Autoantibodies in untreated and treated essential hypertension: relationship to histocompatability leucocyte antigen-B15 and vascular complications

Plasma Cell Depletion Attenuates Hypertension in an Experimental Model of Autoimmune Disease

Numerous studies show a direct relation between circulating autoantibodies, characteristic of systemic autoimmune disorders, and primary hypertension in humans. Whether these autoantibodies mechanistically contribute to the development of hypertension remains unclear. Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder characterized by aberrant immunoglobulin production, notably pathogenic autoantibodies, and is associated with prevalent hypertension, renal injury, and cardiovascular disease. Because plasma cells produce the majority of serum immunoglobulins and are the primary source of autoantibodies in SLE, we hypothesized that plasma cell depletion using the proteasome inhibitor bortezomib would lower autoantibody production and attenuate hypertension. Thirty-week-old female SLE (NZBWF1) and control (NZW [New Zealand White]) mice were injected IV with vehicle (0.9% saline) or bortezomib (0.75 mg/kg) twice weekly for 4 weeks. Bortezomib treatment significantly lowered the percentage of bone marrow plasma cells in SLE mice. Total plasma IgG and anti-dsDNA IgG levels were higher in SLE mice compared with control mice but were lowered by bortezomib treatment. Mean arterial pressure (mm Hg) measured in conscious mice by carotid artery catheter was higher in SLE mice than in control mice, but mean arterial pressure was significantly lower in bortezomib-treated SLE mice. Bortezomib also attenuated renal injury, as assessed by albuminuria and glomerulosclerosis, and reduced glomerular immunoglobulin deposition and B and T lymphocytes infiltration into the kidneys. Taken together, these data show that the production of autoantibodies by plasma cells mechanistically contributes to autoimmune-associated hypertension and suggests a potential role for patients with primary hypertension who have increased circulating immunoglobulins.

Immunosuppression With Mycophenolate Mofetil Attenuates Hypertension in an Experimental Model of Autoimmune Disease

Background

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder that predominantly affects women and is associated with prevalent hypertension, renal injury, and cardiovascular disease. Immune system dysfunction is recognized as an important factor in the pathogenesis of hypertension. We recently showed that preventing autoimmunity prevents the development of hypertension in an experimental model of SLE (female NZBWF1 mice). The present study tests the hypothesis that mycophenolate mofetil (MMF), an immunosuppressive therapy used clinically to treat SLE by depleting proliferating B and T lymphocytes, can improve blood pressure control.

Methods and Results

Female SLE and control (NZW/LacJ) mice were treated daily for 8 weeks with 60 mg/kg MMF. Circulating CD45R⁺ B cells were lower in MMF‐treated SLE mice after 4 weeks of treatment, but neither CD4⁺ nor CD8⁺ T cells were reduced by MMF. Plasma anti–double‐stranded DNA IgG autoantibodies, a marker of SLE disease activity, were higher in SLE mice compared with controls and were lower in SLE mice after 8 weeks of MMF. Mean arterial pressure was elevated in SLE mice compared with controls and lower in SLE mice treated with MMF compared with vehicle‐treated SLE mice. MMF also reduced both renal injury (urinary albumin excretion and glomerulosclerosis) and the infiltration of CD45R⁺ B cells and CD3⁺CD4⁺ T cells in kidneys from mice with SLE.

Conclusions

These data suggest that MMF selectively depleted CD45R⁺ B cells and lowered subsequent autoantibody production, furthering the concept that autoantibodies mechanistically contribute to the pathogenesis of hypertension.

Serum concentrations of immunoglobulins and free light chains before and after vascular events in essential hypertension

Serum concentrations of immunoglobulins (Ig) and free light chains (LC) of Ig have been determined at regular intervals during five years in patients with essential hypertension and correlated to development of vascular complications. In 6 cardiac event patients serum IgG increased by 11.9% (p less than 0.05) and LC by 19.8% (p less than 0.05). IgG levels correlated positively with LC levels (r = 0.59, p less than 0.001) and changes in IgG correlated positively with changes in LC (r = 0.46, p less than 0.01). The post-event increments in IgG persisted up to 21 months. No significant changes in serum concentrations of IgA, IgM, albumin and creatinine were found. In 10 cerebral event patients and in matched groups of 15 uncomplicated hypertensive patients, no significant changes in the above parameters could be demonstrated. It is concluded that heart tissue damage in essential hypertension induces a long-lasting stimulation of B-lymphocytes, and it is suggested that the high Ig levels found in as yet uncomplicated hypertensive patients may reflect an ongoing damage of the vascular bed.

Abnormal immune system and hypertension: where are we?

In reviewing the available evidence, the involvement of an immunological mechanism behind hypertension has been proposed. However, whether altered immunological function is a primary factor in the pathogenesis of hypertension or secondary to tissue damage of vascular beds induced by hypertension is still poorly defined. A major difficulty has been the relative paucity of information about the nature of specific immune targets which initiate and perpetuate abnormal immune responses in hypertension. This article will discuss the status of understanding of the involvement of immunological factors in both clinical and experimental hypertension.

Essential hypertension and histocompatibility antigens. An association study

Data from a previous study concerning the distribution of human leukocyte antigen (HLA) haplotypes in siblings with essential hypertension suggested that at least one of the genes responsible for the genetic susceptibility to this disease is located in or near the HLA complex. The objective of the present study was to investigate if a given HLA-A, B, or DR gene could represent a marker for susceptibility to essential hypertension at the population level. Thus, the frequencies of HLA antigens were determined in Caucasian patients with essential hypertension (HLA-A and B antigens were determined in 89 cases, 85 of which were also typed for HLA-DR antigens). The results showed an increased frequency (p = 0.00064) of HLA-DR4, which was present in 34% of the patients and in 16% of local ethnically matched control subjects. We conclude that HLA-DR4 may represent a marker for susceptibility to essential hypertension in the Brazilian Caucasian population.

Essential hypertension and histocompatibility antigens. A linkage study

It is well established that genetic and environmental factors are involved in the etiology of essential hypertension. The presence of genes predisposing to essential hypertension in the human leukocyte antigen (HLA) complex is controversial because studies of an association between HLA antigens and essential hypertension have failed to yield consistent results. Our aim in the present study was to further investigate this issue through the method of linkage analysis. Analysis of 96 hypertensive siblings distributed in 31 families indicated a significant distortion (p = 0.0009) of the normal segregation pattern of inheritance of HLA haplotypes. Thus, our data indicate that at least one of the genes responsible for genetic predisposition to essential hypertension is located very near or within the HLA complex.

The application of molecular genetics to the study of familial arterial hypertension

The hereditary nature of familial hypertension has been clearly established by a number of clinical studies. Most of the present work has been concentrated on the correlation between various phenotypic traits and the level of blood pressure. The development of molecular genetics allow now to establish a link between high blood pressure and specific phenotypes. As analyzed in this paper, several strategies can be used for the genetic study of arterial hypertension: linkage studies in informative families, population association studies, analysis of subjects with contrasted predisposition to high blood pressure, affected sib-pair method. The identification of the loci implicated in blood pressure regulation and which contribute to the development of arterial hypertension can then be performed in this clinical material by two main approaches. One is based on the study of candidate genes, genes whose products are known to participate in blood pressure regulation, such as those of the renin-angiotensin system which are examplified. The other involves testing a series of markers distributed randomly throughout the genome in order to establish a link between increased blood pressure and a particular region of the genome.

Role of the altered transmural permeability in the pathomechanism of arteriosclerosis. History of arteriosclerosis theories. Role of the altered permeability in experimental arteriosclerosis models

After presenting an overview on classification and history of arteriosclerosis theories, the physiological factors involved in the transmural permeability of the arteries are discussed in detail. The development and characteristic features of the altered transmural permeability were studied in various experimental models such as in rat's hypercholesterolemia, local aortic hypoxia, lymphedema of the vascular wall and in hypertension. Results appear to show that alterations in permeability invariably developed in all of the pathological conditions examined, they were transient in nature and preceded the onset of intimal proliferation(s). The disturbance of transmural permeability might be the common pathologic clue which initiates uniform vascular responses to injuries produced by a variety of noxious stimuli. The possible role of the altered transmural permeability in the induction of smooth muscle cell proliferation is also discussed and evidence is provided that after withdrawal of stimulus for vascular injury intimal proliferation will not develop despite the manifest disorders in permeability.

Severe hypertension in the Spanish population. Association with specific HLA antigens

There is now increasing evidence for immunological changes in essential hypertension. Immunological response is determined in part by genes linked to the HLA system. It has been reported a positive association between HLA B15 and the risk for cerebral events in essential hypertensive (EH) patients. We studied the distribution of HLA antigens in 128 EH (age range, 13-85 years) and 1000 normotensive controls. EH were classified in accordance with the World Health Organization (WHO) criteria: in WHO Stages I and II, there were 100 patients; in WHO Stage III, there were 28 patients. HLA-A and B antigens of peripheral blood lymphocytes were studied according to the microlymphocytotoxicity test. The results were compared by chi-square analysis, and the p value was multiplied by the number of antigens studied at each locus, to avoid overestimation of an association. Frequency of HLA-BW 22 was higher in EH compared with controls (5.4% vs 1.2%, p less than 0.01). Frequency of HLA-B12 in EH with WHO Stage III hypertension (64.2%) was significantly increased compared either with EH in WHO Stage I or II (29%, p less than 0.01) or the control group (26.9% p less than 0.001). The incidence of HLA-B15 antigen in the whole hypertensive group was 3.1%, lower than in normotensive controls (6.4%, p less than 0.8). None of the patients with WHO Stage III hypertension had the HLA-B15 antigen. In conclusion, the results seemed to indicated that the Spanish population had an association between HLA-B12 and severe hypertension.

Immunogenetic markers in essential hypertension

In a series of 148 patients with essential hypertension, the presence of the atherosclerotic C3-F gene and HLA-antigen frequences were investigated, and the results were compared with those in 62 age and sex matched normotensive controls. The frequency of C3-F was significantly higher in patients (p less than 0.03), as was HLA-B15 in patients with a positive family history of hypertension (p less than 0.05). The presence of the C3-F gene was associated with an increased risk (= 10.2) for coronary heart disease, and B15 was associated with an increased risk (= 6.0) for cerebral events in both familial and non familial cases of hypertension. It is suggested that determination of the C3-F gene and HLA-antigens might be a tool in the identification of hypertensive patients at particular high risk for vascular events, irrespective of BP levels. The study support the suggestions that some genetic factors may act via immunological pathways.