Can We Talk about CD4+CD28– Lymphocytes as a Risk Factor for Ischemic Stroke?

Molecular Pathogenesis of Ischemic and Hemorrhagic Strokes: Background and Therapeutic Approaches

Stroke represents one of the neurological diseases most responsible for death and permanent disability in the world. Different factors, such as thrombus, emboli and atherosclerosis, take part in the intricate pathophysiology of stroke. Comprehending the molecular processes involved in this mechanism is crucial to developing new, specific and efficient treatments. Some common mechanisms are excitotoxicity and calcium overload, oxidative stress and neuroinflammation. Furthermore, non-coding RNAs (ncRNAs) are critical in pathophysiology and recovery after cerebral ischemia. ncRNAs, particularly microRNAs, and long non-coding RNAs (lncRNAs) are essential for angiogenesis and neuroprotection, and they have been suggested to be therapeutic, diagnostic and prognostic tools in cerebrovascular diseases, including stroke. This review summarizes the intricate molecular mechanisms underlying ischemic and hemorrhagic stroke and delves into the function of miRNAs in the development of brain damage. Furthermore, we will analyze new perspectives on treatment based on molecular mechanisms in addition to traditional stroke therapies.

Neuroinflammatory Mechanisms in Ischemic Stroke: Focus on Cardioembolic Stroke, Background, and Therapeutic Approaches

One of the most important causes of neurological morbidity and mortality in the world is ischemic stroke. It can be a result of multiple events such as embolism with a cardiac origin, occlusion of small vessels in the brain, and atherosclerosis affecting the cerebral circulation. Increasing evidence shows the intricate function played by the immune system in the pathophysiological variations that take place after cerebral ischemic injury. Following the ischemic cerebral harm, we can observe consequent neuroinflammation that causes additional damage provoking the death of the cells; on the other hand, it also plays a beneficial role in stimulating remedial action. Immune mediators are the origin of signals with a proinflammatory position that can boost the cells in the brain and promote the penetration of numerous inflammatory cytotypes (various subtypes of T cells, monocytes/macrophages, neutrophils, and different inflammatory cells) within the area affected by ischemia; this process is responsible for further ischemic damage of the brain. This inflammatory process seems to involve both the cerebral tissue and the whole organism in cardioembolic stroke, the stroke subtype that is associated with more severe brain damage and a consequent worse outcome (more disability, higher mortality). In this review, the authors want to present an overview of the present learning of the mechanisms of inflammation that takes place in the cerebral tissue and the role of the immune system involved in ischemic stroke, focusing on cardioembolic stroke and its potential treatment strategies.

HLA and killer cell immunoglobulin-like receptor (KIRs) genotyping in patients with acute ischemic stroke

INTRODUCTION

In humans, a major component of natural killer (NK) and T cell target recognition depends on the surveillance of human leukocyte antigen (HLA) class I molecules by killer immunoglobulin-like receptors (KIRs).

AIMS

To implement the knowledge about the immunological genetic background of acute ischemic stroke susceptibility in relation to the frequency of the KIR genes and HLA alleles.

METHODS

Subjects with acute ischemic stroke and subjects without stroke were genotyped for the presence of KIR genes and of the three major KIR ligand groups, HLA-C1, HLA-C2, and HLA-Bw4, both HLA-B and HLA-A loci.

RESULTS

Between November 2013 and February 2016, consecutive patients with acute ischemic stroke were recruited. As healthy controls, we enrolled subjects without acute ischemic stroke. Subjects with acute ischemic stroke in comparison with controls showed a higher frequency of 2DL3, 2DL5B, 2DS2, and 2DS4 KIR genes and a lower frequency of HLA-B-Bw4I alleles. Subjects without acute ischemic stroke showed a higher frequency of interaction between KIR 2DS2 and HLAC2. We also observed a higher frequency of 2DL3 and 2 DL4 KIR genes in subjects with atherosclerotic (LAAS) subtype. Multiple logistic regression analysis showed a protective effect towards stroke of HLA-B-Bw4I and interaction between KIR 2DL2 and HLAC1 and 2DS2-HLAC2 and a detrimental effect of 2DL2-HLA-C1_A interactions.

CONCLUSION

Our findings of a higher frequency of activating KIR genes seem to be consistent with findings previously reported patients with coronary syndrome. This higher frequency of "proinflammatory" genes in subjects with ischemic stroke could also explain the immunoinflammatory activation of the acute phase of stroke.

Expanded peripheral CD4+CD28null T cells and its association with atherosclerotic changes in patients with end stage renal disease on hemodialysis

End-stage renal disease (ESRD) patients, including those on hemodialysis, possess a high risk for cardiovascular diseases, as the first leading cause of death among them. Traditional risk factors do not utterly elucidate this. Throughout the last two decades, CD4⁺CD28^null T cells; an unusual subset of T lymphocytes, was detected high with excess cardiovascular (CV) mortality. We aimed to investigate the circulating CD4⁺CD28^null T cells frequency in ESRD patients on hemodialysis and to evaluate their relationship with atherosclerotic changes. High-resolution carotid ultrasonography was done to assess the common carotid artery intima media thickness in a number of ESRD patients, accordingly patients were selected and subdivided into two groups; 30 with atherosclerosis (mean [SD] age, 51.6 [6.3] years) and 30 without (mean [SD] age, 48.9 [5.5] years). Another 30 healthy individuals (mean [SD] age, 48.5 [6.8] years) were enrolled. Analysis of CD4⁺CD28^null T-cells frequency by flow-cytometry was performed in all studied subjects. CD4⁺CD28^null T cell percentage was significantly higher in ESRD patients, (mean [SD], 7.3 [2.7] %) compared to healthy individuals (mean [SD], 3.0 [0.8] %), (p < 0.001). Additionally, the expansion of these unusual T lymphocytes was significantly higher in ESRD patients with atherosclerotic changes (mean [SD], 9.47 [0.75] %) compared to those without atherosclerosis (mean [SD], 5.22 [2.14] %), (p < 0.001). In conclusion circulating CD4⁺CD28^null T lymphocyte population showed expansion in ESRD patients, and of interest in correlation to preclinical atherosclerotic changes.

Increased Soluble CD137 Levels and CD4+ T-Cell-Associated Expression of CD137 in Acute Atherothrombotic Stroke

As a proinflammatory cytokine, CD137 (4‐1BB, TNFRSF9) is present in membrane‐bound and soluble forms. Increased expression of CD137 was recently found in T cells in human atherosclerotic plaques. However, the exact role of CD137 in ischemic stroke is not clear. In this study we analyzed the protein levels of soluble CD137 (sCD137) and the expression of CD137 on CD4+ T cells in the peripheral blood of patients with acute atherothrombotic stroke by using the cytometry beads array (CBA) and flow cytometry. Within 24 hours of onset, the stroke patients showed elevated levels of sCD137 (2.7 pg/ml) and CD137 expression on CD4+ T cells (4.9 ± 3.2%) compared with normal controls (1.1 pg/ml, P < 0.01; 1.3 ± 1.0%, P < 0.01). Alterations in CD137 expression may enhance ischemia‐induced inflammatory responses via bidirectional signaling and, consequently, aggravate brain injury in early stages of this disorder.

Interleukin-19 alleviates brain injury by anti-inflammatory effects in a mice model of focal cerebral ischemia

Stroke causes brain injury with neuroinflammation which exacerbates the neuronal damage. Recent studies show that anti-inflammatory cytokine interleukin-19 (IL-19) plays a critical part in the inflammatory and ischemic vascular diseases, yet its potential role in ischemic stroke is unknown. Here, we tested the hypothesis that IL-19 exerts protective effects against brain ischemia by modulating inflammation after stroke. Mice were injected intraperitoneally with 10ng/g per day recombinant mouse IL-19 starting pre-stroke, and were subjected to transient middle cerebral artery occlusion. Infarct volume was assessed by triphenyltetrazolium chloride and neurobehavioral outcome by neurological scores. Inflammation was measured using real-time quantitative PCR, immunochemistry, and fluorescence-activated cell sorting. Infarct volume at 72h after stroke was significantly smaller in IL-19 treated group and focal neurological score was significantly better. IL-19 treatment markedly attenuated elevation of the expression of TNF-α and IL-6 mRNA, suppressed increases in the number of microglia, macrophages, CD4⁺ T cells, CD8⁺ T cells as well as B cells, and blocked activation of macrophages and neutrophils in the ischemic brain. In peripheral blood, IL-19 injection helped to robustly preserve the reduced immune cells, including macrophages, CD4⁺ T cells, CD8⁺ T cells and B cells, compared to control group. IL-19 reduced brain infarction and attenuated neurological deficits following stroke in mice, probably by inhibiting infiltration and activation of immune cells, and by suppressing increases in gene expression of proinflammatory cytokines. This may identify IL-19 as a new therapeutic to limit neuroinflammation after stroke.

Cytomegalovirus infection is associated with an increase in systolic blood pressure in older individuals

BACKGROUND

Cytomegalovirus (CMV) is a chronic infection that is widely distributed in the population. CMV infects a range of tissues, including endothelium, and viral replication is suppressed by the host immune system. Infection is associated with increased risk of mortality from vascular disease in older people, but the mechanisms behind this have not been determined.

AIM

We investigated the association between CMV infection and cardiovascular phenotype in a cohort of healthy elderly donors.

DESIGN

CMV serostatus and cardiovascular parameters were determined in the Lothian Birth cohort, which comprises 1091 individuals aged 70 years in whom many environmental, biochemical and radiological correlates of vascular function have been determined.

METHODS

CMV serostatus was determined by enzyme-linked immunosorbant assay and correlated with a range of biochemical and phenotypic measures.

RESULTS

Sixty-five percent of participants were CMV seropositive, which indicates chronic infection. The mean sitting systolic blood pressure (SBP) was 149.2 mmHg in CMV seropositive individuals compared with 146.2 mmHg in CMV seronegative subjects (SD 18.7 vs. 19.7; P < 0.017). This association between CMV infection and SBP was not attenuated after adjustment for a wide range of biological and socio-economic factors.

CONCLUSIONS

These data show that CMV infection is associated with an increase in SBP in individuals at age 70 years. The magnitude is comparable to environmental variables such as obesity, diabetes or high salt intake. This is the first evidence to show that a chronic infection may be an important determinant of blood pressure and could have significant implications for the future management of hypertension.

Peripheral frequency of CD4+ CD28- cells in acute ischemic stroke: relationship with stroke subtype and severity markers

CD4+ CD28- T cells also called CD28 null cells have been reported as increased in the clinical setting of acute coronary syndrome. Only 2 studies previously analyzed peripheral frequency of CD28 null cells in subjects with acute ischemic stroke but, to our knowledge, peripheral frequency of CD28 null cells in each TOAST subtype of ischemic stroke has never been evaluated. We hypothesized that CD4+ cells and, in particular, the CD28 null cell subset could show a different degree of peripheral percentage in subjects with acute ischemic stroke in relation to clinical subtype and severity of ischemic stroke.The aim of our study was to analyze peripheral frequency of CD28 null cells in subjects with acute ischemic stroke in relation to TOAST diagnostic subtype, and to evaluate their relationship with scores of clinical severity of acute ischemic stroke, and their predictive role in the diagnosis of acute ischemic stroke and diagnostic subtypeWe enrolled 98 consecutive subjects admitted to our recruitment wards with a diagnosis of ischemic stroke. As controls we enrolled 66 hospitalized patients without a diagnosis of acute ischemic stroke. Peripheral frequency of CD4+ and CD28 null cells has been evaluated with a FACS Calibur flow cytometer.Subjects with acute ischemic stroke had a significantly higher peripheral frequency of CD4+ cells and CD28 null cells compared to control subjects without acute ischemic stroke. Subjects with cardioembolic stroke had a significantly higher peripheral frequency of CD4+ cells and CD28 null cells compared to subjects with other TOAST subtypes. We observed a significant relationship between CD28 null cells peripheral percentage and Scandinavian Stroke Scale and NIHSS scores. ROC curve analysis showed that CD28 null cell percentage may be useful to differentiate between stroke subtypes.These findings seem suggest a possible role for a T-cell component also in acute ischemic stroke clinical setting showing a different peripheral frequency of CD28 null cells in relation of each TOAST subtype of stroke.

Relationship of CD146 expression to activation of circulating T cells: exploratory studies in healthy donors and patients with connective tissue diseases

The endothelial cell adhesion molecule, CD146, is expressed on ≈ 2% of normal circulating T cells, correlating with T cell activation, endothelial interactions and T helper type 17 (Th17) effector functions. In this study, we have characterized CD146 expression in circulating T cells from healthy controls and patients with stable, well-controlled autoimmune connective tissue diseases (CTDs). In vitro, anti-CD3/anti-CD28 stimulation induced CD146 expression in both CD4 and CD8 T cells. In healthy controls and CTD patients, CD146 was associated with expression of recent and chronic activation markers (CD25(+), OX-40(+), CD69(+), CD27(-)) and was confined to CD45RO(+)/RA(-)/CD28(+) populations within the CD4 subset. Except for CD69, these markers were not associated with CD146 in the CD8 subset. Surprisingly, most CTD patients exhibited no T cell hyperactivation ex vivo. In five of five patients with secondary Sjögren's syndrome circulating T cells appeared activated despite therapy, and CD146 up-regulation, associated with activation markers, was observed both on CD4 and CD8 T cells. There was no association between CD146 and putative pro-atherogenic T cell subsets. In conclusion, the relationship of CD146 expression to T cell activation differs between T cell subsets in healthy subjects and correlates with systemic hyperactivity, where present, in patients with CTDs, as exemplified by the patients with secondary Sjögren's syndrome in this study.

Circulating CD4(+)CD28null T Cells May Increase the Risk of an Atherosclerotic Vascular Event Shortly after Kidney Transplantation

Proinflammatory CD4(+) T cells without the costimulatory molecule CD28 (CD4(+)CD28null T cells) are expanded in patients with end-stage renal disease (ESRD) and associated with atherosclerotic vascular events (AVE). In a prospective study, the number of circulating CD4(+)CD28null T cells was established in 295 ESRD patients prior to receiving a kidney allograft. Within the first year after transplantation, an AVE occurred in 20 patients. Univariate analysis showed that besides a history of cardiovascular disease (CVDpos, HR 8.1, P < 0.001), age (HR 1.04, P = 0.02), dyslipidaemia (HR 8.8, P = 0.004), and the % of CD4(+)CD28null T cells (HR 1.04 per % increase, 95% CI 1.00-1.09, P = 0.01) were significantly associated with the occurrence of a posttransplantation AVE. In a multivariate analysis, only CVDpos remained a significant risk factor with a significant and positive interaction between the terms CVDpos and the % of CD4(+)CD28null T cells (HR 1.05, 95% CI 1.03-1.11, P < 0.001). Within the CVDpos group, the incidence of an AVE was 13% in the lowest tertile compared to 25% in the highest tertile of % of CD4(+)CD28null T cells. In conclusion, the presence of circulating CD4(+)CD28null T cells is associated with an increased risk for a cardiovascular event shortly after kidney transplantation.

CD4⁺CD28⁻ lymphocytes and cerebral ischaemic stroke. Part II: CD4⁺CD28⁻ lymphocytes and carotid artery atherosclerotic plaque characteristics

BACKGROUND AND PURPOSE

CD4⁺CD28⁻ lymphocytes can directly contribute to the instability of atherosclerotic plaque. This paper attempts to answer the question of the potential influence of the CD4⁺CD28⁻ lymphocyte population on the ultrasound image of atherosclerotic plaque in the common carotid artery (CCA) wall.

MATERIAL AND METHODS

The study involved a group of 109 patients, aged 45 to 65 years, including 42 patients with first ever ischaemic stroke, experiencing symptoms resulting from disturbances of the anterior area of cerebral circulation, arterial hypertension and/or type 2 diabetes mellitus (group 1). Group 2 consisted of 34 patients with mentioned risk factors, without ischaemic stroke. The control group comprised 33 heal-thy individuals. The percentage of CD4⁺CD28⁻ lymphocytes was assessed with flow cytometry.

RESULTS

A significant difference in the incidence of heterogeneous plaques was noted between groups 1 and 3 (p = 0.0023) as well as between group 2 and 3 (p = 0.0005), whereas groups 1 and 2 did not differ from each other. The proportion of CD4⁺CD28⁻ lymphocytes was similar in groups 1 and 2 (p = 0.97), but it differed between groups 1 and 3 (p < 0.0001) and between groups 2 and 3 (p < 0.001). A correlation was found between the proportion of CD4⁺CD28⁻ lymphocytes in the blood and the number of CCA atherosclerotic plaques (Rs = 0.191, p = 0.046). The proportion of CD4⁺CD28⁻ lymphocytes in peripheral blood did not correlate with the ultrasound types of atherosclerotic plaques. No correlation between the proportion of CD4⁺CD28 ⁻lymphocytes and the area of atherosclerotic plaques was found.

CONCLUSIONS

The correlation between the proportion of CD4⁺CD28⁻ lymphocytes and the number of atherosclerotic plaques within the CCA suggests that the cells are involved in the mechanism of carotid plaque formation. There is no proof of the involvement of the above-mentioned cells in the mechanism of plaque destabilization in those arteries.

CD4⁺CD28⁻ lymphocytes and ischaemic stroke. Part I: CD4⁺CD28⁻ lymphocytes and common carotid artery intima-media thickness

BACKGROUND AND PURPOSE

More and more data point to the involvement of the CD4⁺CD28⁻ lymphocyte subpopulation in the pathogenesis of ischaemic stroke. This paper attempts to answer the question of whether an increase in the percentage of CD4⁺CD28⁻ lymphocytes in the blood may be associated with carotid artery intima-media thickness (IMT).

MATERIAL AND METHODS

The study involved a group of 109 patients, aged 45 to 65 years, including 42 patients with first-ever ischaemic stroke, experiencing symptoms resulting from disturbances of the anterior area of cerebral circulation, arterial hypertension and/or type 2 diabetes mellitus (group 1). Group 2 consisted of 34 patients with above-mentioned risk factors but without ischaemic stroke. The control group comprised 33 healthy individuals. Distribution of sex and mean age was comparable. The IMT of carotid arteries was measured by ultrasonography. Flow cytometry was applied to determine the percentage of CD4⁺CD28⁻ lymphocytes in the peripheral blood.

RESULTS

The IMT was significantly greater in patients with stroke than in patients without stroke. No significant correlation was found between the proportion of CD4⁺CD28⁻ lymphocytes in the blood and the IMT of carotid arteries.

CONCLUSIONS

The significant proportion of CD4⁺CD28⁻ lymphocytes in patients with ischaemic stroke points to the involvement of the cells in the pathogenesis of stroke. The CD4⁺CD28⁻ lymphocytes are not involved in the pathomechanism of common carotid arteries IMT thickening in this group of patients.

Premature aging of circulating T cells in patients with end-stage renal disease

Progressive loss of renal function is associated with a dysregulation of circulating T cells that may underlie their impaired T-cell immunity. Here we tested whether end-stage renal disease (ESRD)-related T-cell alterations are compatible with the concept of premature immunological aging. Younger patients (25-45 years old) with ESRD were found to resemble older healthy controls (60-80 years old) as they had a significant loss of naive T cells and a relative increase of memory T cells showing progressive terminal differentiation. A significant decrease in the content of T-cell receptor excision circles and telomere length in patients with ESRD confirmed these phenotypic data. The loss of naive T cells in patients with ESRD was associated with an excessive age-related decrease of recent thymic emigrants, indicating a premature decline in thymic function. Additionally, increased homeostatic proliferation of naive T cells was found in patients with ESRD, similar to that of older healthy individuals, with an increased susceptibility for activation-induced apoptosis. Therefore, both decreased thymic output and increased susceptibility of naive T cells for apoptosis may play a role in the loss of naive T cells in ESRD patients. Thus, our results are compatible with premature aging of the T-cell system of patients with ESRD comparable with that of healthy individuals 20-30 years older.

Circulating pro-inflammatory CD4posCD28null T cells are independently associated with cardiovascular disease in ESRD patients

BACKGROUND

Cytomegalovirus seropositivity is associated with an increased risk for cardiovascular disease in end-stage renal disease (ESRD) patients. Circulating pro-inflammatory CD4posCD28null T cells are expanded in cytomegalovirus-seropositive ESRD patients and potentially could mediate atherosclerotic plaque instability and rupture.

METHODS

In this study, we tested the hypothesis that increased numbers of circulating CD4posCD28null T cells may represent a risk factor for cardiovascular disease in ESRD patients. Prospectively collected data from 240 cytomegalovirus-seropositive stable ESRD patients were analysed.

RESULTS

Traditional cardiovascular risk factors (age, smoking, hypercholesterolaemia and diabetes mellitus) and the percentage and absolute number of CD4posCD28null T cells were significantly associated with the presence of atherosclerotic disease, after univariate and multivariate statistical analysis. An ~2-3-fold increase in the prevalence of atherosclerotic disease was noted between patients with the highest and lowest number of CD4posCD28null cells. CD8posCD28null T-cell populations were also significantly expanded in cytomegalovirus-seropositive ESRD patients and closely correlated with the number of CD4posCD28null T cells. However, this cell population was not related to an increased prevalence of cardiovascular disease.

CONCLUSIONS

Cytomegalovirus-seropositive ESRD patients may have substantially increased numbers of circulating pro-inflammatory CD4posCD28null T cells that are independently associated with the presence of atherosclerotic disease. The expansion of these cells may therefore represent a novel non-traditional cardiovascular risk factor for ESRD patients.