The IgG autoimmune response is direct to cytoplasm of pancreatic islet cells (both ά- and β-cells), sparing exocrine cells. There are numerous antigens associated with these cells and any number could be targeted. Antibody may appear prior to clinical symptoms and titre may fall with an increase in the destruction of the β-cells. Consequently, patient develops insulin dependent diabetes mellitus (IDDM).

Islet cell antibodies have a prevalence of 75% in IDDM at diagnosis.

Image: Primate pancreas showing staining of the islet cells. The nuclei are stained red with ethidium bromide. Note the exocrine tissue lacks stained.