SELL and systemic lupus erythematosus: We first validated that basophils from patients with SLE (n = 222) had an activated phenotype as shown by increased CD203c and CD62L expressions as compared to healthy control (HC) (n = 140) (Supplementary Table 1 and Supplementary Fig. 1a–d)4 without displaying a degranulated phenotype as measured by their CD63 expression level (Supplementary Fig. 1e).