IL33 and rheumatoid arthritis: The proportion of EC nuclei positive for IL‐33 within each vasa vasorum (IL‐33+ ECs) was also substantially greater in RA patients compared with non‐RA patients (mean ± SEM 58.7 ± 34.1% versus 32.9 ± 28.5%; P = 0.02) (Figure 2B).