Immunopathogenesis of Libman-Sacks endocarditis. Assessment by light and immunofluorescent microscopy in two patients.

The possible contribution of immunological mechanisms in the development of Libman-Sacks endocarditis was studied in 2 patients with systemic lupus erythematosus who underwent aortic valve replacement. Sections of verrucous lesions, stained with haematoxylin and eosin, showed three apparently distinct zones: an outer exudative zone of fibrin, nuclear debris, and haematoxylin-stained bodies; a middle organizing zone of proliferating capillaries and fibroblasts; and an inner zone of neovascularization which showed distinct, thin-walled junctional vessels. The striking finding was the apparently selective deposition of immunoglobulins and complement identified by direct immunofluorescence, within the walls of the small junctional vessels of the zone of neovascularization. We suggest that the observed immune deposits are immune complexes and that circulating immune complexes may play a critical role in the growth and proliferation of the verrucous lesion.