Evaluation of soluble IL‐6 receptor concentration in serum and epithelial lining fluid from patients with interstitial lung diseases
We measured soluble IL‐6 receptor (sIL‐6R) levels in serum and bronchoalveolar lavage fluids (BALF) from patients with interstitial pneumonia of unknown etiology (IP) (n= 17), sarcoidosis (n= 8) and normal control subjects (n= 10), to investigate its role in pulmonary diseases. Soluble IL‐6R was determined by an ELISA. The volume of epithelial lining fluid (ELF) in BALF was estimated using an urea method. We found that levels of sIL‐6R in serum, BALF, and ELF from patients with IP or sarcoidosis were significantly higher than those from normal subjects. Furthermore, levels of sIL‐6R in BALF or ELF were significantly correlated with those of albumin, indicating that sIL‐6R, together with albumin, may enter ELF as a result of the increased permeability caused by pulmonary inflammation. Thus most of the sIL‐6R in ELF would be from serum, and relatively small amounts of it might be produced locally. However, sIL‐6R levels in ELF, but neither serum nor BALF, were significantly correlated with levels of C‐reactive protein in patients with IP. These results suggest that both systemic and local production of sIL‐6R are increased, and raised sIL‐6R is involved in the modulation of systemic and local inflammatory responses in patients with IP and sarcoidosis.