Soluble TNF mediates the transition from pulmonary inflammation to fibrosis.
BACKGROUND
Fibrosis, the replacement of functional tissue with excessive fibrous tissue, can occur in all the main tissues and organ systems, resulting in various pathological disorders. Idiopathic Pulmonary Fibrosis is a prototype fibrotic disease involving abnormal wound healing in response to multiple sites of ongoing alveolar epithelial injury.


RESULTS
To decipher the role of TNF and TNF-mediated inflammation in the development of fibrosis, we have utilized the bleomycin-induced animal model of Pulmonary Fibrosis and a series of genetically modified mice lacking components of TNF signaling. Transmembrane TNF expression is shown to be sufficient to elicit an inflammatory response, but inadequate for the transition to the fibrotic phase of the disease. Soluble TNF expression is shown to be crucial for lymphocyte recruitment, a prerequisite for TGF-b1 expression and the development of fibrotic lesions. Moreover, through a series of bone marrow transfers, the necessary TNF expression is shown to originate from the non-hematopoietic compartment further localized in apoptosing epithelial cells.


CONCLUSIONS
These results suggest a primary detrimental role of soluble TNF in the pathologic cascade, separating it from the beneficial role of transmembrane TNF, and indicate the importance of assessing the efficacy of soluble TNF antagonists in the treatment of Idiopathic Pulmonary Fibrosis.
Oikonomou
Nikos
N
Institute of Immunology, Biomedical Sciences Research Center Alexander Fleming, Athens, Greece.
Harokopos
Vaggelis
V
Zalevsky
Jonathan
J
Valavanis
Christos
C
Kotanidou
Anastasia
A
Szymkowski
David E
DE
Kollias
George
G
Aidinis
Vassilis
V
D000818:Animals; D001761:Bleomycin / Q000633:toxicity; D016026:Bone Marrow Transplantation; D004195:Disease Models, Animal; D006801:Humans; D054990:Idiopathic Pulmonary Fibrosis / Q000188:drug therapy / Q000209:etiology; D007249:Inflammation / Q000139:chemically induced / Q000209:etiology* / Q000378:metabolism* / Q000473:pathology; D008214:Lymphocytes / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011658:Pulmonary Fibrosis / Q000139:chemically induced / Q000209:etiology* / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018124:Receptors, Tumor Necrosis Factor / Q000172:deficiency / Q000235:genetics; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000172:deficiency / Q000235:genetics; D015398:Signal Transduction; D012995:Solubility; D053773:Transforming Growth Factor beta1 / Q000096:biosynthesis; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
D012333:RNA, Messenger; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; C469948:Tnfrh2 protein, mouse; C506236:Tnfrsf1a protein, mouse; D053773:Transforming Growth Factor beta1; D014409:Tumor Necrosis Factor-alpha; D001761:Bleomycin