Interleukin 6 secretion by monocytes and alveolar macrophages in systemic sclerosis with lung involvement

Interleukin-6 (IL-6) has been involved in the pathogenesis of inflammatory and/or autoimmune diseases. We characterized the production of IL-6 by blood monocytes and alveolar macrophages (AM) in 11 patients with definite systemic sclerosis (SSc) with lung involvement and in eight normal control subjects. IL-6 levels were determined in serum, bronchoalveolar lavage (BAL) supernatants, monocytes, and AM cell culture supernatants using an ELISA kit. BAL cell analysis evidenced an alveolitis with hypercellularity and increased neutrophils and mast cells absolute counts. Serum and BAL IL-6 levels were low and similar in SSc and control groups. The monocytes of the group with SSc secreted more IL-6 than did the control group, both spontaneously (p = 0.01) and after LPS stimulation (p = 0.0007). Spontaneous secretion of IL-6 by AM tended to be higher in the SSc group than in the control group (p = 0.22). LPS-induced IL-6 secretion by AM was similar in both groups. Our study demonstrates that during SSc lung disease, spontaneous and stimulated IL-6 secretion by blood monocytes is increased, compared with secretion by healthy control subjects. By contrast, IL-6 secretion by AM is normal despite evidence of mild alveolitis.