristics have been described. We have analyzed the molecular forms of human (h) PRL released in culture by pure hPRL-secreting tumors with a particular attention to glycosylated hPRL. The prolactinoma cells from six different tumors released, in serum-free conditions, 10-28 mg hPRL. The combination of polyacrylamide gel electrophoresis and immunoblotting techniques using a [125I]anti-hPRL monoclonal antibody allowed qualitative and quantitative analysis of the hPRL variants. The ratio of the glycosylated 25,000-mol wt form (G-hPRL) to the 23,000-mol wt nonglycosylated monomeric hPRL (NG-hPRL) varied from 0.13 to 0.25. Under the conditions of our studies, cleaved forms of the hormone (19,000 and 15,000 mol wt) accounted for less than 5% of the total immunoreactivity. G- and NG-hPRL were subsequently purified by gel filtration and lectin affinity chromatography. G-hPRL appeared fully sensitive to endoglycosidase F digestion, further supporting the presence of a freely accessible N-linked carbohydrate chain. When assayed for their ability to react with polyclonal antibodies directed against hPRL in a competitive RIA, G-hPRL was 3 times less immunoreactive than NG-hPRL. However, both types of hPRL exhibited superimposable displacement curves when tested in an immunoassay using an anti-hPRL monoclonal antibody. In binding studies using crude rabbit mammary gland membranes G-hPRL was half as potent as NG-hPRL. In stimulating the growth of the Nb2 lymphoma cell line, G-hPRL was 50% less active than NG-hPRL. Thus 1) under basal conditions, hPRL undergoes partial and variable glycosylation; 2) glycosylation of the hormone may modulate its immunoreactivity; 3) glycosylation of hPRL not only lowers its mammary gland receptor binding capacity but also its growth-promoting activity.

On the relationship between completion of N-acetyllactosamine oligosaccharide units and iodine content of thyroglobulin: a reinvestigation.

Lack of completion of N-acetyllactosamine-type glycosylation on thyroglobulin (Tg) has been implicitly considered as an etiological factor of some thyroid disorders, i.e. goiter and hypothyroidism. However, there is some evidence that Tg with incompletely processed N-acetyllactosamine glycans occurs in the normal gland. Recent findings demonstrated that exposed N-acetylglucosamine (GlcNAc) residues present on internalized glycoprotein in the thyrocyte may act as a retention signal that prevents lysosomal homing and triggers recycling of GlcNAc-bearing molecules through galactosyltransferase- and thyroperoxidase-containing compartments of the Golgi apparatus. This finding raises the possibilities 1) that exposed GlcNAc residues are not randomly distributed, but are mainly present on immature Tg; and 2) that this process promotes elongation of complex glycans, thereby eliminating the retention signal. To further validate this hypothesis, we reinvestigated the relationship between the iodine content and the glycan completion of porcine Tg of luminal origin. Tg subpopulations were separated according to their iodine content on rubidium chloride centrifugation gradients, and their interactions with various plant and animal lectins were analyzed in solid phase assays. Iodine content used as an index of age ranged from 0.6-1.2%. There was no significant correlation between iodine content and either neutral sugar or oligosaccharide content, as judged by chemical methods or interaction with [125I]Solanum tuberosum and [125I]Pisum sativum agglutinins. In contrast, the number of GlcNAc-accessible residues (as judged by interaction with [125I]Bandeiraea simplificolia II) decreased as iodine content increased. These changes were concomitant with an increase in galactose (measured by interaction with [125I]R-icinus communis and [125I]galactosidase (Gal)/GalNAc rat hepatic lectin) and sialic acid content. Related experiments using a Tg subpopulation depleted in GlcNAc-exposed residues by passage through a B. simplificolia II affinity column showed that the capacity of this subpopulation to bind to membranes was lowered compared to that of the total Tg. These results support the following conclusions: 1) in normal glands, all or part of the Tg molecules are secreted in an incompletely glycosylated form; and 2) iodine organification is correlated with glycan completion. Therefore, asialoagalactothyroglobulin appears to be a physiological precursor for an efficient recycling mediated by the GlcNAc receptor to the iodination site. New insights in thyroid disorders are discussed.

Effect of various glycosidase treatments on the resistance of the HIV-1 envelope to degradation.

Using a CD4-binding assay to assess the conformation of the human immunodeficiency virus envelope glycoprotein (CHO+ Env), we studied the effect of treatment with various glycosidases on the stability of Env in denaturing environments and in biological media: cleavage from Env of either high-mannose-type glycans (HMT- Env) by endoglycosidase H or sialic acid residues (Sial- Env) by sialidase did not alter Env stability whereas its complete deglycosylation (CHO- Env) by N-glycanase had a large effect. The influence of glycan removal on Env sensitivity to proteases was also studied. Thrombin cleavage within V3 was affected by N-glycanase treatment; both HMT- Env and CHO- Env displayed an increased sensitivity to other endoproteases. Thus, partial deglycosylation increases Env sensitivity to proteases but only its total deglycosylation alters its stability.

Effect of sialic acid removal on the antibody response to the third variable domain of human immunodeficiency virus type-1 envelope glycoprotein.

The gp160 envelope glycoprotein of human immunodeficiency virus type-1 (HIV-1) is an essential component of current vaccine trials. The glycans of gp160, part of which are highly sialylated, have been shown to influence gp160 immunogenicity. Here, using a panel of synthetic V3 peptides, we characterized the anti-V3 antibodies generated in rabbits immunized by desialylated recombinant gp160LAI. Amino acid residues flanking the GPGR tip of V3 were necessary for the recognition by anti-V3 antibodies raised against either the native or desialylated gp160. Both types of antibodies reacted to V3 peptides of MN and SF2 strains and with a North American/European V3 consensus peptide, while anti-desialylated gp160LAI antibodies reacted in addition to the V3 of CDC4, WMJ2 and NY5 strains. Yet, the V3 peptides did not significantly differ in their secondary structure, as determined by circular dichroism. The titer and avidity for V3MN of anti-desialylated gp160LAI antibodies were significantly lower than those of anti-native gp160LAI, which likely accounts for the inability of anti-desialylated gp160LAI sera to neutralize HIV-1MN-induced syncytia. These results indicate that V3 immunogenicity may be influenced by subtle directed changes in the gp160 glycosylation pattern.

Glycosylation and stability of mature HIV envelope glycoprotein conformation under various conditions.

The role of the glycans of the mature human immunodeficiency virus (HIV) envelope (gp160) in its stability in various conditions was studied. gp160 conformation was monitored through its subsequent ability to bind [125I]CD4. Treatment of glycosylated (CHO+) gp160 with (i) sodium dodecyl sulfate (SDS) concentrations above 0.01% impaired subsequent CD4 binding while 0.3% SDS abolished it; (ii) beta-mercaptoethanol (MSH) concentrations above 0.01% impaired CD4 binding while 0.03% MSH abolished it; (iii) 2 M guanidine-HCl had no effect; (iv) temperatures between 50 degrees C and 80 degrees C altered CD4 binding while, above 80 degrees C, the binding was abolished; (v) CD4 binding was decreased by 50% by 2 freeze-thaw cycles but was not further affected by subsequent (up to 15) cycles; (vi) gp160 incubation in serum or cell lysate had no effect on CD4 binding. Glycanase treated (CHO-) gp160 binding activity was only 3-fold lower than that of CHO+ gp160. Only 2 M guanidine-HCl and heating at 70 degrees C differentially affected the binding of CHO+ and CHO- gp160, the effects being larger for CHO- gp160. CHO- gp160 binding was impaired after incubation in either serum or cell lysate. Thus, glycans stabilize gp160 conformation in some environments. However, CHO- gp160 appears to be resistant to denaturation as compared to other glycoproteins reported in the literature.

Novel anti-platelet aggregation polypeptides from Vipera lebetina venom: isolation and characterization.

Lebetins 1 and Lebetins 2, two polypeptide groups that inhibit platelet aggregation, were isolated from Vipera lebetina venom by gel filtration and reverse phase chromatography. Amino acid sequencing indicated that the first group contains two major polypeptides of 13 and 12 residues; their molecular weight was determined by electrospray mass spectrometry. The second was composed of two peptides of 38 and 37 residues, each with one disulfide bond. Sequence analysis revealed neither RGD sequence nor homology with other proteins including known snake or tick polypeptides. Lebetins 1 were Pro and Lys rich peptides and their sequences were identical to the N-terminus of Lebetins 2. Lebetins inhibited platelet aggregation induced by thrombin, collagen and PAF-acether. The 50% concentration that inhibited human and rabbit platelet aggregation induced by thrombin was 590 nM and 125 nM for Lebetins 1 and 100 nM and 8 nM for Lebetins 2, respectively. Lebetins 1 and Lebetins 2 also inhibited fibrinogen-induced aggregation of alpha-chymotrypsin-treated platelets as well as in vivo collagen-induced thrombocytopenia in rats with half effective doses of 2 nmol/kg and 4.2 nmol/kg, respectively. Lebetins were not toxic after intravenous injection into mice and rats. These polypeptides form novel platelet inhibitors that could be used to delineate further the mechanisms of platelet aggregation and serve as a model for developing antithrombotic agents.

Pharmacophore determination of a gp120 C terminal-derived anti-HIV peptide construct interfering with membrane fusion suggesting that processing of the gp120 C terminus is a prelude to fusion.

A multiple antigen peptide [CLIV; (PTKAKRR1VVQREKR2)4-K2-K-betaA] from the C terminus of the gp120 subunit of HIV Env inhibits Env-mediated cell-to-cell fusion through direct interference with the process (Virology 2000;273:169). We have examined various CLIV analogs using a cell-to-cell fusion assay, receptor binding assays, and molecular modeling to further address the characteristics of the peptide responsible for its anti-HIV activity. We show that (1) CLIV does not interfere with Env binding to CD4 and does not interact with the binding site of Env on CXCR4; (2) CLIV does not inhibit protease activities already reported to play a role in fusion; and (3) the pharmacophore is composed of cleavage site1 with amino acid residues at its C terminal end. Based on our data and on the literature, we propose that CLIV interferes with processing of the gp120 C terminus at site1 by the lymphocyte surface after CD4 binding. Our hypothesis implies that the cleavage region of Env is submitted to a stepwise processing including the known intracellular cleavage of gp160 at site2 in order to set the activation of the fusion peptide and a yet unexplored cleavage at site1 by the target cell surface that triggers fusion.

Relationship between anti-p24 antibody levels and p24 antigenemia in HIV-infected patients.

We studied the influence of HIV p24 antigen immune complexing with anti-p24 antibodies on the assessment of their respective levels in HIV-positive sera. ELISAs were used to evaluate anti-p24 antibody levels and p24 antigenemia, with or without acid dissociation. Observations include the following: (1) p24 antigenemia usually coexisted with low anti-p24 levels; (2) the p24 antigen concentration inversely correlated with anti-p24 antibody levels; and (3) acid dissociation increased the percentage of p24 antigen-positive sera, mostly when anti-p24 was low. In contrast, (1) antigenemia and antibodies varied independently in antiretroviral-treated AIDS patients, undetectable p24 antigen coexisting then with low anti-p24; (2) after acid dissociation, antigen was still undetectable in 83% of sera with high antibody levels, and in 20% with low antibody levels; and (3) acid dissociation did not increase low anti-p24 levels. Whereas the first set of observations indicates that p24 antigen and anti-p24 antibodies can be engaged in immune complexes, the second set indicates that p24 antigen and antibodies were not inevitably linked in such complexes: they may actually be indicative of two distinct biological phenomena.

A peptide substitution in HIV-1 gp120 first hypervariable domain enhances its immunogenicity in mice.

The envelope (Env) protein from HIV-1 is the focus of several vaccine trials in humans. It could be considered for the optimization of Env vaccinal preparations to add within the molecule defined epitopes, for instance epitopes conserved among viral isolates from HIV-1, such as from Gag or Nef proteins. As a first step to this approach, we have constructed by in vitro mutagenesis HIV-1(LAI) Env gp120 molecules in which a 12-amino acid sequence in the first (V1) or the third (V3) hypervariable region was substituted by the hemagglutinin (HA) 307-318 peptide from the influenza virus, a dominant T helper cell epitope in humans. The proteins were produced by recombinant vaccinia viruses. They had kept their structural properties in terms of serological recognition and binding to CD4. Of note, we observed that the gp120 protein substituted in the V1 domain elicited a stronger serological immune response in mice compared to native or V3 substituted gp120. This indicates that gp120 can accommodate large substitutions without major structural perturbations and that, on the contrary, some of them could prove beneficial in terms of immunogenicity.

Relationships between the anti-HIV V(3)-derived peptide SPC(3) and lymphocyte membrane properties involved in virus entry: SPC(3) interferes with CXCR(4).

SPC(3) is a multiple antigen peptide derived from the V(3) loop of human immunodeficiency virus (HIV) envelope (Env). It exerts a potent anti-HIV activity whereas it alters neither Env expression nor binding to CD(4). Here, SPC(3) binding characteristics, its subsequent intracellular fate and the fact that it inhibited SDF(1)alpha binding to the lymphocyte surface provided strong arguments to conclude that it exerts its anti-HIV activity through interference with the CXCR(4) coreceptor. In contrast, it interferes with none of the other major surface proteins and mechanisms involving V(3) and implicated in infection, as shown here. This work identifies the target mechanism of SPC(3).

Anti-platelet activity of the peptides composing the lebetin 1 family, a new class of inhibitors of platelet aggregation.

We have purified from Vipera lebetina venom a family of inhibitors of platelet aggregation, named Lebetins. They are composed of two peptide groups of short (Lebetin 1: L1alpha: GDNKPPKKGPPNG; L1beta: DNKPPKKGPPNG) and long (Lebetin 2: L2alpha: GDNKPPKKGPPNGCFGHKIDRIGSHSGLGCNKVDDNKG; L2beta: DNKPPKKGPPNGCFGHKIDRIGSHSGLGCNKVDDNKG) size. The sequence presenting anti-platelet activity is mainly present within the Lebetin 1 sequence [Barbouche, R. Marrakchi, N., Mansuelle, P., Krifi, M., Fenouillet, E., Rochat, H. and El Ayeb, M. (1996) Novel anti-platelet aggregation polypeptides from Vipera lebetina venom: isolation and characterization. FEBS Lett. 392, 6-10]. Here, the peptides that compose the Lebetin 1 family were synthesized. Their respective activity was determined. Synthetic L1alpha and L1beta inhibited collagen-induced platelet aggregation in the nanomolar range. A peptide corresponding to L1beta deleted by D at its N terminus (L1gamma) also inhibited platelet aggregation potently; further truncation of L1gamma impaired its activity. Because L1 peptides efficiently inhibited fibrinogen-induced alpha-chymotrypsin treated-platelet aggregation, we tested whether they act mainly through the inhibition of platelet binding to fibrinogen and showed that they failed to inhibit platelet binding to fibrinogen-coated wells. The activity of L1 peptides was also tested in vivo: their intravenous administration strongly inhibited collagen-induced thrombocytopenia in rats.

Adenosine and hemodialysis in humans.

BACKGROUND: Infections and hypotension are serious complications that develop during hemodialysis (HD) treatment. Adenosine (ADO), a strong hypotensive and immunosuppressive agent, may participate in these two HD complications, because high concentrations of ADO metabolites are found in dialyzed human plasma. ADO, which is released by endothelial cells, is quickly transformed into inosine (INO) by plasmatic ADO deaminase (ADA) and mononuclear cell ADO deaminase (MCADA). In plasma, the degradation of ADO into INO and its uptake by red blood cells (RBC) are both very rapid, resulting in the short half-life of ADO in blood. METHODS: Using liquid chromatography, we evaluated ADO and INO plasma concentrations before and after HD session. RESULTS: Before the HD session, ADO and INO plasma concentrations were higher in hemodialyzed patients than in controls and in peritoneally dialyzed patients. At the end of the HD session, ADO plasma concentration was increased. ADO plasma concentration for the undialyzed patients was in the same range as that of the controls. Before HD, ADA activity was higher in hemodialyzed patients (559 +/- 349 IU) than in controls (219 +/- 48 IU), and the activity rose during the session (665 +/- 135 IU). ADA activity in the undialyzed patients (222 +/- 80 IU) was in the same range as that of the controls (219 +/- 48 IU). Before the HD session, the MCADA activity (247 +/- 144 IU) was lower than in controls (624 +/- 99 IU). HD did not modify ADO RBC uptake. ADO inhibited mononuclear cell proliferation and interferon-gamma production in humans. Finally, as much as 50 microM INO does not inhibit ADO uptake by RBC and does not modify ADA and MCADA activities. CONCLUSIONS: These data indicate that chronic HD inhibited MCADA activity and increased ADO plasma concentration. Both high ADO plasma concentration and low MCADA activity may be involved in dialysis-induced immune system failure and thereby favor infectious diseases.