A HIGH-MOLECULAR IGF-2 IMMUNOREACTIVE PEPTIDE (PRO-IGF-2-QUESTIONABLE) IN THE INSULIN CELLS OF THE ISLETS OF LANGERHANS IN PANCREAS OF MAN AND RAT

Histopathologically normal pancreatic parenchyma from 12 adult men and women, as well as that from 14 adult rats (Sprague-Dawley and Wistar strains), were investigated immunohistochemically with a mouse monoclonal antibody, raised against recombinant human pro-IGF-2. The antiserum showed no cross-reactivity with insulin; IGF-1 had 0.1% of the reactivity of IGF-2. The immunohistochemical observations were checked by means of a radioimmunoassay (RIA), based on the same antibody, of an extract of a sample of one of the human pancreatic glands. Analogous investigations for insulin were made in parallel, using polyclonal insulin antisera. A high-molecular (12 kDa) IGF-2-like peptide was found in the islets of Langerhans, being localized to the insulin cells. These cells were identified as beta-cells by immunohistochemistry with insulin antisera on adjacent paraffin sections. From observations made by means of acid-gel-chromatography, the peptide was tentatively supposed to represent either pro-IGF-2, or a partially processed form of it.