Characterization of Eae4 and Eae19-22 in autoimmune neuroinflammation

Sammanfattning: Multiple Sclerosis (MS) is the most common chronic inflammatory disorders of the central nervous system (CNS) with a prevalence of 1-211000 in the Northern European population. MS is caused by a combination of environmental factors and multiple genes. Animal models offer possibilities to keep environmental factors and selected genes constant and very large, genetically homogene, "families" may be created. Therefore, an animal model known as experimental autoimmune encephalomyelitis (EAE), which shows functional and pathological similarities to human -MS is here utilized to characterize underlying genes and pathogenic mechanisms. We established congenic strains, DA.BN-Eae4, DA.ACI-Eae20-22 and DA.PVGEae19, encompassing previously identified EAE-QTLs on rat chromosomes 9, 4 and 15 respectively. The DA strain is EAE susceptible both in the MOG- and SC-induced models while the ACI, PVG and BN strains are EAE-resistant. We further bred interval-specific recombinants that allowed us to narrow down the susceptibility region of Eae4 to ~1 cM. In addition to differences in the clinical phenotype, we investigated disease regulating mechanisms by exploring the influence of Eae4 on immune response parameters. We detected lower expression levels and lower protein secretion of TNF IFNgamma and IL-2 in ConA-stimulated splenocytes from congenic strains compared to the background DA strain. This difference in cytokine expression co-segregated with regulation of EAEseverity in all yet screened congenics. A difference in the cytokine responses was noticed in CD4+ and CD8+ T-cell populations but not in macrophages and NK-cells. With a combination of F10 AIL (DAxPVG.AV1) and congenic breeding (DA.c15ACI), Eae19 on chromosome 15 was narrowed down to confidence interval of 13Mb This regions harbours 32 predicted and confirmed genes among them the immune-responsive gene 1 and neuronal ceroid lipofuscione gene 5. Among the QTLs overlapping with Eae19, adjuvantinduced arthritis QTL 4 (Aia4) might be the most interesting one since EAE regulatory effects were demonstarted in rat strains congenic for arthritis-regulating QTL. We also identified two closely located QTLs on chromosome 4, Eae20 and Eae21, in addition to a third QTL, Eae22, identified as an epistatic region to Eae20. These 3 QTLs were mapped on a region spanning 16.8Mb colocalized with several QTLs regulating experimental autoimmune diseases such as Oia2, Pia1 and Cia13. We demonstrated an influence of Eae20 on incidence and severity of EAE while was found to regulate the EAE phenotype once a certain threshold of the disease is exceeded.