Islet transplantation in experimental diabetes of the rat. XIII, Cryopreservation reduces MHC class II but not class I antigens of rat pancreatic islets

Pretreatment of islet allografts prior to transplantation may reduce islet immunogenicity and prolong graft acceptance. We have studied the MHC antigen reducing effect of cryopreservation onto rat pancreatic islets performing indirect immunofluorescence tests and peroxidase-anti-peroxidase staining (PAP). Three different freezing programs were used. Program A: 0.5 degrees C/min to -35 degrees C and 1 degree C/min from -35 to -100 degrees C. Program B: 2 degrees C/min to -35 degrees C and 6 degrees C/min from -35 to -100 degrees C. Program C: 0.25 degrees C/min to -40 degrees C. Cryopreservation clearly reduced the number of class II antigen positive cells per islet in all cases. Program A was most effective with 45.5% of class II antigen negative islets compared to 6.4% of class II antigen negative fresh islets as shown by indirect immunofluorescence. The class II antigen reducing effect of cryopreservation proved to be permanent and not only temporary. Reduced class II antigen expression of cryopreserved islets could not be reestablished by incubation of the islets with rat IFN. A combination of cryopreservation followed by a 10 day culture period proved to be most effective with 85.6% of class II antigen negative islets. In contrast, we could not show any effect of cryopreservation on class I antigen expression. Viability of the cryopreserved rat islets was shown in-vitro by glucose stimulated insulin secretion.