Activation of natural killer T cells by alpha-galactosylceramide treatment prevents the onset and recurrence of autoimmune Type 1 diabetes.

Type 1 diabetes (T1D) in non-obese diabetic (NOD) mice may be favored by immune dysregulation leading to the hyporesponsiveness of regulatory T cells and activation of effector T-helper type 1 (Th1) cells. The immunoregulatory activity of natural killer T (NKT) cells is well documented, and both interleukin (IL)-4 and IL-10 secreted by NKT cells have important roles in mediating this activity. NKT cells are less frequent and display deficient IL-4 responses in both NOD mice and individuals at risk for T1D (ref. 8), and this deficiency may lead to T1D (refs. 1,6-9). Thus, given that NKT cells respond to the alpha-galactosylceramide (alpha-GalCer) glycolipid in a CD1d-restricted manner by secretion of Th2 cytokines, we reasoned that activation of NKT cells by alpha-GalCer might prevent the onset and/or recurrence of T1D. Here we show that alpha-GalCer treatment, even when initiated after the onset of insulitis, protects female NOD mice from T1D and prolongs the survival of pancreatic islets transplanted into newly diabetic NOD mice. In addition, when administered after the onset of insulitis, alpha-GalCer and IL-7 displayed synergistic effects, possibly via the ability of IL-7 to render NKT cells fully responsive to alpha-GalCer. Protection from T1D by alpha-GalCer was associated with the suppression of both T- and B-cell autoimmunity to islet beta cells and with a polarized Th2-like response in spleen and pancreas of these mice. These findings raise the possibility that alpha-GalCer treatment might be used therapeutically to prevent the onset and recurrence of human T1D.

Interleukin 7 induces preferential expansion of V beta 8.2+CD4-8- and V beta 8.2+CD4+8- murine thymocytes positively selected by class I molecules.

We analyzed the phenotype and V beta-T cell receptor (TCR) repertoire, together with interleukin 7 receptor (IL-7R) expression in unfractionated thymocytes stimulated in vitro with IL-7. This culture system results in a specific proliferation of mature thymocytes belonging to the CD3+CD4-, CD4+8-, and CD4-8+ subsets. IL-7 induced a preferential expansion of V beta 8.2+CD4-8- and V beta 8.2+CD4-8- thymocytes. This phenomenon is not observed in beta 2-microglobulin-deficient mice, showing that a fraction of CD4+8- thymocytes, enriched in V beta 8.2+ cells, is selected by class I molecules in normal mice, as are a large proportion of CD4-8- alpha beta TCR+ thymocytes. Our findings also establish that IL-7 plays a major role in the expansion of rare thymocyte subsets, which could exert important functions in inflammatory and immune responses.

IL-33 receptor ST2 deficiency attenuates renal ischaemia-reperfusion injury in euglycaemic, but not streptozotocin-induced hyperglycaemic mice.

AIM: Kidney hypoxia can predispose to the development of acute and chronic renal failure in diabetes. Ischaemia-reperfusion injury (IRI) causes inflammation, and diabetes is known to exacerbate this inflammatory response in the kidney, whereas alarmin IL-33 could act as an innate immune mediator during kidney IRI. Thus, the present study examined the impact of genetic IL-33 receptor ST2 deficiency (ST2-/-) on renal IRI in euglycaemic and hyperglycaemic mice. METHODS: Hyperglycaemia was induced with streptozotocin (STZ) in adult male C57BL/6JRj wild-type (WT) mice and ST2-/- mice. Unilateral renal IRI was achieved 3months after STZ treatment by left kidney nephrectomy (non-ischaemic control kidney) and clamping of the right renal artery for 32min in STZ- and vehicle-treated animals. At 24h after reperfusion, renal function and injury were determined by levels of plasma creatinine, blood urea nitrogen (BUN) and histological tubule scores. Also, in a complementary pilot clinical study, soluble ST2 concentrations were compared in diabetics and non-diabetics. RESULTS: Urinary albumin was significantly increased in STZ-induced hyperglycaemic mice, regardless of genotypic background. At 24h post-ischaemia, plasma creatinine, BUN and tubular injury were significantly reduced in ST2-/- mice compared with vehicle-treated WT mice, but this protective effect was lost in the STZ-induced hyperglycaemic ST2-/- animals. Plasma concentrations of soluble ST2 were significantly greater in type 2 diabetes patients vs non-diabetics. CONCLUSION: Our data suggest that the IL-33/ST2 pathway exerts differential effects depending on the glucose environment, opening-up new avenues for future research on alarmins and diabetes in ischaemia-related diseases.

In vivo soluble tumor necrosis factor receptor release in OKT3-treated patients. Differential regulation of TNF-sR55 and TNF-sR75.

Administration of monoclonal antibodies to CD3 triggers acute and massive release of several cytokines, including tumor necrosis factor alpha (TNF-alpha), essentially T cell-derived. This cytokine release is responsible for the spontaneously reversible acute clinical syndrome observed in most OKT3-treated patients. We found that the first OKT3 injection in human renal allograft recipients led to the release in significant amounts of soluble TNF receptors (TNF-sR55 and TNF-sR75) that are considered main natural inhibitors of TNF bioactivity. As for OKT3-induced TNF-alpha, peak TNF-sR levels were observed 1 hr postinjection, and this release was limited to the first monoclonal antibody injection. A distinct regulation of OKT3-mediated release of TNF-sR75 and TNF-sR55 was observed, since (1) in clear contrast with OKT3-mediated TNF-sR75 induction, TNF-sR55 release was completely blocked by a high dose of corticosteroids prior to OKT3 injection and (2) secretion of TNF-sR75 but not TNF-sR55 correlated with immunoreactive TNF-alpha release. In hemodialyzed patients prior to transplantation and OKT3 treatment, a condition characterized by chronic TNF-alpha release, TNF-sR efficiently block TNF bioactivity. In contrast, the system is overwhelmed by the massive acute TNF-alpha release that follows the first OKT3 injection: in such a condition TNF-sR looses its capacity to counteract TNF bioactivity.

CD3 antibody-induced IL-10 in renal allograft recipients: an in vivo and in vitro analysis.

BACKGROUND: The first administration of CD3 monoclonal antibodies, such as anti-human CD3 (OKT3), induces a massive release of several cytokines, including tumor necrosis factor alpha (TNF-alpha), interferon (IFN)-gamma, interleukin (IL)-2, IL-3, IL-6, and granulocyte-macrophage colony-stimulating factor. METHODS: Cytokine levels in patient's sera were measured by specific ELISA. In vitro cultures were performed using OKT3-stimulated peripheral blood mononuclear cells and/or whole blood from patients and normal controls. RESULTS: Here we describe that OKT3 administration to human renal allograft recipients also leads to a significant release of IL-10. Contrasting with most OKT3-induced cytokines, such as TNF-alpha whose release is transient, IL-10 levels show a more progressive increase, they peak only by 4-8 hr after the first OKT3 injection and persist longer. Thus, significant IL-10 levels are still detectable at the time of the second and the third OKT3 injection. Administration of corticosteroids, 1 hr before the first OKT3 injection, significantly reduced both TNF-alpha and IL-10 release. Experiments were performed to evaluate the source(s) of IL-10 and its (their) influence on the initial T-cell activation. When stimulated in culture with soluble OKT3, the production of IL-10 was dependent on the cooperation between T lymphocytes and monocytes. It is important that, as assessed through the use of a specific neutralizing antibody, the endogenous IL-10 produced in the co-culture system exerted a negative feed-back on the release of the other pro-inflammatory CD3-induced cytokines, which was reproducible. CONCLUSION: These results are supportive of a major role of IL-10 in the down-modulation of the OKT3-triggered T-cell activation cascade.

Characterization of thymic cell subpopulations involved in IL-1- or GM-CSF-induced IL-6 production.

IL-6 has been demonstrated by in vitro studies to be a cytokine involved in thymocyte activation We show herein that thymocytes cultured at high concentrations in the absence of comitogen respond to IL-1 and, to a lesser degree, to GM-CSF, by producing IL-6. This phenomenon disappears rapidly with decreasing cell densities, suggesting the involvement of a minor cellular component of the thymus which may be solely responsible for or cooperate in IL-6 production. We have analysed several thymic subpopulations for IL-6 production and show that accessory cells, and eventually their precursors, are the major if not exclusive, producers of this cytokine. Mature steroid-resistant thymocytes do not secrete IL-6. Production of IL-6 by total CD4-CD8- thymic cells is largely reduced by the depletion of mature accessory cells which express I-A and Mac-1 antigens. As shown previously, accessory cell precursors within the CD4-CD8- compartment are induced to differentiate into M phi and DC in response to IL-1 and GM-CSF. We provide evidence that this maturation is associated with IL-6 production. Thymic DC and phagocytic cells of the thymic reticulum (P-TR) in vitro produce high levels of IL-6 which are enhanced by GM-CSF or IL-1. These factors have a synergistic effect on IL-6 production by total thymocytes, and on CD4-CD8- cells that are not depleted for mature I-A+ Mac-1+ accessory cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Inflammation: "a natural experiment" for the systemic pathogenicity of cytokines.

It has previously been demonstrated that the overproduction of interleukin-6 (IL-6) is a key element in the clinical and biological abnormalities encountered in Castleman's disease (CD). The particular case of a male child with a localized form of CD is reported. In this patient, evidence was found of a correlation between systemic manifestations and circulating IL-6, and IL-6 gene overexpression in the germinal centers of hyperplastic lymph nodes. Circulating IL-6 levels were 10- to 100-fold higher than in all CD cases previously documented. This unique biological feature was closely associated with high levels of circulating IL-1 and tumor necrosis factor-alpha (TNF-alpha), which are known for their ability to induce and/or amplify IL-6 production. One month after surgical removal of the pathological lymph node, the clinical and biological abnormalities diminished, while circulating IL-6 levels dropped dramatically eight months later. It is worth noting that after resection, the time-course of the IL-6 decrease closely correlated with that of IL-1 and TNF-alpha. Considering that in various inflammatory diseases IL-1, TNF-alpha and IL-6 may act in a synergistic manner in inducing systemic manifestations, this case report raises new questions as to the nature of the systemic pathogenicity of cytokines in CD.

[Dysregulation of the immune system in chronic uremic and hemodialysed patients]. / Dysrégulation du système immunitaire chez l'urémique chronique et le dialysé.

Concomitant immune deficiency and activation of immuno-competent cells, together with a disequilibrium between inflammation-inducing cytokines and their specific natural inhibitors is the basis of our current understanding of immune system dysregulation in patients with chronic uraemia. These anomalies may even be accentuated by dialysis. Clinically, bacterial infections, viral hepatitis and amyloidosis all play important roles. Humoral factors include abnormal immunoglobulin response to specific antibodies and complement activation. The response of T lymphocytes, long sought as the origin of the immunodeficiency associated with chronic uraemia, is also significantly decreased in these patients. The decreased antibody responses to specific stimuli may be related to B cell dysfunction. Monocyte and polymorphonuclear cell reactions are also perturbed. A deficiency in natural killer cells is observed although the mechanisms involved and the consequences are still debated. The factors determining the anomalies leading to immune system dysregulation in chronic uraemia and dialysis and their relationship with the reduction in active nephron mass as well as their metabolic and/or endocrine consequences remain to be fully described. A better understanding of the mechanisms involved should lead to new strategies for immuno-intervention in patients with chronic renal failure and help in optimizing haemodialysis.

Identification of invariant natural killer T cells in porcine peripheral blood.

The pig is a relevant preclinical model for numerous pathologies used to validate therapeutic strategies for translation to human. Although invariant natural killer T (iNKT) lymphocytes are a component of innate immunity implicated in many pathological processes, little is known on their characterization in swine. By addressing this issue using mouse α-galactosylceramide-loaded CD1d tetramers (α-GC-CD1dTT), which are commonly used to track iNKT cells, we were able to unequivocally identify CD3(+)α-GC-CD1dTT(+) cells in porcine peripheral blood, hereafter referred to as swine iNKT cells. These lymphocytes are enriched in CD4(-)CD8(+) and CD4(-)CD8(-) cells, harbor an activated-memory phenotype (SLA-DR(+)CD45RA(-)), express the intracellular promyelocytic-leukemia-zinc-finger (PLZF) transcription factor and are significantly enriched in IFN-γ-producing cells after in vitro activation in comparison with conventional T cells. Importantly, in presence of IL-2 and IL-15, the iNKT cell ligand α-GC induces selective expansion of CD3(+)α-GC-CD1dTT(+) cells, confirming the reactivity of swine iNKT cells against α-GC. When associated with α-GC, IL-33, an alarmin of IL-1 family recently described to target iNKT cells, leads to a greater expansion of CD3(+)α-GC-CD1dTT(+) cells than IL-2 and IL-15. Altogether, our results provide the first phenotypic and functional description of swine iNKT cells allowing to further study the critical role of iNKT cells in porcine models of organ injury.

Freshly isolated Valpha24+ CD4+ invariant natural killer T cells activated by alpha-galactosylceramide-pulsed B cells promote both IgG and IgE production.

CD1d-restricted invariant natural killer T (iNK T) cells activated by their experimental ligand alpha-galactosylceramide (alpha-GC) can produce both T helper 1 (Th1) and Th2 cytokines and display regulatory functions. Recent studies identified CD4(+) and CD4(-) CD8(-) double-negative (DN) iNK T cells as the two major components of the human population and suggest that they display a Th2 and a Th1 profile, respectively. We compared the Th2-promoting activity of freshly isolated human CD4(+) and DN iNK T cells in terms of their capacity to induce Ig production by autologous B cells. Secretion of IgG and IgE but not IgM was enhanced by the CD4(+) T cell subset (including iNK T cells) but not by its DN counterpart. iNK T cells were directly responsible for this pro-Th2 effect, as demonstrated by the requirement for both alpha-GC stimulation and CD1d presentation, as well as by its disappearance upon iNK T cell depletion. Interaction with iNK T cells led to progressive accumulation of isotype-switched and activated B cells. Myeloid dendritic cells (DC) completely block the induction of Ig production in co-culture. This dominant inhibitory effect of myeloid DC was concomitant with a specific loss of interleukin (IL)-4 production by CD4(+) iNK T but not by conventional T cells. These data support the conclusion that, conversely to the interferon (IFN)-gamma-producing DN human iNK T cell population, interleukin (IL)-4-producing CD4(+) iNK T cells can activate and help B cells to produce both IgG and IgE through a CD1d-dependent mechanism, in keeping with a functional Th1/Th2 dichotomy between these subsets.

[Effects of hematopoietic growth factor (GM-CSF: granulocyte-macrophage colony-stimulating factor) on thymocyte proliferation induced by interleukin-1 (IL-1)]. / Effet d'un facteur de croissance hématopoiétique (GM-CSF: granulocyte-macrophage colony-stimulating factor) sur la prolifération thymocytaire induite par l'interleukine-1 (IL-1).

A semi-purified fraction obtained from P388 D1 cell line conditioned medium (P388 D1 CM) which contains Interleukin-1 (IL-1) and Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) stimulates murine thymocyte proliferation both in the absence and the presence of a suboptimal dose of phytohemagglutinin (PHA). Because this effect on thymocyte proliferation is always larger than that obtained with optimal concentrations of pure IL-1, we have investigated the possible involvement of GM-CSF in this semi-purified fraction mediated-thymocyte proliferation. We here show that the maximal level of thymocyte proliferation induced by the semi-purified fraction is comparable to that obtained by the co-addition of recombinant GM-CSF and IL-1. In addition, although GM-CSF alone induces no significant thymocyte proliferation, the presence of an anti-GM-CSF antiserum partially blocks the thymocyte proliferation induced by the semi-purified fraction. Thus, the capacity of the semi-purified fraction of P388 D1 to stimulate thymocyte proliferation appears to result from a synergistic action between GM-CSF and IL-1.

Potentiating effect of granulocyte-macrophage colony-stimulating factor on interleukin-1-induced thymocyte proliferation: evidence for an interleukin-2 and tumor necrosis factor-independent pathway.

The effect of Colony-Stimulating Factors (CSFs) on the growth of murine thymocytes was investigated. None among the following factors tested alone, i.e., Interleukin-3 (IL-3), Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF), Granulocyte Colony-Stimulating Factor (G-CSF) or Macrophage Colony-Stimulating Factor (M-CSF) has been found to stimulate thymidine uptake by thymocytes. However, GM-CSF synergistically enhances thymocyte proliferation induced by Interleukin-1 (IL-1). Synergistic responses are obtained at a very pronounced level after 3 days of culture with very low factor concentrations (1.5 to 15 pM) and in the complete absence of mitogen. Similar effects are induced by IL-3, though to a lesser degree. In contrast, neither G-CSF nor M-CSF potentiate thymocyte proliferation promoted by IL-1. Kinetic studies show that the synergy between IL-1 and GM-CSF reaches its maximum after about 72 h of thymocyte culture and that it requires the simultaneous presence of both factors during the first 24 h. In addition, our data suggest that GM-CSF acts in synergy with IL-1 by an Interleukin-2 (IL-2)-independent pathway since: (i) incubation of thymocytes with GM-CSF in the presence of IL-1 does not significantly enhance the expression of the IL-2 receptors (IL-2R) as demonstrated by flow cytometry, and, (ii) specific monoclonal antibodies against murine IL-2 or IL-2R fail to reduce thymocyte proliferation in response to the synergistic combination. Similarly, the potentiating effect of GM-CSF on IL-1 thymocyte growth does not depend on Tumor Necrosis Factor alpha (TNF) since (i) the synergy for IL-1 and GM-CSF and that previously described for IL-1 and TNF cumulate and (ii) anti-TNF antibodies do not abolish the potentiating effect of GM-CSF.

Functional bioassays for B cell growth factors using polyclonally activated murine spleen B cells.

In this study, we have set up and optimized three distinct T cell-independent polyclonal B cell activation assay systems using highly T cell-depleted murine spleen B cells which were either preactivated in vitro with lipopolysaccharide (LPS) or costimulated with anti-IgM antibodies (anti-mu) or dextran sulfate (DxS). Using these assays, we have investigated the effects of recombinant human or murine interleukins, as well as those of a partially purified T cell-derived factor, designated BSF-LPS. Our results show that none of the interleukins, alone or in combination, is able to maintain growth of the LPS-preactivated B cell blasts, even at the highest concentrations tested, whereas the addition of our BSF-LPS preparation to the cultures significantly increases DNA synthesis. As expected, recombinant murine IL-4 (r mu IL-4) causes a substantial proliferation of anti-mu costimulated B cells. Such anti-mu costimulated B cells also respond, to a lower degree, to recombinant human IL-1 alpha (r hu IL-1 alpha), and do not significantly proliferate upon addition of r mu IL-2, r mu IL-5 or BSF-LPS. On the other hand, r mu IL-5 stimulates very efficiently DxS-costimulated B cells proliferation, whereas r hu IL-1 alpha only exerts a marginal effect; r mu IL-2, r mu IL-4 or BSF-LPS did not maintain growth of DxS-costimulated B cells. We believe that such a thorough investigation of the particular behaviour of activated B cell subpopulations towards various lymphokines provides the background for setting up a valuable bioassay method to differentiate the various interleukins acting on B cells through parallel use of the three distinct T cell-independent polyclonal B cell activation assay systems.

Endogenous anxiogenic peptide, ODN-diazepam-binding inhibitor, and benzodiazepines enhance the production of interleukin-1 and tumor necrosis factor by human monocytes.

Benzodiazepines (BZD) have been described to interact with specific peripheral-type receptors on phagocytes. The present study demonstrates that pico- to nanomolar concentrations of BZD compounds enhance the lipopolysaccharide (LPS)-induced production of tumor necrosis factor (TNF) and interleukin-1 (IL-1) by human monocytes, as determined by specific immunoreactive and biological assays for these cytokines. BZD remained ineffective in the absence of LPS. The activity of BZD was restricted to peripheral (Ro 5-4864) and mixed (diazepam, Valium) type ligands, while anxiogenic (beta-carbolines) or anxiolytic (clonazepam) central type ligands had no effect. Interestingly, peptide fragments of the endogenous anxiogenic ligand diazepam-binding inhibitor (DBI), such as octadecaneuropeptide (ODN-DBI) and the octaneuropeptide corresponding to its COOH-terminal sequence, very efficiently modulated the LPS-induced production of both monokines. Similar results were obtained directly within whole blood samples. These results indicate that widely prescribed pharmacological compounds and endogenous anxiety modulators affect molecular mediators of human host defense mechanisms and inflammatory reactions.

CD11c+ eosinophils in the murine thymus: developmental regulation and recruitment upon MHC class I-restricted thymocyte deletion.

Eosinophils are bone marrow-derived cells released into the circulation during hypersensitivity reactions and parasitic infections. Under normal conditions most eosinophils are tissue bound, where their physiologic role is unclear. During in situ analysis of the thymic microenvironment for CD11c+ dendritic cell subpopulations (APC critical in the process of thymic negative selection) a discrete population of CD11b/CD11c double-positive cells concentrated in the cortico-medullary region of young mice was detected. Thymic CD11c+ cells were isolated, and the CD11b+ subpopulation (CD44high, class IIlow, CD11cint) was identified as mature eosinophils based on: scatter characteristics, major basic protein mRNA expression, and eosinophilic granules. They are hypodense, release high levels of superoxide anion, and express CD25, CD69, and mRNA for IL-4 and IL-13, but not GM-CSF or IL-5, suggesting a distinct state of activation. Thymic eosinophils are preferentially recruited during the neonatal period; absolute numbers increased 10-fold between 7-14 days to reach parity with dendritic cells before diminishing. In a model of acute negative selection, eosinophil numbers were increased 2-fold 6 h after cognate peptide injection into MHC class I-restricted female H-Y TCR transgenic mice. In both peptide-treated female and negatively selecting male H-Y TCR mice, clusters of apoptotic bodies were associated with eosinophils throughout the thymus. Our data demonstrate a temporal and spatial association between eosinophil recruitment and class I-restricted selection in the thymus, suggesting an immunomodulatory role for eosinophils under nonpathological conditions.

IL-7 is requisite for IL-1-induced thymocyte proliferation. Involvement of IL-7 in the synergistic effects of granulocyte-macrophage colony-stimulating factor or tumor necrosis factor with IL-1.

In the absence of artificial comitogens murine thymocytes proliferate significantly in response to IL-1 at high but not at low cell densities. This observation has led us to examine a possible indirect mechanism requiring other thymocyte-growth factors, such as IL-2, IL-4, IL-6, and IL-7, in this phenomenon. Our data provide evidence that IL-7 is requisite for the IL-1-induced proliferative response because on the one hand the growth-promoting activity of IL-1 is completely inhibited by an anti-IL-7 mAb, and on the other hand IL-7 synergizes with IL-1 on thymocyte growth. This synergy is observed even at concentrations at which IL-7 is not detected in the pre-B cell proliferation assay, and results, at optimal doses, in TdR incorporation levels similar to those attained in response to IL-1 + IL-2. The anti-IL-7 mAb acts in a dose-dependent manner and does not affect other activities of IL-1, such as its capacity to sustain the growth of the U373 astrocytoma cell line. It is also noteworthy that this mAb does not significantly impair thymocyte growth in response to IL-2 and that the growth-promoting activity of IL-1 is not affected by neutralizing mAb against IL-2, IL-4, and IL-6. In addition, we show that the potentiating effect of granulocyte-macrophage (GM)-CSF and TNF-alpha on IL-1-induced thymocyte growth is dependent on IL-7 because i) the anti-IL-7 mAb abrogates the respective synergistic interactions and ii) both factors potentiate the proliferative response to IL-7. Finally, depletion of thymocyte suspensions for Ia+ Mac-1+ accessory cells results in a considerable decrease in IL-1- and IL-1 + GM-CSF-induced TdR uptake, whereas IL-7-induced growth remains unchanged. Taken together, these results support the notion that, in the absence of artificial comitogens, thymocyte proliferation in response to IL-1 alone or in combination with GM-CSF is dependent on accessory cell-derived IL-7.

Influence of uremia and hemodialysis on circulating interleukin-1 and tumor necrosis factor alpha.

Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) were determined in the plasma of long-term hemodialysis (HD) patients and uremic (UR) patients undergoing their first dialysis session using either cellulosic (CUP) or synthetic (PAN-AN 69) membrane-equipped dialyzers. In long-term HD patients, plasma IL-1 and TNF alpha levels were significantly increased compared to their levels in normal subjects. During a single dialysis session, a significant increase in IL-1 but not in TNF alpha was observed. In not yet dialyzed UR patients, IL-1 plasma levels did not differ from those observed in normal subjects. By contrast, TNF alpha was found significantly increased although less than in long-term HD patients. During the first dialysis session, no significant increase was observed in the levels of either monokine. Lastly, regardless of the group of patients, no significant influence of the dialysis membrane could be detected, suggesting that the observed changes are not exclusively secondary to the activation of complement. Altogether, these results suggest that the passage of the blood through the extracorporeal dialysis circuit triggers the secretion of IL-1 and further exacerbates that of TNF alpha by monocytes. The presence of increased TNF alpha in the plasma of first-dialysis UR patients suggests that factors unrelated to dialysis contribute to the activation of monocytes in these patients. Lastly, the concomitant presence of IL-1 and TNF alpha in the plasma of long-term HD patients could be responsible for some of the clinical features observed in these patients, and provides strong evidence favoring the concept that HD can be assimilated to a recurrent acute-phase inflammatory response.