Inter-relationship between tumour necrosis factor-alpha (TNF-alpha) and TNF soluble receptors in pulmonary sarcoidosis

Background-The importance of tumour necrosis factor-alpha (TNF-alpha) in th e pathogenesis of pulmonary sarcoidosis has remained uncertain because of t he paucity of clinical features associated with excessive levels of this cy tokine. Increased levels of soluble TNF receptors (TNF-R), which are known to inhibit TNF-alpha activity, were recently described in the lungs of subj ects with sarcoidosis. We hypothesised that TNF-alpha bioactivity may be in hibited in sarcoidosis by the presence of TNF-beta. A study was therefore u ndertaken to investigate for the first time the relationship between solubl e receptors and TNF-alpha bioactivity in the lungs of subjects with sarcoid osis. Methods-Alveolar macrophages (AMs) from 16 subjects with histologically pro ven sarcoidosis and 13 healthy controls were cultured in the presence and a bsence of lipopolysaccharide (LPS). The subjects with sarcoidosis were grou ped by radiological assessment into stage I (n = 6) and stage II/III (n = 1 0). The cell culture supernatants and bronchoalveolar lavage (BAIL) fluid w ere assayed for TNF bioactivity using the WEHI 164 clone 13 assay. Immunore active (bound and free) TNF-Rs and free TNF-Rs (p55 and p75) were determine d by ELISA. Results-Bioactive TNF-alpha was undetectable in the BAL fluid of all the su bjects with sarcoidosis and most of the healthy controls. However, there wa s significantly more immunoreactive TNF-alpha in the BAL fluid from subject s with sarcoidosis than from the controls (median values 0.304 ngl mi and 0 .004 ng/ml, respectively, 95% CI 0.076 to 0.455, p<0.001). The levels of bo th p55 and p75 in the BAL fluid were higher in both sarcoidosis groups than in the controls (p<0.0005 and p<0.001, respectively). In LPS stimulated AM supernatants reduced TNF-a bioactivity was seen in subjects with stage I s arcoidosis compared with those with stage II/III disease and healthy contro ls (median 0.333 ng/ml vs 1.362 ng/ml and 2.385 ng/ml, respectively, p<0.01 ). This contrasted with increased p55 levels in the AM supernatants derived from subjects with stage I sarcoidosis compared with those with stage II/I II disease and healthy controls (median 0.449 ng/ml vs 0.058 ng/ml and 0.07 8 ngl mi, respectively, p<0.01). The levels of p75 were increased in unstim ulated AM cultures in subjects with stage II/III disease compared with thos e with stage I disease and healthy controls (median 0.326 ng/ml vs 0.064 ng /ml and 0.102 ng/ml, p<0.05). Conclusions-These results indicate that TNF-alpha bioactivity may be inhibi ted by increased soluble TNF-R in the lungs of subjects with sarcoidosis, a nd this inhibition may be greater in patients with stage I sarcoidosis than in those with stage II/III disease. This may represent a homeostatic mecha nism which protects the lung from excessive TNF production characteristic o f chronic inflammation.