Natural anti-insulin autoantibodies in cats: Enzyme-linked immunosorbent assay for the determination of plasma anti-insulin IgG and its concentrations in domestic cats

Anti-insulin immunoglobulin G (IgG) has been found in the sera of healthy cats. To determine the concentrations of these antibodies, an enzyme-linked immunosorbent assay (ELISA) for anti-insulin IgG was developed. ELISA maintained the linearity of a standard concentration line between 67.5 and 2160 ng/ml. The coefficients of variances (CVs) of intra-assays in two different plasma samples were 4.0% and 3.7%, respectively. The inter-assay CVs in two different plasma samples were 5.1% and 6.9%, respectively. The dilution curves of two samples were rectilinear. Anti-insulin IgG was detected in all 84 of the healthy cats that were tested. Plasma anti-insulin IgG concentrations ranged from 80 to 1578 μg/ml, with a median concentration of 221 μg/ml, and this value correlated positively with total plasma IgG concentrations (r = 0.383, p < 0.01). In an intravenous glucose tolerance test, plasma anti-insulin IgG concentrations did not alter, even with changes in plasma glucose and insulin concentrations. The ELISA that was developed was able to determine plasma anti-insulin IgG in domestic cats, and confirmed that all healthy cats had plasma anti-insulin IgG. Determining the plasma concentrations of anti-insulin IgG in cats with various pathological conditions might clarify the role of anti-insulin IgG.