The B cell mass at the clinical onset of type I diabetes.

In a case of type I diabetes with a duration of 7 days the distribution and volume of the pancreatic endocrine cells were studied using immunocytochemical techniques combined with morphometry. The PP cell rich lobe, making up about 10% of the total pancreatic volume, was not considered in this examination. The volume density and the absolute volume of the B cells was found to be reduced to about one third to one seventh of the values determined in three controls of a similar age and pancreatic volume. The A cell volume was also diminished, whereas the D and PP cell volume remained constant. As B cell necroses could not be detected and insulitis affected only few islets, it was concluded that the destruction of B cells proceeds slowly in type I diabetes and, in the majority of cases, probably starts years before the clinical onset.