Pathogenesis & Immunology

By Finn Sellebjerg

Immunological studies

It is becoming increasingly clear that relapsing-remitting MS is caused by repeated attacks of inflammatory demyelination and axonal damage. These attacks are initiated by inflammatory cells that are activated within the immune systems, recirculate in blood, and access the brain and spinal cord by crossing the different blood-brain barrier systems. Based on animal experiments, MS has been thought to be mainly a T cell-driven disease. Clinical trials do, however, show that in addition to treatment with natalizumab, that blocks the migration of all mononuclear cells into the CNS, B cell depletion is also efficacioius in relapsing-remitting MS. More recent studies have suggested that even in progressive MS, which has been thought to be caused mainly by neurodegenerative processes, inflammation may be crucial in the pathogenesis.

We study the mechanism of immune activation in MS, addressing the reactivity of subsets of T cells and B cells to autoantigens expressed in the brain and spinal cord, and address how these and other leukocytes contribute to the activation of T cells. We also study the effect of immunomodulatory treatment on these processes, and focus specifically on the mechanism of action of interferon-beta.

In other studies we study the phenotype of individual, circulating lymphocytes by measuring the binding of fluorochrome-coupled, monoclonal antibodies to distinct molecules by use of flow cytometry. By combining the analysis of different molecules expressed on the cell surface, the lymphocytes can be divided into a large number of functionally relevant subtypes, which can be quantitated both in relative and absolute terms. We are currently studying an array of activation and differentiation markers on T cell subsets, B cells, NK cells, monocytes and dendritic cells to explore the activation status of these cell types in patients with relapsing-remitting, primary and secondary progressive MS. These studies will provide novel insights into immune activation in subtypes of MS.

Molecular biology

Activation of immune responses depends on interactions between different immune cells and coordinated, tightly regulated expression of a vast number of molecules within single cells. Gene expression is controlled by the activity of transcription factors that are either constitutively expressed in active forms, expressed in forms that require activation by other signals, or are inducible on cellular activation. The transcription factors direct the expression of messenger RNA (mRNA) from the genes encoded by the DNA sequence, and after export from the nucleus the mRNA provides a template for protein synthesis on ribosomes in the cytosol. Within the last decade it has become apparent that endogenous, small RNA molecules termed microRNA (miRNA) have a key role in regulating the translation of protein from mRNA in the cytosol. It can either induce the degradation of mRNA, or can inhibit the translation of mRNA into protein by binding to the 3’ untranslated region of mRNA molecules. Furthermore, the accessibility of a genomic region can be regulated by epigenetic modifications of the DNA strand.

Recent studies have identified miRNA molecules that are differentially expressed in MS patients and healthy controls, and it has been suggested that pathogenic immune activation in MS may, indeed, reflect changes in miRNA expression. We have studied miRNA expression in MS, and have found that even patients with MS in clinical remission show clear changes in the expression of miRNA compared to healthy control subjects. Furthermore, we have identified miRNA molecules that are specifically regulated by treatment with interferon-beta. We are now studying the extent to which miRNA expression changes in pregnant women with MS, as pregnancy is known to dampen disease activity in relapsing-remitting MS. These studies are complemented by mRNA expression studies in subtypes of mononuclear cells, isolated by immunomagnetic technology, from patients with relapsing-remitting, primary and secondary progressive MS.

Taken together our studies provide novel insights into the molecular mechanisms of the pathogenic immune responses in MS. As miRNA can now be therapeutically introduced into specific human cells, the identification of miRNAs that can modulate pathogenic immune responses have a strong potential for the treatment of MS in the future.

Biomarker studies

The term biomarker is used for gene products or proteins that can be measured in blood or other body fluids, and reflects a pathogenetically or therapeutically relevant in vivo process. Immunological and molecular biology studies provide the platform for the development of biomarkers, but the validation of these also requires access to collections of well characterized blood and CSF samples from MS patients, who are followed prospectively. Such biomarker studies can provide insights into the pathogenesis of MS and our understanding of the therapeutic effects of immunomodulatory and immunosuppressive treatments. The development of biomarkers that can serve as surrogate outcomes in clinical trials is an important aim of the ongoing biomarker research at our MS-center.

We have studied the immunological effects of treatment with natalizumab, interferon-beta and glatiramer acetate. The studies have resulted in the validation of biomarkers that may reflect the therapeutic effect of treatment better than the currently used biomarkers, and are now being studied in clinical trials of patients with primary and secondary progressive MS.

We continue to study the mechanisms and effects of antibodies to biopharmaceutical therapies – interferon-beta and natalizumab - in MS. Most recently we have shown that although antibody responses to glatiramer acetate develop during therapy, they do not appear to influence the response to therapy. Finally, we have identified immune activation markers that are upregulated in a subgroup of patients treated with interferon-beta. This response is associated with increased disease activity during interferon-therapy. We are now exploring how this response is induced and how it may increase the pathogenic processes in MS.

With the introduction of a number of new MS therapeutics in the coming years, a better understanding of the different therapies is urgently needed. Indeed, some patients may do well on a safe first-line therapy with moderate efficacy, others require more efficacious therapies, which are usually associated with an increased risk of severe side effects. We will continue to study how genetic markers and other biomarkers can be used to tailor individual MS therapy.