Strain specificities in cellular and molecular immunopathogenic mechanisms underlying development of experimental autoimmune encephalomyelitis in aged rats

Mirjana Nacka-Aleksić, Zorica Stojić-Vukanić, Ivan Pilipović, Ivana Vujnović, Biljana Bufan, Mirjana Dimitrijević, Gordana Leposavić

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-γ+ 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-1β, 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.