Beside stroke, IL-17A is also implicated in the pathology of several autoimmune diseases such as rheumatoid arthritis, and psoriasis which led to Food and Drug Administration approved anti-IL-17A treatments.17 In murine models of experimental stroke, evidence for a detrimental role of IL-17A was seen in multiple single-centre studies.13,14,18-20 While these data support an important role of IL-17A in stroke, single-centre studies are biased by site-specific confounders, including animal housing conditions, the microbiome, the experimental set-up and even the investigators. This evidence concerns the gene IL17A and autoimmune disease.