Insulin immunization of guinea-pigs: biochemical, immunohistochemical and morphometric findings with and without the use of adjuvant

Abstract

Changes in the blood glucose level, glucose (GTT) and insulin (ITT) tolerance tests, anti-insulin antibody production and morphological changes in pancreatic tissues (in particular the islets of Langerhans) were studied. After immunization by insulin (I) or insulin combined with an adjuvant (IE, IF), the blood glucose level rose, changes were observed in the GTT and ITT and after four successive immunizations the immunofluorescence technique also demonstrated anti-insulin antibodies. None of the above changes was observed in the controls, to which saline containing complete Freund adjuvant (SF) or Listeria factor (SE) was administered. On the other hand, the morphological picture changed in both the experimental (IE, IF) and control (SE, SF) groups, in which (round) cell infiltration of the fine connective tissue of the omentum and even of mesentery, with nonspecific granuloma formation was observed, while huge multinuclear cells appeared in the SF group. The changes were more frequent in the IE and IF groups. The volume density of the pancreatic endocrine tissue increased significantly only in the experimental groups (I, IE, IF), in which the increase was accompanied, to a varying degrees, by degranulation of the B-cells. The results of analysis of volume density changes of A-, B-, and D-cell populations were correlated with the blood glucose levels. The morphological findings may explain why the originally insignificant production of anti-insulin antibodies and the increase in the blood glucose level observed in guinea pigs after the repeated administration of chromatographically purified insulin are significantly enhanced by the administration of adjuvants together with the immunizing agent. Complete Freund adjuvant was found to be more effective than the Ei Listeria factor.