Abstract
The purpose of the present study was to investigate the pancreatic polypeptide (PP) binding antibodies and their immunological properties in the sera of insulin-treated diabetics. The amount of contaminating immunoreactive PP in commercial insulin preparations was measured by radioimmunoassay, and the PP binding antibodies were determined by three methods, i.e. with polyethylene glycol (PEG), gel filtration, and specific radioimmuno-precipitation (SRIP). The results were obtained were as follows.
1) Significant amounts of immunoreactive PP (2.5-1, 700 pg/unit insulin) were detected in some commercial insulin preparations, but not in a highly purified new insulin preparation.
2) Although no specific binding of 125I-bovine PP with sera was found in 30 healthy subjects and 75 non-insulintreated diabetics, PP binding antibodies were found in 24 out of 106sera (22.4%) from insulin-treated diabetics.
3) The immunoglobulin class of these PP binding antibodies was uniformly classified as IgG. Their types of light chains showed variety, including bitypic patterns (both the K-and λ-type) and monotypic patterns (the K-or λ-type).
In 10 out of 13 cases, the PP binding antibodies showed a significantly high affinity for bovine PP as compared to human PP. However, in the other 3 cases, they showed almost the same affinities for bovine and human PP.
It is concluded that the PP binding antibodies which can be demonstrated in insulin-treated diabetics might to induced by the administration of commercial insulin containing small amounts of PP (porcine or bovine).
