Reducing affinity as a strategy to boost immunomodulatory antibody agonism.

Antibody responses during infection and vaccination typically undergo affinity maturation to achieve high-affinity binding for efficient neutralization of pathogens1,2. Similarly, high affinity is routinely the goal for therapeutic antibody generation. However, in contrast to naturally occurring or direct-targeting therapeutic antibodies, immunomodulatory antibodies, which are designed to modulate receptor signalling, have not been widely examined for their affinity-function relationship. Here we examine three separate immunologically important receptors spanning two receptor superfamilies: CD40, 4-1BB and PD-1. We show that low rather than high affinity delivers greater activity through increased clustering. This approach delivered higher immune cell activation, in vivo T cell expansion and antitumour activity in the case of CD40. Moreover, an inert anti-4-1BB monoclonal antibody was transformed into an agonist. Low-affinity variants of the clinically important antagonistic anti-PD-1 monoclonal antibody nivolumab also mediated more potent signalling and affected T cell activation. These findings reveal a new paradigm for augmenting agonism across diverse receptor families and shed light on the mechanism of antibody-mediated receptor signalling. Such affinity engineering offers a rational, efficient and highly tuneable solution to deliver antibody-mediated receptor activity across a range of potencies suitable for translation to the treatment of human disease.

A cell-penetrating CD40-TRAF2,3 blocking peptide diminishes inflammation and neuronal loss after ischemia/reperfusion.

While the administration of anti-CD154 mAbs in mice validated the CD40-CD154 pathway as a target against inflammatory disorders, this approach caused thromboembolism in humans (unrelated to CD40 inhibition) and is expected to predispose to opportunistic infections. There is a need for alternative approaches to inhibit CD40 that avoid these complications. CD40 signals through TRAF2,3 and TRAF6-binding sites. Given that CD40-TRAF6 is the pathway that stimulates responses key for cell-mediated immunity against opportunistic pathogens, we examined the effects of pharmacologic inhibition of CD40-TRAF2,3 signaling. We used a model of ischemia/reperfusion (I/R)-induced retinopathy, a CD40-driven inflammatory disorder. Intravitreal administration of a cell-penetrating CD40-TRAF2,3 blocking peptide impaired ICAM-1 upregulation in retinal endothelial cells and CXCL1 upregulation in endothelial and Müller cells. The peptide reduced leukocyte infiltration, upregulation of NOS2/COX-2/TNF-α/IL-1ß, and ameliorated neuronal loss, effects that mimic those observed after I/R in Cd40-/- mice. While a cell-penetrating CD40-TRAF6 blocking peptide also diminished I/R-induced inflammation, this peptide (but not the CD40-TRAF2,3 blocking peptide) impaired control of the opportunistic pathogen Toxoplasma gondii in the retina. Thus, inhibition of the CD40-TRAF2,3 pathway is a novel and potent approach to reduce CD40-induced inflammation, while likely diminishing the risk of opportunistic infections that would otherwise accompany CD40 inhibition.

ESCMID Study Group for Infections in Compromised Hosts (ESGICH) Consensus Document on the safety of targeted and biological therapies: an infectious diseases perspective (Agents targeting lymphoid or myeloid cells surface antigens [II]: CD22, CD30, CD33, CD38, CD40, SLAMF-7 and CCR4).

BACKGROUND: The present review is part of the ESCMID Study Group for Infections in Compromised Hosts (ESGICH) Consensus Document on the safety of targeted and biological therapies. AIMS: To review, from an Infectious Diseases perspective, the safety profile of agents targeting CD22, CD30, CD33, CD38, CD40, SLAMF-7 and CCR4 and to suggest preventive recommendations. SOURCES: Computer-based MEDLINE searches with MeSH terms pertaining to each agent or therapeutic family. CONTENT: The risk and spectrum of infections in patients receiving CD22-targeted agents (i.e. inotuzumab ozogamicin) are similar to those observed with anti-CD20 antibodies. Anti-Pneumocystis prophylaxis and monitoring for cytomegalovirus (CMV) infection is recommended for patients receiving CD30-targeted agents (brentuximab vedotin). Due to the scarcity of data, the risk posed by CD33-targeted agents (gemtuzumab ozogamicin) cannot be assessed. Patients receiving CD38-targeted agents (i.e. daratumumab) face an increased risk of varicella-zoster virus (VZV) infection. Therapy with CD40-targeted agents (lucatumumab or dacetuzumab) is associated with opportunistic infections similar to those observed in hyper-IgM syndrome, and prevention strategies (including anti-Pneumocystis prophylaxis and pre-emptive therapy for CMV infection) are warranted. SLAMF-7 (CD319)-targeted agents (elotuzumab) induce lymphopenia and increase the risk of infection (particularly due to VZV). The impact of CCR4-targeted agents (mogamulizumab) on infection susceptibility is difficult to distinguish from the effect of underlying diseases and concomitant therapies. However, anti-Pneumocystis and anti-herpesvirus prophylaxis and screening for chronic hepatitis B virus (HBV) infection are recommended. IMPLICATIONS: Specific management strategies should be put in place to reduce the risk and/or the severity of infectious complications associated to the reviewed agents.

Prospects for modulating the CD40/CD40L pathway in the therapy of the hyper-IgM syndrome.

The critical role of the CD40/CD40L pathway in B-cell proliferation, immunoglobulin (Ig) isotype switching and germinal center formation has been studied and described extensively in previous literature. Interruption of the CD40/CD40L signal causes hyper-IgM (HIGM) syndrome, which has been classified and recognized as a group of rare inherited immune deficiency disorders. Defects in CD40 and CD40L interactions or in downstream signaling molecules, including activation-induced cytidine deaminase, uracyl-DNA-glycosylase, NF-κB and DNA repair enzymes, result in an increased level of serum IgM and a significantly decreased or absent level of IgA, IgG and IgE that is accompanied by severe recurrent infections and autoimmune diseases. Many genetic defects in HIGM have been identified and, as a result, it is possible for patients to be definitively diagnosed by gene sequencing and to delineate the immunological features of the patients. Modifying the CD40/CD40L signaling pathway may offer the possibility of restoring the normal serum Ab production and curing the immunodeficiency. Hematopoietic stem cell transplantation has achieved a high rate of success using a sibling donor. In addition, successful examples of treating other immunodeficiencies using gene therapy indicated that there was a possibility of eradicating HIGM with this approach. In this review, we summarize the current drugs and a variety of therapeutic approaches for the treatment of the HIGM syndrome by interfering with the defective CD40/CD40L pathway.

VEGF Requires the Receptor NRP-1 To Inhibit Lipopolysaccharide-Dependent Dendritic Cell Maturation.

To stimulate a productive T cell response, dendritic cells (DC) must undergo maturation characterized by heightened cell surface expression of MHC and costimulatory molecules as well as cytokine production. Conversely, the inhibition of DC maturation is a central mechanism of immune tolerance. The control of the DC maturation process relies on the integration of several cellular stimulatory or inhibitory signals. The soluble factors and their receptors controlling this central aspect of DC biology are incompletely characterized. We show that murine bone marrow-derived DC (BMDC) maturation induced by LPS, as opposed to polyinosinic:polycytidylic acid or cytosine-phosphate-guanine, is robustly inhibited by vascular endothelial growth factor (VEGF), a previously identified immunosuppressive cytokine. Using BMDC from wild type and conditional knockout mice, we show that neuropilin-1 (NRP-1), a known receptor of VEGF, is necessary to suppress LPS-dependent BMDC maturation. The absence of NRP-1 had no ostensible effects on the biology of BMDC in the absence of VEGF. However, NRP-1-deficient BMDC remained completely insensitive to the VEGF-dependent inhibition of BMDC maturation in culture. In the presence of VEGF, NRP-1 directly interacted with the LPS receptor TLR4 and suppressed downstream signaling through ERK and NF-κß, resulting in a sharp inhibition of MHC class II and costimulatory molecules (CD40, CD86) expression as well as proinflammatory cytokine production. Consequently, we identify NRP-1 as a target to optimize DC maturation within environments that are rich in VEGF, such as tumors.

Anti-Tumor Necrosis Factor Therapy Restores Peripheral Blood B-cell Subsets and CD40 Expression in Inflammatory Bowel Diseases.

BACKGROUND: Anti-tumor necrosis factor (TNF) therapy has become a standard therapy for severe inflammatory bowel diseases (IBD), but its effect on B lymphocytes is largely unexplored. In this study we investigated peripheral blood B cells, B-cell subsets, and CD40 expression in patients with IBD before and during anti-TNF therapy with infliximab (IFX). METHODS: Blood was taken from healthy controls (n = 52) and patients with active IBD before (n = 46) and/or during anti-TNF therapy (n = 55). B-cell markers were detected by immunofluorescent staining and FACS analysis. Patients were classified as responders or nonresponders to anti-TNF therapy. RESULTS: We found a numerical deficiency of circulating CD19 B cells, a lower activation state (CD40 expression) and lower proportions of CD5 B cells and IgMIgDCD27 preswitched memory cells among B cells in active patients with IBD before IFX therapy compared with healthy controls. IFX treatment increased CD19 B-cell numbers as well as the proportions of named B-cell subsets in responders but not in nonresponders. IFX more effectively upregulated CD40 expression in responders than in nonresponders. Restoration of B cells correlated with the biological response to therapy (C-reactive protein). Trough serum levels of IFX correlated with the number of B cells during therapy. CONCLUSIONS: A lower number of circulating B cells, a low CD40 expression, and a decrease in the proportion of CD5 and in the preswitched memory subset characterize active IBD. Restoration of these abnormalities correlates with the clinical response to anti-TNF therapy. The mechanism for this effect on B cells should be further explored.

Rapamycin and CTLA4Ig synergize to induce stable mixed chimerism without the need for CD40 blockade.

The mixed chimerism approach achieves donor-specific tolerance in organ transplantation, but clinical use is inhibited by the toxicities of current bone marrow (BM) transplantation (BMT) protocols. Blocking the CD40:CD154 pathway with anti-CD154 monoclonal antibodies (mAbs) is exceptionally potent in inducing mixed chimerism, but these mAbs are clinically not available. Defining the roles of donor and recipient CD40 in a murine allogeneic BMT model, we show that CD4 or CD8 activation through an intact direct or CD4 T cell activation through the indirect pathway is sufficient to trigger BM rejection despite CTLA4Ig treatment. In the absence of CD4 T cells, CD8 T cell activation via the direct pathway, in contrast, leads to a state of split tolerance. Interruption of the CD40 signals in both the direct and indirect pathway of allorecognition or lack of recipient CD154 is required for the induction of chimerism and tolerance. We developed a novel BMT protocol that induces mixed chimerism and donor-specific tolerance to fully mismatched cardiac allografts relying on CD28 costimulation blockade and mTOR inhibition without targeting the CD40 pathway. Notably, MHC-mismatched/minor antigen-matched skin grafts survive indefinitely whereas fully mismatched grafts are rejected, suggesting that non-MHC antigens cause graft rejection and split tolerance.

Ileal immune dysregulation in necrotizing enterocolitis: role of CD40/CD40L in the pathogenesis of disease.

OBJECTIVES: CD40, a co-stimulatory molecule, plays a critical role in coordinating enteric inflammatory immune responses. In necrotizing enterocolitis (NEC), upregulation of IL-10, a CD40-modulated cytokine, has been described, but the role of the IL-10 receptor (IL-10Rß), CD40, and its ligand CD40L in disease pathogenesis is unknown. The study herein investigates ileal expression of CD40, CD40L, and IL-10R in a rat model of NEC. SUBJECTS AND METHODS: NEC was induced in newborn rats using established methods of formula feeding, asphyxia, and cold stress. Expression of CD40, CD40L, IL-10Rß, and other proinflammatory molecules, including Toll-like receptor-4 (TLR-4) and IL-18, was assessed by immunoblotting. Tissue infiltration by macrophages, monocytes, and T cells was examined by confocal immunohistochemistry. RESULTS: Ileum from rat pups with NEC showed increased expression of TLR-4, IL-18, and IL-10Rß. Sections from both NEC and control pups demonstrated preservation of ileal cells expressing CD40/CD40L. The distal ileum of controls expressed both CD40 and CD40L; conversely, neither molecule was detected in ileal tissue from NEC pups. Additional studies showed that treatment with epidermal growth factor (EGF), previously shown to ameliorate the severity of NEC in an animal model, did not restore CD40 expression. CONCLUSIONS: Ileal cytokine dysregulation, manifested by decreased CD40/CD40L and increased IL-10Rß expression, may be involved in the pathogenesis of NEC. Dampened CD40 signaling may be related to enhanced IL-10 expression and a suppressed T-cell response to injury. We speculate that augmenting CD40-CD40L interactions may achieve a protective effect in this NEC model.

Impact of the CD40-CD40L dyad in Alzheimer's disease.

As the number of elderly individuals rises, Alzheimer's disease (AD), marked by amyloid-beta deposition, neurofibrillary tangle formation, and low-level neuroinflammation, is expected to lead to an ever-worsening socioeconomic burden. AD pathoetiologic mechanisms are believed to involve chronic microglial activation. This phenomenon is associated with increased expression of membrane-bound CD40 with its cognate ligand, CD40 ligand (CD40L), as well as increased circulating levels of soluble forms of CD40 (sCD40) and CD40L (sCD40L). Here, we review the role of this inflammatory dyad in the pathogenesis of AD. In addition, we examine potential therapeutic strategies such as statins, flavonoids, and human umbilical cord blood transplantation, all of which have been shown to modulate CD40-CD40L interaction in mouse models of AD. Importantly, therapeutic approaches focusing on CD40-CD40L dyad regulation, either alone or in combination with amyloid-beta immunotherapy, may provide for a safe and effective AD prophylaxis or treatment in the near future.

Effect of high bolus dose tirofiban on the inflammatory response following percutaneous coronary intervention.

BACKGROUND: Tirofiban at the bolus dose of 10 microg/kg does not suppress the inflammatory response following percutaneous coronary intervention (PCI). This may be due to less than optimal inhibition of platelet aggregation. High bolus dose tirofiban (25 microg/kg) allows better inhibition of platelet aggregation but its anti-inflammatory effect remains unknown. HYPOTHESIS: High bolus dose tirofiban exhibits anti-inflammatory activity. METHODS: A total of 100 patients referred for PCI were randomized to receive high bolus dose tirofiban followed by a 24-h infusion or a bolus and an infusion of saline. Patients with elevated troponin or with thrombus in the culprit lesion were excluded. Inflammatory markers were measured at baseline and at 24 h. RESULTS: Levels of soluble CD40 ligand (sCD40L) were not affected by PCI while those of interleukin-6 (IL-6) and of high sensitivity C-reactive protein (hs-CRP) significantly increased. Despite inhibiting platelet's aggregation by > 90%, tirofiban did not suppress the rise of IL-6 and hs-CRP. Median (interquartile range) elevation of IL-6 was 0.6 pg/mL (-1.5-3.6) versus 0.4 pg/mL (-0.7-1.8) and that of hs-CRP was 2.1 mg/L (0.7-5.2) versus 2.4 mg/L (1-4.7) in the tirofiban and the control groups, respectively (p = ns). However, in patients with diabetes mellitus, tirofiban significantly suppressed the rise of hs-CRP by 65% (p = 0.01), but did not significantly affect the rise of IL-6. CONCLUSION: In low-risk patients undergoing PCI, tirofiban did not attenuate the rise of inflammatory markers. However, the significant effect in diabetics suggests that tirofiban may have anti-inflammatory activity in higher risk patients.

Short-term administration of ethanol in mice deviates antigen presentation activity towards B cells.

Alcohol has a variety of short- and long-term effects on cell-mediated and humoral immune response. Herein, we have characterized the impact of high-dose EtOH administration on phenotypic and functional features of murine APC subsets, including dendritic cell (DC), macrophages and B cells. Impaired cytokine synthesis and Leishmania-phagocytosis was observed in peritoneal macrophages following EtOH administration. Moreover, EtOH exposure led to decreased levels of splenic myeloid DC and increased percentage of macrophages with no changes in splenic lymphoid DC and B cells. Adverse effects of short-term EtOH administration also resulted in impaired OVA-endocytosis by DC and macrophages. In contrast, EtOH consumption upregulates OVA-internalization by B cells. These changes on APC hierarchy may play a role shifting the fate of the immune response after EtOH ingestion. In addition to an overall downregulation of Toll-like receptor-TLR-4 expression by splenic APC, a downregulation of TLR-2 expression in macrophages was observed. Moreover, EtOH exposure altered the expression of co-signalling molecules on splenic APC, downregulating CD40 on macrophages and upregulating CD80 on B cells, with no impact on DC subsets. The net result of changes in TLR-mediated and co-stimulatory signals may determine the altered immunological status induced by acute consumption of alcohol. A direct impact of high-dose EtOH administration in the activation status of splenic CD4(+) T cells was observed. Together, our results demonstrated that short-term high-dose EtOH administration has differential impact on APC populations, downregulating splenic macrophages and DC activity but up-regulating B lymphocyte function as APC, and ultimately yielding a micro-environment that led to increased activation of CD4(+) T cells.

CD40 ligation mediates plaque-associated tau phosphorylation in beta-amyloid overproducing mice.

Neuritic dystrophy with amyloid burden and neurofibrillary tangles are pathological hallmarks of Alzheimer's disease. Genetic disruption of CD40 or CD40L alleviates amyloid burden, astrocytosis, and microgliosis in transgenic animal models of Alzheimer's disease. It has been reported that phosphorylated tau-positive dystrophic neurites are observed in transgenic mice over-expressing human mutant beta-amyloid precursor protein (Tg2576). Here, we studied the pattern of phosphorylated tau (labeled with AT8, CP13, PG5, and PHF1 antibodies) and plaques using immunohistochemical techniques. Phosphorylated tau-positive dystrophic neurites were exclusively associated with Congo red-positive plaques as previously reported. Further, we show that CD40L or CD40 deficiency reduces the mean ratio of dystrophic neurite area to congophilic plaque area and the level of expression of cdk5 and p35/p25 in mice. In addition, we show that in a human neuroblastoma cell line treated with CD40L, cdk5 and p35/p25 are increased. Together, our data suggest that CD40-CD40L interaction has an effect on tau phosphorylation independent of beta-amyloid pathology, and that this effect may occur through a decrease of cdk5 and p35/p25.

N-acetylcysteine derivative inhibits CD40-dependent proinflammatory properties of human pancreatic duct cells.

OBJECTIVES: We recently observed that duct cells constitutively express CD40, a membrane molecule whose engagement results in duct cell activation and proinflammatory cytokine secretion. This observation suggests a potential role of this pathway in the pathogenesis of type 1 diabetes, islet graft rejection, or acute pancreatitis. In this article, we investigated whether a salt derivative of N-acetyl-L-cysteine, Nacystelyn, could modulate CD40 expression on duct cells and the response of activated duct cells to CD40 engagement. METHODS: We assessed the effects of Nacystelyn on CD40 expression and function in human caucasian pancreatic adenocarcinoma, ATCC n degrees THB-80 (CAPAN-2) cells, a human pancreatic duct cell line. CD40 expression was analyzed by flow cytometry. To assess CAPAN-2 cell responses to CD40 engagement, we looked at nuclear factor-kappaB transcription factor activation using enzyme-linked immunosorbent assay and electrophoretic mobility shift assay and cytokine mRNA levels by quantitative real-time reverse transcriptase polymerase chain reaction. RESULTS: We observed that Nacystelyn dose-dependently inhibited CD40 expression on CAPAN-2 cells as well as CD40-induced nuclear factor kappaB activation and proinflammatory cytokines up-regulation. CONCLUSIONS: Our data suggest that Nacystelyn could be considered as a useful tool to prevent immune and inflammatory responses in pancreatic disorders by interfering with the CD40 pathway in pancreatic duct cells.

Effects of IL-17 on human gingival fibroblasts.

Interleukin (IL)-17 is present in inflammatory periodontal lesions, thus suggesting a role in mediating inflammation. We tested the hypothesis that IL-17, especially when combined with interferon (IFN)-gamma, may modulate the responses of human gingival fibroblasts (HGFs). IL-17 induced IL-8 and minimal intercellular adhesion molecule (ICAM)-1 expression. It had no effect on expression of HLA-DR, CD40, or the immune-suppressive enzyme indoleamine 2,3-dioxygenase (IDO). The effects of IL-17 on HGFs were compared with those of IFN-gamma. Unlike IL-17, IFN-gamma augmented the expression of HLA-DR, ICAM-1, and IDO, but not IL-8. Thus, IL-17 and IFN-gamma induce different HGF responses when administered separately. Interestingly, when IL-17 and IFN-gamma were combined, marked enhancement of ICAM-1, IL-8, and IDO expression by HGFs was observed. These findings suggest that IL-17, especially when combined with IFN-gamma, could play an important role in immune modulation through stimulation of HGFs in periodontal disease.

Indinavir influences biological function of dendritic cells and stimulates antifungal immunity.

In this study, we analyzed the possibility that Indinavir (IDV), a well-known protease inhibitor (PI) used in highly active antiretroviral therapy, could affect immune response against the opportunistic fungus Cryptococcus neoformans. In particular, the quality of dendritic cell (DC) response was analyzed. The results reported here show that IDV treatment induces an expansion of DC with CD8alpha phenotype in spleens of infected hosts. Splenic CD11c+ DC expressed elevated costimulatory molecules such as CD40 and CD80, showed an increased expression of mRNA for proinflammatory cytokines, and secreted abundant IL-12. Integration of all aforementioned regulatory effects results in development of an efficient, T cell-protective response that reflects a consistent reduction in fungus colonization at a cerebral level. These results could help to elucidate the immunoregulatory activity of PI and point out the beneficial effects of IDV in regulating DC functions and antifungal activity. Therefore, although new PI are being introduced in the clinical setting, nevertheless, given its low cost and proven efficacy, IDV could still be considered a potential key compound in the treatment of HIV in resource-limited settings.

Tanshinone IIA downregulates the CD40 expression and decreases MMP-2 activity on atherosclerosis induced by high fatty diet in rabbit.

Tanshinone IIA (Tan IIA) is a member of the major lipophilic components abstracted from the root of Salvia miltiorrhiza Bunge and has the capacity of anti-atherosclerosis. To investigate the potential mechanism, we established an animal model by giving high fatty diet to rabbits and Tan IIA was given in different dose. Then, superoxide dismutase (SOD) activity and the malondialdehyde (MDA) level in serum were detected using spectrophotometry; cluster of differentiation 40 (CD40) expression of cellular membrane fraction of aortas and matrix metalloproteinase-2 (MMP-2) activity of total protein extract of aortas were detected by Western Blotting and Zymography, respectively. Compared with the control group, the level of MDA, the expression of CD40 and the MMP-2 activity were increased while the SOD activity was decreased significantly in model group. After Tan IIA administration, the SOD activity was significantly increased while the level of MDA was decreased; both the expression of CD40 and the activity of MMP-2 were decreased. It is suggested that Tan IIA not only inhibits the oxidation but also suppresses the inflammation in atherosclerotic lesion. Our data suggest that not only anti-oxidation but also anti-inflammation by decrease the expression of CD40 and MMP-2 activity maybe the potential mechanisms by which Tan IIA anti-atherosclerosis.

Simvastatin reduces platelet-endocardium adhesion in atrial fibrillation.

OBJECTIVES: To evaluate the relationship between CD40/CD40L system and increased thrombogenesis in AF, and to test the effects of simvastatin treatment. METHODS: In vitro study using human tissue, University Hospital (tertiary referral center). Experiments on right atrial segments obtained before the onset of cardiopulmonary bypass were done in either presence or absence of 5 microM simvastatin. Two groups of patients in either chronic atrial fibrillation or sinus rhythm at the time of cardiac surgery. The endocardial expression of CD40, the release of CD40L, and adhesion of platelets to endocardium. Additionally, the thickness of platelet aggregates and the platelet distribution on the endocardium were also evaluated. RESULTS: Atrial fibrillation was associated with a significant increase of endocardial CD40 expression (293.1+/-55.1 pg/ml vs. 230.9+/-53.3 pg/ml, p<0.01), and platelet-endocardial adhesion compared with sinus rhythm atria (10.8+/-2.2 vs. 5.2+/-1.3 platelet CD41 AU p<0.01). At immunofluorescence about 62% of fibrillating endocardium was covered by platelets, compared with 12% of not sinus rhythm atria. Addition of simvastatin significantly reduced CD40 expression as well as platelet adhesion to fibrillating atria; its efficacy was not reversed by the addition of mevalonic acid. CONCLUSIONS: Chronic atrial fibrillation acutely upregulates CD40 expression as well as platelet adhesion to the endocardium. Simvastatin is effective in modulating this expression, thus it may potentially contribute to reduce the risk of intra-atrial thrombus formation.

Modulation of amyloid-beta-induced and age-associated changes in rat hippocampus by eicosapentaenoic acid.

The age-related deficit in long-term potentiation (LTP) in the dentate gyrus is positively correlated with hippocampal concentration of the pro-inflammatory cytokine, interleukin-1beta (IL-1beta). Previous evidence also indicates that the inhibition of LTP induced by intracerebroventricular injection of amyloid-beta(1-40) (Abeta) is accompanied by increased hippocampal IL-1beta concentration and IL-1beta-stimulated signalling, specifically activation of the stress-activated protein kinase, c-jun N-terminal kinase (JNK). We considered that the underlying age-related neuroinflammation may render older rats more susceptible to Abeta administration and, to investigate this, young, middle-aged and aged rats were injected intracerebroventricularly with Abeta or vehicle. Hippocampal IL-1beta concentration, JNK phosphorylation, expression of the putative Abeta receptor, Receptor for advanced glycation end products (RAGE) and the microglial cell surface marker, CD40 were assessed. We report that Abeta inhibited LTP in a concentration-dependent manner in young rats and that this was accompanied by concentration-dependent increases in hippocampal IL-1beta and expression of phosphorylated JNK, RAGE and CD40. While 20 micromol/L Abeta exerted no significant effect on LTP in young rats, it inhibited LTP in middle-aged and aged rats and the increased vulnerability of aged rats was associated with increased IL-1beta concentration. Treatment of rats with eicosapentaenoic acid attenuated the inhibitory effect of 60 micromol/L Abeta on LTP in young rats and the effect of 20 micromol/L Abeta in middle-aged and aged rats. We present evidence which indicates that the effect of eicosapentaenoic acid may be linked with its ability to stimulate activation of peroxisome proliferator-activated receptor gamma.