Immunoglobulin G anti-endothelial cell antibodies: inducers of endothelial cell apoptosis in pulmonary arterial hypertension?

Endothelial cell (EC) apoptosis seems to play an important role in the pathophysiology of pulmonary arterial hypertension (PAH). We aimed to test the hypothesis that circulating anti-endothelial cell antibodies (AECA) of PAH patients induce EC apoptosis. Immunoglobulin (Ig)G was purified from sera of PAH patients (n = 26), patients with systemic lupus erythematosus (SLE) nephritis without PAH (n = 16), patients with systemic sclerosis (SSc) without PAH (n = 58) and healthy controls (n = 14). Human umbilical vein endothelial cells (HUVECs) were incubated with patient or healthy control IgG for 24 h. Thereafter, apoptosis was quantified by annexin A5 binding and hypoploid cell enumeration by flow cytometry. Furthermore, real-time cell electronic sensing (RT-CES™) technology was used to monitor the effects of purified IgG from patient and healthy control IgG on HUVECs. As demonstrated previously, IgG of AECA-positive SLE nephritis patients (n = 7) induced a higher percentage of apoptosis of HUVECs compared to IgG of AECA-negative SLE nephritis patients and healthy controls. Furthermore, IgG of AECA-positive SLE nephritis patients induced a marked decrease in cell index as assessed by RT-CES™ technology. IgG of AECA-positive PAH patients (n = 12) and SSc patients (n = 13) did not alter the percentage of HUVEC apoptosis or cell index compared to IgG of AECA-negative PAH and SSc patients and healthy controls. AECA-positive PAH patients, in contrast to SLE nephritis patients, do not have circulating IgG AECA that enhances apoptosis of HUVECs in vitro. Further studies should focus on other mechanisms by which AECA may enhance EC apoptosis in PAH, such as antibody-dependent cell-mediated cytotoxicity.

Haptoglobin phenotype may alter endothelial progenitor cell cluster formation in cerebral small vessel disease.

Cerebral small vessel disease results in silent ischemic lesions (SIL) among which is leukoaraiosis. In this process, endothelial damage is probably involved. Endothelial progenitor cells (EPC), are involved in endothelial repair. By restoring the damaged endothelium, EPC could mitigate SIL and cerebral small vessel disease. Haptoglobin 1-1, one of three phenotypes of haptoglobin, relates to SIL and may therefore attenuate the endothelial repair by EPC. Our aim was to quantify EPC number and function and to assess haptoglobin phenotype and its effect on EPC function in patients with a high prevalence of SIL: lacunar stroke patients. We assessed EPC In 42 lacunar stroke patients and 18 controls by flow cytometry and culture with fetal calf serum, patient and control serum. We determined haptoglobin phenotype and cultured EPC with the three different haptoglobin phenotypes. We found that EPC cluster counts were lower in patients (96.9 clusters/well +/- 83.4 (mean +/- SD)), especially in those with SIL (85.0 +/- 64.3), than in controls (174.4 +/- 112.2). Cluster formation was inhibited by patient serum, especially by SIL patient serum, but not by control serum. Patients with haptoglobin 1-1 had less clusters in culture, and when haptoglobin 1-1 was added to EPC cultures, cluster numbers were lower than with the other haptoglobin phenotypes. We conclude that lacunar stroke patients, especially those with SIL, have impaired EPC cluster formation, which may point at decreased endothelial repair potential. The haptoglobin 1-1 phenotype is likely a causative factor in this impairment.

Induction of endothelial cell apoptosis by IgG antibodies from SLE patients with nephropathy: a potential role for anti-endothelial cell antibodies.

Systemic lupus erythematosus (SLE) is a prototype of an autoimmune disease with vasculopathy as demonstrated by the presence of vascular immune-complex deposition, inflammation, and thrombosis. A pivotal role in the initiation of vasculopathy is ascribed to vascular endothelium. In this respect, anti-endothelial cell antibodies (AECA), which are highly associated with SLE, are putative candidates for the initiation of SLE vasculopathy. In addition to the potency of AECA to induce a proinflammatory endothelial cell phenotype, AECA have also been described to trigger endothelial cell apoptosis. However, in SLE data are not uniform on the potentials of AECA to induce endothelial cell apoptosis in vitro. We have addressed this question in a cohort of SLE patients with nephropathy. AECA levels, and the apoptosis-inducing potentials of serum IgG were measured at the time of renal complication and biopsy. Also serum antibody reactivity with various SLE-related autoantigens including HSP60 was determined in patients. The results show that the SLE patient group has increased AECA levels as well as increased levels of induction of endothelial cell apoptosis by serum IgG. AECA and apoptosis values largely varied among the patients. Our data show that antibodies other than anti-HSP60 are also involved in apoptosis induction. The results are discussed in the context of recent findings on the role of AECA in endothelial cell apoptosis and renal vasculopathy in SLE.