sIL-6R is increased in BALF of asthmatic patients as compared to control subjects, and its levels correlate with the number of IL-5–producing CD4⁺ T cells in BALF after allergen challenge. (A) sIL-6R was measured before (untreated) and 24 hours after allergen or saline challenge in control subjects (gray bars) or in subjects with asthma (black bars). In the asthmatic patients, sIL-6R levels were increased at baseline and were further increased after allergen challenge. *P < 0.05; ***P < 0.001. (B–D) In these patients, a positive correlation was found between the levels of sIL-6R and the number of CD4⁺ T cells (r = 0.9027; P < 0.0001) after allergen challenge (C). Furthermore, the value of sIL-6R positively correlated with the number of CD4⁺ T cells producing IL-5 in BALF (r = 0.9171; P = 0.0001) (D), while a lower correlation was found between sIL-6R and the number of eosinophils (Eos.) in BALF (r = 0.6059; P = 0.0282) (B). Furthermore, the value of sIL-6R in the airways of asthmatic subjects after allergen challenge correlates positively with the respective sIL-6R of IL-5 (E) and IL-13 (F) in BALF.