The clinical implications and the pathogenetic significance of circulating immune complexes in infective endocarditis

Circulating immune complexes were determined with the 125I-Clq binding assay and the conglutinin binding assay in a prospective, longitudinal study of 40 patients with infective endocarditis, 34 patients with endocardial defects and nonseptic fever and 25 patients with septicemia without endocarditis. Fourteen patients with uncomplicated valvular lesions constituted a control group. Upon admission, 63 percent of the patients with infective endocarditis had a positive 125I-Clq binding assay versus 9, 12 and 7 percent, respectively, of the other three groups (p < 0.001). The incidence of positive conglutinin binding assays became significantly higher during the course of infective endocarditis (53 percent) than during the course of nonseptic fever (21 percent), but, upon admission, this difference was not significant. The high incidence of Clq-binding immune complexes among patients with infective endocarditis could be attributed mainly to those patients with the characteristic features of subacute endocarditis. The incidence of circulating immune complexes in acute endocarditis was low and did not contribute to making the clinically important distinction from septicemia without endocarditis. A rise in the 125I-Clq binding assay levels during the course of infective endocarditis correlated significantly (p < 0.01) with failure of antibiotic treatment. With the 125I-Clq binding assay, significantly higher levels were found in patients with signs of renal involvement or cutaneous vasculitis than in patients without these extracardiac manifestations of endocarditis. These results show that the determination of circulating immune complexes has clinical implications for both the diagnosis and the management of infective endocarditis and that circulating immune complexes are probably involved in the development of glomerulonephritis and vasculitis.