In the present study, the antigen proteins of Sprague-Dawley rat pancreas islets recognized by islet cell cytoplasmic antibodies (ICA) cross-reactive with rat islets were characterized. A detergent lysate of rat islets (islet lysate) and Maclura pomifera agglutinin-binding glycoprotein (MPA-GP) of rat pancreas were used as antigen sources. Reactivities of these two crude antigen proteins against 4 ICA-positive sera from patients with Type 1 (insulin-dependent) diabetes mellitus (IDDM) were examined by SDS-polyacrylamide gel electrophoresis followed by immunoblotting, and by fluoroimmunoassay (FIA). Two of the 4 ICA-positive sera specifically bound a peptide of 59kdalton (Kd) from islet lysates. This peptide was detected even after absorption of sera with rat acetone liver powder or viable rat islet cells. One serum sample was examined for rectivities to MPA-GP, and the serum bound a peptide of 59Kd from MPA-GP. In an absorption test of the serum with MPA-GP, decreased specific fluorescence of rat pancreas islets was shown by an indirect immunofluorescent technique. The binding activity of MPA-GP to ICA-positive sera measured by the FIA method was higher in the ICA-positive sera than in the ICA-negative sera. It was concluded that a peptide of 59Kd is one of the target antigen proteins of ICA, and that the peptide has binding activity with MPA. It was suggested that ICA can be measured by the FIA method using MPA-GP. It was also suggested that ICA in sera from Type 1 diabetic patients is heterogenous and that the target antigen is polyvalent.
islet cell cytoplasmic antibodies (ICA)
islet cell antigens
Maclura pomifera agglutinin