Early influx of macrophages determines susceptibility to experimental allergic encephalomyelitis in Dark Agouti (DA) rats.

Experimental allergic encephalomyelitis (EAE) is characterized by inflammatory infiltrates of myelin antigen(s) specific T cells and consecutive demyelination. Injection of encephalitogen into the footpads induces disease in genetically susceptible Dark Agouti rats (DA) but not in Albino Oxford (AO) rats although mild inflammatory infiltrates are observed in both strains early after disease induction. In addition, only DA rats develop disease when cells from (AO×DA) F(1) hybrids are passively transferred into sub-lethally radiated AO and DA parent hosts. The aim of the study was therefore to examine the participation of accessory cells, macrophages, dendritic cells and microglia in EAE development at the level of the target tissue in these two strains using specific membrane markers. We demonstrate here that in the induction phase of EAE in DA rats, macrophages (CD68(+); CD45(hi)CD11b(+)) are the first detectable infiltrating cells in the subpial regions of the spinal cord but were not found in AO rats. During the same period, resident microglial cells which are of the ramified variety are observed in both DA and AO rats. In DA rats at the peak of disease, when profuse influx of T cells is seen, macrophages and dendritic cells appear in the parenchyma of the CNS. In addition, at that time, microglial cells are activated. FACS analyses also reveal a significant increase in CD45(hi)CD11c(+) dendritic cells and CD45(hi)D11b(+) macrophages compared with levels in naïve and immunized AO rats. During resolution of disease in DA rats, the expression of microglia and macrophage markers is comparable with those in naïve non-immunized DA and immunized AO rats. We conclude that an initial influx of macrophages is indispensible for the development of EAE in DA rats. The presence of dendritic cells and myeloid dendritic cells at the peak of disease supports the role of these cells in EAE especially in relapses and chronicity. The activation pattern of microglia in DA rats does not indicate their role as antigen presenting cells in disease induction since they are ramified at the induction phase and only become activated after the overwhelming influx of T cells.

IL-23 leads to diabetes induction after subdiabetogenic treatment with multiple low doses of streptozotocin.

IL-23, a proximal regulator of IL-17, may be a major driving force in the induction of autoimmune inflammation. We have used a model of subdiabetogenic treatment with multiple low doses of streptozotocin (MLD-STZ; 4 x 40 mg/kg body weight) in male C57BL/6 mice to study the effect of IL-23 on immune-mediated beta cell damage and the development of diabetes, as evaluated by blood glucose, quantitative histology, immunohistochemistry and expression of relevant cytokines in the islets. Ten daily injections of 400 ng IL-23, starting on the first day of MLD-STZ administration led to significant and sustained hyperglycemia along with weight loss compared with controls (no IL-23), and a significant increase in the number of infiltrating cells, a lower insulin content, enhanced apoptosis, expression of IFN-gamma and IL-17 (not seen in the controls) and a significant increase in the expression of TNF-alpha and IL-18 in the pancreatic islets. IL-23 treatment started 5 days prior to MLD-STZ administration had no effect on diabetogenesis or cytokines expression in the pancreatic islets. We provide the first evidence in an animal model that IL-23 is involved in the development of type-1 diabetes, by inducing IL-17 and possibly IFN-gamma production in the target tissue.