Serum immunoglobulin G reactive with endothelial cells in inflammatory bowel disease

Endothelial cell autoantibodies are a marker of disease susceptibility in inflammatory bowel disease but apparently not linked to persistent measles virus infection

Intestinal vasculitis caused by persistent measles virus infection of intestinal endothelial cells was described in Crohn's disease. Furthermore, endothelial cell autoantibodies have been demonstrated in inflammatory bowel disease (IBD). Autoantibodies against intestinal endothelial cells were visualized by indirect immunofluorescence in patients with IBD, in their healthy first-degree relatives, in patients with infectious enterocolitis, and in healthy, unrelated controls. In intestinal tissue specimens of 22 antibody-positive IBD patients a search for the measles virus genome was performed. Endothelial cell autoantibodies were significantly more frequent in patients with IBD, in both groups of first-degree relatives, and in patients with infectious enterocolitis than in the healthy controls (P = 0.0002 or less). The measles virus genome was found in none of the intestinal biopsies. Endothelial cell autoantibodies are not a genetic but rather an epigenetic (infectious) marker of disease susceptibility. The expression of these autoantibodies is unlikely to be triggered by a persistent measles virus infection.

Specificity, pathogenecity, and clinical value of antiendothelial cell antibodies

OBJECTIVE

To characterize the putative target antigens for antiendothelial cell antibodies (AECA), the possible pathophysiological role of AECA, and the clinical value of these antibodies as markers of disease activity.

METHODS

A structured literature search was done using Medline in combination with a manual search. Two physicians reviewed all articles of special interest.

RESULTS

AECA are a heterogenous group of antibodies directed against a variety of antigen determinants on endothelial cells (EC). The EC antigens can be constitutively expressed, constitutively expressed and modulated by cytokines, or cryptic. In addition, antigen determinants for AECA may also be molecules that adhere to EC ("planted" antigens). However, many AECA antigens are currently not well characterized. AECA are detected in a wide variety of inflammatory disorders. Although probably of limited value in disease diagnosis, the detection of these antibodies may be valuable in following disease activity. In several diseases such as systemic lupus erythematosus and systemic vasculitis, high AECA titers are found during active disease whereas lower titers or disappearence of AECA have been reported during remission. The correlation between changes in AECA titers and disease activity suggests an important role for AECA in processes in which vessel wall damage occurs, although it does not exclude the possibility that AECA are an epiphenomenon of vascular injury. Several recent in vitro studies support a role of AECA in the pathophysiology of these inflammatory disorders. AECA may play a role in the pathophysiology by inducing activation of EC resulting in upregulation in the expression of endothelial adhesion molecules and/or secretion of chemoattractants and cytokines. An alternative mechanism by which AECA could be a trigger in the pathogenesis of some diseases is complement dependent cytotoxicity (CDC) and/or antibody dependent cellular cytotoxicity (ADCC). In experimental animal models, antibodies to antigenic determinants expressed on EC were capable of inducing vascular injury.

CONCLUSION

AECA represent a heterogenous group of antibodies directed against a variety of antigenic determinants on EC. They are present in a variety of inflammatory disorders. The detection of these antibodies may be valuable in following disease activity. Further characterization of putative antigens is needed to better understand their pathophysiological role.

Antiendothelial cell antibodies (AECA) in patients with uveoretinitis

AECAs have been found in 26% of patients with uveoretinitis in studies arising from three different laboratories, and their presence cannot simply be explained by coexisting extraocular disease. There is little correlation with ocular disease activity or other markers of systemic inflammation and vascular damage that can be found in this group of patients, but this lack of correlation has also been found in studies of more widespread inflammatory diseases. The changes found in the peripheral blood of patients with uveoretinitis are the result of a mixture of acute and chronic inflammation, reactions to coexisting tissue damage, as well as predisposing abnormalities of inflammation and hemostasis. Even patients with similar clinical appearances are unlikely to be pathologically homogeneous, and the reasons for the presence of AECA are likely to be various. Some patients may demonstrate a heightened antibody response to endothelium damaged by unknown mechanisms, whereas others may develop cytotoxic AECA as an integral part of the inflammatory process. The majority of serum samples with AECA demonstrated antibody-dependent cell-mediated cytotoxicity, but this potentially pathogenetic mechanism was only demonstrable in a minority of patients. It is unlikely that IgM AECA or complement-mediated cytotoxicity is a relevant mechanism of vascular damage in this group of patients. A subgroup of patients may be genetically predisposed to produce excess autoantibodies in response to tissue damage caused by a wide variety of insults. Sawyerr et al.(36) has suggested that increased serum levels of agalactosyl IgG may account for some of the AECA binding found in chronic inflammatory diseases: we have also found changes in agalactosyl IgG in patients with active isolated uveoretinitis (40), but levels did not correlate with levels of IgG AECA (unpublished results). Further longitudinal studies will be necessary on each subgroup of patients in order to determine the true clinical significance of these findings.