Integrating genetic and proteomic data to elucidate the association between immune system and blood-brain barrier dysfunction with multiple sclerosis risk and severity.

Immune system dysfunction and blood-brain barrier (BBB) impairment are implicated in multiple sclerosis (MS) risk and severity. However, the causal relationships and potential therapeutic targets remain unclear. Leveraging the MRC IEU OpenGWAS data infrastructure, we extracted 1254 peripheral immune systems and 792 BBB biomarkers as genetic instruments for exposure. MS risk data from the International Multiple Sclerosis Genetics Consortium (IMSGC) (47,429 MS cases, 68,374 controls) served as one outcome, replicated in FinnGen (1048 cases, 217,141 controls) and the UK Biobank (1679 cases, 461,254 controls). Genetic associations with MS severity derived from IMSGC and MultipleMS Consortium GWAS data (12,584 cases). Two-sample, bidirectional, and protein drug-target MR analyses were conducted, along with interaction analysis of identified proteins and druggability assessment. Causal relationships between 45 immunological markers, 15 BBB markers, and MS risk were strongly supported. In peripheral immunity, the causal associations with MS are predominantly concentrated in CD4+ T cells and CD8+ T cells. Notably, anti-Epstein-Barr virus nuclear antigen (EBNA) IgG levels exhibited the most significant causal effect on MS risk (OR = 225.62, P = 5.63E-208), replicated in the MS severity (OR = 1.11, P = 0.04). Weak causal evidence was found between 62 immunological markers, 35 BBB markers, and MS severity. Reverse MR analysis suggested potential causal effects of MS risk on 8 markers. Drug-targeted MR analysis indicated potential therapeutic benefits in reducing MS risk for CD40 (OR = 0.71, P = 7.24E-13, PPH4 = 97.6 %), AHSG (OR = 0.88, P = 2.91E-05, PPH4 = 94.4 %), and FCRL3 (Sun BB et al.: OR = 0.83, P = 8.93E-09, PPH4 = 94.2 %, Suhre K et al.: OR = 0.88, P = 5.20E-08, PPH4 = 99.2 %). This study provides evidence supporting the causal effects of immune system and BBB dysfunction on MS risk and severity. It emphasizes the significant role of anti-EBNA IgG levels, CD4+ T cells, and CD8+ T cells in MS, and delineates the potential therapeutic benefits of targeting three proteins associated with MS risk: CD40, AHSG, and FCRL3. • Genetic evidence supports the causal effects of immune system and BBB dysfunction on MS risk and severity. • Anti-EBNA IgG levels, CD4+ T cells, and CD8+ T cells play significant roles in MS. • Targeting CD40, AHSG, and FCRL3 shows potential therapeutic benefits. [ABSTRACT FROM AUTHOR]