Enhanced immunoglobulin formation of immortalized B cells from hypertensive patients

Peripheral Immune Cell Composition is Altered in Women Before and After a Hypertension Diagnosis

BACKGROUND

The development and consequences of hypertension involve multiple biological systems that may include changes in immune profiles. Whether hypertension is related to peripheral immune cell composition has not been examined in large human cohorts.

METHODS

We estimated circulating proportions of 12 leukocyte subsets from the lymphoid and myeloid lineages by deconvolving cell-type-specific DNA methylation data from 4124 women. Hypertension status at baseline was defined by current use of antihypertensive medication and blood pressure measurements while new incident cases were identified during follow-up via annual health questionnaires.

RESULTS

Among hypertension-free women at baseline, higher B cell and lower naïve CD4+ helper T cell proportions were associated with subsequent increased hazard of hypertension incidence (B cells; adjusted HR: 1.17 [95% CI: 1.02-1.35]; P=0.03; naïve CD4+ T cell, adjusted HR: 0.88 [95% CI: 0.78-0.99]; P=0.04). Blood pressure measurements at baseline were similarly positively associated with B cells and inversely associated with naïve CD4+ helper T cells. Compared to normotensive women, women with hypertension had higher circulating proportions of neutrophils (adjusted odds ratio: 1.18 [95% CI: 1.07-1.31]; P=0.001) and lower proportions of CD4+ helper T cells (adjusted odds ratio: 0.90 [95% CI: 0.81-1.00] P=0.05), natural killers (adjusted odds ratio: 0.82 [95% CI: 0.74-0.91]; P<0.001), and B cells (adjusted odds ratio: 0.84 [95% CI: 0.74-0.96]; P=0.01).

CONCLUSIONS

These observations suggest that shifts in lymphocyte subsets occur before hypertension development, followed by later changes to neutrophils and additional lymphocytes.

Heterogeneity of B Cell Functions in Stroke-Related Risk, Prevention, Injury, and Repair

It is well established that post-stroke inflammation contributes to neurovascular injury, blood-brain barrier disruption, and poor functional recovery in both animal and clinical studies. However, recent studies also suggest that several leukocyte subsets, activated during the post-stroke immune response, can exhibit both pro-injury and pro-recovery phenotypes. In accordance with these findings, B lymphocytes, or B cells, play a heterogeneous role in the adaptive immune response to stroke. This review highlights what is currently understood about the various roles of B cells, with an emphasis on stroke risk factors, as well as post-stroke injury and repair. This includes an overview of B cell functions, such as antibody production, cytokine secretion, and contribution to the immune response as antigen presenting cells. Next, evidence for B cell-mediated mechanisms in stroke-related risk factors, including hypertension, diabetes, and atherosclerosis, is outlined, followed by studies that focus on B cells during endogenous protection from stroke. Subsequently, animal studies that investigate the role of B cells in post-stroke injury and repair are summarized, and the final section describes current B cell-related clinical trials for stroke, as well as other central nervous system diseases. This review reveals the complex role of B cells in stroke, with a focus on areas for potential clinical intervention for a disease that affects millions of people globally each year.

Anti-beta2-Glycoprotein I Antibody and Hypertension in Cerebral Ischemia

Hypertension is known as a cause of endothelial cell damage and it activates humoral immunity. Therefore, it may modulate the anti-beta2-glycoprotein I antibody (aβGPI) to commit for thrombosis. To elucidate the relation between aβGPI and hypertension in cerebral ischemia, the blood aβGPI level was examined in healthy subjects, hypertensive subjects, and patients with cerebral ischemia with and without hypertension, respectively. The results showed that the blood aβGPI level increased in cerebral ischemia patients with hypertension rather than hypertensive subjects, and patients without hypertension rather than healthy individuals. However, the blood aβGPI level showed no difference between healthy individuals and hypertensive subjects, nor cerebral ischemia patients with and without hypertension. The serum globulin level did not change among them. Therefore, aβGPI displays a vital role for cerebral ischemia in both hypertensive and normotensive subjects. An activation of humoral immunity involving aβGPI warrants further investigation in cerebral ischemia.

Antibodies in the pathogenesis of hypertension

It has long been known that circulating levels of IgG and IgM antibodies are elevated in patients with essential and pregnancy-related hypertension. Recent studies indicate these antibodies target, and in many cases activate, G-protein coupled receptors and ion channels. Prominent among these protein targets are AT₁ receptors, α₁-adrenoceptors, β₁-adrenoceptors, and L-type voltage operated Ca²⁺ channels, all of which are known to play key roles in the regulation of blood pressure through modulation of vascular tone, cardiac output, and/or Na⁺/water reabsorption in the kidneys. This suggests that elevated antibody production may be a causal mechanism in at least some cases of hypertension. In this brief review, we will further describe the protein targets of the antibodies that are elevated in individuals with essential and pregnancy-related hypertension and the likely pathophysiological consequences of antibody binding to these targets. We will speculate on the potential mechanisms that underlie elevated antibody levels in hypertensive individuals and, finally, we will outline the therapeutic opportunities that could arise with a better understanding of how and why antibodies are produced in hypertension.

Platelet-activating factor and normal or leukaemic haematopoiesis

Platelet-activating factor (PAF), a phospholipid mediator with a wide range of actions on mature leukocytes, acts directly during early human haematopoiesis by affecting the growth of haematopoietic progenitors and indirectly, by modulating cytokine synthesis by bone marrow stromal cells. At this time, its role during leukaemic diseases remains speculative. The lack of membrane PAF receptor (PAF-R) on leukaemic blasts suggest that this receptor represents a marker of mature cells and its membrane induction a consequence of cell maturation. While the couple PAF/PAF-R has been largely studied using B cell lines, few results are available using B cells of patients with haematopoietic malignancies casting some doubts concerning the potential role (if any) of this molecule during leukaemic diseases.

[Telomerase activity in peripheral blood leukocytes from patients with essential hypertension]

BACKGROUND AND OBJECTIVE

Primary or secondary activation of the immune mechanisms that lead to proliferation and dysfunction of specific cellular groups appears to be involved in the pathogenesis and complications of essential hypertension. In view of the evidence that, on one hand, telomeric length determines the replicative capacity and life span of cells and, on the other hand, idiopathic hypertensive patients have peripheral white cell replicative disorders, we decided to investigate the relationship between the influence of telomerase activity in peripheral leukocytes as an indirect marker of telomeric length and the presence of arterial hypertension.

PATIENTS AND METHOD

Telomerase activity in peripheral white blood cells was measured in healthy individuals, in effectively treated hypertensive patients and in a non-well controlled hypertensive group. White blood cells were separated through a density gradient, then lysed and their DNA amplified by a polimerase chain reaction (PCR). Telomerase activity was determined with an ELISA specific kit.

RESULTS

The white blood cell count was higher in the hypertensive than the control group (p < 0.05). Telomerase activity was positive in all three groups but higher in patients under 45 year-old with bad controlled hypertension as compared with healthy individuals and patients under 45 year-old with well controlled hypertension (p < 0.05); in the latter group, telomerase activity was significantly lower than in the other groups (p < 0.05).

CONCLUSIONS

Our results indicate that there exists a relationship between telomerase activity in peripheral leukocytes, the proliferation of these white blood cells and the presence of essential arterial hypertension.

Frequencies of the G-protein beta3 subunit C825T polymorphism and the delta 32 mutation of the chemokine receptor-5 in patients with multiple sclerosis

In the pathogenesis of multiple sclerosis (MS) genetic factors are known to influence autoreactive T-cell-actions like proliferation and chemotaxis across the blood-brain barrier via chemokine receptors (CCR) and G-protein coupled activating mechanisms. For the first time, we studied the frequencies of a recently described C825T polymorphism in the G-protein encoding gene for the beta3 subunit (GNB3) together with frequencies of a 32-base-pair deletion in the CCR5 gene (delta32 CCR5) in patients with MS (n = 253: relapsing-remitting (RR), n = 124 and chronic progressive course, n = 129). Apart from a trend to a reduced frequency of delta32 CCR5 and increased GNB3 825T polymorphism in primary chronic progressive patients, numbers did not reach statistical significance in any group of MS. These results could not support differences in the genetic background of MS based on that CCR5 mutation or the described GNB3 polymorphism.

Platelet-activating factor (PAF) receptor and genetically engineered PAF receptor mutant mice

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a biologically active phospholipid mediator. Although PAF was initially recognized for its potential to induce platelet aggregation and secretion, intense investigations have elucidated potent biological actions of PAF in a broad range of cell types and tissues, many of which also produce the molecule. PAF acts by binding to a unique G-protein-coupled seven transmembrane receptor. PAF receptor is linked to intracellular signal transduction pathways, including turnover of phosphatidylinositol, elevation in intracellular calcium concentration, and activation of kinases, resulting in versatile bioactions. On the basis of numerous pharmacological reports, PAF is thought to have many pathophysiological and physiological functions. Recently advanced molecular technics enable us not only to clone PAF receptor cDNAs and genes, but also generate PAF receptor mutant animals, i.e., PAF receptor-overexpressing mouse and PAF receptor-deficient mouse. These mutant mice gave us a novel and specific approach for identifying the pathophysiological and physiological functions of PAF. This review also describes the phenotypes of these mutant mice and discusses them by referring to previously reported pharmacological and genetical data.

Detection of Functional Platelet-Activating Factor Receptors on Human Tonsillar B Lymphocytes

Although platelet-activating factor (PAF) receptors have been found on B lymphoblastoid cell lines, the action of PAF on freshly isolated human B cells has not been clearly demonstrated. Using a sensitive semiquantitative reverse-transcriptase PCR, we have found PAF receptor mRNA expressed by tonsillar B lymphocytes, but little in T lymphocytes. Examination of Percoll-fractionated tonsillar B cells indicated that the low density (primarily germinal center cells) and medium density fractions had approximately twofold more PAF receptor mRNA relative to the high density fraction. PAF (10−7 M) stimulated increases in intracellular Ca2+ that were consistently higher in the low and medium density B lymphocytes compared with high density cells. The PAF receptor antagonist Web 2170 inhibited this. Addition of PAF, but not lyso- or enantio-PAF, induced four- to sixfold greater synthesis of IgM and IgG in low and medium density cells compared with unstimulated controls, but had little effect on Ig production by high density cells. To investigate how PAF may influence Ig synthesis, PAF-stimulated B cells were examined for production of the Th2-type cytokines IL-4 and IL-13. PAF induced IL-4 and IL-13 mRNA expression in 17% of CD20+ cells, and IL-4 was detected in cell supernatants after 48–72 h of culture. Together, these data strongly suggest that functional PAF receptors are expressed on B cells in tonsils.

Glucocorticoid modulation of Ca2+ homeostasis in human B lymphoblasts

1. We determined the effect of cortisol (200 nM for 48 h) on the intracellular Ca2+ concentration ([Ca2+]i) and parameters of Ca2+i signalling in 19 lymphoblastoid cell lines (LCLs). 2. Using the fluorescent dye fura-2, the basal [Ca2+]i in Ca2+-containing medium was 63.5 +/- 2.4 nM in vehicle (ethanol)-treated LCLs and 55.7 +/- 2. 6 nM (mean +/- s.e.m.) in cortisol-treated LCLs. 3. Ca2+i signalling following platelet-activating factor (PAF, 100 nM) addition was enhanced by cortisol treatment, with LCLs having small PAF responses showing the largest percentage increase after cortisol treatment. Mean peak [Ca2+]i responses to PAF were enhanced 67.0% and 55.7% in Ca2+-free and Ca2+-containing medium, respectively. 4. The endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin (100 nM) caused a transient increase in [Ca2+]i in Ca2+-free medium in which the peak change was increased in cortisol-treated cells (98.5 +/- 5.8 vs. 79.8 +/- 4.5 nM). Peak changes in the freely exchangeable Ca2+ in response to 5 microM ionomycin were also enhanced in cortisol-treated cells (923.7 +/- 113.9 vs. 652.2 +/- 64.5 nM) and correlated to the PAF-evoked [Ca2+]i response. 5. Cortisol-treated LCLs exposed to thapsigargin to empty intracellular Ca2+ stores (10 min treatment in Ca2+-free medium) and exposed to CaCl2 or MnCl2 had a greater rate of Ca2+ entry (18.6 +/- 1.8 vs. 13.8 +/- 1.5 nM s-1) and higher rate constant for Mn2+ entry (0.0345 +/- 0.0029 vs. 0. 0217 +/- 0.0020) than vehicle-treated cells. Peak [Ca2+]i in cells exposed to CaCl2 was also enhanced (869.4 +/- 114.7 vs. 562.6 +/- 61.7 nM). Parameters of divalent cation influx were highly correlated to the peak [Ca2+]i elicited by thapsigargin or ionomycin. 6. Inclusion of RU 486 (a glucocorticoid antagonist) with cortisol prevented the decrease in basal [Ca2+]i and stimulatory actions of cortisol on all Ca2+i parameters. RU 486 alone had no apparent effects on basal [Ca2+]i or Ca2+i signalling. 7. Based on data obtained over a wide range of responses (in the presence and/or absence of cortisol or RU 486), the results show that cortisol stimulation of glucocorticoid receptors decreases basal [Ca2+]i and enhances PAF-evoked [Ca2+]i signalling, most probably through its effects on intracellular Ca2+ stores. In turn, the extent of Ca2+ entry via store-operated plasma membrane Ca2+ channels is closely linked to the size of the Ca2+ stores.

Dose-dependent agonist and antagonist effects of the platelet-activating factor analogue 1-palmitoyl-2-acetoyl-sn-glycero-3-phosphocholine on B lymphocytes

BACKGROUND

Platelet activating-factor (PAF), an ether-linked phospholipid, is a potent activator of B lymphocyte cell lines. The related ester-linked phospholipid, 1-palmitoyl-2-acetoyl-sn-glycero-3-phosphocholine (PAGPC), is synthesized by tissues important in B-cell development.

OBJECTIVES

We examined whether PAGPC was capable of influencing immunoglobulin synthesis in B lymphocytes and compared its action with that of PAF. We also examined the interaction of the two mediators as agonists or competitive antagonists.

METHODS

Ramos, an IgM-secreting immature B-cell line that expresses PAF receptor, was used in these experiments. The effect of PAF, PAGPC, or both mediators together on IgM secretion and anti-IgM-mediated apoptosis was measured.

RESULTS

Both PAF and PAGPC stimulated IgM production in Ramos cells in a dose-dependent fashion, with PAGPC being approximately three logs less potent than PAF. The effect of both mediators was inhibited by specific PAF receptor antagonists. Preincubation with suboptimal concentrations of PAGPC inhibited the ability of PAF to increase IgM secretion by Ramos cells. Additionally, preincubation with low concentrations of PAGPC prevented PAF from rescuing Ramos cells from apoptosis induced by cross-linking the B-cell receptor with anti-IgM antibodies. PAGPC caused PAF receptor desensitization because displacement of bound PAGPC with high concentrations of bovine serum albumin did not reverse its PAF antagonist effect.

CONCLUSIONS

PAF and PAGPC are biologically active phospholipids, but PAF is approximately 1000 times more potent. At high concentrations, PAGPC acts similarly to PAF, whereas at lower concentrations, PAGPC acts as a functional PAF antagonist. Because it is secreted at sites of inflammation and allergic reactions, PAGPC may be an endogenous regulator of the effects of PAF.

Growth factor-like action of lysophosphatidic acid on human B lymphoblasts

Proliferation and immunoglobulin secretion of B lymphocytes are regulated by specific antigens and numerous accessory immunomodulatory factors. Lysophosphatidic acid (LPA) is a glycerophospholipid mediator that is released from activated blood platelets, attains high levels in serum, and exerts potent stimulatory effects on, e.g., neutrophils, monocytes, and T lymphocytes. LPA is also generated by a secretory, cytokine-inducible phospholipase A2 present in high concentrations in inflammatory exudates and septic states. We investigated effects of LPA on human Epstein-Barr virus-immortalized B lymphoblasts, a model for immunoglobulin-secreting B cells. Intracellular Ca2+ was determined with fura 2 and the formation of inositol 1,4, 5-trisphosphate by anion-exchange chromatography. LPA stimulated an increase in inositol 1,4,5-trisphosphate levels and induced a transient rise in intracellular free Ca2+ concentration from 105 +/- 17 to 226 +/- 21 nM. This Ca2+ signal resulted from Ca2+ mobilization and Ca2+ influx and was subject to homologous desensitization. Pertussis toxin inhibited these responses by approximately 70%. Furthermore, LPA stimulated a 27.5% increase in guanosine 5'-O-(3-thiotriphosphate) binding to permeabilized B lymphoblasts, which suggests the direct activation of pertussis toxin-sensitive G proteins by LPA. LPA stimulated a strong increase in the specific phosphorylation of the mitogen-activated protein kinase (immunoblot analysis) that was prevented by the MEK inhibitor PD-98059. Finally, LPA triggered a 2-fold increase in DNA synthesis ([3H]thymidine incorporation) and a 2-fold increase in B lymphoblast number and evoked a 20- to 50-fold increase in immunoglobulin formation. By RT-PCR we detected specific mRNA transcripts for the recently cloned human LPA receptor. Thus our data suggest that LPA behaves as a B cell growth factor.

Prevalence of increased intracellular signal transduction in immortalized lymphoblasts from patients with essential hypertension and normotensive subjects

OBJECTIVE

To determine the prevalence of enhanced signal transduction in immortalized B lymphoblasts from normotensive subjects and patients with essential hypertension.

METHODS

We established Epstein-Barr virus-immortalized lymphoblast cell lines from 26 normotensive and 37 hypertensive subjects. Subsequently, we quantified rises in the cytosolic free Ca2+ concentration, [Ca2+]i, evoked by 0.1 micromol/l platelet-activating factor (PAF) in Fura-2-loaded cells.

RESULTS

PAF-induced [Ca2+]i rises were independent of donor age in cells from normotensive and hypertensive subjects. Baseline values of [Ca2+]i were not significantly different in the two groups. Using the mean + 2SD of the PAF-evoked rises in [Ca2+]i above basal (110 nmol/l) as the upper normal value, we estimate that enhanced [Ca2+]i rises are distinctly more prevalent in hypertensive subjects (27%) than they are in normotensive subjects (4%). Similarly, upon definition of normal values by the 99% confidence interval (75 nmol/l), 19% of cells from normotensive versus 43% from hypertensive subjects display enhanced intracellular signaling.

CONCLUSION

Enhanced intracellular signal transduction could be the primary defect in approximately one-third of the overall population with essential hypertension.

Na+/H+ exchange in hypertension and in diabetes mellitus--facts and hypotheses

An enhancement of Na+/H+ exchange (NHE) in blood cells of selected patients with essential hypertension and with diabetic nephropathy has been described by various investigators. Recent studies have shown that enhanced NHE activity persists in immortalized lymphoblasts from these patients after prolonged cell culture and, thus, appears to be under genetic control. Available evidence strongly argues against a mutation in the encoding gene or an overexpression of the NHE. Immortalized cells from hypertensive patients with enhanced NHE activity display two-fold enhanced agonist-induced rises of the cytosolic free Ca2+ concentration and the underlying reason was identified as an increased activation of pertussis toxin (PTX)-sensitive G proteins. The molecular mechanism(s) of this phenomenon have not yet been elucidated. It appears likely that similar changes contribute to the enhanced NHE activity phenotype in diabetic nephropathy, although experimental evidence for this is still lacking. An enhanced activation of PTX-sensitive G proteins could explain many of the hitherto unexplained phenomena in essential hypertension, e.g. inheritance, increased vasoconstriction, hypertrophy of remodeling of arterial blood vessels and the heart, enhanced platelet aggregation etc. In diabetes the same defect could provide the basis for the susceptibility to nephropathy, e.g. by enhancing the deleterious effects of autocrine and paracrine growth factors. Thus, the experimental approach of immortalizing blood cells from patients with essential hypertension and diabetic nephropathy has opened new horizons in the identification of genetically fixed abnormalities in intracellular signal transduction which could contribute to both pathologies and which can now be studied without the confounding influences of the diabetic or hypertensive in vivo milieu.