Histological study of pancreatic beta-cell loss in relation to the insulitis process in the non-obese diabetic mouse

Abstract

Non-obese diabetic (NOD) mice spontaneously develop an autoimmune diabetes with higher incidence in females than in males. In order to elucidate possible factors involved in the different incidence of diabetes between male and female mice, we studied the progression of pancreatic beta-cell loss in relation to mononuclear cell infiltration of the pancreas (insulitis). We examined the pancreas of 76 NOD mice (39 males and 37 females) of different ages. The beta-cell content was assessed by immunoperoxidase staining of sections with an anti-insulin serum and the severity of insulitis was determined by haematoxylin staining of the same sections. A semi-quantitative criterion was used to grade both parameters. The results showed that females have a faster loss of beta-cell mass, which progressively decreases with the increase of severity of insulitis. In males, a medium to severe degree of insulitis is required before initial loss of beta cells occurs. Under the age of 10 weeks there was a significantly lower content of beta cells in females than males (2.84 +/- 0.03 vs 2.67 +/- 0.07; P = 0.02). Since we never observed a significant difference in the degree of mononuclear cell infiltration in age-matched males and females, these data support the hypothesis of weaker beta-cell resistance to immunological attack in female mice. Thus beta-cell sensitivity, in addition to immunological activity, is an important factor in the pathogenesis of insulin dependent diabetes.

Regulatory and Effector T Cell Activation Levels Are Prime Determinants of In Vivo Immune Regulation

“…Here, we directly tested whether T reg would play a regulatory function predominantly in young NOD mice. Depleting endogenous T reg led to T1D exacerbation only if performed in young (3-6 wk old) NOD mice, when inflammation in islets is still mild (33)(34)(35). At this stage, depletion of endogenous T reg would remove basal immunosuppression leading to increased activation of islet-specific CD25 Ϫ T cells.…”

“…Indeed, the autoimmune process in NOD mice is progressive with the first signs of autoimmunity starting at 3 wk of age, with few APCs and lymphocytes invading the periphery of pancreatic islets. This is followed by a chronic and progressive increase of the level of inflammation and infiltrating T cells around and then inside the islets (33)(34)(35), which is associated with a decrease in the proportion of T reg in islets and draining pancreatic LN and thus a dysbalance of the T reg -T cell ratio (36). Eventually, mice develop clinical diabetes in 75% of females and 25% of males at 25 wk of age.…”

Active stage of autoimmune diabetes is associated with the expression of a novel cytokine, IGIF, which is located near Idd2.

“…Inflammation of the endocrine pancreas is accompanied by the preferential loss of ␤ cells, eventually leading to insulin deficient diabetes. The disease process is asynchronous between individual islets and progresses to overt diabetes in 20-80% of mice, with a peak incidence between 3 and 6 mo of age (2,3). Diabetes development in young animals can be accelerated and synchronized by a single injection of cyclophosphamide (CY).…”

Imaging the Pancreatic Beta Cell

“…The insulitis score is usually expressed in conventional units and reflects the degree of islet infiltration by mononuclear cells. In many experimental studies, this technique has been employed for the evaluation of the dynamics of islet infiltration as well as for the assessment of progressive BCM loss in relation to insulitis in animal models for T1D (Wicker et al, 1987;Signore et al, 1994). The ratio of islet area to the entire pancreatic area is considered a very informative indicator of pancreatic islet development and reflects the dynamics of BCM reduction with T1D progression (Li et al, 2000).…”