CD40 ligand is selectively expressed on CD4+T cells and platelets: implications for CD40-CD40L signalling in atherosclerosis

Postoperative Pulmonary Hemodynamics and Systemic Inflammatory Response in Pediatric Patients Undergoing Surgery for Congenital Heart Defects

There is scarce information about the relationships between postoperative pulmonary hemodynamics, inflammation, and outcomes in pediatric patients with congenital cardiac communications undergoing surgery. We prospectively studied 40 patients aged 11 (8–17) months (median with interquartile range) with a preoperative mean pulmonary arterial pressure of 48 (34–54) mmHg who were considered to be at risk for postoperative pulmonary hypertension. The immediate postoperative pulmonary/systemic mean arterial pressure ratio (PAP/SAP_IPO, mean of first 4 values obtained in the intensive care unit, readings at 2-hour intervals) was correlated directly with PAP/SAP registered in the surgical room just after cardiopulmonary bypass (r = 0.68, p < 0.001). For the entire cohort, circulating levels of 15 inflammatory markers changed after surgery. Compared with patients with PAP/SAP_IPO ≤ 0.40 (n = 22), those above this level (n = 18) had increased pre- and postoperative serum levels of granulocyte colony-stimulating factor (p = 0.040), interleukin-1 receptor antagonist (p = 0.020), interleukin-6 (p = 0.003), and interleukin-21 (p = 0.047) (panel for 36 human cytokines) and increased mean platelet volume (p = 0.018). Using logistic regression analysis, a PAP/SAP_IPO > 0.40 and a heightened immediate postoperative serum level of macrophage migration inhibitory factor (quartile analysis) were shown to be predictive of significant postoperative cardiopulmonary events (respective hazard ratios with 95% CIs, 5.07 (1.10–23.45), and 3.29 (1.38–7.88)). Thus, the early postoperative behavior of the pulmonary circulation and systemic inflammatory response are closely related and can be used to predict outcomes in this population.

Plasma Protein Profile of Carotid Artery Atherosclerosis and Atherosclerotic Outcomes: Meta-Analyses and Mendelian Randomization Analyses

[Figure: see text].

Role of platelets and megakaryocytes in adaptive immunity

The immune system is comprised of two principal interconnected components called innate and adaptive immunity. While the innate immune system mounts a nonspecific response that provides protection against the spread of foreign pathogens, the adaptive immune system has developed to specifically recognize a given pathogen and lead to immunological memory. Platelets are small fragments produced from megakaryocytes in bone marrow and lungs. They circulate throughout the blood to monitor the integrity of the vasculature and to prevent bleeding. Given their large repertoire of immune receptors and inflammatory molecules, platelets and megakaryocytes can contribute to both innate and adaptive immunity. In adaptive immunity, platelets and megakaryocytes can process and present antigens to lymphocytes. Moreover, platelets, via FcγRIIA, rapidly respond to pathogens in an immune host when antibodies are present. This manuscript reviews the reported contributions of platelets and megakaryocytes with emphasis on antigen presentation and antibody response in adaptive immunity.

Pro-inflammatory Cytokines in Acute Coronary Syndromes

BACKGROUND

Over the last decades, the role of inflammation and immune system activation in the initiation and progression of coronary artery disease (CAD) has been established.

OBJECTIVES

The study aimed to present the interplay between cytokines and their actions preceding and shortly after ACS.

METHODS

We searched in a systemic manner the most relevant articles to the topic of inflammation, cytokines, vulnerable plaque and myocardial infarction in MEDLINE, COCHRANE and EMBASE databases.

RESULTS

Different classes of cytokines (intereleukin [IL]-1 family, Tumor necrosis factor-alpha (TNF-α) family, chemokines, adipokines, interferons) are implicated in the entire process leading to destabilization of the atherosclerotic plaque, and consequently, to the incidence of myocardial infarction. Especially IL-1 and TNF-α family are involved in inflammatory cell accumulation, vulnerable plaque formation, platelet aggregation, cardiomyocyte apoptosis and adverse remodeling following the myocardial infarction. Several cytokines such as IL-6, adiponectin, interferon-γ, appear with significant prognostic value in ACS patients. Thus, research interest focuses on the modulation of inflammation in ACS to improve clinical outcomes.

CONCLUSION

Understanding the unique characteristics that accompany each cytokine-cytokine receptor interaction could illuminate the signaling pathways involved in plaque destabilization and indicate future treatment strategies to improve cardiovascular prognosis in ACS patients.

Impact of CD40 gene polymorphisms on the risk of immune thrombocytopenic purpura

OBJECTIVES

To evaluate the relationship between two common single nucleotide polymorphisms (SNPs) of CD40 gene (rs1883832 C/T and rs4810485 G/T) and the risk of immune thrombocytopenia (ITP) in the Egyptian population.

METHODS

A case-control study was conducted retrospectively on 101 cases with ITP and 97 healthy subjects. Two SNPs of CD40 gene (rs1883832 C/T and rs4810485 G/T) were genotyped via Taqman allele discrimination real-time PCR. The frequencies of different genetic models of both SNPs were calculated and compared between ITP cases and controls. Linkage analysis was performed between the studied SNPs. Odds ratio (OR) and 95% confidence interval (CI) were assessed using multinomial logistic regression analysis to determine the association of CD40 gene SNPs genotypes, alleles, and haplotypes with the risk of ITP. The odds ratio was further adjusted to the confounders for risk stratification.

RESULTS

CD40 (rs1883832) TT genotype carriers have a significantly higher risk of ITP when compared to CC genotype carriers (adjusted OR: 3.792, 95%CI: 1.252-11.49, P = 0.018). T allele also represents 1.711-fold increased risk of ITP which is more evident in males (P = 0.016). No significant difference was observed in the frequency of CD40 (rs4810485 G/T) genetic models between cases and controls. Linkage disequilibrium was found between the two SNPs and revealed four main haplotypes (C-G; C-T; T-G; T-T) with a significantly higher frequency of T-G haplotype in ITP cases than in healthy controls which confers an increased risk of ITP development (OR: 2.349, 95%CI: 1.271-4.339, P = 0.006).

CONCLUSIONS

CD40 gene SNP rs1883832 is associated with an increased risk of ITP development in the Egyptian population, while the SNP rs4810485 has no association. Moreover, T-G haplotype is a risk genetic model for ITP.

Effects of BI 655064, an antagonistic anti-CD40 antibody, on clinical and biomarker variables in patients with active rheumatoid arthritis: a randomised, double-blind, placebo-controlled, phase IIa study

OBJECTIVE

To evaluate the safety, efficacy and therapeutic mechanism of BI 655064, an antagonistic anti-CD40 monoclonal antibody, in patients with rheumatoid arthritis (RA) and an inadequate response to methotrexate (MTX-IR).

METHODS

In total, 67 patients were randomised to receive weekly subcutaneous doses of 120 mg BI 655064 (n=44) or placebo (n=23) for 12 weeks. The primary endpoint was the proportion of patients who achieved 20% improvement in American College of Rheumatology criteria (ACR20) at week 12. Safety was assessed in patients who received at least one dose of study drug.

RESULTS

At week 12, the primary endpoint was not met, with 68.2% of patients treated with BI 655064 achieving an ACR20 vs 45.5% with placebo (p=0.064); using Bayesian analysis, the posterior probability of seeing a difference greater than 35% was 42.9%. BI 655064 was associated with greater changes in CD40-CD40L pathway-related markers, including reductions in inflammatory and bone resorption markers (interleukin-6, matrix metalloproteinase-3, receptor activator of nuclear factor-κB ligand), concentration of autoantibodies (immunoglobulin [Ig]G rheumatoid factor [RF], IgM RF, IgA RF) and CD95+ activated B-cell subsets. No serious adverse events (AEs) related to BI 655064 treatment or thromboembolic events occurred; reported AEs were mainly of mild intensity.

CONCLUSION

Although blockade of the CD40-CD40L pathway with BI 655064 in MTX-IR patients with RA resulted in marked changes in clinical and biological parameters, including reductions in activated B-cells, autoantibody production and inflammatory and bone resorption markers, with a favourable safety profile, clinical efficacy was not demonstrated in this small phase IIa study.

TRIAL REGISTRATION NUMBER

NCT01751776.

Expression of CD40 Correlates Negatively with Overall and Progression-Free Survival of Low- and High-Grade Gliomas

BACKGROUND

Low-grade gliomas (LGGs) are known to progress to glioblastoma (GBM), decreasing the chances of survival. The tumor necrosis factor receptor CD40 and its ligand CD40L have shown value as biomarkers for GBM. The present study evaluated the role of CD40/CD40L in LGG and GBM in differentiating isocitrate dehydrogenase (IDH) wild-type and IDH-mutant GBM.

METHODS

The present study was based on patient-derived samples (74 grade II gliomas, 36 grade III gliomas, and 40 cases of GBM) and expression analysis using real-time polymerase chain reaction. Open-access data from The Cancer Genome Atlas (TCGA) and the strong cohorts of TCGA data sets "brain lower grade glioma" and "glioblastoma" were used to run the analysis on mRNA expression as a validation data set.

RESULTS

We found that patients with LGG and CD40 overexpression experienced shorter progression-free survival (43 vs. 29 months; hazard ratio, 0.5715; P = 0.0262) and overall survival (116 vs. 54 months; hazard ratio, 0.3431; P < 0.0001). Consistently, relapsed grade II glioma showed greater CD40 expression compared with primary grade II glioma (P = 0.0028). Just as with LGG, CD40 was a negative marker for overall survival in GBM (12 vs. 10 months; hazard ratio, 0.5178; P = 0.0491). In this context, we found greater CD40 expression in IDH wild-type GBM than in IDH-mutant GBM. The data obtained from TCGA supported our findings, with similar results for PFS and OS in LGG and GBM. CD40L expression showed no correlation with the survival data.

CONCLUSION

High CD40 expression showed a significant correlation with poor outcomes for both LGG and GBM and was overexpressed in IDH wild-type GBM.

Start a fire, kill the bug: The role of platelets in inflammation and infection

Platelets are the main players in thrombosis and hemostasis; however they also play important roles during inflammation and infection. Through their surface receptors, platelets can directly interact with pathogens and immune cells. Platelets form complexes with neutrophils to modulate their capacities to produce reactive oxygen species or form neutrophil extracellular traps. Furthermore, they release microbicidal factors and cytokines that kill pathogens and influence the immune response, respectively. Platelets also maintain the vascular integrity during inflammation by a mechanism that is different from classical platelet activation. In this review we summarize the current knowledge about how platelets interact with the innate immune system during inflammation and infection and highlight recent advances in the field.

Matrix Metalloproteinases and Platelet Function

Platelets contain and release several matrix metalloproteinases (MMPs) and their tissue inhibitors of matrix metalloproteinases (TIMPs), including MMP-1, -2, -3, -9, and -14 and TIMP-1, -2, and -4. Although devoid of a nucleus, platelets also synthesize TIMP-2 upon activation. Platelet-released MMPs/TIMPs, as well as MMPs generated by other cells within the cardiovascular system, modulate platelet function in health and disease. In particular, a normal hemostatic platelet response to vessel wall injury may be transformed into pathologic thrombus formation by the release from platelets and/or by the local generation of some MMPs. Moreover, platelets may localize the production of leukocyte-derived MMPs to sites of vascular damage, contributing to atherosclerosis development and complications and to arterial aneurysm formation. Finally, the interaction between platelets and tumor cells is strongly influenced by MMPs/TIMPs. All these mechanisms are emerging as important in atherothrombosis, inflammatory disease, and cancer growth and dissemination. Increasing knowledge of these mechanisms may open the way to novel therapeutic approaches.

Beyond pan-B-cell-directed therapy - new avenues and insights into the pathogenesis of SLE

New insights into the mechanisms of autoimmune diseases have been obtained not only from preclinical studies, but also from clinical trials of pan-B-cell-directed therapy. Overall, the results of these clinical trials suggest that more-specific approaches focusing on pathogenic B-cell functions, and perhaps sparing or even enhancing regulatory B-cell activity, might be attractive alternatives. Importantly, pathogenic B-cell subpopulations function within a network of cellular interactions, many of which might require additional interventions to restore immunologic balance and suppress autoimmune disease. Thus, approaches that simultaneously target innate immune cells as well as multiple nodes of T-cell and B-cell interactions might hold the promise of improved therapeutic efficacy. Interfering with B-cell intracellular signalling pathways, altering their intracellular metabolic pathways and perturbing transcription factors are additional options. This Review critically analyses these approaches, examines the role of cytokines and other functions of B-lineage cells separate from antibody secretion, and provides insights into the potential next generation of therapies targeting B-lineage cells.

Angiotensin II promotes the inflammatory response to CD40 ligation via TRAF-2

A plethora of evidence supports a link between inflammation and atherogenesis. Both the vasoactive peptide angiotensin II (ANG II) as well as the CD40/CD154 signaling pathway exhibit proinflammatory properties with a direct influence on atherogenesis. We therefore tested the hypothesis that ANG II interacts with CD40/CD154 in human vascular smooth muscle cells (SMC). ANG II did not increase expression of CD40 in human SMC. However, when SMC were prestimulated with ANG II and thereafter stimulated with CD154, the ligand for CD40, the release of IL-6 as a marker of inflammatory activation was augmented compared to cells not primed with ANG II. TNF receptor-associated factor 2 (TRAF-2), an important adaptor protein involved in CD40 signaling, but not TRAF-5 or -6, was increased by ANG II via activation of the angiotensin II type 1 (AT1) receptor subtype. These results suggest that a signaling pathway downstream of CD40 may be altered by ANG II prestimulation. Thus, ANG II can also indirectly cause inflammatory activation of vascular SMC. The data show a novel link between the proatherogenic vasoactive peptide ANG II and cell—cell contact-mediated inflammatory pathways and implicate options for the prevention and therapy of atherosclerotic disease.

Are Platelets Cells? And if Yes, are They Immune Cells?

Small fragments circulating in the blood were formally identified by the end of the nineteenth century, and it was suggested that they assisted coagulation via interactions with vessel endothelia. Wright, at the beginning of the twentieth century, identified their bone-marrow origin. For long, platelets have been considered sticky assistants of hemostasis and pollutants of blood or tissue samples; they were just cell fragments. As such, however, they were acknowledged as immunizing (to specific HPA and HLA markers): the platelet’s dark face. The enlightened face showed that besides hemostasis, platelets contained factors involved in healing. As early as 1930s, platelets entered the arsenal of medicines were transfused, and were soon manipulated to become a kind of glue to repair damaged tissues. Some gladly categorized platelets as cells but they were certainly not fully licensed as such for cell physiologists. Actually, platelets possess almost every characteristic of cells, apart from being capable of organizing their genes: they have neither a nucleus nor genes. This view prevailed until it became evident that platelets play a role in homeostasis and interact with cells other than with vascular endothelial cells; then began the era of physiological and also pathological inflammation. Platelets have now entered the field of immunity as inflammatory cells. Does assistance to immune cells itself suffice to license a cell as an “immune cell”? Platelets prove capable of sensing different types of signals and organizing an appropriate response. Many cells can do that. However, platelets can use a complete signalosome (apart from the last transcription step, though it is likely that this step can be circumvented by retrotranscribing RNA messages). The question has also arisen as to whether platelets can present antigen via their abundantly expressed MHC class I molecules. In combination, these properties argue in favor of allowing platelets the title of immune cells.

Neutrophil and platelet complexes and their relevance to neutrophil recruitment and activation

The manifestation of platelet 'satallitism' around neutrophils in whole blood is a long acknowledged phenomenon [1]. Circulating platelet-neutrophil complexes (PNC) occur in a diverse range of inflammatory disorders and infections that affect numerous organs of the body. Animal models have revealed that the formation of PNC is required for the recruitment of neutrophils to inflamed tissue, since platelets 'prime' neutrophils for efficient adhesion to vascular endothelium via the up-regulation of integrins and enhanced responsiveness to chemokines (Fig. 1). Perhaps surprisingly, the surface contact between platelets and neutrophils additionally enhances other neutrophil functions, such as chemotaxis that is required for migration into tissues, trans-cellular production of eicosanoids, phagocytosis and trapping of pathogens, increased respiratory burst leading to the production of reactive oxygen species (ROS), and modulation of neutrophil apoptosis (Fig. 1). Platelet P-selectin appears to have a particular role in enhancing the majority of these activities, and the influence of platelet P-selectin is not therefore confined to the initial rolling events in the process of neutrophil extravasation.

Tight control - decision-making during T cell-vascular endothelial cell interaction

Vascular endothelial cells (ECs) form the inner layer of blood vessels and exert crucial functions during immune reactions including coagulation, inflammation, and regulation of innate immunity. Importantly, ECs can interact with T cells in an antigen-specific, i.e., T cell receptor-dependent manner. In this review, we will discuss EC actions and reactions during acute inflammation and focus on the interaction of T cells with ECs at two vascular sites: the high endothelial venule (HEV) of lymph nodes, and the vascular lesion during transplant vasculopathy (TV). HEVs are characterized by a highly active endothelium that produces chemoattracting factors and expresses adhesion molecules to facilitate transit of lymphocytes into the lymph node (LN) parenchyma. Yet, T cell-EC interaction at this anatomical location results neither in T cell activation nor tolerization. In contrast, the endothelium at sites of chronic inflammation, such as solid organ transplants, can promote T cell activation by upregulation of major histocompatibility complex (MHC) and costimulatory molecules. Importantly, a major function of ECs in inflamed tissues must be the maintenance of vascular integrity including the efficient attenuation of effector T cells that may damage the vascular bed. Thus, antigen-specific T cell-EC interaction is characterized by a tightly controlled balance between immunological ignorance, immune activation, and tolerization.

Platelets and cytokines: How and why?

For patients with platelet deficiencies, platelet components are therapeutic products for which there is no substitute. However, transfusion complications are more frequent with this labile blood product than with others. This is attributable to products secreted by the platelets themselves, including a variety of cytokines, chemokines, and biological response modifiers, some of which are secreted in large quantities following platelet activation. Why platelets are activated and prone to releasing these molecules during certain inflammatory and innate immune responses is not yet fully understood, but it could be due to several parameters including incompatibilities between blood donors and recipients, the process of platelet preparation and preservation, and the ability of the donor's immune system to sense danger presented by external stimuli during the blood donation process. This review presents our current knowledge of how the platelets that constitute the platelet component for transfusion are sources of cytokines and biological response modifiers and discusses methods to improve the quality of blood transfusion products and safety for patients.

[Blood platelets and biological response to 'danger' signals and subsequent inflammation: towards a new paradigm?]

Blood platelets are cellular elements of primary haemostasis. During the last decade research on platelets has been subsequently based on this paradigm, with separate observations on issues such as the ability for platelets to bind infectious agents or even engulf them, to drop in counts in case of evolving infectious processes, etc. More recently, novel work has set up bases for novel functions for platelets, as members of functional immune cells, principally in innate immunity but capable of influencing adaptive immunity. Platelets are thus essential to haemostasis and to inflammation, questioning their essential functionality and the set up of a novel paradigm: could platelets be tissue-repairing cells? Such an assumption would open an entire new field of investigations. The present "State of the Art" essay attempts to discuss the main arguments on this.

Interaction with damaged vessel wall in vivo in humans induces platelets to express CD40L resulting in endothelial activation with no effect of aspirin intake

Activated platelets express CD40L on their plasma membrane and release the soluble fragment sCD40L. The interaction between platelet surface CD40L and endothelial cell CD40 leads to the activation of endothelium contributing to atherothrombosis. Few studies have directly demonstrated an increased expression of platelet CD40L in conditions of in vivo platelet activation in humans, and no data are available on its relevance for endothelial activation. We aimed to assess whether platelets activated in vivo at a localized site of vascular injury in humans express CD40L and release sCD40L, whether the level of platelet CD40L expression attained in vivo is sufficient to induce endothelial activation, and whether platelet CD40L expression is inhibited by aspirin intake. We used the skin-bleeding-time test as a model to study the interaction between platelets and a damaged vessel wall by measuring CD40L in the blood emerging from a skin wound in vivo in healthy volunteers. In some experiments, shed blood was analyzed before and 1 h after the intake of 500 mg of aspirin. Platelets from the bleeding-time blood express CD40L and release soluble sCD40L, in a time-dependent way. In vivo platelet CD40L expression was mild but sufficient to induce VCAM-1 expression and IL-8 secretion in coincubation experiments with cultured human endothelial cells. Moreover, platelets recovered from the bleeding-time blood activated endothelial cells; an anti-CD40L antibody blocked this effect. On the contrary, the amount of sCD40L released by activated platelets at a localized site of vascular injury did not reach the concentrations required to induce endothelial cell activation. Soluble monocyte chemoattractant protein-1, a marker of endothelium activation, was increased in shed blood and correlated with platelet CD40L expression. Aspirin intake did not inhibit CD40L expression by platelets in vivo. We concluded that CD40L expressed by platelets in vivo in humans upon contact with a damaged vessel wall activates endothelium; aspirin treatment does not inhibit this mechanism.

The effect of hormone therapy and tibolone on serum CD40L and ADAM-8 in healthy post-menopausal women

BACKGROUND/AIM

The role of neutrophils and platelets in atherothrombotic disease is well established. The aim of our study was to investigate the effect of HT and tibolone on the soluble markers of neutrophil and platelet activation, "a disentigrin and metalloproteinase domain" (ADAM-8) and CD40 ligand (CD40L) respectively, in healthy post-menopausal women.

SUBJECTS AND METHODS

One hundred and six healthy post-menopausal women were randomly allocated to: estradiol plus drospirenone (E₂/DSP), E₂ hemihydrate 1 mg plus norethisterone acetate (E₂/NETA) 0.5 mg, and tibolone 2.5 mg. Serum ADAM-8 and CD40L were measured at baseline and at 6 months.

RESULTS

Baseline values of ADAM-8 and CD40L were similar between groups. No significant correlation was revealed between ADAM-8 or CD40L and parameters related to cardiovascular risk factors in each group. No significant changes were observed between baseline values and values at 6 months (E₂/DSP group: ADAM-8: 267.4±71.3 pg/ml vs 270.7±42.8 pg/ml, p=0.86, CD40L: 6.43±3.13 vs 6.79±2.70 ng/ml, p=0.67), (E₂/NETA group: ADAM-8: 308.3±64.3 vs 294.7±57.7 pg/ml, p=0.40, CD40L: 9.68±2.81 vs 8.59±5.13 ng/ml, p=0.51), (tibolone group: ADAM-8: 307.5±87.5 vs 289±48.1 pg/ml, p=0.48, CD40L: 9.46±4.30 vs 9.26±4.60 ng/ml, p=0.99).

CONCLUSIONS

Our study has not revealed an association between estrogen plus progestin treatment or tibolone on serum ADAM-8 and CD40L levels in healthy post-menopausal women. Larger prospective studies are needed to further investigate the effect of low-dose HT or tibolone on serum markers of neutrophil and platelet activation.

New steroidal glycosides isolated as CDL inhibitors of activated platelets

Three new compounds were isolated from the dried bulbs of Allium macrostemon Bunge. Their structures were elucidated from their spectral data as (25R)-26-O-β-D-glucopyranosyl-5α-furostane-3β,12β,22,26-tetraol-3-O-β-D-glucopyranos-yl (1→2) [β-D-glucopyranosyl (1→3)]-β-D-glucopyranosyl (1→4)-β-D-galactopyranoside (1), (25R)-26-O-β-D-glucopyranosyl-5α-furostane-3β,12α,22,26-tetraol-3-O-β-D-gluco- pyranosyl (1→2) [β-D-glucopyranosyl (1→3)]-β-D-glucopyranosyl (1→4)-β-D-galacto- pyranoside (2) and (25R)-26-O-β-D-glucopyranosyl-5β-furostane-3β,12α,22,26-tetraol-3-O-β-D-glucopyranosyl (1→2)-β-D-galactopyranoside (3), respectively. The inhibition effect of all compounds on CD40 ligand (CD40L) expression on the membrane of activated platelets stimulated by ADP was tested. Compounds 1 and 2 exhibited significant inhibitory activities in a dose dependent manner (P < 0.05), suggesting their potential application as CD40L inhibitors.

CD40/CD40L signaling and its implication in health and disease

CD40, a transmembrane receptor of the tumor necrosis factor gene superfamily is expressed on a variety of cells, such as monocytes, B-cells, antigen presenting cells, endothelial, smooth muscle cells, and fibroblasts. The interaction between CD40 and CD40 ligand (CD40L) enhances the expression of cytokines, chemokines, matrix metalloproteinases, growth factors, and adhesion molecules, mainly through the stimulation of nuclear factor kappa B. The aim of this review is to summarize the molecular and cellular characteristics of CD40 and CD40L, the mechanisms that regulate their expression, the cellular responses they stimulate and finally their implication in the pathophysiology of inflammatory and autoimmune diseases.

[Platelet immunology and the immune response]

Platelets exert not only hemostatic activities, but also pro-inflammatory effects. Platelet-linked inflammation seems essentially related to their capacity of secreting cytokines, chemokines and related molecules. This activity is important in terms of concentration of secreted products. This secretory function confers to platelets a regulatory role in immunity. Besides, platelets do exhibit non-self infectious danger detection molecules on their surfaces, belonging in particular to the "Toll-like receptor family"; through this property, platelets can bind infectious agents but also deliver differential signals for the secretion of cytokines and chemokines. Platelets, which are non-nucleated cells deprived of nuclear DNA, possess however some cellular machinery which permits intracellular signalling and even the production of RNA transcripts for certain cytokines. Last, platelets express variant surface determinants of hemostatic molecules (referred to as HPA antigens) along with HLA class I variant molecules, the function of which on platelets is still unknown. An intriguing question is to reconcile those diverse properties and to understand whether the pro-inflammatory secretory process can affect the immunogenicity of transfused, allogeneic, platelet components.

Intercellular Communication in Atherosclerosis

Cell-to-cell communication is a process necessary for physiological tissue homeostasis and appears often altered during disease. Gap junction channels, formed by connexins, allow the direct intercellular communication between adjacent cells. After a brief review of the pathophysiology of atherosclerosis, we will discuss the role of connexins throughout the different stages of the disease.

CD40: an upstream master switch for endothelial cell activation uncovered by RNAi-coupled transcriptional profiling

The CD40-CD154 dyad seems to play a prominent role fostering the immune-inflammatory response triggered by endothelial cell (EC)–T-cell communication. To delineate comprehensively the involvement of CD40 (TNFRSF5) in EC activation, we combined RNAi-mediated CD40 knockdown with comparative genome-wide transcriptional profiling of ECs interacting with (CD154+) T cells. We report the initiation of a profound stress response in ECs upon CD40-CD154 engagement through early up-regulation of, among others, the major proinflammatory NF-κB and MAPK/SAPK pathways and their associated transcription factors. Moreover, we have identified novel genes regulated through the CD40-CD154 interaction, and pathways previously unrecognized to be induced by CD40 signaling in ECs. Thus, we document a significant down-regulation of endothelial APLN by CD40-CD154 interaction, TNFα/IFNγ exposure, and in immune-inflammatory pathologies, which could lead to hemodynamic dysfunction. Conversely, CD40-mediated up-regulation of the viral immune surveillance system, notably TLR3, IFIH1, RIG-I, and RNASEL, establishes a reverse link from adaptive to innate immunity in ECs. Moreover, systematic enrichment analysis substantiates endothelial CD40 involvement in the transcriptional regulation of gene networks associated with adhesion and motility, immunity, cell fate control, hemostasis, and metabolism. Our study also highlights the anti-inflammatory potential of RNAi-mediated CD40 inhibition, and the relevance of CD40 signaling for therapeutic intervention.

Platelet-mediated modulation of adaptive immunity: unique delivery of CD154 signal by platelet-derived membrane vesicles

Although mounting evidence indicates that platelets participate in the modulation of both innate and adaptive immunity, the mechanisms by which platelets exert these effects have not been clearly defined. The study reported herein uses a previously documented adoptive transfer model to investigate the ability of platelet-derived membrane vesicles to communicate activation signals to the B-cell compartment. The findings demonstrate for the first time that platelet-derived membrane vesicles are sufficient to deliver CD154 to stimulate antigen-specific IgG production and modulate germinal center formation through cooperation with responses elicited by CD4(+) T cells. The data are consistent with the hypothesis that platelets modulate inflammation and adaptive immunity at sites distant from the location of activation and that platelet-derived membrane vesicles are sufficient to mediate the effect.

Platelet-lymphocyte cross-talk

Platelets and lymphocytes reciprocally regulate mutual functions, i.e., platelet-lymphocyte cross-talk. The heterotypic interactions have emerged as important regulatory mechanisms in the pathophysiological processes of thrombosis, inflammation, immunity, and atherosclerosis. Platelets influence lymphocyte function via direct cell-cell contact and/or soluble mediators. Hence, platelets enhance adhesion and cell migration of T(H), T cytolytic (T(C)), NK, and B cells. Platelets affect other functional aspects of lymphocyte subpopulations in a complex manner. They may attenuate cytokine secretion and immunosuppressive responses of T(H) cells and enhance T(C) cell proliferation and cytotoxicity. Platelets promote isotype shifting and antibody production of B cells but ameliorate cytolytic activity of NK cells. On the other hand, lymphocytes can also regulate platelet aggregation and secretion, as well as the effector cell function of platelets in immune defense. The two cell types collaborate in transcellular phospholipid metabolism, CD40-CD40 ligand-mediated intercellular signaling, and their involvements in atherogenesis. The research perspectives of platelet-lymphocyte cross-talk have also been addressed.

Role of metalloproteinases in platelet function

Platelets contain and release matrix metalloproteinases (MMPs), their inhibitors (TIMPs) and disintegrin metalloproteinases (ADAMs) including MMP-1, MMP-2, MMP-3, MMP-9, MT1-MMP (MMP-14), ADAM-10, ADAM-17, ADAMTS-13, TIMP-1, TIMP-2 and TIMP-4. These proteins exert several effects regulating platelet functions such as agonist-stimulated platelet adhesion and aggregation, tumour cell-induced platelet aggregation and platelet-leukocyte aggregation. In this review, mechanisms of MMPs, TIMPs and ADAMs on platelets are discussed.

Novel uses for anti-platelet agents as anti-inflammatory drugs

An alteration in the character and function of platelets is manifested in patients with inflammatory diseases, and these alterations have been dissociated from the well-characterized involvement of platelets in thrombosis and haemostasis. Recent evidence reveals platelet activation is sometimes critical in the development of inflammation. The mechanisms by which platelets participate in inflammation are diverse, and offer numerous opportunities for future drug intervention. There is now acceptance that platelets act as innate inflammatory cells in immune responses, with roles as sentinel cells undergoing surveillance, responding to microbial invasion, orchestrating leukocyte recruitment, and migrating through tissue, causing damage and influencing repair processes in chronic disease. Some of these processes are targeted by drugs that are being developed to target platelet participation in atherosclerosis. The actions of platelets therefore influence the pathogenesis of diverse inflammatory diseases in various body compartments, encompassing parasitic and bacterial infection, allergic inflammation (especially asthma and rhinitis), and non-atopic inflammatory conditions, for example, chronic obstructive pulmonary disease (COPD), rheumatoid arthritis (RA), inflammatory bowel disease (IBD) and atherosclerosis. This review will first discuss the evidence for platelet activation in these various inflammatory diseases, and secondly discuss the mechanisms by which this pathogenesis occurs and the various anti-platelet agents which have been developed to combat platelet activation in atherosclerosis and their potential future use for the treatment of other inflammatory diseases.

Selective expansion of influenza A virus-specific T cells in symptomatic human carotid artery atherosclerotic plaques

BACKGROUND AND PURPOSE

Evidence is accumulating that infection with influenza A virus contributes to atherothrombotic disease. Vaccination against influenza decreases the risk of atherosclerotic syndromes, indicating that inflammatory mechanisms may be involved. We tested the hypothesis that influenza A virus-specific T cells contribute to atherosclerotic plaque inflammation, which mediates the onset of plaque rupture.

METHODS

T-cell cultures were generated from atherosclerotic segments and peripheral blood of 30 patients with symptomatic carotid artery disease. The response of plaque and peripheral blood T cells to influenza A virus was analyzed and expressed as a stimulation index (SI). Selective outgrowth of intraplaque influenza A-specific T cells was calculated by the ratio of plaque T cell SI and peripheral blood T cell SI for each patient. Accordingly, the patients were categorized as high- (SI ratio >or=5), intermediate- (5 <SI ratio <or=2), and non- (SI ratio <2) responders. The presence of influenza A virus in the vessel fragments was evaluated by reverse transcription-polymerase chain reaction.

RESULTS

High proliferative responses of plaque-derived T cells to influenza A virus were frequently observed. Among the 30 patients, 5 were categorized as high responders, 10 were intermediate responders, and 15 were nonresponders. Live influenza A virus could not be detected in the atherosclerotic plaques by polymerase chain reaction.

CONCLUSIONS

Selective outgrowth of influenza A virus-specific T cells occurs within the microenvironment of human atherosclerotic plaques. Influenza virus-derived antigens or alternatively, mimicry antigens, appear to be potential candidates for triggering or sustaining plaque inflammation, which eventually leads to symptomatic plaque complications.

Alimentary lipemia enhances procoagulatory effects of inflammation in patients with a history of acute myocardial infarction complicated by ventricular fibrillation

INTRODUCTION

Acute myocardial infarction, often occurring postprandially, can be complicated by ventricular fibrillation. The role of acute alimentary lipemia and inflammation in the occurrence of ventricular arrhythmias in acute myocardial infarction has not been described yet.

METHODS AND RESULTS

Before and 2 h after consumption of a defined fatty meal, blood samples of 27 patients with a history of acute myocardial infarction (AMI) were incubated with lipopolysaccharide (LPS). In 10 patients, AMI was complicated by ventricular fibrillation (VF), in 17 patients, AMI occurred without VF. CD40-ligand and CD62P expression on platelets, tissue-factor binding on monocytes and platelet-monocyte aggregates were measured with flow cytometry. Soluble CD40-ligand plasma levels were measured with an ELISA. With the meal, serum triglyceride levels increased from 211.85+/-94.60 mg/dl to 273.59+/-122.52 mg/dl (p=0.0002). LPS stimulation before the meal showed a non-significant tendency to increase platelet-monocyte aggregates and tissue factor on monocytes in both patient groups. LPS stimulation in acute alimentary lipemia significantly increased tissue-factor expression on monocytes in both patient groups and platelet-monocyte aggregates in patients with VF. Baseline plasma levels of soluble CD40L did not differ significantly between both groups. Acute alimentary lipemia significantly decreased total plasma levels of sCD40L, leading to a significantly lower level of sCD40L in patients with a history of VF.

CONCLUSIONS

Alimentary lipemia enhances procoagulatory effects of inflammatory stimulation in patients with a history of AMI complicated by ventricular fibrillation. These observations might reveal a mechanism for an increased risk of VF in acute coronary syndromes in a postprandial state.

Platelets as immune cells: bridging inflammation and cardiovascular disease

Beyond an eminent role in hemostasis and thrombosis, platelets are characterized by expert functions in assisting and modulating inflammatory reactions and immune responses. This is achieved by the regulated expression of adhesive and immune receptors on the platelet surface and by the release of a multitude of secretory products including inflammatory mediators and cytokines, which can mediate the interaction with leukocytes and enhance their recruitment. In addition, platelets are characterized by an enormous surface area and open canalicular system, which in concert with specialized recognition receptors may contribute to the engulfment of serum components, antigens, and pathogens. Platelet-dependent increases in leukocyte adhesion may not only account for an exacerbation of atherosclerosis, for arterial repair processes, but also for lymphocyte trafficking during adaptive immunity and host defense. This review compiles a selection of platelet-derived tools for bridging inflammation and vascular disease and highlights the molecular key components governing platelet-mediated mechanisms operative in immune surveillance, vascular remodeling, and atherosclerosis.

Platelet membrane CD154 and sCD154 in progressive peripheral arterial disease: A pilot study

OBJECTIVE

The expression and potential role of platelet membrane CD154 and sCD154 in atherosclerosis was investigated in patients with peripheral arterial disease.

METHODS

This prospective observational study measured the expression of platelet-bound CD154 and soluble CD154 (sCD154) in 39 patients with critical limb ischaemia (CLI, n=15), stable intermittent claudication (SIC, n=12) and age-matched controls (AMC, n=12). Basal and agonist-stimulated CD154, P-selectin expression and fibrinogen binding was measured by whole blood flow cytometry, while sCD154 was measured in paired plasma samples by ELISA.

RESULTS

Basal expression of CD154 on the platelet surface was enhanced in both groups of patients with peripheral arterial disease. However, the critical limb ischaemics showed the highest level of basal expression 0.7+/-0.3 [median+/-IQR] and was significantly increased compared to both stable intermittent claudicants and age-matched controls (P<0.001). On agonist stimulation with either ADP or thrombin critical limb ischaemics demonstrated greater platelet reactivity and propensity to express CD154 compared to age-matched controls (P<0.05). Confirmation of the cellular expression of CD154 results was obtained by measuring sCD154 concentrations in autologous plasma samples. Here plasma levels of sCD154 in critical limb ischaemics were significantly greater than both stable intermittent claudicants and age-matched controls (P<0.005).

CONCLUSIONS

Enhanced basal platelet expression and increased propensity to express CD154 and sCD154 in critical limb ischaemics compared to both controls and patients with stable intermittent claudication support evidence for the role of CD154 in atherogenesis and suggest a novel function in progressive and acute peripheral arterial disease.

Effects of alimentary lipemia and inflammation on platelet CD40-ligand

INTRODUCTION

In patients with chronic hypercholesterolemia, the CD40-CD40L dyad is upregulated, contributing to the initiation and progression of atherosclerosis. Our aim was to describe the role of postprandial lipemia and inflammatory stimulation on platelet and monocyte activation and CD40-ligand (CD40L) levels.

METHODS AND RESULTS

Before and 2 h after consumption of a defined fatty meal, whole blood samples of 31 healthy subjects were incubated with endotoxin (LPS). CD40-ligand and CD62P expression on platelets, tissue-factor expression on monocytes and platelet-monocyte aggregates were measured with flow cytometry. Soluble CD40-ligand plasma levels were measured with an ELISA. After the meal, serum triglyceride levels increased from 137.6+/-60.5 mg/dl to 201.5+/-75.0 mg/dl. Expression of CD40L and CD62P on platelets and plasma levels of soluble CD40L were significantly decreased. No significant changes after the meal were observed concerning tissue factor expression on monocytes and platelet-monocyte aggregates. Addition of LPS showed no significant effect concerning CD40L or CD62P expression on platelets, whereas the amount of platelet-monocyte aggregates significantly increased under LPS stimulation after the fatty meal.

CONCLUSIONS

Acute alimenatry lipemia leads to a decreased expression of CD40L on platelets and a reduced plasma level of sCD40L, suggesting an increased turnover in the CD40L system.

CONDENSED ABSTRACT

Before and after a fatty meal, blood samples of 31 healthy subjects were incubated with LPS. After the meal, expression of CD40L and CD62P on platelets and plasma levels of soluble CD40L were significantly decreased. Addition of LPS showed no effect concerning CD40L or CD62P expression, whereas the amount of platelet-monocyte aggregates significantly increased under LPS stimulation after the fatty meal.

CD4+ lymphocytes require platelets for adhesion to immobilized fibronectin in flow: role of beta(1) (CD29)-, beta(2) (CD18)-related integrins and non-integrin receptors

The role of platelets in T-lymphocytes adhesion is not clear yet. Herpesvirus saimiri (HVS)-infected CD4(+) T-lymphocytes were placed into polystyrene plates pre-coated with fibronectin. The adherent T-cells were enumerated by image analysis. Under static condition, 38+/-10cells/mm(2) adhered and addition of gel-filtered platelets (GFP) and PMA enhanced cell adhesion 4.3- and 4.1-fold. Using PMA plus GFP 11.9-fold enhancement in cell adhesion was achieved. In contrast, under flow (200s(-1)), neither basal adhesion nor following separate addition of PMA or GFP was observed, whereas combined addition of PMA and GFP induced noticeable adhesion (34cells/mm(2)). The adhesion was inhibited by blockade of alpha(5)-integrin (CD49e, 87%), beta(2)-integrin (CD18, 78%), CD40L (60%), PSGL-1 (CD162, 60%), and CD40L plus PSGL-1 (83%). Thus, activated platelets promote activated T-cell adhesion to fibronectin under flow via integrins (alpha(5)beta(1), and alpha(L)beta(2)), CD40-CD40L and P-selectin-PSGL-1 mediated interactions.

Giving blood: a new role for CD40 in tumorigenesis

CD40 was initially identified as a receptor expressed by B cells that is crucial for inducing an effective adaptive immune response. CD40 was subsequently shown to be expressed by endothelial cells and to promote angiogenesis. New data now show that in tumor-prone transgenic mice, CD40-mediated neovascularization is essential for early stage tumorigenicity. This suggests, at least in this mouse model, that CD40 has an important role in the angiogenic process that is coupled to carcinogenesis, a finding that could lead to novel therapeutic opportunities.

Costimulatory molecules as immunotherapeutic targets in systemic lupus erythematosus

T cells undergo full and productive activation when they traffic to lymph nodes where they encounter dendritic cells displaying foreign antigen in the context of MHC molecules on their surface. Recognition of these antigen-MHC complexes by the T cell's receptor for antigen, or T cell receptor, provides the first of two obligate signals needed to drive cell proliferation. The second antigen-independent signal is provided by the costimulatory receptor, CD28, as it engages its ligand on the antigen-presenting cells. Failure of the T cell to receive this second signal after antigen recognition leaves the T cell in a state of anergy. Understanding the role of T cell costimulatory receptors in T cell activation has led to the development of novel approaches for regulating immune responses in subjects with cancer or autoimmune disease by experimentally triggering or blocking costimulatory receptor signaling. In this review, we will discuss, first, several costimulatory pathways known to participate or regulate the progression of autoimmune disease, and, second, how manipulation of T cell costimulation and/or costimulation blockade has been used to treat systemic lupus erythematosus.

Enhanced expression of platelet CD40-ligand by in vitro lipopolysaccharide-challenge in patients with ventricular fibrillation complicating acute myocardial infarction

BACKGROUND

Acute myocardial infarction can be complicated by ventricular arrhythmias due to electrophysiological changes in the ischemic myocardium, but the exact predisposing factors causing ventricular fibrillation during myocardial infarction still remain unclear. A role of inflammatory stimulation on platelets as a potential risk factor for ventricular fibrillation during acute myocardial infarction has not been described yet.

METHODS AND RESULTS

Whole blood samples of 21 patients with a history of acute myocardial infarction (AMI) and ventricular fibrillation (VF) were incubated with lipopolysaccharide (LPS). As a control group, we studied 19 patients without VF during AMI. CD40-ligand and CD62P expression on platelets and tissue factor binding on monocytes were measured by flow cytometry. Platelet-monocyte aggregates were measured by CD41 expression on platelets adherent to monocytes. Soluble CD40-ligand plasma levels were measured with an ELISA. Without LPS, no significant difference between the patient groups concerning CD40L expression on platelets was observed, but plasma levels of soluble CD40L were significantly higher in patients with a history of AMI with VF. After LPS stimulation, patients with a history of VF showed a significantly increased expression of CD40L in comparison to the patients without ventricular fibrillation, based on a significantly higher increase of CD40L expression. CD62P expression on platelets was significantly increased in patients with a history of VF.

CONCLUSIONS

Patients with a history of VF complicating AMI show an enhanced expression of CD40L on platelets after in vitro lipopolysaccharide-challenge with an enhanced platelet activation.

Soluble CD40L Levels Are Regulated by the −3459 A>G Polymorphism and Predict Myocardial Infarction and the Efficacy of Antithrombotic Treatment in Non-ST Elevation Acute Coronary Syndrome

Objectives— Current evidence suggests the CD40–CD40L pathway as a key process in the development, progression, and outcome of acute coronary syndrome (ACS). The aim was to investigate the prognostic importance of soluble (s) CD40L levels, single nucleotide polymorphisms (SNP) in the CD40LG gene, and the relation between sCD40L and SNPs in patients with acute coronary syndromes (ACS).

Methods and Results— Samples were obtained on admission from 2359 patients with non-ST elevation ACS randomized to an early invasive versus a conservative and to placebo controlled long-term dalteparin treatment in the FRISC-II study. The −3459 A>G SNP was identified as a novel regulator of sCD40L levels ( P =0.001). In the placebo-treated group, sCD40L levels above median were associated with a 2.5-fold increased risk of myocardial infarction (MI) ( P ≤0.001) but not with raised mortality. In the dalteparin treated group, sCD40L showed no association with MI ( P =0.75). Consequently, dalteparin treatment was effective in reducing the risk of MI only in patients with sCD40L levels above median. A combined assessment of troponin-T and sCD40L complemented the prognostic information on risk of MI.

Conclusions— We identified a SNP in the CD40LG gene as a novel regulator of sCD40L plasma concentrations. Soluble CD40L levels above median reflect a prothrombotic state, which can be managed with the use of intense anti-thrombotic treatments.

The immune response in atherosclerosis: a double-edged sword

Immune responses participate in every phase of atherosclerosis. There is increasing evidence that both adaptive and innate immunity tightly regulate atherogenesis. Although improved treatment of hyperlipidaemia reduces the risk for cardiac and cerebral complications of atherosclerosis, these remain among the most prevalent of diseases and will probably become the most common cause of death globally within 15 years. This Review focuses on the role of immune mechanisms in the formation and activation of atherosclerotic plaques, and also includes a discussion of the use of inflammatory markers for predicting cardiovascular events. We also outline possible future targets for prevention, diagnosis and treatment of atherosclerosis.

CD40-CD154 expression in calcified and non-calcified coronary lesions of patients with chronic renal failure

The high incidence of cardiovascular complications in patients with chronic renal failure (CRF) is partly explained by more aggressive atherosclerosis, i.e. increased incidence and severity of lesions with higher tendency to calcification. The pathogenesis of this accelerated atherosclerosis, however, is not completely understood. Among other risk factors, chronic micro-inflammation may be involved. Activation of cells and adhesion molecules in atherosclerosis is governed by CD40-CD154 (CD40 ligand) interaction. Therefore, we investigated the expression and distribution of CD40-CD154 in different coronary atherosclerotic lesions of CRF patients and non-renal control patients. Coronary plaques of 57 patients with and without CRF were categorized according to the Stary classification and analysed for in situ protein expression of CD40, CD154 and CRP using immunohistochemistry and a semiquantitative scoring system. The nature, number and distribution of infiltrating cells was analysed and correlated to the types of coronary lesions and in particular to the presence of calcification. CD40 was over expressed in media myocytes of coronary plaques of both uremic and control patients. Inside the plaques, CD40 was expressed on endothelial cells, T lymphocytes, macrophages, fibroblasts, and smooth muscle cells. CD154 expression was seen on T cells in areas densely infiltrated by CD40 positive macrophages. In uremic and control patients higher in situ expression of CD40, CD154 and CRP was seen in calcified compared to non-calcified lesions. Inside the plaques, there were significant differences in the expression pattern of CD40 and CD154 between uremic and control patients. In addition, in uremic patients coronary plaques showed higher CRP protein expression compared to control patients. The data indicate a higher inflammatory status of coronary lesions as well as involvement of the CD40-CD154 signaling cascade in CRF patients, especially in cases of calcified atherosclerotic lesions.

Epstein Barr virus specific T-cells generated from unstable human atherosclerotic lesions: Implications for plaque inflammation

OBJECTIVE

T-cell activation is an essential feature of atherosclerotic plaque inflammation, which eventually may lead to plaque rupture. In this study, we investigated if EBV, a common herpes virus, is capable of stimulating atherosclerotic plaque derived T-cells and thus could contribute to atherosclerotic plaque inflammation.

METHODS

Plaque derived T-cell cultures were established from symptomatic carotid atherosclerotic plaques of 19 patients. B-cells from the same patients were transformed with EBV to form lymphoblastoid cell lines (B-LCL) that served as antigen presenting cells. The proliferation of T-cells in the presence of autologous B-LCL was analyzed using 3H-thymidine incorporation. The presence of EBV in atherosclerotic material was analyzed by PCR.

RESULTS

Of the 19 cell obtained T-cell cultures, 11 responded to EBV (58%, mean stimulation index: 10.1+/-3.1). PCR analysis showed that EBV DNA was present in 15 of the tissue samples (79%). All the specimens that contained EBV responding T-cells also contained EBV. EBV specific T-cells secreted granzymes, as indication of functional cytotoxic potential.

CONCLUSIONS

EBV-specific cytotoxic T-cells and EBV DNA can be frequently observed in human atherosclerotic plaques. This suggests that a T-cell response against EBV could contribute to plaque inflammation, and thus to the onset of acute clinical symptoms.

Platelets, Inflammation, and Atherothrombotic Neurovascular Disease: The Role of Endothelial Dysfunction

The vascular endothelium is an indispensable organ in the regulation of tonicity and vascular homeostasis. Endothelial dysfunction is a marker of atherosclerosis and contributes to the atherogenic process and the development of atherothrombotic complications. Endothelial dysfunction is the common meeting point among factors for vascular risk and launches complex cellular and biochemical interactions that are characterized by oxidative stress and an intense inflammatory response. The strategic importance of the concept of endothelial dysfunction arises from the following facts: its diagnosis is simple, it allows the identification of asymptomatic arteriosclerotic subjects with a high risk of developing atherothrombotic complications, it is reversible, and it responds to various therapeutic strategies.

[Platelet-associated CD154: a new interface in haemostasis and in the inflammatory reaction]

Blood platelets play a crucial part in the blood clotting process by forming the platelet plug. Recent evidence indicates that they are likely to play a key role in the inflammatory reaction via CD154/CD40 interactions. CD40 was known to be widely expressed, for instance on cells of the vasculature including endothelial cells, smooth muscle cells and macrophages. It was also known that the triggering of CD40 on these cells led to the acquisition of an activated pro-inflammatory and pro-coagulant phenotype. It was subsequently shown that platelets express CD154 which is cryptic in unstimulated platelets but is expressed at the platelet surface upon platelet activation. When expressed at the platelet surface and exposed to CD40-expressing vascular cells, the platelet-associated CD154 triggers a variety of pro-inflammatory and pro-coagulant responses including induction of adhesion receptors, release of cytokines and chemokines, induction of tissue factor and of metalloproteinases. Platelet-associated CD154 is also involved in platelet/platelet interactions during platelet aggregation. Furthermore, in vivo models have emphasized the critical role of the platelet-associated CD154 in the progression of atherosclerotic disease and in the stabilization of arterial thrombi. Recent data show that CD40-bearing cells involved in fibrosis such as hepatic stellate cells and glomerular mesangial cells also respond to platelet-associated CD154, thus suggesting a new mechanism by which platelets may be instrumental in the inflammatory diseases of the liver or the kidney. Finally, platelet-associated CD154 has been shown to have immune competence both in vitro and in vivo, observations that open new fields of research on the potential implications of platelets in the immune response and auto-immune diseases.

Death receptor-mediated apoptosis in human malignant glioma cells: modulation by the CD40/CD40L system

CD40, a TNF-R-related cell surface receptor, is shown here to be expressed by glioma cells in vitro and in vivo. Glioma cell lines expressing low levels of CD40 at the cell surface resist cytotoxic effects of CD40L. CD40 gene transfer sensitizes glioma cells to CD40L. Inhibition of protein synthesis potentiates cell death which involves CD40 clustering and caspases 8 and 3 processing. CD40-transfected LN-18 cells acquire resistance to CD95L. In contrast, subtoxic concentrations of CD40L strongly sensitize these cells for TNF-alpha-induced apoptosis. Bispecific CD40xCD95 antibodies specifically kill glioma cells, disclosing the property of endogenous CD40 to facilitate death signalling.

IDEC-131 (anti-CD154), sirolimus and donor-specific transfusion facilitate operational tolerance in non-human primates

CD154-specific antibody therapy prevents allograft rejection in many experimental transplant models. However, initial clinical transplant trials with anti-CD154 have been disappointing suggesting the need for as of yet undetermined adjuvant therapy. In rodents, donor antigen (e.g., a donor blood transfusion), or mTOR inhibition (e.g., sirolimus), enhances anti-CD154's efficacy. We performed renal transplants in major histocompatibility complex-(MHC) mismatched rhesus monkeys and treated recipients with combinations of the CD154-specific antibody IDEC-131, and/or sirolimus, and/or a pre-transplant donor-specific transfusion (DST). Therapy was withdrawn after 3 months. Triple therapy prevented rejection during therapy in all animals and led to operational tolerance in three of five animals including donor-specific skin graft acceptance in the two animals tested. IDEC-131, sirolimus and DST are highly effective in preventing renal allograft rejection in primates. This apparently clinically applicable regimen is promising for human renal transplant trials.