Effects of Pregnancy and Hormones on T cell Immune Regulation in Multiple Sclerosis

Abstract

Multiple sclerosis (MS) is characterized by a dysregulated immune system leading to chronic inflammation in the central nervous system. Despite increasing number of treatments, many patients continue to deteriorate. A better understanding of the underlying disease mechanisms involved in driving disease is a prerequisite for finding new biomarkers and new treatment targets. The improvement of MS during pregnancy, comparable to the beneficial effects of the most effective treatment, suggests that the transient and physiological immune tolerance established during pregnancy could serve as a model for successful immune regulation. Most likely the immune-endocrine alterations that take place during pregnancy to accommodate the presence of the semi-allogenic fetus contribute to the observed disease improvement. The aim of this thesis was to characterize the dysregulated immune system in MS and define potential factors and mechanisms established during pregnancy that could be involved in the pregnancy-induced effects in MS, focusing on CD4 + T cells as one of the main drivers in immunity and in the MS pathogenesis. Using a network-based modular approach based on gene expression profiling, we could show that CD4 + T cells from patients with MS displayed an altered dynamic gene response to activation, in line with a dysregulated immune system in MS. The resulting gene module disclosed cell activation and chemotaxis as central components in the deviating response, results that form a basis for further studies on its modulation during pregnancy. Moreover, a combination of secreted proteins (OPN+CXCL1-3+CXCL10-CCL2), identified from the module, could be used to separate patients and controls, predict disease activity after 2 years and discriminate between high and low responders to treatment, highlighting their potential use as biomarkers for predicting disease activity and response to treatment. The pregnancy hormone progesterone (P4), a potential factor involved in the pregnancy-induced amelioration of MS, was found to significantly dampen CD4 + T cell activation. Further detailed transcriptomic profiling revealed that P4 almost exclusively down-regulated immune-related pathways in activated T cells, several related to or downstream of T cell activation such as JAK-STAT signaling, T cell receptor signaling and cytokine-cytokine receptor interaction. In particular, P4 significantly affected genes of relevance to diseases known to be modulated during pregnancy, where genes associated to MS were most significantly affected, supporting a role for P4 in the pregnancy-induced immunomodulation. By using another approach, the role of thymus in T cell regulation during pregnancy was assessed. Two established measures of thymic output, CD31