Altered IL-6 signalling and risk of tuberculosis: a multi-ancestry mendelian randomisation study

The role of IL-6 responses in human tuberculosis risk is unknown. IL-6 signalling inhibitors, such as tocilizumab, are thought to increase the risk of progression to tuberculosis, and screening for latent Mycobacterium tuberculosis infection before using these drugs is widely recommended. We used single nucleotide polymorphisms (SNPs) in and near the IL-6 receptor gene (IL6R), including the non-synonymous variant, rs2228145, for which the C allele contributes to reduced classic (cis) IL-6 signalling activity, to test the hypothesis that altered IL-6 signalling is causally associated with the risk of developing tuberculosis.

We performed a meta-analysis of genome-wide association studies (GWAS) published in English from database inception to Jan 1, 2024. GWAS were identified from the European Bioinformatics Institute, MRC Integrative Epidemiology Unit catalogues, and MEDLINE, selecting publicly available studies for which tuberculosis was an outcome and that included the IL6R rs2228145 SNP. Using each study's population-level summary statistics, effect estimates were extracted for each additional copy of the C allele of rs2228145. We used these estimates to perform multi-ancestry, two-sample mendelian randomisation analyses to estimate the causal effect of reduced IL-6 signalling on tuberculosis. Our primary analyses used rs2228145-C as a genetic instrument, weighted on C-reactive protein (CRP) reduction as a measure of the effect on IL-6 signalling. We also took an alternative, ancestry-specific, multiple SNP approach using IL-6 receptor plasma protein as an exposure. Additionally, we compared the effects of rs2228145 in tuberculosis with those in critical COVID-19, rheumatoid arthritis, Crohn's disease, and coronary artery disease using the summary statistics extracted from GWAS.

17 GWAS were included, collating data for 19 302 individuals with tuberculosis (cases) and 1 019 821 population controls across multiple ancestries. For each additional rs2228145-C allele, the odds of tuberculosis reduced (odds ratio [OR] 0·94 [95% CI 0·92-0·97]; p=6·8 × 10^-6). Multi-ancestry mendelian randomisation analyses supported these findings, with decreased odds of tuberculosis associated with readouts of reduced IL-6 signalling (0·52 [0·39-0·69] for each natural log CRP decrease; p=6·8 × 10^-6), with weak evidence of heterogeneity (I²=0·315; p=0·11). Ancestry-specific, multiple SNP mendelian randomisation using increase in IL-6 receptor plasma protein as an exposure revealed a similar reduced risk of tuberculosis (OR 0·94 [95% CI 0·93-0·96]; p=2·4 × 10^-10). The protective effects on tuberculosis seen with rs2228145-C were similar in size and direction to those observed in critical COVID-19 (0·66 [0·50-0·86]), Crohn's disease (0·57 [0·44-0·74]), and rheumatoid arthritis (0·45 [0·36-0·58]), all of which benefit from the therapeutic effects of IL-6 antagonism.

Our findings propose a causal relationship between reduced IL-6 signalling and lower risk of tuberculosis, akin to the effect seen in other IL-6 mediated diseases. This study suggests that IL-6 antagonists do not increase the risk of tuberculosis but rather should be investigated as therapeutic adjuncts in its treatment.

UK National Institute for Health and Care Research, Wellcome Trust, EU European Regional Development Fund, the Welsh Government, and UK Research and Innovation.