This thesis focuses on disease activity in clinically isolated syndrome (CIS) and newly diagnosed relapsing remitting multiple sclerosis (RRMS). The papers are based on data from 41 patients in a prospective longitudinal cohort study. All patients were untreated at baseline. Age- and sex-matched healthy controls (n=22) for blood and cerebrospinal fluid (CSF) samples were recruited from blood donors.

Paper I evaluated the prognostic value of baseline levels of CXCL1, CXCL8, CXCL10, CXCL13, CCL22, neurofilament light chain (NFL), neurofilament heavy chain, glial fibrillary acidic protein, chitinase-3-like-1 (CHI3L1), matrix metalloproteinase-9 (MMP-9) and osteopontin in CSF in relation to disease activity during the first two years of follow-up. Disease activity was defined as clinical relapses, new T2 lesions in brain magnetic resonance imaging (MRI) and/or sustained Expanded Disability Status Scale (EDSS) progression. Absence of these three signs of disease activity was called no evidence of disease activity (NEDA-3). Logistic regression analysis showed that NFL in CSF was the best predictive marker of disease activity and correctly classified 93% of the patients with evidence of disease activity during two years of follow-up and 67% of those without.

Paper II presented four year follow-up data from the cohort and also included brain volume data as well as serum levels of NFL. The correlation between NFL in CSF and serum was fairly strong (r=0.74, p<0.001). NFL in CSF was associated with new T2 lesions as well as with brain volume loss, whereas CHI3L1 in CSF was associated mainly with brain volume loss and CXCL1, CXCL10, CXCL13, CCL22 and MMP-9 in CSF were mainly associated with new T2 lesions. Taken together, paper I and II confirm and extend the knowledge of NFL as a useful biomarker in CIS and RRMS and suggests that NFL, rather than total brain volume loss, could be included in an expanded NEDA concept and used in clinical monitoring of disease activity/treatment effect. Although serum levels of NFL were correlated with the corresponding CSF levels, CSF-NFL showed a stronger association to subsequent disease activity (NEDA-3).

Paper III addressed the patients´ self-reported Modified Fatigue Impact Scale (MFIS) scores in relation to other cohort study data. MFIS scores correlated with other self-assessment questionnaire data (Hospital Anxiety and Depression scale (HAD), Multiple Sclerosis Impact Scale 29 (MSIS-29) and Short Form 36 (SF-36) scores (Spearman´s rho 0.45-0.78, all p≤0.01)) but not with EDSS ratings, number of T2 lesions, total brain volume or NFL levels, indicating that subjective fatigue scores are not well reflected by some commonly used and objectively measurable disease parameters.

Paper IV focused on the complement factors C1q, C3, C3a and sC5b-9 in CSF and plasma. CSFC1q was significantly higher in patients than in controls at baseline. The subgroup of patients with ongoing relapse at baseline also had higher levels of CSF-C3a than controls. Baseline levels of CSF-C1q and CSF-C3a correlated significantly with several pro-inflammatory chemokines as well as with MMP-9, CHI3L1 and NFL in CSF. Baseline CSF-C3a also correlated significantly with the number of T2 lesions and Gadolinium enhancing lesions in brain MRI at baseline, as well as with the number of new T2 lesions during follow-up. This study indicates that the complement system is involved already at early stages of MS. It also suggests that especially CSF-C1q and CSF-C3a levels are associated with other neuroinflammatory and neurodegenerative markers and that CSF-C3a levels may carry some prognostic information.