Lipoprotein like antigen on rat renal tubular epithelium

Three lipoprotein fractions were obtained from rat serum by density gradient ultracentrifugation; Fraction A (Fr. A, d less than 1.019), Fraction B (Fr B, 1.019 less than d less than 1.063), and Fraction C (Fr. C., 1.063 less than d less than 1.21). Kidney, liver and heart of rats were investigated by immunofluorescence using fluorescein isothiocyanate (FITC) conjugated rabbit anti-rat Fr. A and anti-rat Fr. C sera. Significant fluorescence was observed only in rat renal tubular epithelium (RTE) suggesting the presence of identical antigenic determinants in it as rat serum lipoproteins. Relatively small doses of each fraction of serum lipoproteins were injected with Freund's complete adjuvant (FCA) in rear foot pads. Two to four weeks after the injection, very mild proteinuria appeared in all rats immunized with Fr. B and Fr. C and three months later serum cholesterol was elevated in 3 of 8 rats. But no deposition of immunoglobulins (IgG, IgM) were observed in glomeruli of all rats examined, and any histological changes could not be found in renal tissue by light or electron microscopic observation.