Abstract
Fluorescein-labeled immunoglobulin G (IgG) fractions of serum from patients with acute poststreptococcal glomerulonephritis stained parts of the glomerular basement membrane and mesangium of kidney tissue obtained from the same patients during the early phase of the disease. Renal tissue obtained from normal individuals and from patients with other kidney diseases failed to stain with these IgG fractions. Preabsorption of the serum fractions with various freezethawed bacteria demonstrated that only certain group A streptococci abolished the staining capacity. Fractionation of the streptococci into cellular constituents indicated that it was predominantly the plasma membrane fraction which blocked the immune staining. Spectrofluorometry using alkali-solubilized renal tissue confirmed these observations in a quantitative manner. By sucrose density-gradient ultracentrifugation of the plasma membrane two possible antigens were isolated. One was soluble in phosphate-buffered saline and the other was insoluble. The soluble component was a lipoprotein with a molecular weight of approximately 120,000.