Anti-endothelial cell antibodies in mixed connective tissue disease: frequency and association with clinical symptoms.

OBJECTIVE Anti-endothelial cell antibodies (AECA) have been described in a number of systemic autoimmune-inflammatory diseases. However, little is known about the relationship of AECA with mixed connective tissue disease (MCTD). METHODS Using an ELISA, the presence of AECA was evaluated in the sera of 33 patients with MCTD and of 30 healthy subjects as controls. Serum levels of AECA were correlated with clinical activity, as well as the existence of various organ manifestations. RESULTS Significantly increased AECA production was observed in MCTD patients (OD = 0.337+/-0.193) compared to controls (OD = 0.136+/-0.065). In addition, patients with active MCTD exerted significantly elevated serum AECA levels (OD = 0.487+/-0.090) than did patients with inactive MCTD (OD = 0.135+/-0.040) or controls. MCTD patients with pulmonary hypertension had a tendency of increased serum AECA levels (OD = 0.452+/-0.080) compared to patients without this manifestation (OD = 0.307+/-0.039). Sera of MCTD patients with AECA concentrations higher or lower than the mean serum AECA level in controls+2SD (OD = 0.266) were considered as AECAhigh (n = 19/33) and AECAlow (n = 14/33), respectively. Interestingly, all patients with active disease had AECAhigh, while all inactive MCTD patients had AECAlow sera. IgG purified from ten MCTD sera (OD = 0.415+/-0.290) showed a tendency to up-regulate E-selectin expression on cultured human umbilical vein endothelial cells (HUVEC) compared to IgG from control sera. In addition, AECAhigh MCTD sera exerted significantly increased stimulatory effect on endothelial E-selectin expression (OD = 0.651+/-0.190) compared to AECAlow (OD = 0.178+/-0.110) or control sera (OD = 0. 131+/-0.080). CONCLUSION AECA may activate endothelial cells by the up-regulation of E-selectin expression and thus may be implicated in the pathogenesis of MCTD. Furthermore, serum AECA may be a useful marker of endothelial activation and clinical activity in this disease.