In the internal thoracic artery, the proportion of IL‐33+ vasa vasorum was similar in RA patients (89%) and non‐RA patients (79%), but RA patients had a higher proportion of IL‐33+ ECs (30.6 ± 26.3% versus 13.1 ± 12.5%; P = 0.04). Here, IL33 is linked to rheumatoid arthritis.