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To understand strain-specificities of immune system in aged rats and their immunopathological implications, CD4+T lymphocyte-mediated neuroinflammation in experimental autoimmune encephalomyelitis (EAE) was studied in two strains. Upon immunization for EAE, 22-24-month-old Albino Oxford (AO) rats developed milder neurological deficit of prolonged duration compared with their Dark Agouti (DA) counterparts. Consistently, they exhibited: (i) diminished neuroantigen-specific CD4+T lymphocyte generation in draining lymph nodes (reflecting lower density of high-affinity IL-2 receptor complex on their surface and higher CD4+FoxP3+CD25+regulatory cell frequency); (ii) less favorable spinal cord expression of CXCL12 and CCL2, and consequently diminished infiltration of neuroantigen-specific CD4+T lymphocytes, including highly pathogenic IL-17+IFN-gamma+ones, and inflammatory monocytes into the spinal cord and (iii) subsequently impaired CD4+T lymphocyte reactivation/survival and differentiation into highly pathogenic IL-17+cells (reflecting downregulated expression of IL-1 beta, IL-6 and IL-23/p19). On the other hand, when the neurological deficit reached maximum/plateau, in AO rat spinal cord was found lower CD4+FoxP3+CD25+ cell frequency followed by higher frequency of IL-10-producing CD8+T cells, which most likely also belong to regulatory T lymphocytes. Thus, the altered relation between regulatory T cell and effector CD4+T cell subsets was linked with persistence of mild neuroinflammation in AO rat EAE model. (C) 2017 Elsevier B.V. All rights reserved.

Considering the crucial pathogenic role of CD4+ T cells in experimental autoimmune encephalomyelitis (EAE) and the opposite direction of the sexual dimorphism in the severity of the disease in 22-24-and 3-month-old dark agouti rats, sex differences in CD4+ T-cell-mediated immune response in aged rats immunized for EAE were examined and compared with those in young animals. In the inductive phase of EAE, fewer activated CD4+ lymphocytes were-retrieved from draining lymph nodes of male (developing less severe disease) compared with female rats, due, at least partly, to their lesser expansion. The former reflected a greater suppressive capacity of CD4+CD25+Foxp3+ cells. Consequently, CD4+ lymphocyte infiltration into the spinal cord of aged male rats was diminished. At the peak of EAE, the frequency of reactivated cells was lower, whereas that of the regulatory CD4+ cells was higher in male rat spinal cord. Consistently, microglial activation and the expression of proinflammatory/damaging cytokines in male rat spinal cord mononuclear cells were diminished. Additionally, the frequency of the highly pathogenic IL-17+IFN-gamma+ T lymphocytes infiltrating their spinal cord was lower. Together, these results point to (i) an age-specificity in CD4+ cell-mediated immune response and (ii) mechanisms underlying the sex differences in this response in aged rats. (C) 2015 Elsevier Ireland Ltd. All rights reserved.