Clinical significance of auto natural anti-insulin antibodies in normal cats

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It has been revealed that there have been anti-insulin natural auto anti-insulin antibodies in serum of cats, and those were the IgG. To clarify the significance of anti-insulin IgGs, we developed a sandwich ELISA for determination of the IgGs in serum of cats. The accuracy of the ELISA was sufficient for determination of insulin-bound IgG concentrations. By used of this ELISA, we determined plasma anti-insulin IgG concentrations in 130 domestic cats and 11 other felidae(lions, leopards, snow leopards, bobcats and lynx). Anti-insulin IgGs were detected in ranges from 80 to 4, 884μg/ml in all individuals. Anti-insulin IgG concentrations were high in lean cats, and correlated positively with total IgG concentrations, but not with plasma glucose and insulin concentrations. In cats with diabetes mellitus, plasma anti-insulin IgG concentrations were slightly high, but within the range of normal cats. Anti-insulin IgGs were not detected in cord blood of newborn kittens, and increased after suckling. These maternal antibodies decreased gradually during suckling period, and reversed the falling trend at weaning.Anti-insulin IgGs were fractionated by affinity chromatography with a column fixed bovine insulin. Epitope mapping was carried out by use of partial peptides of bovine insulin. The antigen-recognition parts were extrapolated hydrophilic terminals of A and B chains of insulin molecule.Serum anti-insulin IgGs were divided into 4 fractions by high performance liquid chromatography. By use of a fraction with highest peak, we detected a phosphorylated tyrosine proteins in cultured adipocytes derived from the cat. The phospholylation was stronger after addition of the IgG-binding insulin than free insulin, suggesting that the anti-insulin IgG might enhance the action of insulin.