Strain specificities in age-related changes in mechanisms promoting and controlling rat spinal cord damage in experimental autoimmune encephalomyelitis

The study investigated strain specificities in age-related differences in CD8+ T cell-and microglial cell-mediated mechanisms implicated in induction/perpetuation and/or control of neuroinflammation in experimental autoimmune encephalomyelitis (EAE) in Albino Oxford (AO) and Dark Agouti (DA) rats exhibiting age-related changes in the susceptibility to EAE in the opposite direction (increase in relatively resistant AO rats vs decrease in DA rats). In the inductive phase of EAE, the greater number of fully differentiated effector CD8+ T lymphocytes was found in draining lymph nodes (dLNs) from aged rats of both strains than in strain-matched young rats, but this was particularly prominent in AO rats, which exhibited milder EAE of prolonged duration compared with their DA counterparts. Consistently, dLN IFN-gamma+ and IL-17+ CD8+ T cell counts were greater in aged AO than in DA rats. Additionally, the magnitudes of myelin basic protein (MBP)-induced rise in the frequency of IFN-gamma+ and IL-17+ CD8+ T cells (providing important help to neuroantigen-specific CD4+ T cells in EAE models characterized by clinically mild disease) were greater in dLN cell cultures from aged AO rats. Consistently, the magnitudes of MBP-induced rise in the frequency of both IFN-gamma+ and IL-17+ CD8+ T cells were greater in spinal cord mononuclear cell cultures from aged AO rats compared with their DA counterparts. Besides, with aging CD4+ CD25+ Foxp3+/CD8+ CD25+ Foxp3+ regulatory T cell ratio changed in spinal cord in the opposite direction. Consequently, in aged AO rats it was shifted towards CD8+ CD25+ Foxp3+ regulatory T cells (exhibiting lower suppressive capacity) when compared with DA rats. Moreover, the frequency of CX3CR1+ cells among microglia changed with aging and the disease development. In aged rats, in the effector phase of EAE it was lower in AO than in DA rats. This was accompanied by higher frequency of cells expressing IL-1 beta (whose down-regulation is central for CX3CR1-mediated neuroprotection), but lower that of phagocyting cells among microglia from aged AO compared their DA counterparts. The study indicates the control points linked with strain differences in age-related changes in EAE pathogenesis