Presence of circulating anti-myosin antibodies in endomyocardial fibrosis

Abstract

Background: Endomyocardial Fibrosis (EMF) is a tropical restrictive cardiomyopathy of unknown etiology with high prevalence in Sub-Saharan Africa, for which it is unclear whether the primary target of injury is the endocardial endothelium, the subendocardial fibroblast, the coronary microcirculation or the myocyte. In an attempt to explore the possibility of endocardial lesions being a result of an immune response against the myocyte we assessed the presence and frequency of circulating anti-myocardial antibodies in EMF patients.

Methodology/principal findings: EMF classification, assessment of severity and staging was based on echocardiography. We used sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) of myocardial proteins followed by western blotting to screen serum samples for antiheart antibodies G and M classes. The degree of serum reactivity was correlated with the severity and activity of EMF. We studied 56 EMF patients and 10 healthy controls. IgG reactivity against myocardial proteins was stronger and more frequent in patients with EMF when compared to controls (30/56; 53.6% vs. 1/10; 10%, respectively). IgM reactivity was weak in both groups, although higher in EMF patients (11/56; 19.6%) when compared to controls (n = 0). EMF patients showed greater frequency and reactivity of IgG antibodies against myocardial proteins of molecular weights 35 kD, 42 kD and 70 kD (p values <0.01, <0.01 and <0.05 respectively).

Conclusions: The presence of antibodies against myocardial proteins was demonstrated in a subset of EMF patients. These immune markers seem to be related with activity and might provide an adjunct tool for diagnosis and classification of EMF, therefore improving its management by identifying patients who may benefit from immunosuppressive therapy. Further research is needed to clarify the role of autoimmunity in the pathogenesis of EMF.

Figure 1. Severe right endomyocardial fibrosis.

Echocardiography usually reveals partial obliteration of the right ventricle with cavity reduction, marked thickening of the moderate band, right atrial and tricuspid annulus dilatation, associated severe with tricuspid regurgitation. Although there is thickening of both leaflets of the atrioventricular valves, no endocardial thickening is seen on the left side of heart.

Figure 2. Severe left endomyocardial fibrosis.

Echocardiography shows thickening of endocardium at the apex of the left ventricle that has a spherical shape and has reduced longitudinal dimension and thickening of the anterior leaflet of the mitral valve; left atrial dilatation is associated with both mitral regurgitation and reduced ventricular compliance. Notice the dilatation of the right cavities caused by elevation in pulmonary pressures.