The relationship of anti-endothelial cell antibodies to anti-phospholipid antibodies in patients with giant cell arteritis and/or polymyalgia rheumatica

Immune system activation in polymyalgia rheumatica: Which balance between autoinflammation and autoimmunity? A systematic review

BACKGROUND AND AIM

Polymyalgia rheumatica (PMR) is an inflammatory rheumatic disease that is common in elderly people. Its classification in the spectrum of autoinflammatory and autoimmune diseases is difficult because of its only partially understood immune-mediated mechanisms. The literature concerning the innate and adaptive immune system activation in PMR was systematically reviewed highlighting the relative weight of autoinflammation and autoimmunity in its pathogenesis and disease progression.

METHODS

A literature search on PubMed Central and Embase scientific databases was performed by two independent reviewers. To be eligible, the studies needed to fully satisfy our initial PICO framework: a primary diagnosis of PMR as a population, the search for immune/inflammatory cells, cytokines and autoantibodies as an intervention, a control group consisting in healthy controls, patients with other inflammatory rheumatic diseases or PMR patients in remission after treatment and as outcomes the results of the investigations in the analyzed tissue samples. The most relevant data of the included papers were extracted by using a standardized template.

RESULTS

Of the 933 screened abstracts, 52 papers were included in the systematic review and categorized depending on their primary research objectives. The hyper-activity of neutrophils and monocytes, expressing toll-like receptor 7 in active disease, an impaired phagocytosis and endothelial dysfunction, as well as an increased count of innate T cells in patients with remission emerged among the major derangements of the innate immune response in PMR. Among the cytokines profile, interleukin-6 plays a key role but other pro-inflammatory mediators and angiogenesis markers such as chemokines, B-cell activating factor, vascular endothelial growth factor and angiopoietins seem to be involved in refractory or glucocorticoid-resistant PMR. The aberrant adaptive immune response was documented by tissue and serum findings of polarized T cells towards T helper 1 and 17 phenotypes, an increased expression of immunosenescent surface markers and a downregulated immunoregulatory response. The altered distribution of peripheral B cells, detected during active disease, suggested their peripheral migration towards unidentified sites. The interaction between innate and adaptive immune response was documented by a synovial infiltrate of macrophages and T cells. Despite multiple autoantibodies have been detected in PMR patients, none proved to correlate with disease activity seeming to be reactive to the marked inflammation or antigenic determinants provided by environmental triggers or tissue/cell damage.

CONCLUSIONS

The complex network between innate and adaptive immune system in PMR is supported by findings at molecular and cellular levels. By considering both the ends of the pathophysiological spectrum of immune-mediated rheumatic diseases, PMR may be regarded as an inflammatory immune-mediated disease with mixed mechanisms in a background of genetic and epigenetic factors together with immunological and endocrine senescence.

Pathogenic role of anti-endothelial cell antibodies in autoimmune rheumatic diseases

Anti-endothelial cells antibodies have been detected in numerous autoimmune and inflammatory diseases, including systemic lupus erythematous, rheumatoid arthritis, vasculitis and sarcoidosis. Anti-endothelial cells antibodies bind to endothelial cell antigens and induce endothelial damage. Their effects on the endothelial cell have been considered responsible, at least in part, by the vascular injury which occurs in these pathological conditions.

Antiendothelial cell antibodies in vasculitis and connective tissue disease

Antiendothelial cell antibodies (AECA) are a heterogeneous family of antibodies reacting with endothelial cell antigens. These antibodies are found in various diseases and recognise several antigen determinants. Different pathophysiological effects have been observed in in vitro experiments, which include direct or indirect cytotoxicity and endothelial cell apoptosis. Furthermore, some AECA activate endothelial cells, resulting in increased leucocyte adhesiveness, activation of coagulation and vascular thrombosis. In animal models, it has been shown that AECA could promote vascular damage. Neither the endothelial cell antigens nor their precise role in the pathogenecity of different diseases in which AECA are found is well characterised. Nowadays, it is not known whether AECA are an epiphenomenon accompanying vascular injury or whether they are pathogenic. It is controversial whether fluctuations in AECA titres are associated with disease activity during follow-up studies. This review summarises the present knowledge about AECA, AECA antigens and their potential role in the pathogenecity of vasculitis and connective tissue diseases.

Two populations of endothelial cell antibodies cross-react with heparin

As endothelial cells (EC) express heparin-like glycosaminoglycans, such as heparan sulfate, it was essential to investigate the relation of anti-EC antibody (AECA) to heparin reactivity. AECA were detected in 43 of 131 autoimmune sera and anti-heparin antibodies (AHA) in 25. These autoimmune reactivities were significantly associated (P corrected < 0.0005). Seven AECA-positive/AHA-positive and three AECA-negative/AHA-positive sera were affinity-purified using protein G column followed by a heparin-Sepharose column. Two populations of AECA were recovered from the second column. One was eluted with 0.4 M NaCl which bound to EC and to solid-phase heparin with low affinity, but not to soluble heparin. The second population of AECA, which was eluted with 4 M guanidine HCl/2 M NaCl, recognized EC and solid-phase heparin with high affinity, but also soluble heparin. The latter population of AECA might thus be an important cause of autoimmune vascular thrombosis in systemic diseases.

Prevalence of anti-endothelial cell antibodies in patients with Sneddon's syndrome

BACKGROUND

Sneddon's syndrome consists of widespread livedo reticularis and ischemic cerebral manifestations. Its pathogenesis remains unclear. Endothelial cells could be the primary target tissue.

OBJECTIVE

Our aim was to determine the prevalence of anti-endothelial cell antibodies (AECA) in a large series of patients with Sneddon's syndrome. The results were compared with those of three groups of control subjects: 39 patients with active periarteritis nodosa, 20 patients hospitalized for stroke without livedo, and 28 healthy persons.

METHODS

AECA were detected with enzyme-linked immunosorbent assay with hybrid cells (EA.hy926) before and after absorption on epithelial cells (A 549/8) to avoid false positivity from antibodies reacting with membranous epithelial antigens.

RESULTS

Twenty-two patients with Sneddon's syndrome had AECA (35%). Of the control subjects, 11 patients with active periarteritis nodosa (28%), 1 of 20 patients with a recent stroke without livedo, and no healthy persons had AECA.

CONCLUSION

AECA were frequently found in patients with Sneddon's syndrome, in contrast to the patients with stroke without livedo. The clinical significance and involvement of these antibodies in the pathogenesis of endothelial lesions in Sneddon's syndrome remain to be ascertained.