Immunologic factors in pathogenesis and treatment of human and animal diabetes

Histologic findings in islets of whole pancreas allografts: lack of evidence for recurrent cell-mediated diabetes mellitus

Cell-mediated cytotoxicity directed toward pancreatic islets plays a significant role in the pathogenesis of type 1 diabetes mellitus. Histologically, autoimmune insulitis appears as mononuclear infiltrates that precede actual beta cell loss. Experimental studies by Bartlett et al. on the BB rat model suggest that whole pancreas transplants are not susceptible to recurrent autoimmune diabetes. To test this hypothesis on clinical grounds, we evaluated the islets in pancreatectomies and percutaneous needle biopsies from 55 whole pancreas allografts. In this material, islet inflammation was never seen independently of allograft rejection, but was always associated with inflammation of the surrounding acinar structures. The degree of islet inflammation and the occasional presence of islet necrosis correlated well with the degree of rejection and only occurred in the higher grades of the latter (grades III-V). We did not observe isolated insulitis as a histological indication of selective cell-mediated cytotoxicity against beta cells.

A comparative study of antigen expression by skin and pancreas in the prediabetic and diabetic state of the BB rat

Type 1, insulin-dependent diabetes mellitus is an autoimmune disease with destruction of beta-cells in islets of Langerhans by activated (antigen-positive) infiltrating mononuclear cells accompanied by serological immune phenomena. The pathological mechanism has not yet been clarified in detail, and some inversion in the proportion of epidermal antigen expression has recently been described in spontaneous diabetes. The BB rat is one of the animal models most closely resembling human type 1 diabetes of autoimmune origin. We compared the class I and class II antigen expression in the islets of Langerhans and in the skin of spontaneously diabetic (BBD) and normoglycaemic (BBND) BB rats in the prediabetic, diabetic and non-diabetic states. Class I and class II antigen expression increased significantly in the islets of BBD rats from prediabetes to diabetes and compared with non-diabetic controls. In the same period, the dermal antigen expression (class I and class II) did not decrease and was not lower in BBD than in BBND animals. These results do not support a loss of activated (antigen-positive) dermal cells at the onset of diabetes in the BB rat and do not show a clear correlation with the antigen expression in infiltrated islets of Langerhans.

Continuous flow electrophoretic separation of proteins and cells from mammalian tissues

A new continuous flow electrophoretic separator for cells and macromolecules was built and tested in laboratory experiments and in the microgravity environment of space flight. Buffer flows upward in a 120-cm long flow chamber, which is 6 cm wide X 1.5 mm thick in the laboratory version and 16 cm wide X 3.0 mm thick in the microgravity version. Electrophoretic subpopulations are collected in 197 fractions spanning 16 cm at the upper end of the chamber. The electrode buffer is recirculated through front and back cooling chambers, which are also electrode chambers. Ovalbumin and rat serum albumin were used as test proteins in resolution and throughout tests; resolution of these two proteins at 25% total w/v concentration in microgravity was the same as that found at 0.2% w/v concentration in the laboratory. Band spreading caused by Poiseuille flow and conductance gaps was evaluated using polystyrene microspheres in microgravity, and these phenomena were quantitatively the same in microgravity as in the laboratory. Rat anterior pituitary cells were separated into subpopulations enriched with cells that secrete specific hormones; growth-hormone-secreting cells were found to have high electrophoretic mobility, whereas prolactin-secreting cells were found to have low electrophoretic mobility. Cultured human embryonic kidney cells were separated into several electrophoretic subfractions that produced different plasminogen activators; a medium-high-mobility subpopulation and a medium-low-mobility subpopulation each produced a different molecular form of urokinase, whereas a high- and an intermediate-mobility subpopulation produced tissue plasminogen activator. Canine pancreatic islets of Langerhans cells were separated into subpopulations, which, after reaggregation into pseudoislets, were found to be enriched with cells that secrete specific hormones; insulin-secreting beta cells were found in lowest mobility fractions, whereas glucagon-secreting alpha cells were found in the highest mobility fractions. Results of particle electrophoresis experiments were comparable in microgravity and in the laboratory, since cell densities that overloaded the carrier buffer (resulting in zone sedimentation) were avoided, and a 500-fold increase in protein throughput was achieved without compromising resolution in microgravity.